RT Journal Article
SR Electronic
T1 Disentangling the causes for faster-X evolution in aphids
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 125310
DO 10.1101/125310
A1 J Jaquiéry
A1 J Peccoud
A1 T Ouisse
A1 F Legeai
A1 N Prunier-Leterme
A1 A Gouin
A1 P Nouhaud
A1 JA Brisson
A1 R Bickel
A1 S Purandare
A1 J Poulain
A1 C Battail
A1 C Lemaitre
A1 L Mieuzet
A1 G Le Trionnaire
A1 JC Simon
A1 C Rispe
YR 2017
UL http://biorxiv.org/content/early/2017/05/10/125310.abstract
AB Faster evolution of X chromosomes has been documented in several species and results from the increased efficiency of selection on recessive alleles in hemizygous males and/or from increased drift due to the smaller effective population size of X chromosomes. Aphids are excellent models for evaluating the importance of selection in faster-X evolution, because their peculiar life-cycle and unusual inheritance of sex-chromosomes lead to equal effective population sizes for X and autosomes. Because we lack a high-density genetic map for the pea aphid whose complete genome has been sequenced, we assigned its entire genome to the X and autosomes based on ratios of sequencing depth in males and females. Unexpectedly, we found frequent scaffold misassembly, but we could unambiguously locate 13,726 genes on the X and 19,263 on autosomes. We found higher non-synonymous to synonymous substitutions ratios (dN/dS) for X-linked than for autosomal genes. Our analyses of substitution rates together with polymorphism and expression data showed that relaxed selection is likely to contribute predominantly to faster-X as a large fraction of X-linked genes are expressed at low rates and thus escape selection. Yet, a minor role for positive selection is also suggested by the difference between substitution rates for X and autosomes for male-biased genes (but not for asexual female-biased genes) and by lower Tajima’s D for X-linked than for autosomal genes with highly male-biased expression patterns. This study highlights the relevance of organisms displaying alternative inheritance of chromosomes to the understanding of forces shaping genome evolution.