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RE: C. bottae taxonomy

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Posted by: CKing at Fri May 16 21:00:17 2008  [ Report Abuse ] [ Email Message ] [ Show All Posts by CKing ]  

>>Concerning your next to last paragraph and the results of crosses that have been made thus far, I suggest ignoring the point about large and dwarf morphs. In other words, both reciprocal crosses (3 each) were made between boas of the Sierra Nevada and Northwestern subcades. All such crosses proved to be viable in that full term neonates were produced. Since these crosses occurred in recent years, insufficient time has elapsed in order to determine if the F-1 offspring are fertile.>>

Are these offsprings small or large morphs? You did not say. It is important to keep such phenotypic data because it can help a geneticist in figuring out how the different morphs are controlled genetically.

>>However with respect to reproductive compatibility, it should be noted that the original cross in 1996 was between a Southern Clade male and Northern Clade female which produced 4 full term neonates. Of the two surviving male and female F-1 progeny, the F-1 female has been determined to be fertile. That a cross between specimens that have been isolated from between 4.4 to 12.3 million years (according to Javier's paper) can reproduce, produce full term neonates, and produce progeny that are themselves fertile does not lend support to any assumption that matings between members of the two subclades would result in infertile progeny. >>

Time really has very little (if anything) to do with reproductive compatibility. As Ernst Mayr points out, there are some plants that have been isolated on opposite sides of an ocean for millions of years and yet they remain reproductively compatible. OTOH, polyploidy can result in instantaneous speciation, within a single generation since the hybrids in general have low viability. Unfortunately, such knowledge has not prevented some taxonomists from using genetic distance to draw species boundaries. If they found that two populations have been isolated from one another for a few million years, then they assume that these two populations are different species. Speciation is not a function of time, but a function of adaptations to niches. Rapid speciation can occur if there are many unfilled niches and intense intraspecific competition within the old niche. The often cited Cichlid fishes of the African lakes are classic examples of rapid speciation. Conversely, two populations that have been isolated for over 10 million years may still be conspecific because neither had changed or adapted to a new niche.

>>Secondly, F-1 results between crosses of the two large morph populations would not likely shed any light on the factor(s) that produce the large morph condition.>>

You may be correct. But reproductive compatibility cannot be assumed. Of course, the best sort of data would be evidence from nature. If intergrades between the Northwestern and Sierra Nevada subclades are found in nature, then the question is answered.

>>That is because regardless of the male parent, large morph females of the Northwestern subclade have produced only large morph progeny.>>

That is a very interesting fact. However, you also stated in an earlier post that "Crosses between dwarf morph females and large morph males have produced only dwarf morph neonates."

That would suggest to me some sort of sex linkage in the inheritance of the large and small morph phenotypes.

>>Nothing of certainty can be mentioned about what large morph females of the Sierra Nevada subclade would produce but odds are that they too would produce only large morph progeny if mated to males the Northwestern subclade or males of the Southern Clade.>>

That is a reasonable hypothesis but it cannot be assumed. It has to be tested.

>>One would have to take such crosses to either backcross or F-2 generations to potentially reveal differences that may occur.
>>Richard F. Hoyer

Hopefully someone would take the time and effort to perform these captive breeding experiments, and then report the results to the scientific community. It would be of interest to evolutionary biologists how the large morphs evolved from the small morph snakes that seem to represent the ancestral condition in the rubber boa. What environmental conditions and/or historical events in the past favored the evolution of the large morphs, for example, would be of interest to evolutionary biologists, even though these questions may not be of interest to the taxonomists.


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