The scope and strength of sex-specific selection in genome evolution.
Bottom Line: Sex-specific selection is strongly influenced by mating system, which also causes neutral evolutionary changes that affect different regions of the genome in different ways.Here, we synthesize theoretical and molecular work in order to provide a cohesive view of the role of sex-specific selection and mating system in genome evolution.We also highlight the need for a combined approach, incorporating both genomic data and experimental phenotypic studies, in order to understand precisely how sex-specific selection drives evolutionary change across the genome.
Affiliation: Department of Zoology, University of Oxford, Edward Grey Institute, Oxford, UK. email@example.comShow MeSH
Mentions: Identifying signatures of genetic drift at the genetic level provides insight into the strength of neutral evolution. Mating systems define the variance in reproductive success between the sexes and thus the transmission of genetic material to subsequent generations, and the effect of mating system on the direction and rate of transmissions differs among regions of the genome. Although males and females share the autosomal portion of their genome equally, there is a pronounced asymmetry in the inheritance of the X chromosome (more often present in females), the Y chromosome (male-limited), the Z chromosome (more often present in males) and the W chromosome (female-limited). These inheritance patterns mean that different regions of the genome differ from each other in both their absolute effective populations size (NE), as well as their response in NE to differences in male and female mating success (Fig.3). Drift for autosomal loci is minimized in monogamous species compared to other mating systems, and deviations from monogamy will lead to elevated rates of genetic drift and decrease the efficacy of selection across the genome as a whole (Hartl & Clark, 2006). However, the relationship between drift and selection plays out differently on the sex chromosomes. The effective population size of both the X and Z chromosomes (NEX and NEZ) = ¾ that of the autosomes (NEA) in monogamous mating systems, creating a potential for increased genetic drift to act on homogametic sex chromosomes (Charlesworth et al., 1993; Vicoso & Charlesworth, 2009). Increased variance in male reproductive success associated with most forms of sexual selection increases NEX and decreases NEZ relative to NEA (Fig.3b–c); therefore, sexual selection on males is predicted to increase rates of neutral evolution for Z chromosomes more than X chromosomes, termed Faster-Z and Faster-X evolution (Mank et al., 2010c). This is supported by some evidence from birds (Mank et al., 2007, 2010b), mammals (Lau et al., 2009) and Drosophila (Connallon, 2007; Singh et al., 2007; Baines et al., 2008); however, other data are discordant with the role of mating sytem and sex chromosome evolution (Haddrill et al., 2010).
Affiliation: Department of Zoology, University of Oxford, Edward Grey Institute, Oxford, UK. firstname.lastname@example.org