PT  - JOURNAL ARTICLE
AU  - Guy Amster
AU  - Guy Sella
TI  - Life history effects on neutral polymorphism levels of autosomes and sex chromosomes
AID  - 10.1101/206862
DP  - 2017 Jan 01
TA  - bioRxiv
PG  - 206862
4099  - http://biorxiv.org/content/early/2017/10/20/206862.short
4100  - http://biorxiv.org/content/early/2017/10/20/206862.full
AB  - In human and other hominid (great apes) populations, estimates of the relative levels of neutral polymorphism on the X and autosomes differ from each other and from the naive theoretical expectation of ¾. These differences have garnered considerable attention over the past decade, with studies highlighting the potential importance of several factors, including historical changes in population size and linked selection near genes. Here, we examine a more realistic neutral model than has been considered to date, which incorporates sex-and age-dependent mortalities, fecundities, reproductive variances and mutation rates, and ask whether such a model can account for diversity levels observed far from genes. To this end, we derive analytical expressions for the X to autosome ratio of polymorphism levels, which incorporate all of these factors and clarify their effects. In particular, our model shows that the genealogical effects of life history can be reduced to ratios of sex-specific generation times and reproductive variances. Applying our results to hominids by relying on estimated life-history parameters and approximate relationships of mutation rates to age and sex, we find that life history effects, and the effects of male and female generation times in particular, may account for much of the observed variation in X to autosome ratios of polymorphism levels across populations and species.