Tuesday, February 17, 2009

Macroevolution: Examples and Evidence


AUTHOR: Allen MacNeill

SOURCE:
Observed Instances of Speciation


COMMENTARY: That's up to you...

In honor of Darwin’s birthday, here is a response to yet another unsupported assertion by creationists and ID supporters, who often state (without evidence) that although microevolution might happen, there is no evidence for macroevolution.

The distinction between microevolution – the mechanisms by which evolution has occurred – and
macroevolution
– the large-scale pattern of change over time that has resulted from the operation of microevolutionary mechanisms – is as old as evolutionary theory. In the Origin of Species, Darwin himself argued for both microevolution (i.e. natural and sexual selection) and macroevolution (descent with modification), without using these terms. Following the publication of the Origin, Darwin’s theory of descent with modification was quickly accepted by virtually the entire scientific community. However, his proposed mechanisms of natural and sexual selection were not as widely accepted as the “engines” of descent with modification, falling into disrepute by the turn of the 20th century.

However, the founders of the “modern evolutionary synthesis” rehabilitated Darwin’s microevolutionary mechanisms by integrating them with Mendel’s theory of genetics and new discoveries in botany, ecology, ethology, historical geology, and paleontology. So successful was this synthesis that today all but the most committed young-Earth creationists accept that microevolution happens. However, it has become an article of faith among anti-evolutionists of all denominations, including “intelligent design” supporters, that there is no scientific explanation for macroevolution, and that in the case of the origin of humans, it didn’t happen.

There isn’t enough room in this post to address both of these misconceptions, so I will concentrate here on the first: that there is no evidence that macroevolution has happened, and that therefore it didn’t happen (or if it did, it required supernatural intervention). What follows is a brief sample of some examples of macroevolution and the mechanisms by which they have taken place, from the level of species up to the level of whole kingdoms. This is not an exhaustive sample by any means. However, it should give anyone with an open mind enough examples and evidence to form their own conclusions about the validity of modern macroevolutionary theory.

[I am particularly indebted to Joseph Boxhorn’s essay on the evidences for speciation (located at talk.origins.org) from which I have drawn many of these examples. Please go there to read more about them.]

MACROEVOLUTION AT THE LEVEL OF SPECIES

PLANTS


While studying the genetics of the evening primrose, Oenothera lamarckiana, de Vries (1905) found an unusual variant among his plants. Oenothera lamarckiana has a chromosome number of 2N = 14. The variant had a chromosome number of 2N = 28. He found that he was unable to breed this variant with Oenothera lamarckiana. He named this new species Oenothera gigas.


Digby (1912) crossed the primrose species Primula verticillata and Primula floribunda to produce a sterile hybrid. Polyploidization occurred in a few of these plants to produce fertile offspring. The new species was named Primula kewensis. Newton and Pellew (1929) note that spontaneous hybrids of Primula verticillata and Primula floribunda set tetraploid seed on at least three occasions. These happened in 1905, 1923 and 1926.


Owenby (1950) demonstrated that two species in the genus Tragopogon were produced by polyploidization from hybrids. He showed that Tragopogon miscellus found in a colony in Moscow, Idaho was produced by hybridization of Tragopogon dubius and Tragopogon pratensis. He also showed that Tragopogon mirus found in a colony near Pullman, Washington was produced by hybridization of Tragopogon dubius and Tragopogon porrifolius. Evidence from chloroplast DNA suggests that Tragopogon mirus has originated independently by hybridization in eastern Washington and western Idaho at least three times (Soltis and Soltis 1989). The same study also shows multiple origins for Tragopogon micellus.


The Russian cytologist Karpchenko (1927, 1928) crossed the radish, Raphanus sativus, with the cabbage, Brassica oleracea. Despite the fact that the plants were in different genera, he got a sterile hybrid. Some unreduced gametes were formed in the hybrids. This allowed for the production of seed. Plants grown from the seeds were interfertile with each other. They were not interfertile with either parental species. Unfortunately the new plant (genus Raphanobrassica) had the foliage of a radish and the root of a cabbage.


A species of hemp nettle, Galeopsis tetrahit, was hypothesized to be the result of a natural hybridization of two other species, Galeopsis pubescens and Galeopsis speciosa (Muntzing 1932). The two species were crossed. The hybrids matched Galeopsis tetrahit in both visible features and chromosome morphology.


Clausen et al. (1945) hypothesized that Madia citrigracilis was a hexaploid hybrid of Madia gracilis and Madia citriodora. As evidence they noted that the species have gametic chromosome numbers of n = 24, 16 and 8 respectively. Crossing Madia gracilis and Madia citriodora resulted in a highly sterile triploid with n = 24. The chromosomes formed almost no bivalents during meiosis. Artificially doubling the chromosome number using colchecine produced a hexaploid hybrid which closely resembled Madia citrigracilis and was fertile.


Frandsen (1943, 1947) showed that Brassica carinata (n = 17) may be recreated by hybridizing Brassica nigra (n = 8) and Brassica oleracea, Brassica juncea (n = 18) may be recreated by hybridizing Brassica nigra and Brassica campestris (n = 10), and Brassica napus (n = 19) may be recreated by hybridizing Brassica oleracea and Brassica campestris.


Rabe and Haufler (1992) found a naturally occurring diploid sporophyte of maidenhair fern (Adiantum pedatum) which produced unreduced (2N) spores. These spores resulted from a failure of the paired chromosomes to dissociate during the first division of meiosis. The spores germinated normally and grew into diploid gametophytes. These did not appear to produce antheridia. Nonetheless, a subsequent generation of tetraploid sporophytes was produced. When grown in the lab, the tetraploid sporophytes appear to be less vigorous than the normal diploid sporophytes. The 4N individuals were found near Baldwin City, Kansas.


Woodsia Fern (Woodsia abbeae) was described as a hybrid of Woodsia cathcariana and Woodsia ilvensis (Butters 1941). Plants of this hybrid normally produce abortive sporangia containing inviable spores. In 1944 Butters found a Woodsia abbeae plant near Grand Portage, Minn. that had one fertile frond (Butters and Tryon 1948). The apical portion of this frond had fertile sporangia. Spores from this frond germinated and grew into prothallia. About six months after germination sporophytes were produced. They survived for about one year. Based on cytological evidence, Butters and Tryon concluded that the frond that produced the viable spores had gone tetraploid. They made no statement as to whether the sporophytes grown produced viable spores.


Gottlieb (1973) documented the speciation of Stephanomeria malheurensis. He found a single small population (< 250 plants) among a much larger population (> 25,000 plants) of Stephanomeria exigua in Harney Co., Oregon. Both species are diploid and have the same number of chromosomes (N = 8). Stephanomeria exigua is an obligate outcrosser exhibiting sporophytic self-incompatibility. Stephanomeria malheurensis exhibits no self-incompatibility and self-pollinates. Though the two species look very similar, Gottlieb was able to document morphological differences in five characters plus chromosomal differences. F1 hybrids between the species produces only 50% of the seeds and 24% of the pollen that conspecific crosses produced. F2 hybrids showed various developmental abnormalities.


Pasterniani (1969) produced almost complete reproductive isolation between two varieties of maize (Zea mays). The varieties were distinguishable by seed color, white versus yellow. Other genetic markers allowed him to identify hybrids. The two varieties were planted in a common field. Any plant's nearest neighbors were always plants of the other strain. Selection was applied against hybridization by using only those ears of corn that showed a low degree of hybridization as the source of the next years seed. Only parental type kernels from these ears were planted. The strength of selection was increased each year. In the first year, only ears with less than 30% intercrossed seed were used. In the fifth year, only ears with less than 1% intercrossed seed were used. After five years the average percentage of intercrossed matings dropped from 35.8% to 4.9% in the white strain and from 46.7% to 3.4% in the yellow strain.


At reasonably low concentrations, copper is toxic to many plant species. However, several plants have been seen to develop a tolerance to this metal (Macnair 1981). Macnair and Christie (1983) used this to examine the genetic basis of a postmating isolating mechanism in yellow monkey flower (Mimulus guttatus). When they crossed plants from the copper tolerant "Copperopolis" population with plants from the nontolerant "Cerig" population, they found that many of the hybrids were inviable. During early growth, just after the four leaf stage, the leaves of many of the hybrids turned yellow and became necrotic. Death followed this. This was seen only in hybrids between the two populations. Through mapping studies, the authors were able to show that the copper tolerance gene and the gene responsible for hybrid inviability were either the same gene or were very tightly linked. These results suggest that reproductive isolation may require changes in only a small number of genes.

ANIMALS

Speciation through hybridization and/or polyploidy is now considered to be as important in animals as it is in plants. (Lokki and Saura 1980; Bullini and Nascetti 1990; Vrijenhoek 1994). Bullini and Nasceti (1990) review chromosomal and genetic evidence that suggest that speciation through hybridization may occur in a number of insect species, including walking sticks, grasshoppers, blackflies and cucurlionid beetles. Lokki and Saura (1980) discuss the role of polyploidy in insect evolution. Vrijenhoek (1994) reviews the literature on parthenogenesis and hybridogenesis in fish.

