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.