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Mol Biol Evol. 2018 Dec 27. doi: 10.1093/molbev/msy243. [Epub ahead of print]

Influence of recombination and GC-biased gene conversion on the adaptive and non-adaptive substitution rate in mammals vs. birds.

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UMR 5554 Institut des Sciences de l'Evolution, CNRS, Université de Montpellier, IRD, EPHE, Place E. Bataillon, Montpellier, France.


Recombination is expected to affect functional sequence evolution in several ways. On the one hand, recombination is thought to improve the efficiency of multi-locus selection by dissipating linkage disequilibrium. On the other hand, natural selection can be counteracted by recombination-associated transmission distorters such as GC-biased gene conversion (gBGC), which tends to promote G and C alleles irrespective of their fitness effect in high-recombining regions. It has been suggested that gBGC might impact coding sequence evolution in vertebrates, and particularly the ratio of non-synonymous to synonymous substitution rates (dN/dS). However, distinctive gBGC patterns have been reported in mammals and birds, maybe reflecting the documented contrasts in evolutionary dynamics of recombination rate between these two taxa. Here, we explore how recombination and gBGC affect coding sequence evolution in mammals and birds by analyzing proteome-wide data in six species of Galloanserae (fowls) and six species of catarrhine primates. We estimated the dN/dS ratio and rates of adaptive and non-adaptive evolution in bins of genes of increasing recombination rate, separately analyzing AT→GC, GC→AT and G↔C/A↔T mutations. We show that in both taxa, recombination and gBGC entail a decrease in dN/dS. Our analysis indicates that recombination enhances the efficiency of purifying selection by lowering Hill-Robertson effects, while gBGC leads to an overestimation of the adaptive rate of AT→GC mutations. Finally, we report a mutagenic effect of recombination, which is independent of gBGC.


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