Dobzhansky and Pavlovsky (1971) reported a speciation event that occurred in a laboratory culture of Drosophila paulistorum sometime between 1958 and 1963. The culture was descended from a single inseminated female that was captured in the Llanos of Colombia. In 1958 this strain produced fertile hybrids when crossed with conspecifics of different strains from Orinocan. From 1963 onward crosses with Orinocan strains produced only sterile males. Initially no assortative mating or behavioral isolation was seen between the Llanos strain and the Orinocan strains. Later on Dobzhansky produced assortative mating (Dobzhansky 1972).


Thoday and Gibson (1962) established a population of Drosophila melanogaster from four gravid females. They applied selection on this population for flies with the highest and lowest numbers of sternoplural chaetae (hairs). In each generation, eight flies with high numbers of chaetae were allowed to interbreed and eight flies with low numbers of chaetae were allowed to interbreed. Periodically they performed mate choice experiments on the two lines. They found that they had produced a high degree of positive assortative mating between the two groups. In the decade or so following this, eighteen labs attempted unsuccessfully to reproduce these results. References are given in Thoday and Gibson 1970.

Crossley (1974) was able to produce changes in mating behavior in two mutant strains of Drosophila melanogaster. Four treatments were used. In each treatment, 55 virgin males and 55 virgin females of both ebony body mutant flies and vestigial wing mutant flies (220 flies total) were put into a jar and allowed to mate for 20 hours. The females were collected and each was put into a separate vial. The phenotypes of the offspring were recorded. Wild type offspring were hybrids between the mutants. In two of the four treatments, mating was carried out in the light. In one of these treatments all hybrid offspring were destroyed. This was repeated for 40 generations. Mating was carried out in the dark in the other two treatments. Again, in one of these all hybrids were destroyed. This was repeated for 49 generations. Crossley ran mate choice tests and observed mating behavior. Positive assortative mating was found in the treatment which had mated in the light and had been subject to strong selection against hybridization. The basis of this was changes in the courtship behaviors of both sexes. Similar experiments, without observation of mating behavior, were performed by Knight, et al. (1956).

Kilias, et al. (1980) exposed Drosophila melanogaster populations to different temperature and humidity regimes for several years. They performed mating tests to check for reproductive isolation. They found some sterility in crosses among populations raised under different conditions. They also showed some positive assortative mating. These things were not observed in populations which were separated but raised under the same conditions. They concluded that sexual isolation was produced as a byproduct of selection.

In a series of papers (Rice 1985, Rice and Salt 1988 and Rice and Salt 1990) Rice and Salt presented experimental evidence for the possibility of sympatric speciation in Drosophila melanogaster. They started from the premise that whenever organisms sort themselves into the environment first and then mate locally, individuals with the same habitat preferences will necessarily mate assortatively. They established a stock population of Drosophila melanogaster with flies collected in an orchard near Davis, California. Pupae from the culture were placed into a habitat maze. Newly emerged flies had to negotiate the maze to find food. The maze simulated several environmental gradients simultaneously. The flies had to make three choices of which way to go. The first was between light and dark (phototaxis). The second was between up and down (geotaxis). The last was between the scent of acetaldehyde and the scent of ethanol (chemotaxis). This divided the flies among eight habitats. The flies were further divided by the time of day of emergence. In total the flies were divided among 24 spatio-temporal habitats.

They next cultured two strains of flies that had chosen opposite habitats. One strain emerged early, flew upward and was attracted to dark and acetaldehyde. The other emerged late, flew downward and was attracted to light and ethanol. Pupae from these two strains were placed together in the maze. They were allowed to mate at the food site and were collected. Eye color differences between the strains allowed Rice and Salt to distinguish between the two strains. A selective penalty was imposed on flies that switched habitats. Females that switched habitats were destroyed. None of their gametes passed into the next generation. Males that switched habitats received no penalty. After 25 generations of this mating tests showed reproductive isolation between the two strains. Habitat specialization was also produced.

They next repeated the experiment without the penalty against habitat switching. The result was the same -- reproductive isolation was produced. They argued that a switching penalty is not necessary to produce reproductive isolation. Their results, they stated, show the possibility of sympatric speciation.


In a series of experiments, del Solar (1966) derived positively and negatively geotactic and phototactic strains of Drosophila pseudoobscura from the same population by running the flies through mazes. Flies from different strains were then introduced into mating chambers (10 males and 10 females from each strain). Matings were recorded. Statistically significant positive assortative mating was found.

In a separate series of experiments Dodd (1989) raised eight populations derived from a single population of Drosophila pseudoobscura on stressful media. Four populations were raised on a starch based medium, the other four were raised on a maltose based medium. The fly populations in both treatments took several months to get established, implying that they were under strong selection. Dodd found some evidence of genetic divergence between flies in the two treatments. He performed mate choice tests among experimental populations. He found statistically significant assortative mating between populations raised on different media, but no assortative mating among populations raised within the same medium regime. He argued that since there was no direct selection for reproductive isolation, the behavioral isolation results from a pleiotropic by-product to adaptation to the two media. Schluter and Nagel (1995) have argued that these results provide experimental support for the hypothesis of parallel speciation.


Less dramatic results were obtained by growing Drosophila willistoni on media of different pH levels (de Oliveira and Cordeiro 1980). Mate choice tests after 26, 32, 52 and 69 generations of growth showed statistically significant assortative mating between some populations grown in different pH treatments. This ethological isolation did not always persist over time. They also found that some crosses made after 106 and 122 generations showed significant hybrid inferiority, but only when grown in acid medium.

Some proposed models of speciation rely on a process called reinforcement to complete the speciation process. Reinforcement occurs when to partially isolated allopatric populations come into contact. Lower relative fitness of hybrids between the two populations results in increased selection for isolating mechanisms. I should note that a recent review (Rice and Hostert 1993) argues that there is little experimental evidence to support reinforcement models. Two experiments in which the authors argue that their results provide support are discussed below.

Ehrman (1971) established strains of wild-type and mutant (black body) Drosophila melanogaster. These flies were derived from compound autosome strains such that heterotypic matings would produce no progeny. The two strains were reared together in common fly cages. After two years, the isolation index generated from mate choice experiments had increased from 0.04 to 0.43, indicating the appearance of considerable assortative mating. After four years this index had risen to 0.64 (Ehrman 1973). Along the same lines, Koopman (1950) was able to increase the degree of reproductive isolation between two partially isolated species, Drosophila pseudoobscura and Drosophila persimilis.

The founder-flush (a.k.a. flush-crash) hypothesis posits that genetic drift and founder effects play a major role in speciation (Powell 1978). During a founder-flush cycle a new habitat is colonized by a small number of individuals (e.g. one inseminated female). The population rapidly expands (the flush phase). This is followed by the population crashing. During this crash period the population experiences strong genetic drift. The population undergoes another rapid expansion followed by another crash. This cycle repeats several times. Reproductive isolation is produced as a byproduct of genetic drift.

Dodd and Powell (1985) tested this hypothesis using Drosophila pseudoobscura. A large, heterogeneous population was allowed to grow rapidly in a very large population cage. Twelve experimental populations were derived from this population from single pair matings. These populations were allowed to flush. Fourteen months later, mating tests were performed among the twelve populations. No postmating isolation was seen. One cross showed strong behavioral isolation. The populations underwent three more flush-crash cycles. Forty-four months after the start of the experiment (and fifteen months after the last flush) the populations were again tested. Once again, no postmating isolation was seen. Three populations showed behavioral isolation in the form of positive assortative mating. Later tests between 1980 and 1984 showed that the isolation persisted, though it was weaker in some cases.

Galina, et al. (1993) performed similar experiments with Drosophila pseudoobscura. Mating tests between populations that underwent flush-crash cycles and their ancestral populations showed 8 cases of positive assortative mating out of 118 crosses. They also showed 5 cases of negative assortative mating (i.e. the flies preferred to mate with flies of the other strain). Tests among the founder-flush populations showed 36 cases of positive assortative mating out of 370 crosses. These tests also found 4 cases of negative assortative mating. Most of these mating preferences did not persist over time. Galina, et al. concluded that the founder-flush protocol yields reproductive isolation only as a rare and erratic event.

Ahearn (1980) applied the founder-flush protocol to Drosophila silvestris. Flies from a line of this species underwent several flush-crash cycles. They were tested in mate choice experiments against flies from a continuously large population. Female flies from both strains preferred to mate with males from the large population. Females from the large population would not mate with males from the founder flush population. An asymmetric reproductive isolation was produced.

In a three year experiment, Ringo, et al. (1985) compared the effects of a founder-flush protocol to the effects of selection on various traits. A large population of Drosophila simulans was created from flies from 69 wild caught stocks from several locations. Founder-flush lines and selection lines were derived from this population. The founder-flush lines went through six flush-crash cycles. The selection lines experienced equal intensities of selection for various traits. Mating test were performed between strains within a treatment and between treatment strains and the source population. Crosses were also checked for postmating isolation. In the selection lines, 10 out of 216 crosses showed positive assortative mating (2 crosses showed negative assortative mating). They also found that 25 out of 216 crosses showed postmating isolation. Of these, 9 cases involved crosses with the source population. In the founder-flush lines 12 out of 216 crosses showed positive assortative mating (3 crosses showed negative assortative mating). Postmating isolation was found in 15 out of 216 crosses, 11 involving the source population. They concluded that only weak isolation was found and that there was little difference between the effects of natural selection and the effects of genetic drift.


