Female choice, male strategies and the role of vocalizations in the Australian frog Uperoleia rugosa

Abstract

Males of Uperoleia rugosa call from aggregations around ponds in south-eastern Australia on warm, humid nights between September and February. Within the aggregations the males maintain an acoustic territory; they attack calling intruders that are smaller than themselves, but retreat from larger intruders or become their silent satellites. Only males call. They produce three distinct vocalizations: (1) an advertisement call that attracts both males and females, and is used to maintain the male's spatial distribution; (2) an encounter call which is used in territorial interactions; and (3) a courtship call that is only produced when males perceive a female in their immediate vicinity. Females only visit the pond when gravid and spend three or four nights moving slowly through the aggregations of males, apparently listening to a sample of males before initiating amplexus with one of them. Females placed between two loudspeakers playing recordings of the advertisement calls of a heavy and a light male always select the calls of the heavier male. There is a strong correlation between the weights, but not the lengths, of males and females found in amplexus; females select mates that are about 70% of their body weight. Females undoubtedly choose particular males on the basis of acoustic cues; if amplectant pairs are separated, the female consistently returns to her original mate, despite repeatedly being released beside other calling males. The probable acoustic cue is dominant frequency (kHz) which is inversely correlated with the callers' body size and weight. The mating system is a lek, in which males compete intensively for exclusive display sites that contain no resources for females or their offspring, and females sample the displaying males before selecting a mate.