Spotted turtle dispersal microsatellite DNA sex and site data

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.

性偏向扩散（sex-biased dispersal）在诸多动物类群中普遍存在，其中雄性偏向扩散（male-biased dispersal）常见于哺乳动物和爬行动物的相关研究中，这类研究对空间遗传结构的解释通常归因于雄性间竞争以及雄性育幼行为的缺失。目前针对龟类开展的性别偏向扩散研究较少，但已有少量针对海龟和陆龟的研究检测到了符合预期的雄性偏向扩散现象。本研究以濒危淡水龟类斑龟（Clemmys guttata）为研究对象，通过分析雌雄个体的精细尺度遗传空间结构，检验其是否存在性别偏向扩散。结果显示，雌雄两性均存在显著的空间遗传结构，且二者的空间遗传模式高度相似：在距离小于25km的范围内，雌雄个体的亲缘系数均高于预期值；而在多数大于25km的距离区间内，亲缘系数则低于预期值。无论仅使用哈迪-温伯格平衡（Hardy-Weinberg equilibrium）位点（n=7），还是同时纳入携带潜在无效等位基因（null alleles）的位点（n=5），均得到了一致的结果模式。据此我们得出结论：与预期相悖，该物种并未出现性别偏向扩散，这可能与该物种的反向性二态性（sexual dimorphism）有关——雌性个体具有更为鲜亮的体色。此外，我们在单独分析雌雄个体以及合并分析时均检测到了显著的空间遗传结构，表明斑龟的遗传斑块尺度小于25km，存在恋巢性（philopatry）；这对于该濒危物种而言并非利好，其野外种群间的隔离距离往往大于该遗传斑块尺度。