Meffert and Bryant (1991) used houseflies (Musca domestica) to test whether bottlenecks in populations can cause permanent alterations in courtship behavior that lead to premating isolation. They collected over 100 flies of each sex from a landfill near Alvin, Texas. These were used to initiate an ancestral population. From this ancestral population they established six lines. Two of these lines were started with one pair of flies, two lines were started with four pairs of flies and two lines were started with sixteen pairs of flies. These populations were flushed to about 2,000 flies each. They then went through five bottlenecks followed by flushes. This took 35 generations. Mate choice tests were performed. One case of positive assortative mating was found. One case of negative assortative mating was also found.

Soans, et al. (1974) used houseflies (Musca domestica) to test Pimentel's model of speciation. This model posits that speciation requires two steps. The first is the formation of races in subpopulations. This is followed by the establishment of reproductive isolation. Houseflies were subjected to intense divergent selection on the basis of positive and negative geotaxis. In some treatments no gene flow was allowed, while in others there was 30% gene flow. Selection was imposed by placing 1000 flies into the center of a 108 cm vertical tube. The first 50 flies that reached the top and the first 50 flies that reached the bottom were used to found positively and negatively geotactic populations. Four populations were established:
Population A: positive geotaxis, no gene flow
Population B: negative geotaxis, no gene flow
Population C: positive geotaxis, 30% gene flow
Population D: negative geotaxis, 30% gene flow

Selection was repeated within these populations each generations. After 38 generations the time to collect 50 flies had dropped from 6 hours to 2 hours in Pop A, from 4 hours to 4 minutes in Pop B, from 6 hours to 2 hours in Pop C and from 4 hours to 45 minutes in Pop D. Mate choice tests were performed. Positive assortative mating was found in all crosses. They concluded that reproductive isolation occurred under both allopatric and sympatric conditions when very strong selection was present. Hurd and Eisenberg (1975) performed a similar experiment on houseflies using 50% gene flow and got the same results.

Recently there has been a lot of interest in whether the differentiation of an herbivorous or parasitic species into races living on different hosts can lead to sympatric speciation. It has been argued that in animals that mate on (or in) their preferred hosts, positive assortative mating is an inevitable byproduct of habitat selection (Rice 1985; Barton, et al. 1988). This would suggest that differentiated host races may represent incipient species.


The Apple Maggot Fly (Rhagoletis pomonella) is a fly that is native to North America. Its normal host is the hawthorn tree (Crataegus monogyna). Sometime during the nineteenth century it began to infest apple trees. Since then it has begun to infest cherries, roses, pears and possibly other members of the Rosaceae. Quite a bit of work has been done on the differences between flies infesting hawthorn and flies infesting apple. There appear to be differences in host preferences among populations. Offspring of females collected from on of these two hosts are more likely to select that host for oviposition (Prokopy et al. 1988). Genetic differences between flies on these two hosts have been found at 6 out of 13 allozyme loci (Feder et al. 1988, see also McPheron et al. 1988). Laboratory studies have shown an asynchrony in emergence time of adults between these two host races (Smith 1988). Flies from apple trees take about 40 days to mature, whereas flies from hawthorn trees take 54-60 days to mature. This makes sense when we consider that hawthorn fruit tends to mature later in the season that apples. Hybridization studies show that host preferences are inherited, but give no evidence of barriers to mating. This is a very exciting case. It may represent the early stages of a sympatric speciation event (considering the dispersal of Rhagoletis pomonella to other plants it may even represent the beginning of an adaptive radiation). It is important to note that some of the leading researchers on this question are urging caution in interpreting it. Feder and Bush (1989) stated:
"Hawthorn and apple "host races" of Rhagoletis pomonella may therefore represent incipient species. However, it remains to be seen whether host-associated traits can evolve into effective enough barriers to gene flow to result eventually in the complete reproductive isolation of Rhagoletis pomonella populations."



Gall Former Fly (Eurosta solidaginis) is a gall forming fly that is associated with goldenrod ( Solidago sp.) plants. It has two hosts: over most of its range it lays its eggs in Solidago altissima, but in some areas it uses Solidago gigantea as its host. Recent electrophoretic work has shown that the genetic distances among flies from different sympatric hosts species are greater than the distances among flies on the same host in different geographic areas (Waring et al. 1990). This same study also found reduced variability in flies on Solidago gigantea. This suggests that some Eurosta solidaginis have recently shifted hosts to this species. A recent study has compared reproductive behavior of the flies associated with the two hosts (Craig et al. 1993). They found that flies associated with Solidago gigantea emerge earlier in the season than flies associated with Solidago altissima. In host choice experiments, each fly strain ovipunctured its own host much more frequently than the other host.

Craig et al. (1993) also performed several mating experiments. When no host was present and females mated with males from either strain, if males from only one strain were present. When males of both strains were present, statistically significant positive assortative mating was seen. In the presence of a host, assortative mating was also seen. When both hosts and flies from both populations were present, females waited on the buds of the host that they are normally associated with. The males fly to the host to mate. This may represent the beginning of a sympatric speciation.


Halliburton and Gall (1981) established a population of flour beetles (Tribolium castaneum) collected in Davis, California. In each generation they selected the 8 lightest and the 8 heaviest pupae of each sex. When these 32 beetles had emerged, they were placed together and allowed to mate for 24 hours. Eggs were collected for 48 hours. The pupae that developed from these eggs were weighed at 19 days. This was repeated for 15 generations. The results of mate choice tests between heavy and light beetles was compared to tests among control lines derived from randomly chosen pupae. Positive assortative mating on the basis of size was found in 2 out of 4 experimental lines.


In 1964 five or six individuals of the polychaete worm, Nereis acuminata, were collected in Long Beach Harbor, California. These were allowed to grow into a population of thousands of individuals. Four pairs from this population were transferred to the Woods Hole Oceanographic Institute. For over 20 years these worms were used as test organisms in environmental toxicology. From 1986 to 1991 the Long Beach area was searched for populations of the worm. Two populations, P1 and P2, were found. Weinberg, et al. (1992) performed tests on these two populations and the Woods Hole population (WH) for both postmating and premating isolation. To test for postmating isolation, they looked at whether broods from crosses were successfully reared. The results below give the percentage of successful rearings for each group of crosses.
WH × WH = 75%
P1 × P1 = 95%
P2 × P2 = 80%
P1 × P2 = 77%
WH × P1 = 0%
WH × P2 = 0%

They also found statistically significant premating isolation between the WH population and the field populations. Finally, the Woods Hole population showed slightly different karyotypes from the field populations.

In some species the presence of intracellular bacterial parasites (or symbionts) is associated with postmating isolation. This results from a cytoplasmic incompatability between gametes from strains that have the parasite (or symbiont) and stains that don't. An example of this is seen in the mosquito Culex pipiens (Yen and Barr 1971). Compared to within strain matings, matings between strains from different geographic regions may may have any of three results: These matings may produce a normal number of offspring, they may produce a reduced number of offspring or they may produce no offspring. Reciprocal crosses may give the same or different results. In an incompatible cross, the egg and sperm nuclei fail to unite during fertilization. The egg dies during embryogenesis. In some of these strains, Yen and Barr (1971) found substantial numbers of Rickettsia-like microbes in adults, eggs and embryos. Compatibility of mosquito strains seems to be correlated with the strain of the microbe present. Mosquitoes that carry different strains of the microbe exhibit cytoplasmic incompatibility; those that carry the same strain of microbe are interfertile.

Similar phenomena have been seen in a number of other insects. Microoganisms are seen in the eggs of both Nasonia vitripennis and Nasonia giraulti. These two species do not normally hybridize. Following treatment with antibiotics, hybrids occur between them (Breeuwer and Werren 1990). In this case, the symbiont is associated with improper condensation of host chromosomes. For more examples and a critical review of this topic, see Thompson 1987.

MACROEVOLUTION ABOVE THE LEVEL OF SPECIES


Boraas (1983) reported the induction of multicellularity in a strain of Chlorella pyrenoidosa (since reclassified as Chlorella vulgaris) by predation. He was growing the unicellular green alga in the first stage of a two stage continuous culture system as for food for a flagellate predator, Ochromonas sp., that was growing in the second stage. Due to the failure of a pump, flagellates washed back into the first stage. Within five days a colonial form of the Chlorella appeared. It rapidly came to dominate the culture. The colony size ranged from 4 cells to 32 cells. Eventually it stabilized at 8 cells. This colonial form has persisted in culture for about a decade. The new form has been keyed out using a number of algal taxonomic keys. They key out now as being in the genus Coelosphaerium, which is in a different family from Chlorella.

Shikano, et al. (1990) reported that an unidentified bacterium underwent a major morphological change when grown in the presence of a ciliate predator. This bacterium's normal morphology is a short (1.5 um) rod. After 8 - 10 weeks of growing with the predator it assumed the form of long (20 um) cells. These cells have no cross walls. Filaments of this type have also been produced under circumstances similar to Boraas' induction of multicellularity in Chlorella. Microscopic examination of these filaments is described in Gillott et al. (1993). Multicellularity has also been produced in unicellular bacterial by predation (Nakajima and Kurihara 1994). In this study, growth in the presence of protozoal grazers resulted in the production of chains of bacterial cells.


