Male reproductive traits among natural populations of P. guentheri

Ejaculate traits vary extensively among individuals and species, but
little is known about their variation among populations of the same
species. Here, we investigated patterns of intraspecific variation in male
reproductive investment in the terrestrial-breeding frog Pseudophryne
guentheri. Like most anurans, breeding activity in P. guentheri is cued by
precipitation, and therefore the timing and duration of breeding seasons
differ among geographically separated populations, potentially leading to
differences in the level of sperm competition. We therefore anticipated
local adaptation in sperm traits that reflect these phenological
differences among populations. Our analysis of six natural populations
across a rainfall gradient revealed significant divergence in testes and
ejaculate traits that correspond with annual rainfall and rainfall
seasonality; males from the northern and drier edge of the species range
had significantly smaller testes containing fewer, smaller and less motile
sperm compared to those from mesic central populations. These findings may
reflect spatial variation in the strength of postcopulatory sexual
selection, likely driven by local patterns of precipitation.