Evoked vocal response in male túngara frogs: pre-existing biases in male responses?

Female túngara frogs, Physalaemus pustulosus, are preferentially attracted to a whine-chuck advertisement call over a simple whine (Rand & Ryan 1981, Zeitschrift für Tierpsychologie, 57, 209-214). Females also show phonotactic preferences for the whine when a number of other heterospecific or artificial stimuli are added to it, and these calls tend to be as attractive to females as a whine-chuck (Ryan & Rand 1990, Evolution, 44, 305-314). We tested male túngara frogs with the same suite of stimuli using evoked vocal responses as a bioassay to examine sexual differences in responses to signal variation. A whine-chuck elicited greater responses from males than a whine-only. Artificial and heterospecific stimuli that enhanced call attractiveness to females also elicited greater vocal responses from males and, as with females, the effects of these stimuli were similar to that of the whine-chuck. Thus, in both sexes there are pre-existing biases for a suite of stimuli not produced by conspecifics. (c) 1998 The Association for the Study of Animal Behaviour.