The “species flock” of over 600 species of cichlid fish in Lake Victoria have all diverged within the past 15,000 years, according to Tijs Goldschmidt. Lake Victoria, the source of the Nile River in east Africa, was formed by block faulting in the African great rift valley. Geological evidence indicates that the lake was originally formed about 400,000 years ago, but dried out about 15,000 years ago. It subsequently refilled, and the 600+ species of cichlid fish have adaptively radiated during that period of time.

As the lake constitutes a single, although very large ecosystem, the adaptive radiation of the cichlid fish of Lake Victoria must be considered to have undergone a massive sympatric divergence. That this is the case is further supported by the observation that the extraordinary phenotypic variation seen among these fish has been accompanied by almost no genetic variation, except for a very small number of homeotic genes. Goldschmidt has suggested that the adaptive radiation of the cichlids of Lake Victoria has been driven by a combination of adaptation to a myriad of trophic niches, combined with sexual selection resulting from female choice (Goldschmidt, 1998).

MACROEVOLUTION AT THE LEVEL OF KINGDOMS


In 1970, Lynn Margulis proposed that the four kingdoms of eukaryotes (Protoctista, Fungi, Plantae, and Animalia, now combined in the domain Eukarya) originated from the endosymbiotic combination of four prokaryotic (i.e. bacterial) ancestors. The first step in this endosymbiotic partnership was the endosymbiotic incorporation of an aerobic bacterium with an acid-tolerant (probably Archaean) prokaryotic ancestor. The aerobic bacterium eventually evolved into what we now recognize as mitochondria. That this was the first step in the endosymbiotic origin of eukaryotes is supported by the observation that all eukaryotic cells (except such specialized cells as erythrocytes) have mitochondria, indicating that bacteria-derived mitochondria became associated with the ancestors of eukaryotes prior to the splitting of the eukaryotic clade into the plant, fungus, and animal kingdoms.

Margulis cites several lines of evidence supporting the hypothesis that mitochondria originated as endosymbiotic aerobic bacteria:

• Mitochondria have a double membrane. The outer membrane is very similar to the membrane of the vacuoles of eukaryotic cells, while the inner membrane is much more similar to the plasma membrane of bacteria.

• Like bacteria, mitochondria have circular DNA molecules, whereas the DNA molecules in the nuclear chromosomes of eukaryotes is linear.

• Also like bacteria, the circular DNA molecules of mitochondria are not complexed with histone proteins, whereas the linear DNA molecules in the chromosomes of the eukaryotic nucleus are tightly complexed with histone proteins.

• The DNA molecules of mitochondria (like the DNA of bacteria) do not include intron sequences, whereas the DNA molecules in the chromosomes of the eukaryotic nucleus generally include at least one, and often many intron sequences.

• Most of the genetic components of the mitochondrial genome, including such genetic “machinery” as promoter sequences and terminator sequences, are coded in the same way as in bacteria, and are significantly different from the genetic “machinery” in the DNA in the chromosomes of the eukaryotic nucleus.

•Mitochondria have their own ribosomes, which are virtually identical with bacterial ribosomes, but very different in size and structure from the ribosomes in the cytosol of eukaryotic cells.

• Mitochondria reproduce independently inside their host cells via binary fission, the same mechanism by which other bacteria reproduce, and very different from the process of mitosis by which eukaryotic cells divide.

The second step in the endosymbiotic origin of eukaryotes was the incorporation of motile, microtubule-containing bacteria similar to spirochaete bacteria into the mitochondrion-containing eukaryotic ancestor. Margulis proposed that these bacteria evolved into the cilia and flagella of eukaryotic cells (called undulapodia), which eventually evolved into the mitotic spindle apparatus by which all eukaryotic cells divide. She predicted that the basal bodies of cilia and flagella would have their own DNA, a prediction that was verified by researchers who (ironically) were trying to disprove her hypothesis. Another observation supporting Margulis’s hypothesis about the endosymbiotic origin of undulapodia is the fact that, like mitochondria, cilia and flagella reproduce independently of the cells to which they are attached, via a mechanism similar to binary fission. That the incorporation of spirochaete-like bacteria into the ancestors of all eukaryotes was the second step in the endosymbiotic origin of eukaryotes is supported by the observation that almost all eukaryotic cells (except a few very primitive species) reproduce via mitosis, indicating again that the undulapodia-derived spindle apparatus became associated with the ancestors of eukaryotes prior to the splitting of the eukaryotic clade into the plant, fungus, and animal kingdoms.

The final step in the endosymbiotic origin of eukaryotes was the incorporation of photosynthetic bacteria similar to cyanobacteria into the mitochondria-and-undulapodia-containing eukaryotic ancestor. These photosynthetic bacteria evolved into the chloroplasts of eukaryotic algae and plants. Like mitochondria, chloroplasts have a number of structural and functional similarities to photosynthetic bacteria that point to their endosymbiotic origin:
• Like mitochondria, chloroplasts have a double membrane. The outer membrane is very similar to the membrane of the vacuoles of eukaryotic cells, while the inner membrane is much more similar to the plasma membrane of bacteria.

• Like bacteria and mitochondria, chloroplasts have circular DNA molecules, whereas the DNA molecules in the nuclear chromosomes of eukaryotes is linear.

• Also like bacteria and mitochondria, the circular DNA molecules of chloroplasts are not complexed with histone proteins, whereas the linear DNA molecules in the chromosomes of the eukaryotic nucleus are tightly complexed with histone proteins.

• The DNA molecules of chloroplasts (like the DNA of bacteria and mitochondria) do not include intron sequences, whereas the DNA molecules in the chromosomes of the eukaryotic nucleus generally include at least one, and often many intron sequences.

• Most of the genetic components of the chloroplast genome, including such genetic “machinery” as promoter sequences and terminator sequences, are coded in the same way as in bacteria, and are significantly different from the genetic “machinery” in the DNA in the chromosomes of the eukaryotic nucleus.

•Like mitochondria, chloroplasts have their own ribosomes, which are virtually identical with bacterial ribosomes, but very different in size and structure from the ribosomes in the cytosol of eukaryotic cells.

• Like mitochondria, chloroplasts reproduce independently inside their host cells via binary fission, the same mechanism by which other bacteria reproduce, and very different from the process of mitosis by which eukaryotic cells divide.

• If separated from their eukaryotic host cells, chloroplasts can grow and reproduce on their own, looking and acting for all the world like photosynthetic bacteria.

That this was the final step in the endosymbiotic origin of eukaryotes is supported by the observation that only plant cells (and some protists) have chloroplasts, indicating that bacteria-derived chloroplasts became associated with the ancestors of eukaryotes after to the splitting of the eukaryotic clade into the plant, fungus, and animal kingdoms. This suggestion is strengthened by recent research indicating that fungi and animals are more closely related to each other than either are to plants, indicating that the split between photosynthetic eukaryotes (i.e. algae and plants) and heterotrophic eukaryotes (i.e. fungi and animals) happened before the incorporation of endosymbiotic photosynthetic bacteria in the ancestors of algae and plants.

REFERENCES CITED

Ahearn, J. N. 1980. Evolution of behavioral reproductive isolation in a laboratory stock of Drosophila silvestris. Experientia. 36:63-64.

Barton, N. H., J. S. Jones and J. Mallet. 1988. No barriers to speciation. Nature. 336:13-14.

Baum, D. 1992. Phylogenetic species concepts. Trends in Ecology and Evolution. 7:1-3.

Boraas, M. E. 1983. Predator induced evolution in chemostat culture. EOS. Transactions of the American Geophysical Union. 64:1102.

Breeuwer, J. A. J. and J. H. Werren. 1990. Microorganisms associated with chromosome destruction and reproductive isolation between two insect species. Nature. 346:558-560.

Budd, A. F. and B. D. Mishler. 1990. Species and evolution in clonal organisms -- a summary and discussion. Systematic Botany 15:166-171.

Bullini, L. and G. Nascetti. 1990. Speciation by hybridization in phasmids and other insects. Canadian Journal of Zoology. 68:1747-1760.

Butters, F. K. 1941. Hybrid Woodsias in Minnesota. Amer. Fern. J. 31:15-21.

Butters, F. K. and R. M. Tryon, jr. 1948. A fertile mutant of a Woodsia hybrid. American Journal of Botany. 35:138.

Brock, T. D. and M. T. Madigan. 1988. Biology of Microorganisms (5th edition). Prentice Hall, Englewood, NJ.

Callaghan, C. A. 1987. Instances of observed speciation. The American Biology Teacher. 49:3436.

Castenholz, R. W. 1992. Species usage, concept, and evolution in the cyanobacteria (blue-green algae). Journal of Phycology 28:737-745.

Clausen, J., D. D. Keck and W. M. Hiesey. 1945. Experimental studies on the nature of species. II. Plant evolution through amphiploidy and autoploidy, with examples from the Madiinae. Carnegie Institute Washington Publication, 564:1-174.

Cracraft, J. 1989. Speciation and its ontology: the empirical consequences of alternative species concepts for understanding patterns and processes of differentiation. In Otte, E. and J. A. Endler [eds.] Speciation and its consequences. Sinauer Associates, Sunderland, MA. pp. 28-59.

