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 Posted: Thu Jul 17, 2008 6:07 pm Post subject: Sympatric Speciation or Speciation without Changes in Genes |
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Sympatric Speciation or Speciation without Changes in Genes
For a long time, sympatric speciation has been considered as an
unlikely mode of speciation because, paradigmatically, the process of
speciation has been considered to require accumulation of differences
in the gene pools of two populations which under panmictic conditions
in sympatry cannot occur.
However, numerous cases of sympatric speciation have been described in
natural populations of invertebrate and vertebrate animals. For
example:
1. The apple fruit fly Rhagoletis pomonella evolved in sympatry from
the Rhagoletis hawthorn feeding flies, during a period of less than 2
centuries since introduction of apple trees in North America.
2. The corn borer Ostrinia nubilalis was introduced in the European
continent only five centuries ago. Ever since two species/host races
have evolved in sympatry, one feeding on maize and the other on
mugwort.
In the case of Rhagoletis pomonella, the sympatric speciation was
based on a neurally, epigenetically determined increased preference
for an apple fruit volatile (butyl hexanoate) olfactory signal. In the
case of the European corn borer the sympatric speciation was a result
of quantitative changes in production of composition of the same
pheromone compound mix and the respective changes in mating
preferences of male individuals for specific. No genetic differences
exist in genes (including genes responsible for pheromonal components)
and mitochondrial DNA of both populations and reproductive isolation
of populations is based on epigenetic neural factors.
In vertebrates, Lake Malawi, East Africa, harbors 500 endemic cichlid
fish species evolved during ~ 700,000 last years without any
geographic isolation that would prevent random mating and genetic and
reproductive isolation. The only factor involved in reproductive
isolation is an epigenetic factor, neuro-cognitively determined mate
preferences for specific visual (and probably olfactory) signals.
Explosive evolution of 35 salamander species in northeastern America
also occurred in sympatry based a behavioral transition from
“scratching” mode to an olfactory mode of delivering pheromones during
mating, rather than any change in a relevant gene(s).
Are changes in genes or in allele frequencies necessary for speciation
to occur?
In depth discussion of the issue can be found in the website
http://www.epigeneticscomesofage.com (chapter 20, pp. 645-732) |
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Tim Tyler
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| Posted: Mon Jul 21, 2008 5:41 am Post subject: Re: Sympatric Speciation or Speciation without Changes in Ge |
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CNCa...@aol.com wrote:
[quote]Sympatric Speciation or Speciation without Changes in Genes
[/quote]
Sympatric speciation is not speciation without changes in genes.
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Entertained by my own EIM
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| Posted: Mon Jul 21, 2008 5:41 am Post subject: Re: Sympatric Speciation or Speciation without Changes in Ge |
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<CNCabej@aol.com> wrote in message news:g5o1p1$kff$1@darwin.ediacara.org...
[quote]Sympatric Speciation or Speciation without Changes in Genes
snip
Are changes in genes or in allele frequencies necessary for speciation
to occur?
In depth discussion of the issue can be found in the website
http://www.epigeneticscomesofage.com (chapter 20, pp. 645-732)
It seems to me that as long as one by "intrinsically *speciating* event"[/quote]
does not specifically or only mean a DNA mutation that makes impossible
sexual reproduction between an individual with the type of genome from which
such a mutation has arisen and a thus mutated individual itself, then any
cyto-chemical and physiological mechanisms (e.g. function of specialized
neurons and glands) that can contribute to causing "reproductive isolation"
(between individuals of the same species) can easily and plausibly be
regarded as potentially - and of course sometimes also actually -
"speciating".
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