(Not) far from home: No sex bias in dispersal, but limited genetic patch size, in an endangered species, the Spotted Turtle (Clemmys guttata).

Abstract

Sex-biased dispersal is common in many animals, with male-biased dispersal often found in studies of mammals and reptiles, including interpretations of spatial genetic structure, ostensibly as a result of male-male competition and a lack of male parental care. Few studies of sex-biased dispersal have been conducted in turtles, but a handful of studies, in saltwater turtles and in terrestrial turtles, have detected male-biased dispersal as expected. We tested for sex-biased dispersal in the endangered freshwater turtle, the spotted turtle (Clemmys guttata) by investigating fine-scale genetic spatial structure of males and females. We found significant spatial genetic structure in both sexes, but the patterns mimicked each other. Both males and females typically had higher than expected relatedness at distances <25 km, and in many distance classes greater than 25 km, less than expected relatedness. Similar patterns were apparent whether we used only loci in Hardy-Weinberg equilibrium (n=7) or also included loci with potential null alleles (n=5). We conclude that, contrary to expectations, sex-biased dispersal is not occurring in this species, possibly related to the reverse sexual dimorphism in this species, with females having brighter colors. We did, however, detect significant spatial genetic structure in males and females, separate and combined, showing philopatry within a genetic patch size of <25 km in C.guttata, which is concerning for an endangered species whose populations are often separated by distances greater than the genetic patch size.