Craig, T. P., J. K. Itami, W. G. Abrahamson and J. D. Horner. 1993. Behavioral evidence for host-race fromation in Eurosta solidaginis. Evolution. 47:1696-1710.

Cronquist, A. 1978. Once again, what is a species? Biosystematics in agriculture. Beltsville Symposia in Agricultural Research 2:3-20.

Cronquist, A. 1988. The evolution and classification of flowering plants (2nd edition). The New York Botanical Garden, Bronx, NY.

Crossley, S. A. 1974. Changes in mating behavior produced by selection for ethological isolation between ebony and vestigial mutants of Drosophilia melanogaster. Evolution. 28:631-647.

de Oliveira, A. K. and A. R. Cordeiro. 1980. Adaptation of Drosophila willistoni experimental populations to extreme pH medium. II. Development of incipient reproductive isolation. Heredity. 44:123-130.

de Queiroz, K. and M. Donoghue. 1988. Phylogenetic systematics and the species problem. Cladistics. 4:317-338.

de Queiroz, K. and M. Donoghue. 1990. Phylogenetic systematics and species revisited. Cladistics. 6:83-90.

de Vries, H. 1905. Species and varieties, their origin by mutation.

de Wet, J. M. J. 1971. Polyploidy and evolution in plants. Taxon. 20:29-35.

del Solar, E. 1966. Sexual isolation caused by selection for positive and negative phototaxis and geotaxis in Drosophila pseudoobscura. Proceedings of the National Academy of Sciences (US). 56:484-487.

Digby, L. 1912. The cytology of Primula kewensis and of other related Primula hybrids. Ann. Bot. 26:357-388.

Dobzhansky, T. 1937. Genetics and the origin of species. Columbia University Press, New York.

Dobzhansky, T. 1951. Genetics and the origin of species (3rd edition). Columbia University Press, New York.

Dobzhansky, T. and O. Pavlovsky. 1971. Experimentally created incipient species of Drosophila. Nature. 230:289-292.

Dobzhansky, T. 1972. Species of Drosophila: new excitement in an old field. Science. 177:664-669.

Dodd, D. M. B. 1989. Reproductive isolation as a consequence of adaptive divergence in Drosophila melanogaster. Evolution 43:1308-1311.

Dodd, D. M. B. and J. R. Powell. 1985. Founder-flush speciation: an update of experimental results with Drosophila. Evolution 39:1388-1392.

Donoghue, M. J. 1985. A critique of the biological species concept and recommendations for a phylogenetic alternative. Bryologist 88:172-181.

Du Rietz, G. E. 1930. The fundamental units of biological taxonomy. Svensk. Bot. Tidskr. 24:333-428.

Ehrman, E. 1971. Natural selection for the origin of reproductive isolation. The American Naturalist. 105:479-483.

Ehrman, E. 1973. More on natural selection for the origin of reproductive isolation. The American Naturalist. 107:318-319.

Feder, J. L., C. A. Chilcote and G. L. Bush. 1988. Genetic differentiation between sympatric host races of the apple maggot fly, Rhagoletis pomonella. Nature. 336:61-64.

Feder, J. L. and G. L. Bush. 1989. A field test of differential host-plant usage between two sibling species of Rhagoletis pomonella fruit flies (Diptera:Tephritidae) and its consequences for sympatric models of speciation. Evolution 43:1813-1819.

Frandsen, K. J. 1943. The experimental formation of Brassica juncea Czern. et Coss. Dansk. Bot. Arkiv., No. 4, 11:1-17.

Frandsen, K. J. 1947. The experimental formation of Brassica napus L. var. oleifera DC and Brassica carinata Braun. Dansk. Bot. Arkiv., No. 7, 12:1-16.

Galiana, A., A. Moya and F. J. Alaya. 1993. Founder-flush speciation in Drosophila pseudoobscura: a large scale experiment. Evolution. 47432-444.

Goldschmidt, T. (1998) Darwin’s Dreampond: Drama in Lake Victoria. MIT Press, Cambridge, MA, 274 pp.

Gottleib, L. D. 1973. Genetic differentiation, sympatric speciation, and the origin of a diploid species of Stephanomeira. American Journal of Botany. 60: 545-553.

Halliburton, R. and G. A. E. Gall. 1981. Disruptive selection and assortative mating in Tribolium castaneum. Evolution. 35:829-843.

Hurd, L. E., and R. M. Eisenberg. 1975. Divergent selection for geotactic response and evolution of reproductive isolation in sympatric and allopatric populations of houseflies. The American Naturalist. 109:353-358.

Karpchenko, G. D. 1927. Polyploid hybrids of Raphanus sativus L. X Brassica oleraceae L. Bull. Appl. Botany. 17:305-408.

Karpchenko, G. D. 1928. Polyploid hybrids of Raphanus sativus L. X Brassica oleraceae L. Z. Indukt. Abstami-a Verenbungsi. 48:1-85.

Kilias, G., S. N. Alahiotis and M. Delecanos. 1980. A multifactorial investigation of speciation theory using Drosophila melanogaster. Evolution. 34:730-737.

Knight, G. R., A. Robertson and C. H. Waddington. 1956. Selection for sexual isolation within a species. Evolution. 10:14-22.

Koopman, K. F. 1950. Natural selection for reproductive isolation between Drosophila pseudoobscura and Drosophila persimilis. Evolution. 4:135-148.

Lee, R. E. 1989. Phycology (2nd edition) Cambridge University Press, Cambridge, UK

Levin, D. A. 1979. The nature of plant species. Science 204:381-384.

Lokki, J. and A. Saura. 1980. Polyploidy in insect evolution. In: W. H. Lewis (ed.) Polyploidy: Biological Relevance. Plenum Press, New York.

Macnair, M. R. 1981. Tolerance of higher plants to toxic materials. In: J. A. Bishop and L. M. Cook (eds.). Genetic consequences of man made change. Pp.177-297. Academic Press, New York.

Macnair, M. R. and P. Christie. 1983. Reproductive isolation as a pleiotropic effect of copper tolerance in Mimulus guttatus. Heredity. 50:295-302.

Manhart, J. R. and R. M. McCourt. 1992. Molecular data and species concepts in the algae. Journal of Phycology. 28:730-737.

Margulis, Lynn, 1970, Origin of Eukaryotic Cells, Yale University Press, ISBN 0-300-01353-1

Margulis, Lynn, ed, 1991, Symbiosis as a Source of Evolutionary Innovation: Speciation and Morphogenesis, The MIT Press, ISBN 0-262-13269-9

Margulis, Lynn and Dorion Sagan, 2002, Acquiring Genomes: A Theory of the Origins of Species, Perseus Books Group, ISBN 0-465-04391-7

Mayr, E. 1942. Systematics and the origin of species from the viewpoint of a zoologist. Columbia University Press, New York.

Mayr, E. 1982. The growth of biological thought: diversity, evolution and inheritance. Harvard University Press, Cambridge, MA.

McCourt, R. M. and R. W. Hoshaw. 1990. Noncorrespondence of breeding groups, morphology and monophyletic groups in Spirogyra (Zygnemataceae; Chlorophyta) and the application of species concepts. Systematic Botany. 15:69-78.

McPheron, B. A., D. C. Smith and S. H. Berlocher. 1988. Genetic differentiation between host races of Rhagoletis pomonella. Nature. 336:64-66.

Meffert, L. M. and E. H. Bryant. 1991. Mating propensity and courtship behavior in serially bottlenecked lines of the housefly. Evolution 45:293-306.

Mishler, B. D. 1985. The morphological, developmental and phylogenetic basis of species concepts in the bryophytes. Bryologist. 88:207-214.

Mishler, B. D. and M. J. Donoghue. 1982. Species concepts: a case for pluralism. Systematic Zoology. 31:491-503.

Muntzing, A. 1932. Cytogenetic investigations on the synthetic Galeopsis tetrahit. Hereditas. 16:105-154.

Nelson, G. 1989. Cladistics and evolutionary models. Cladistics. 5:275-289.

Newton, W. C. F. and C. Pellew. 1929. Primula kewensis and its derivatives. J. Genetics. 20:405-467.

Otte, E. and J. A. Endler (eds.). 1989. Speciation and its consequences. Sinauer Associates. Sunderland, MA.

Owenby, M. 1950. Natural hybridization and amphiploidy in the genus Tragopogon. Am. J. Bot. 37:487-499.

Pasterniani, E. 1969. Selection for reproductive isolation between two populations of maize, Zea mays L. Evolution. 23:534-547.

Powell, J. R. 1978. The founder-flush speciation theory: an experimental approach. Evolution. 32:465-474.

Prokopy, R. J., S. R. Diehl, and S. H. Cooley. 1988. Oecologia. 76:138.

Rabe, E. W. and C. H. Haufler. 1992. Incipient polyploid speciation in the maidenhair fern (Adiantum pedatum, adiantaceae)? American Journal of Botany. 79:701-707.

Rice, W. R. 1985. Disruptive selection on habitat preference and the evolution of reproductive isolation: an exploratory experiment. Evolution. 39:645-646.

Rice, W. R. and E. E. Hostert. 1993. Laboratory experiments on speciation: What have we learned in forty years? Evolution. 47:1637-1653.

