Courtship at reaching-range in the túngara frog.

Courtship in frogs can mediate the final approach between the sexes before amplexus and spawning. It can involve male and female calling, touching, and guidance to the spawning site. Courtship behaviors have been described for several species in nature but little experimentation has been done to uncover the biological mechanisms that control them. We characterized the close-range courtship (within 10 cm) interactions in the túngara frog, an emerging model organism, to provide a quantitative baseline in a neutral arena in support of future experiments. In this initial assessment, we isolated each pair to examine only the social stimulation that is intrinsic to the pair. Among 81 pairs, 80% entered amplexus and of those 57% laid eggs. Males called before amplexus in 86% of the trials in spite of the female's proximity. The female was inferred to execute the final approach before amplexus in 79% of the events. Egg laying was concentrated in the period 6-8 h after sunset and it could be followed by calling. Multiple bouts of egg nest building were observed in 1/4 of the trials and physical contact other than amplexus was common. Male strategy, the last approach before amplexus, and egg laying were not influenced by age or body size but females with high body condition were more likely to lay eggs. Our data revealed that courtship in the túngara frog is not necessarily terminated when the male is approached by the female, but additional close-range interactions may mediate the onset of amplexus and reproductive success.