Interpreting patterns of X chromosomal relative to autosomal diversity in aye-ayes(Daubentonia madagascariensis)

Abstract

We here present high-quality, population-level sequencing data from the X chromosome of the highly-endangered aye-aye, Daubentonia madagascariensis. Using both polymorphism- and divergence-based inference approaches, we quantify fine-scale mutation and recombination rate maps, study the demographic and selective processes additionally shaping variation on the X chromosome, and compare these estimates to those recently inferred from the autosomes in this species. Results suggest that an equal sex ratio is most consistent with observed patterns of variation, and that no sex-specific demographic patterns are needed to fit the empirical site frequency spectrum. Further, reduced rates of recombination were observed relative to the autosomes as would be expected, whereas mutation rates were inferred to be similar. Utilizing the estimated population history together with the mutation and recombination rate maps, we evaluated evidence for both recent and recurrent selective sweeps as well as balancing selection across the X chromosome, finding no significant evidence supporting the action of these episodic processes. Overall, these analyses provide new insights into the evolution of the X chromosome in this species, which represents one of the earliest splits in the primate clade.