Rice, W. R. and G. W. Salt. 1988. Speciation via disruptive selection on habitat preference: experimental evidence. The American Naturalist. 131:911-917.

Rice, W. R. and G. W. Salt. 1990. The evolution of reproductive isolation as a correlated character under sympatric conditions: experimental evidence. Evolution. 44:1140-1152.

Ringo, J., D. Wood, R. Rockwell, and H. Dowse. 1989. An experiment testing two hypotheses of speciation. The American Naturalist. 126:642-661.

Schluter, D. and L. M. Nagel. 1995. Parallel speciation by natural selection. American Naturalist. 146:292-301.

Shikano, S., L. S. Luckinbill and Y. Kurihara. 1990. Changes of traits in a bacterial population associated with protozoal predation. Microbial Ecology. 20:75-84.

Smith, D. C. 1988. Heritable divergence of Rhagoletis pomonella host races by seasonal asynchrony. Nature. 336:66-67.

Soans, A. B., D. Pimentel and J. S. Soans. 1974. Evolution of reproductive isolation in allopatric and sympatric populations. The American Naturalist. 108:117-124.

Sokal, R. R. and T. J. Crovello. 1970. The biological species concept: a critical evaluation. The American Naturalist. 104:127-153.

Soltis, D. E. and P. S. Soltis. 1989. Allopolyploid speciation in Tragopogon: Insights from chloroplast DNA. American Journal of Botany. 76:1119-1124.

Stuessy, T. F. 1990. Plant taxonomy. Columbia University Press, New York.

Thoday, J. M. and J. B. Gibson. 1962. Isolation by disruptive selection. Nature. 193:1164-1166.

Thoday, J. M. and J. B. Gibson. 1970. The probability of isolation by disruptive selection. The American Naturalist. 104:219-230.

Thompson, J. N. 1987. Symbiont-induced speciation. Biological Journal of the Linnean Society. 32:385-393.

Vrijenhoek, R. C. 1994. Unisexual fish: Model systems for studying ecology and evolution. Annual Review of Ecology and Systematics. 25:71-96.

Waring, G. L., W. G. Abrahamson and D. J. Howard. 1990. Genetic differentiation in the gall former Eurosta solidaginis (Diptera:Tephritidae) along host plant lines. Evolution. 44:1648-1655.

Weinberg, J. R., V. R. Starczak and P. Jora. 1992. Evidence for rapid speciation following a founder event in the laboratory. Evolution. 46:1214-1220.

Wood, A. M. and T. Leatham. 1992. The species concept in phytoplankton ecology. Journal of Phycology. 28:723-729.

Yen, J. H. and A. R. Barr. 1971. New hypotheses of the cause of cytoplasmic incompatability in Culex pipiens L.

As always, comments, criticisms, and suggestions are warmly welcomed!

--Allen

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30 Comments:

At 2/18/2009 09:13:00 AM, Blogger Joe G said...

Allen,

First what YECs mean by micro and macroevolution:


evolution, biological n.
1) “microevolution”—the name used by many evolutionists to describe genetic variation, the empirically observed phenomenon in which exisiting potential variations within the gene pool of a population of organisms are manifested or suppressed among members of that population over a series of generations. Often simplistically (and erroneously) invoked as “proof” of “macro evolution”;

2) macroevolution—the theory/belief that biological population changes take (and have taken) place (typically via mutations and natural selection) on a large enough scale to produce entirely new structural features and organs, resulting in entirely new species, genera, families, orders, classes, and phyla within the biological world, by generating the requisite (new) genetic information. Many evolutionists have used “macro-evolution” and “Neo-Darwinism” as synonymous for the past 150 years.


So in that new light perhaps you can address the real issue.

 
At 2/18/2009 12:28:00 PM, Blogger Allen MacNeill said...

The definition of macroevolution used by evolutionary biologists who accept the validity of the term (some don't) is essentially equivalent to the term "cladogenesis". That is, it means the divergence of a new phylogenetic line (or lines) from an existing phylogenetic line. This is why speciation is considered to be a macroevolutionary process, as it involves the divergence of a new phylogenetic line (i.e. a new species) from an existing one. This is also why the post on macroevolution on my blog includes examples of speciation as macroevolution.

In this blog post I have also included examples of cladogenesis/macroevolution at taxonomic levels higher than species. One of the examples in the blog post is the adaptive radiation of the 600+ species of cichlid fish in Lake Victoria. These species are grouped into several different (although closely related) genera. Ergo, this is an example of cladogenesis at the level of genus, which meets Simpson's criterion as listed above.

I also included an example of cladogenesis via phylogenetic fusion at the level of kingdoms. The example is Lynn Margulis's serial endosymbiotic theory for the evolution of eukaryotes, and represents cladogenesis/macroevolution at the level of kingdoms (i.e. five major taxonomic levels higher than genus.

There are a plethora of examples at the levels of family, order, class, and phylum as well. I will include some of them in updated versions of my blog post on macroevolution. Most of these are examples of macroevolution in which the cladogenetic events were apparently driven by changes in homeotic gene expression, as described by Sean Carroll in his book Endless Forms Most Beautiful. I will also be presenting a detailed list of the various mechanisms by which cladogenesis occurs, and the kinds of genetic and environmental events that trigger such macroevolutionary divergences. Some of these mechanisms will be drawn from Elizabeth Vrba and Niles Eldredge's 2005 book, Macroevolution: Diversity, Disparity, Contingency; Essays in Honor of Stephen Jay Gould, published by the Paleontological Society. I'm currently working my way through the book, and recommend it to anyone interested in the subject of macroevolution.

 
At 2/18/2009 12:29:00 PM, Blogger Allen MacNeill said...

One way to visualize how macroevolution can have "gaps" of various sizes is to consider roads diverging at an intersection. At the intersection, the diverging roads are very close together, and the vehicles traveling on the diverging roads start out very close together (i.e. the way diverging phylogenetic lines begin to diverge from a common ancestor that looks and functions almost identically to the diverging lines). However, the further you get from the intersection (i.e. the longer the time since the divergence), the further apart the roads become (i.e. the greater the divergence between the phylogenetic lines). In other words, the gaps between the roads widen the further you get from the intersection.

In evolutionary terms, the original divergence is the result of several different macroevolutionary mechanisms, especially changes in gene expression, which at first can be quite insignificant. However, as time passes, the amount of genotypic and phenotypic divergence between the phylogenetic lines increases, producing the so-called "gaps" between the phylogenetic lines. The divergence is driven by several different mechanisms, including natural and sexual selection, genetic drift, founder effects, and genetic bottlenecks. These occur in an environmental context in which changes in environmental pressures result in changes in gene frequencies and expression.

As I have already pointed out in a previous blog post, the "engines" of phenotypic variation are fully capable of producing all of the phenotypic changes we see in the various phylogenetic lines in both the fossil and historic record. Indeed, the interesting question is not "is there enough capacity for variation to produce all of the changes we observe?", but rather "how do the various mechanisms of microevolution set limits on the variation such that phylogenetic lines do not regularly disintegrate?" This puts a whole new perspective on processes such as natural selection. Rather than being an "engine of change", natural selection becomes a conservative process that maintains phenotypic coherence over time,despite genetic and environmental forces that would otherwise result in rapid incoherence and continuously high levels of local and widespread extinction.

 
At 2/18/2009 12:33:00 PM, Blogger Allen MacNeill said...

Also, "neo_Darwinism" is essentially equivalent to the "modern evolutionary synthesis", in which natural selection, sexual selection, and genetic drift were invoked as the underlying mechanisms of evolution at all levels. These are, of course, microevolutionary mechanisms. Ergo, the basic position of the founders and supporters of the "modern synthesis" was that macroevolution is essentially the same as microevolution, extended over longer periods of time.

There is increasing evidence that this position does not adequately explain some of the macroevolutionary changes we see in the fossil and genomic record. New genetic and epigenetic mechanisms have been proposed to explain this new evidence. In addition, more recent explanations of macroevolution have included a more nuanced understanding of the ecological and historical contexts in which macroevolutionary divergence has taken place. It is these processes about which I will be writing in follow-up blog posts.

 
At 2/18/2009 12:54:00 PM, Anonymous Arthur Hunt said...

Hi Allen,

Thanks for a nicely detailed essay.

I know the field is voluminous far beyond the scope of a blog (perhaps even a library), but I thought I would toss in a few pennies into the well. Enjoy.

Is macroevolution impossible to study?

Transplastomics and evolution

Understanding macroevolutionary mechanisms in plants.

 
At 2/18/2009 05:32:00 PM, Blogger Joe G said...

Allen,

My point is if you want to address what the Creationists are talking about you have to do it on their terms.

IOW what they consider macro-evolution is very different from what you are using- even if what you are using is accpeted by biologists.

YECs do not debate that speciation occurs.

Heck according to them what we observe today "evolved" from the survivors of "The Flood".

And that could include variation up to the "family" level- IOW divergence is accepted- a LOT of divergence is accpted.

New body plans with new body parts- that is something very different.

That is because with that you would need new genes. New genes, new binding sites and all the other meta-information required to get these new genes into the existing combinatorial logic.

But seeing we don't have a theory of form- and evolution doesn't seem interested in addressing that- saying tat small changes add up to large changes is really meaningless without a way to test the premise.

