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

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.