Variation in the extent of sex chromosome differentiation exists within the same population for the common frog, Rana temporaria. This alows to directly compare possible effects on male fitness while controlling for the rest of the genome, and the environment.
R. temporaria shows remarkable variation in the mechanism of sex determination, from environmental to genetic. Previous genotyping of families established from Swiss populations have identified populations in which the two systems coexist (XY and XX males). This allows the opportunity to directly test the evolution of sexually antagonistic effects of the Y chromosome, predicted by theory, while controlling for genetic background.
To this end we have sampled frogs from two high altitude Swiss populations. We will estimate the reproductive success of the XY males relative to the XX males by comparing the frequency of those captured while mating to the population average from the same sampling site.
We will also characterise the effect of the presence of a Y chromosome to common phenotypic measurements such as size, weight and blood hormone levels. This work should complement genomic work on the same populations that characterises the molecular divergence between the X and Y chromosomes.