IOW have we observed small changes adding up and what has that been demonstrated to do?

 
At 2/26/2009 04:02:00 PM, Anonymous Anonymous said...

Allen,

Since you didn't comment at UD when these were posted, I thought you may be more willing to do so at your own site.

So, Since you’ve invoked the Australian termite, I might throw in my hat … In contrast to nearly all other insects, the front and back wings of the termite look totally alike, as I have experienced dealing with these things for many years. The exception is the species Mastotermes darwiniensis, aka “Darwin termite” (It’s named after Darwin, the capital of the Northern Territory, which was named after some bloke named Charles Darwin. He did something or other of note … or notoriety …)

Anyway, the anal lobe is similar to that seen on the cockroach and praying mantis. This is observed when their hind-wings are unfolded. Evolutionists were ecstatic when this was first observed near 110 years ago. The origin of the species, at least of this area, was now a truth … The anal lobe was the proof!!!!

Cockroaches were the termites forbears, they proclaimed. Thankfully, Australia still housed these relics of the past which could be observed. Evolution is true.

OK, that’s not all. Other features that evolutionists claimed that linked cockroaches to Mastotermes termites were:

They had a more complex vein pattern in their wings, whilst other termites’wings were ‘primitive’. This is, of course, using an evolutionary assumption!

Termites have four tarsal segments in their feet, where cockroaches and Mastotermes have five tarsal segments.

Mastotermes eggs are laid in two rows, similar to cockroaches, whereas termite lay their eggs in one row.

If you are like Allen_MacNeill and invoke evolution then these features will be exactly what is required to say macroevolution is ‘Truth’. Yet, from an ID perspective a common designer is as just as likely, even more so when further evidence is brought into the mix.

Firstly, Mastotermes is far from being a primitive ancestor. The communities they build are among the most populous of the social termite species. An evolutionist may even indicate that this species might even be highly-evolved (!).

Termites, and not cockroaches, shed their wings at their pre-formed breakage points. So do Mastotermes. The pre-formed breakage points also point, in my estimation, to something showing design.

The mantis and cockroach anal lobe is folded up in a fan-like manner. Mastotermes bends over flat on the wing. This seems more to be looking for a link than finding one. But when Darwinism is floundering, any anal lobe similarity is proof …

But that’s not all folks! Interestingly, a fossil in Dominican amber, allegedly 35 million years old, of a winged ‘Mastotermes electrodominicus’ is near identical as the ones found still living in Australia:

The species has the same complicated wing-vein pattern;

It has the five-segmented feet;

It has those wonderful anal lobes!

Mastotermes at its first ‘evidentiary’ appearance isn’t any less ‘evolved’ than what you can find in the Australian ‘Darwin termite’. Is there ’scientific’ reason to consider that this termite has evolved at all, in a macro-sense, from cockroaches, Allen_MacNeill?

BTW, the same amber also holds termite species that have ‘modern’ features, as evolutionist would tell us. So, again, what is the evidence that one type is the ancestor of the other?

The link with cockroaches is more fanciful than evidential.

Watchathink Allen?

AussieID

 
At 2/26/2009 04:09:00 PM, Anonymous Anonymous said...

Allen, now more specifically to an example you cite:

Re: evening primrose, Oenothera lamarckiana, de Vries (1905)

Oenothera lamarckiana is an invalid synonym for the plant species Oenothera glazioviana, It’s common name means ‘large-flower evening primrose’. Oenothera gigas was the name used a century ago for tetraploid mutants of the various Oenothera species. This included tetraploids of Oenothera lamarckiana.

de Vries had named named it O. lamarckiana, but it had already been called Oenothera glazioviana by Carl Friedrich Philipp von Martius. So the name O. lamarckiana should be defunct and so it is wrongly cited.

De Vries believed that tetraploid Oenethera plants would ‘breed true’, forming a distinct species. However, the tetraploid specimens of Oenothera that de Vries and other botanists cultivated did not form their own self-perpetuating populations, requiring constant special care and consistently generating a range of chromosome sets (diploid, triploid, tetraploid, etc.) in their offspring. In his zeal to provide evidence for evolution, de Vries had presumptuously proclaimed tetraploid Oenotheras to be a new species This was in spite of direct evidence to the contrary. This included evidence from his own breeding efforts. The idea that these plants constituted an example of speciation is wrong, and this was realized at least as long ago as 1943. [See Davis, B.M., An amphidiploid in the F1 generation from the cross Oenothera franciscana x Oenothera biennis, and its progeny, Genetics 28(4):275–285, July 1943.] On page 278 Davis writes: “In summary it should be emphasized that this amphidiploid did not present a settled behaviour of all pairing on the part of the chromosomes at diakinesis. On the contrary, there was much irregularity in the process of chromosome segregation during meiosis. Accounts of amphidiploids have frequently assumed that these plants even from hybrids would breed true because the double set of chromosomes would permit a regular pairing between homologues. It will be noted that here is an amphidiploid Oenothera hybrid in which the pairing is far from regular with the result that the plant does not breed true, as will appear in the accounts of later generations.”

That O. gigas is still presented as an evidence for evolution reflects very poorly on those amplifying evolution to be able to do things as they claim. There is a matter of pride, honour and status for a scientist to identify and name a new species. This results in the situation where some species have been named and renamed multiple times by different scientists. This is true for botanists to identify varieties as new species, even when the evidence is equivocal. As such, in this case it seems that an intense desire to produce evidence for his evolutionary faith apparently influenced de Vries to ignore conflicting data.

I’m sure you’ll note that all this has nothing to do with evolution of the microbes-to-man sort. Evolution requires the coming into existence of encyclopaedic amounts of new information, coding for new types of organs, new kinds of appendages, etc. Change of this sort, from one kind of organism into a different kind, has not been observed. Observed speciation involves only the elimination, duplication, reshuffling or degradation of existing genetic information. The various mutant varieties of evening primrose are all still evening primroses. If a self-sustaining reproductively-isolated population (i.e. a new ‘species’) of tetraploid Oenothera plants had developed, this would not constitute an example of evolution of the microbes-to-man sort. The same genes are present in the tetraploid, just twice as many of them. The information is merely duplicated in the tetraploid.

I can’t wait to see your chapter in your forthcoming textbook. If you place any of that information on which you blogged in your text because of your comment: “response to yet another unsupported assertion by creationists and ID supporters, who often state (without evidence) that although microevolution might happen, there is no evidence for macroevolution” then it says more about your fundamentalist beliefs than about your science.

AussieID

 
At 2/26/2009 04:12:00 PM, Blogger Allen MacNeill said...

I know almost nothing about termites, including those from Australia, so this would be a question to ask somebody else, preferably a systematic entomologist or someone with some knowledge of the molecular phylogeny of Isoptera.

 
At 2/26/2009 06:54:00 PM, Blogger Allen MacNeill said...

As to the comments about the example of polyploid hybridization in Oenothera, it isn't strictly the case that Oenothera lamarckiana is wrong, but rather that it is what is known in systematics as a synonym for Oenothera glazioviana. That is, several genetically very similar groups of plants were described and a scientific names for them was proposed by more than one systematist. This happens all the time, and is the reason why there are international organizations whose responsibility it is to ensure clarity and priority in the classification of living organisms.

That said, the rest of the comment by "anonymous" is interesting, but not necessarily for the reasons "anonymous" might think. While it is true that polyploid hybrids of Oenothera are not necessarily genetically stable, requiring special conditions and sometimes reverting or converting to other forms, this does not in any way contradict the underlying point that the formation of any and all of these polyploids (via hybridization or some other mechanism) clearly violates the "fixity of species" that is one of the bedrock beliefs of creationists. Indeed, by admitting that this sort of genetic and phenotypic rearranging goes on all the time (especially in certain groups of organisms), creationists are essentially conceding the fact that species are fundamentally not "fixed", but rather quite variable, even ephemeral groupings.

This idea – that species are "specious" – was the underlying point in my previous blogpost on this subject (located at http://evolutionlist.blogspot.com/2006/03/origin-of-specious.html). I will close by quoting from the conclusion to that essay:

"Perhaps Darwin's most important insight was his realization that species are not immutable, that they can intergrade over time in an "insensible series." But what Darwin didn't have the courage to come right out and say, and what most evolutionary biologists in general don't have the courage to propose, is that there are really no such thing as species at all, at least not in the way we have traditionally defined them. Darwin should have realized this: he made it clear that natural selection happens at the level of individuals, never at the level of species. Evolutionary biologists have agreed with him, but have not taken the obvious next step: to declare that individuals living organisms are the only things that exist in the natural world, and that species (including animal species) may quite literally be figments of the human imagination."

 
At 2/26/2009 11:16:00 PM, Anonymous Anonymous said...

Allen, I'll quote you from over at UD: "Serial endosymbiosis has been observed multiple times in nature. Perhaps the most notable example is in the protozoan Mixotricha paradoxa, an endosymbiont of the Australian termite, Mastotermes darwiniensis. " I addressed this point of yours over at over UD, then reposted here.

I thought it was interesting that you now turn around and say you know nothing of termites ... hmmm.

AussieID

 
At 2/27/2009 05:17:00 AM, Anonymous Anonymous said...

