5.4 Housefly Speciation Experiments
5.4.1 A Test of the Founder-flush Hypothesis Using Houseflies Meffert and Bryant (1991) used houseflies 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.
This appears to be rather conclusive proof against the founder-flush hypothesis. Granted, the process happens, but it
does not inspire assortative mating. Only one case was observed and to counter that, one case occured that was opposite of what they expected!
5.4.2 Selection for Geotaxis with and without Gene Flow Soans, et al. (1974) used houseflies 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:
Pop A + geotaxis, no gene flow
Pop B - geotaxis, no gene flow
Pop C + geotaxis, 30% gene flow
Pop D - 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.
This is a brilliant experiment. It was also very successful. It proves that gene flow does indeed occur. The results,
however, can practically be thrown out because of the unbelievable strictness of the experiment. While these types of things may, indeed,
occur in nature, it has been so exaggerated by this experiment that the results are practically worthless with the exception of drawing
a conclusion from them. Also, this is a great example of how specific traits can be exaggerated in a population, but not evidence for
evolution.
5.5 Speciation Through Host Race Differentiation Recently there has been a lot of interest in whether the
dif- ferentiation 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.
5.5.1 Apple Maggot Fly (Rhagoletis pomonella) Rhagoletis pomonella is a fly that is native to North America. Its
normal host is the hawthorn tree. 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 R. 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 inter- preting it. Feder and Bush (1989) stated:
"Hawthorn and apple "host races" of R. 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 R. pomonella
populations."
Well, it's nice to see evolutionists finally getting cautious about something. Let me ask a few questions. Number one,
how is it known that this fly did not occupy any other types of flora during the nineteenth century? To my knowledge,
scientific knowledge was quite under-advanced at that time. Is it possible that these two variations may have existed prior to
their discovery? The fact that they can mate with each other proves that they remain of the same species (which is not
called into question here). In short, I must dismiss this as hype unless further evidence someday proves me wrong and they right.
5.5.2 Gall Former Fly (Eurosta solidaginis) Eurosta solidaginis is a gall forming fly that is associated with
goldenrod plants. It has two hosts: over most of its range it lays its eggs in Solidago altissima, but in some areas
it uses S. 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 S. gigantea.
This suggests that some E. 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 S. gigantea emerge earlier in the season than flies associated with S. 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. Like the Rhagoletis case above,
this may represent the beginning of a sympatric speciation.
I love this assumption: "This suggests that some E. solidaginis have recently shifted hosts to this species."
That doesn't mean anything for evolution. If anything, it speaks against it because it shows that genetic difference
are not great between ALL hosts. What we see is something much like races. Different types of flies live in
different kinds of environments. This does NOT mean that they evolved from one another. What we see in the second half of
this paragraph is a case of familiarity and POSSIBLE genetic memory. The species goes to where it it most familiar
and waits to mate with the type of fly it is most familiar with. This is all.
5.6 Flour Beetles (Tribolium castaneum) Halliburton and Gall (1981) established a population of flour
beetles 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.
2 out of 4? Sounds like perfect random chance to me. 50/50!
5.7 Speciation in a Lab Rat Worm, Nereis acuminata 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 X WH - 75%
P1 X P1 - 95%
P2 X P2 - 80%
P1 X P2 - 77%
WH X P1 - 0%
WH X 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.
Gee, what a surprise! The wood hole worms were used for toxicology (chemical) experiments for 20 years! Their
DNA or genetic structure was slightly altered. Who wouldn't expect that? They were testing potentially harmful chemicals
on those worms. Of course they are going to be affected in some way! Does this exhibit evolution? NO! Does this show
how harmful chemicals, not naturally present in an animals environment, can alter it's genetic structure if subjected to it
long enough? Yes. That's called mutation. It is also caused by radiation.
5.8 Speciation Through Cytoplasmic Incompatability Resulting from the Presence of a Parasite or
Symbiont 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 N. 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.
Wow. Now I can go home and say: "I learned something from Joeseph Boxhorn today!" This is great, but does
nothing for proving evolution. This is a great tid bit, but is essentially worthless information for evolution seekers.
In short, microbes and parasites present in genetic material can inhibit reproduction. If you give incompatible breeds
antibiotics they can become compatible and breed (if treating the egg anyways). Of course, I'm pretty sure this doesn't happen
in nature.
5.9 A Couple of Ambiguous Cases So far the BSC has applied to all of the experiments discussed. The
following are a couple of major morphological changes produced in asexual species. Do these represent
speciation events? The answer depends on how species is defined.
5.9.1 Coloniality in Chlorella vulgaris Boraas (1983) reported the induction of multicellularity in a strain of
Chlorella pyrenoidosa (since reclassified as C. 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.
It is an outrage to science that this has been reclassified as a seperate species! How do they figure this?! It
is ridiculous to suggest that this is now a multicellular creature. It is, in fact, a collection of unicellular creatures
grouped together. It's like suggesting that towns and cities are seperate species because it is a place where people "colonize."
It is a disgrace and an embarassment to science that this has occured. It should be obvious to everyone that eight unicellular
creatures sticking together in a pack is not a seperate species, but merely a group of unicellular creatures exhibiting a previously
unobserved behavioral pattern. A lone lion travels the serengeti. If a lone lion is a lion, then what is a pride of lions? Should
a pride be classified as a seperate species from a single lion? I could go on and on forever, but I won't. I hope you can see
why I am so shocked by this apparent lack of judgement.
5.9.2 Morphological Changes in Bacteria 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.
Unfortunately, the way the author presented the information above, there is little evidence for me to argue against. He does
not tell you what the bacteria is. He does not tell you what the predator is. Even if there was something to argue against, I'm not
sure I would. I don't even know what kind of bacteria we're talking about! Neither do you!
What we see in Joeseph Boxhorn's article, Observed Instances of Speciation, is many assumptions, one sided
statements and virtually dozens (out of dozens) of completely irrelevant examples written to give the appearance of a massive amount
of data backing evolution and speciation. What we really see are examples that have litte or nothing to do with evolution.
I wonder why Talk.Origins Archives would carry and feature such an article. I hope that you have also noticed that every one of these
examples has been guided by a higher intelligence (man) or has previously existed for an unknown, assumed amount of time. Thank you
for taking the time to read this and I hope that I have helped to shed some light on the subject for you.
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