Abstract:
We use a combination of microsatellite marker analysis and mate-choice behavior experiments to assess
patterns of reproductive isolation of the Túngara frog Physalaemus pustulosus along a 550-km transect of 25 populations
in Costa Rica and Panama. Earlier studies using allozymes and mitochondrial DNA defined two genetic groups of
tu´ngara frogs, one ranging from Mexico to northern Costa Rica (northern group), the second ranging from Panama
to northern South America (southern group). Our more fine-scale survey also shows that the northern and southern
tu´ngara frogs are genetically different and geographically separated by a gap in the distribution in central Pacific
Costa Rica. Genetic differences among populations are highly correlated with geographic distances. Temporal call
parameters differed among populations as well as between genetic groups. Differences in calls were explained better
by geographic distance than by genetic distance. Phonotaxis experiments showed that females preferred calls of males
from their own populations over calls of males from other populations in about two-thirds to three-fourths of the
contrasts tested. In mating experiments, females and males from the same group and females from the north with
males from the south produced nests and tadpoles. In contrast, females from the south did not produce nests or tadpoles
with males from the north. Thus, northern and southern Túngara frogs have diverged both genetically and bioacoustically.
There is evidence for some prezygotic isolation due to differences in mate recognition and fertilization success,
but such isolation is hardly complete. Our results support the general observation that significant differences in sexual
signals are often not correlated with strong genetic differentiation.
