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I have recently become fascinated with an awesome topic in biology and evolution that I feel is rarely covered in biology courses. That is, rates of meiotic recombination, or the the amount that an organism's genome is reshuffled before it is passed on to the next generation, varies across species! And no one really knows why. A recent paper by Segura et al which gathered average recombination rates for males across a dozen or so mammals and showed that there is a trend of increasing recombination rate with mammalian divergence.

Why is recombination increasing through mammalian evolution? Is there any reason to believe that there is something special about placental mammals which would drive increased recombination?

There are some catches to this study such as low sampling of marsupials and monotremes and low power for most of species wide recombination rates, ie the average recombination rate of cells in a single individual. But I can see how getting samples from multiple tigers would be difficult.

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If rates of meiotic recombination DIDN'T vary across species - THIS would require an explanation! After all, evolution creates diversity, not homogeneity.

I can only wonder that more recombination would allow for a faster diversification. The more DNA you shuffle, the more distinct each individual offspring may be (though I'm not 100% sure). The recombination rate has an energetic price, so not all animals recombine so much their DNA like later mammals. I.e. they needed a selective pressure to justify paying that price.

Perhaps it was useful for a group rapidly occupying the "vague niches" left by dinosaurs? This make sense, since the primary mammalian irradiation occured in the beginning of the Cenozoic era, right after the Cretaceous mass extinction that killed most big animals, including the biggest dinosaurs.

Unfortunately I have no references on the subject, it is just what makes sense to me, given evolutionary logic.

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    $\begingroup$ My logic would rather tend to predict that high recombination rate should rather be correlated with low speciation rate. Absence of recombination will lead chromosomes to diverge over time. $\endgroup$
    – Remi.b
    Oct 14, 2014 at 12:43
  • $\begingroup$ Yeah, it may be, though I'm not sure exactly how this divergence will happen? Can you explain it better? And is it chromosomic divergence the main genetic cause of speciation in mammals? $\endgroup$
    – Rodrigo
    Oct 19, 2014 at 23:09
  • $\begingroup$ With low recombination chromosomes diverge following the same logic that makes two non-interbreeding population to diverge through time (just by the neutral processes of mutations and drift). $\endgroup$
    – Remi.b
    Oct 19, 2014 at 23:41
  • $\begingroup$ Does chromosomal divergence cause speciation? Intuitively, I'd say yes. Assuming that chromosomal divergence would yield to outbreeding depression (OD), then OD causes post-zygotic isolation which causes a selection pressure to increase the pre-zygotic isolation. I have absolutely no idea however of whether such mechanisms is an important factor to explain speciation in mammals and I might be wrong assuming that chromosomal divergence causes OD. $\endgroup$
    – Remi.b
    Oct 19, 2014 at 23:41
  • $\begingroup$ thanks for the input. After comparing rates across species, (which there are few), it seems to me that recombination rates maybe evolving too quickly to compare very deeply in phylogenetic trees. $\endgroup$
    – petersoapes
    Mar 12, 2015 at 15:28

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