Population structure and male-biased dispersal in the short-tail stingray Bathytoshia brevicaudata (Myliobatoidei: Dasyatidae)

Selective pressures driving dispersal in vagile species often differ between males and females, resulting in sex-biased dispersal. Male-biased dispersal is common in mammals, where there is greater reproductive investment by females, and there is emerging evidence for a similar pattern in elasmobranchs. We examine the population structure of the short-tail stingray (Bathytoshia brevicaudata), a large, viviparous coastal species common in southern hemisphere waters. Using 11 nuclear (nDNA) microsatellite markers from 202 individuals in comparison to mitochondrial (mtDNA) data reported by Le Port and Lavery (J Hered 103:174-185, 2012), we elucidate patterns of dispersal at both southern hemisphere and New Zealand scales. At a global scale, estimates of population differentiation were comparable across marker types (microsatellite F-ST = 0.148, p<0.001, mtDNA phi(ST)=0.67, p<0.001). In contrast, New Zealand structure was much weaker for microsatellite markers (F-ST = 0.0026, p>0.05) than for mtDNA (phi(ST)=0.054, p<0.05). Female-only data displayed a greater degree of population differentiation from both nDNA and mtDNA compared to male-only data, and population assignment tests indicated that males were significantly more likely to be immigrants to the population from which they were sampled. We estimate that within New Zealand, male-mediated gene flow is at least fivefold greater than female-mediated gene flow. This molecular evidence for sex-biased dispersal in a batoid species adds further support to male-biased dispersal as a recurrent pattern in viviparous elasmobranchs. Many elasmobranch species are vulnerable to extinction, and understanding movement patterns is crucial to management of threatened populations.