Data from: Sex reversal and primary sex ratios in the common frog (Rana temporaria)

Sex reversal has been suggested to have profound implications for the evolution of sex chromosomes and population dynamics in ectotherms. Occasional sex reversal of genetic males has been hypothesized to prevent the evolutionary decay of nonrecombining Y chromosomes caused by the accumulation of deleterious mutations. At the same time, sex reversals can have a negative effect on population growth rate. Here, we studied phenotypic and genotypic sex in the common frog (Rana temporaria) in a subarctic environment, where strongly female-biased sex ratios have raised the possibility of frequent sex reversals. We developed two novel sex-linked microsatellite markers for the species and used them with a third, existing marker and a Bayesian modelling approach to study the occurrence of sex reversal and to determine primary sex ratios in egg clutches. Our results show that a significant proportion (0.09, 95% credible interval: 0.04–0.18) of adults that were genetically female expressed the male phenotype, but there was no evidence of sex reversal of genetic males that is required for counteracting the degeneration of Y chromosome. The primary sex ratios were mostly equal, but three clutches consisted only of genetic females and three others had a significant female bias. Reproduction of the sex-reversed genetic females appears to create all-female clutches potentially skewing the population level adult sex-ratio consistent with field observations. However, based on a simulation model, such a bias is expected to be small and transient and thus does not fully explain the observed female-bias in the field.性别反转被认为对变温动物（ectotherms）的性染色体演化以及种群动态具有深远影响。有假说提出，遗传雄性的偶发性性别反转，可阻止由有害突变积累所引发的非重组Y染色体的演化退化。与此同时，性别反转也可能对种群增长率产生负面影响。本研究针对亚北极环境中的普通林蛙（Rana temporaria）展开了表型与基因型性别分析，该区域此前因存在严重的雌性偏倚种群性比，引发了频繁发生性别反转的推测。我们为该物种开发了2个全新的性连锁微卫星标记（microsatellite marker），并结合1个已有的第三方标记与贝叶斯建模（Bayesian modelling）方法，探究了性别反转的发生情况，并测定了卵团的初级性比。研究结果显示，有显著比例（0.09，95%可信区间：0.04~0.18）的遗传雌性成体表现出雄性表型，但未发现能够抵消Y染色体退化所需的遗传雄性性别反转证据。多数卵团的初级性比趋于均衡，但3个卵团仅包含遗传雌性，另有3个卵团则呈现显著的雌性偏倚。发生性别反转的遗传雌性的繁殖，似乎会产生全雌性卵团，这可能会使种群水平的成体性比偏向雌性，与野外观测结果相符。但基于模拟模型的结果显示，此类偏倚预计较为微弱且具有暂时性，因此无法完全解释野外观测到的雌性偏倚现象。