Genetic variation in nuclear and mitochondrial markers supports a large sex difference in lifetime reproductive skew in a lekking species

Abstract

Sex differences in skews of vertebrate lifetime reproductive success are difficult to measure directly. Evolutionary histories of differential skew should be detectable in the genome. For example, male-biased skew should reduce variation in the biparentally inherited genome relative to the maternally inherited genome. We tested this approach in lek-breeding ruff (Class Aves, Philomachus pugnax) by comparing genetic variation of nuclear microsatellites (θ n ; biparental) versus mitochondrial D-loop sequences (θ m ; maternal), and conversion to comparable nuclear (N e ) and female (N ef ) effective population size using published ranges of mutation rates for each marker (μ). We provide a Bayesian method to calculate N e (θ n = 4N e μ n ) and N ef (θ m = 2N ef μ m ) using 95% credible intervals (CI) of θ n and θ m as informative priors, and accounting for uncertainty in μ. In 96 male ruffs from one population, N e was 97% (79-100%) lower than expected under random mating in an ideal population, where N e :N ef = 2. This substantially lower autosomal variation represents the first genomic support of strong male reproductive skew in a lekking species.

Keywords: Effective population size; Philomachus pugnax; ruff; sexual selection; shorebirds.