Geographic variation in male sexual signals in strawberry poison frogs (Dendrobates pumilio)

In this paper, we compare the advertisement calls of 207 neotropical strawberry poison frogs (Dendrobates pumilio) collected in 21 localities along a transect from northern Costa Rica to western Panama. Populations varied most in call duration and call rate, while pulse rate and duty cycle were less variable. Multivariate analyses showed that call variation followed a cline with higher call rates, shorter calls, lower duty cycles and higher pulse rates in the southeast. Body size decreased towards the southeast and explained most variation in dominant frequency, as well as some residual variation in call rate. We conclude that a combination of geography and morphology is largely responsible for call variation within this species. Two inferred bio-acoustic groups were roughly in accordance with two genetic groups, geographically separated in central Costa Rica. However, genetic distances among populations did not co-vary with call dissimilarity after correction for geographic distances. Thus, differences in calls between genetic groups are probably mainly a result of clinal variation. These findings agree with the general observation that bio-acoustic variation is often not (highly) associated with genetic divergence. Moreover, colour polymorphism observed among Panamanian populations was not reflected in a higher variability in call parameters relative to the monomorphic Costa Rican populations.