Estimation of male gene flow: Use caution

Because male gene flow cannot easily be estimated directly in many organisms, Hedrick et al. (2013) provided an approach to estimate male gene flow given estimates of diploid nuclear and female differentiation. This approach appears to work well when there is lower female than male gene flow. However, in a tiger data set there was less female differentiation observed as estimated by mitochondrial DNA than expected given the observed overall nuclear diploid differentiation. To analyze these data, we suggest an alternative approach which allows incorporation of sex-specific gene flow and sex-specific effective population size. We find that the pattern of differentiation observed in tigers was consistent with a lower male than female effective population size using this alternative approach. Further, this finding is consistent with observed data in tigers where the male effective population size was 33% that of the female effective population size.