Female mate choice for socially variable advertisement calls in the cricket frog, Acris crepitans
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Male cricket frogs produce a single call-type, the advertisement call. In interactions with neighboring males, they decrease the dominant frequency and increase the temporal complexity of these calls. It was previously suggested that vocal escalation mediates male-male aggression. This is likely true for spectral call changes, but a review of previous data on male vocal and territorial behavior does not clearly support this hypothesis for temporal call characters. One alternative is that males change their calls in order to increase their relative attractiveness to females. I conducted a series of phonotaxis experiments assessing female responses to socially variable call characters. Female cricket frogs prefer calls with the temporal patterning of interacting males to those with the temporal patterning of undisturbed males, and mean to variant dominant frequencies. I suggest that vocal escalation by male cricket frogs reflects a tradeoff between the benefits of increased attractiveness to females and the costs of attractive calls in other contexts. Some of the observed preferences for complex calls may be influenced by neural processes that are not specific to female cricket frogs, but that are general among species. Females prefer calls that are partitioned into multiple pulse groups. This preference may result from a release of adaptation or habituation to long calls. Females discriminate preferentially with respect to calls nearer the end of calling bouts. I suggest that cognitive constraints on call processing may limit the number of calls to which females can attend in mate choice. Males appear to be sensitive to this limitation, as vocal escalation occurs only for calls near the end of bouts. Although female cricket frogs prefer complex calls, there is no evidence that advertisement call complexity enhances their ability to detect, recognize, or localize males in noisy choruses. In cricket frogs, in fact, complex calls may carry a cost with respect to signal localization. Thus, while vocal escalation increases a male’s relative attractiveness to females, there is currently no evidence to suggest that facultative increases in call complexity address the particular problems of signal detection and localization in a noisy environment.