Soapy Sam
Posts: 659
Joined: Jan. 2012
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| Quote (Wesley R. Elsberry @ Jan. 02 2013,13:16) | | Quote (Soapy Sam @ Jan. 02 2013,04:50) | | Quote (Wesley R. Elsberry @ Jan. 01 2013,03:11) | | Go here, then search for "karyotype". |
I'm not so sure fission/fusion is a common mechanism of speciation per se [...] |
Maybe change in karyotype is mostly incidental and secondary to other isolating mechanisms. If that's the case, what pattern of karyotype changes do you expect to see in taxa? Does it fit with the observed pattern in the taxa I mentioned of swine and peccaries? |
I think the problem would be that it is difficult to make a prediction at taxon level. If a chromosome rearrangement was a prime driver of a bifurcation, or bifurcation occurred and then one lineage subsequently experienced a near-neutral break or fusion, there would be the same number of species, and the same karyotype pattern.
There are 9 pericentric inversions and one fusion between human and other apes. It would be a stretch to consider them all involved in speciation of the LCA, which allows at least the possibility that none of them were.
The signal of a fission/fusion event in speciation would be very hard to detect, because 'gap+' may be functionally equivalent to some bridging patch of neutral sequence, due to the capacity of meiosis to align homologous stretches.
Inversions are more likely to provide a signal, because they act as a partial barrier to gene flow by locally blocking recombination. If diverging populations were in contact, we would get different patterns within and outside the inversion region. Data for humans appears inconclusive.
There's an interesting treatment of karyotype evolution in mammals in Burt and Trivers's 'Genes in Conflict'. Genera almost all have a distribution of karyotypes that cluster at the 'ends' - either 'mostly metacentric' or 'mostly acrocentric', with fewer in the middle, half-and-half. The preferred explanation is that female meioisis periodically switches polarity, alternately favouring breaks (more centromeres) and fusions (fewer). This pattern is too widespread to suppose that, every time a break or fusion tracking the current position of the egg/polar bodies occurred, two new species were formed, with ultimate elimination of the one with the distribution closer to the median.
Since karyotype changes appear to be more common than speciation events, it becomes hard to directly implicate them in any particular one.
Edited by Soapy Sam on Jan. 03 2013,12:39
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SoapySam is a pathetic asswiper. Joe G
BTW, when you make little jabs like “I thought basic logic was one thing UDers could handle,†you come off looking especially silly when you turn out to be wrong. - Barry Arrington
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