Allen touts the ‘fixity of species’ canard. Either he really believes that this is believed by modern creationists or he is just truly out of date, or … he is setting up a straw man for his audience.

Linnaeus’ principle of Nullae species Novae - that God contended to use an ideal template for all creatures that allowed no morphological deviation – was certainly true for a majority of his career, but in his latter years, through his hybridization experiments, he discovered his ‘species’ concept was too constricted for the species to be thought as created kinds. The genus level, he considered, was better at corresponding to the created kind. John Ray, another great of the early years of biology, also made observations that caused him to modify his position allowing speciation by a combination of degenerative changes and/or cross-breeding to occur. They changed their minds back in the 18th century …

If you want to attack the creationist then ask where it touts ‘fixity of species’ in the Bible. They wouldn’t be able to locate it because it isn’t there. The created ‘kind’ is what a creationist would say, and that is still true to this day. So, for the readers here to get a better understanding of what is being related, here is ‘Created Kinds – 101’.

When two animals/plants can hybridize then they have descended from an original created kind. Say, though, the hybridizing species comes from different genera in a family, then the suggestion would be made that the whole ‘family’ would come from one created kind. If the ‘genera’ are in different ‘families’ within an order, then the whole order may have descended from an original created kind.

But if two species can’t hybridize it doesn’t necessarily prove that they are not originally from the same kind. Barriers related to breeding may arise through mutations, etc. Eg: Two types of Drosophila produced offspring that could not breed with the parent species, thus gaining the title of a new biological ‘species’. Because of a minor chromosomal rearrangement breeding was inhibited, not because of any new genetic information. This new ‘species’ was impossible to differentiate from the parents and clearly the same ‘kind’ as the parents, especially since it came from them.

The created kind is often at a higher level than the species, or even the genus. Here are some examples of hybrids that show this:
Crossing Equus asinus and Equus caballus produces a mule, where the reverse produces a hinny. Hybrids between, say, Equus quagga and Equus caballus creates zorses and Equus quagga and Equus asinus make, well, take your pick: zedonk, zonkey or zebras. DNA is extremely similar in each of these ‘species’ but it doesn’t match up accurately to allow fertile offspring. ‘Fixity of species’ is not a contestable argument, especially since creationists don’t argue for it.

Panthera leo and a Panthera tigris can mate to produce a liger or, vice versa, a tigon. Panthera, Felis and Acinonyx are all of the cat family, but mutations and loss of information are the pertinent markers. ‘Fixity of species’ is not a consideration: it is at a higher level that immutable change cannot manifest.

Pseudorca crassidens - a male false killer whale - and a female bottlenose dolphin Tursiops truncates mated and produced a fertile offspring. This is a case where different genera in the same family (Delphinidae) were able to breed. Does this suggest that the genera may have may all be descendants of an original kind, and this is all above the level of species?

Camels and llamas can interbreed, cattle and buffalo can interbreed and there is a case from California where an albino king snake (Lampropeltis triangulum) and a corn snake (Elaphe guttata) produced fertile offspring.

Allen, variation from the daughter species arose from what the creationists called the created kinds. Each would have less information, though more specialised, than the parent. Natural selection gets rid of information and has never added new information. Linnaeus provided a scaffold for classification which, as you would obviously agree, is still in use today. ‘Fixity of species’ isn’t Biblical, isn’t used by any YEC creationists today, and goes against what is obvious in repeatable testing: there is proven speciation within the kind. Creationists regard speciation as an important part of the Creation/Flood/dispersion model, so why would they argue for something that isn’t part of their model?

This non sequitur/straw man enjoys uncritical acceptance today because of ill-informed comments. You are now informed.

You write that species are fundamentally not "fixed". It seems you are already becoming more YEC by the moment!

AussieID

 
At 2/27/2009 07:24:00 AM, Blogger Joe G said...

Allen,

Creationists do NOT insist on "fixity of species".

That was a strawman erected by Darwin.

The Creation baraminology refutes the notion of "fixity of species".


Ever heard of Linneaus?

He was a Creationist trying to define the Created "Kinds".

Eventually he settled on the level of "Genus"- which means that species change.

And that means that Creationists have accepted speciation for over 200 years.

 
At 5/20/2009 05:51:00 PM, Blogger Nelly said...

Hi Allen,
Just a few words to correct a little mistake. The fruitfly picture you present as Drosophila pseuodobscura is not! It is a male Drosophila melanogaster.
D. pseudoobscura is much darker and bigger than D. melanogaster.
Thanks for the discussion,
Cheers,
Nelly

 
At 5/20/2009 05:52:00 PM, Blogger Nelly said...

Hi Allen,
Just a few words to correct a little mistake. The fruitfly picture you present as Drosophila pseuodobscura is not! It is a male Drosophila melanogaster.
D. pseudoobscura is much darker and bigger than D. melanogaster.
Thanks for the discussion,
Cheers,
Nelly

 
At 10/03/2009 08:22:00 AM, Blogger illuzion30 said...

This seems to call the Chlorella bit into question: http://www.asa3.org/archive/asa/199611/0146.html

 
At 10/07/2010 07:09:00 PM, Anonymous Daniel Grove said...

I am not impressed with this supposed proof of macroevolution or speciation, simply because for it to happen it requires an experiment and an experiment requires a scientist.

 
At 4/07/2011 06:38:00 PM, Blogger Phillip Henry said...

Hi, Allen,

Really interesting stuff. Please keep up the good work!

One thing: please don't be quite so paranoid about those who believe ID. There are those of us who believe in evolution. But that's the problem: belief. As a scientist (albeit a physicist who is quite ignorant of biology) I want more than belief.

This blog has gone some way to address my scientific reservations. Thanks!

Phill

 
At 10/22/2011 01:49:00 AM, Anonymous Anonymous said...

You go AussieID!!!

 
At 5/03/2012 08:07:00 AM, Anonymous Anonymous said...

The fly started of as a fly, and ended up as a fly.

 
At 9/09/2012 08:57:00 AM, Anonymous Anonymous said...

I think that the reason people won't believe in evolution is because they can't grasp the idea of time. Evolution takes place gradually over a long period of time. 100 years is a long time, but can you imagine one million years taking place? Or perhaps 100 million years? I can't even imagine how much change went on over the course of evolution because the amount of time it takes is astounding. To go from a single-celled organism to a human in the course of a few billion years is incredible.

 
At 11/02/2012 11:41:00 AM, Anonymous Student said...

You are using microevolution examples as macroevolution examples... everyone notices this right??

 
At 2/26/2013 06:02:00 PM, Anonymous Anonymous said...

Yes, I noticed. (the plants are ending up as plants. The insects are ending up as insects.)

I'm actually doing research trying to figure out what I believe, and the deeper I dig, the more I'm finding 2 different faith systems: "God of the gaps", and "time of the gaps". One one hand, creationists are being hanged for believing that if there is no evidence of the slow gradualism, then that is evidence of an outside agent. However, I'm also finding that those committed to evolution have just as much faith in "time". Given enough "time" anything is possible. I don't understand how science can claim one faith system as more scientific than the other? Both are assumptions based on limited observation.

 
At 5/20/2013 08:57:00 AM, Blogger Alberto F. Taure said...

.
Henderson dicctionary Biology
Macroevolution
Evolutionary proceses extendeding thru geological times leading to the evolution of makeing diferent genere and higher taxa
.
Show me an example where an animal transforms into a new Genere and a new higher taxa
.

 
At 11/22/2013 10:48:00 PM, Blogger ron5 said...

You already are an example unless you can explain another reason why you have a tail bone?

 
At 2/16/2014 11:30:00 AM, Anonymous Anonymous said...

ron5,

I hate to break it to you, but the "tail bone is proof" shtick has been debunked already. We use it, still, today. It's not vestigial.

Now, while keeping your mind open, consider the fact you've just been blindly following a false "proof". Hurts your credibility, doesn't it? What else do you believe is false? Consider that.

 
At 4/30/2014 04:59:00 PM, Anonymous jmichaelbaker96 said...

I appreciate your blog, and admire your professionalism under fire. Although I do not agree with your findings, I see more observations and facts pointing to I.T., but your professionalism is a great example to everyone on both sides of the debate. If Evolution is real then I hope you find rock solid undeniable evidence. I think the mathematics of statistics and the fact that we are observing very delicate, irreducibly complex "machines" at the biochemical level points to a designer of life more so than evolution. This is not about a religious construct, but just a person looking at both sides of the argument

 
At 6/07/2014 04:03:00 PM, Blogger Oliver Wetmore said...

no proof for macro-evolution here.. I have never heard of any credible evidence, all these examples are of micro-evolution. It angers me but it also strengthens my belief in an intelligent designer.

 
At 7/30/2014 10:23:00 AM, Anonymous Anonymous said...

"I hate to break it to you, but the "tail bone is proof" shtick has been debunked already. We use it, still, today. It's not vestigial."

Hate to break it to you but "Vestigiality refers to genetically determined structures or attributes that have apparently lost most or all of their ancestral function in a given species"

Focus on "most". It has. Nothing has been debunked. That's another problem with ID loons. They don't know the meaning of words.

 
At 7/31/2014 09:21:00 AM, Blogger Joe G said...

Vestigial body parts is one of the worst arguments ever. For one it requires many assumptions. And for another can never be scientifically tested.

 

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