Parental investment and sexual selection in dart-poison frogs (genus Dendrobates).

Abstract

Comparative and experimental field studies of species in the genus Dendrobates were carried out to test predictions from two hypotheses that propose to explain the selective pressure causing female-female competition for mates in species of Dendrobates with male parental care. The sex role reversal hypothesis (Trivers, 1972; Wells, 1978) proposes that males invest so much time and energy in parental care that receptive males are rare relative to receptive females, and females compete to find and mate with receptive males. The parental quality hypothesis (Summers, 1989) proposes that females compete to monopolize the parental effort of particular males, because they potentially suffer a cost when their mates care for the offspring of other females. Comparisons of males and females in species with male parental care (Dendrobates auratus and Dendrobates leucomelas) did not support the sex role reversal hypothesis, but were consistent with predictions of the parental quality hypothesis: Males defended territories to attract and mate with females; females did not compete for mates more aggressively than males; males were less selective about mating than females; some females guarded their mates for long periods (over a month). Comparisons between species with male (D. leucomelas) and female (Dendrobates histrionicus) parental care contradicted predictions from the sex role reversal hypothesis, but were consistent with predictions from the parental quality hypothesis: Male D. histrionicus did not compete for mates more aggressively than male D. leucomelas; male D. leucomelas were not more selective about mating than male D. histrionicus, female D. leucomelas and D. histrionicus were both selective about mating; female D. leucomelas associated with, and competed for particular males, whereas female D. histrionicus did not. Observations of male parental care revealed that males will deposit more than one tadpole in the same pool. Field experiments demonstrated that increasing the number of tadpoles in a pool decreases tadpole growth rate and survivorship. Hence, male polygyny potentially imposes a cost on offspring growth and survivorship, and consequently on female reproductive success, as predicted by the parental quality hypothesis.