[Taxacom] Clade age (was: Taxacom Digest)‏

Jason Mate jfmate at hotmail.com
Fri Nov 11 12:55:47 CST 2011

Dear Lynn,

If you are defining species then good luck. There is a variety of definitions to choose from and every single one fails in some case or another. Still, yours should at least tick a few boxes before you can confidently call them good species. So from a phylogenetic/cladistic species´concept they are not distinct (1 point against) but they are identifiable on some morphological level which is geographically correlated (1 in favour) as well, it seems, as ecologically (+1: I assume that the different forms differ in their ecologies somehow even if the choice of habitats is equivalent for all?).  Crossing experiments are the next obvious aspect to check. The fact that they lack the vagility to actually interbreed should not discourage you from trying. The presence of breeding barriers would at least cement the case (no gene flow whatsoever) or if they do cross the heterozygotes are inferior to homozygotes (emerging barrier). Still, fully hybridising organisms can be good species (I feel sorry for botanists) so the concept only works one way.  If it is impossible to work on live specimens then stick your neck out and make a call: "a species is what a competent taxonomist says it is." 
Going back to your original population, if you assume that that it was instantly subdivided, each resulting population may have originally had the same geno/phenotypic variation (assuming panmixis and homogeneous environment) and after division each would would have evolved its own distintiveness from this common base. However widely distributed populations are hardly panmictic so even if it became instantly subdivided each resulting population could potentially have differed from the get go and you could just be reconstructing the ancestral metapopulational structure. Not much help either way other than "knowing" they form a monophylum.


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