Taxis bold as love: the influence of aggressive calls on acoustic attraction of female gray treefrogs, Hyla versicolor

Abstract

We studied female phonotaxis in gray treefrogs to learn how male aggressive calling influences female choice of a mate from the perspective of the aggressive signaler and his male target. Although aggressive calls on their own attracted some females, when allowed to choose, all females preferred advertisement calls to aggressive calls. We wanted to ascertain also whether such calls could reduce the attractiveness of a nearby advertising male relative to an advertising male that was not close to a male giving aggressive calls. If so, it would be a good reason for a male to move away from a male giving aggressive calls. We found that females were indifferent to aggressive calls which were broadcast following and adjacent to a source of advertisement calls when the choice alternative was a more distant source of advertisement calls. However, this was not always the case when aggressive calls and advertisement calls overlapped. Angular separation from a source of overlapping aggressive calls did not improve the attractiveness of advertisement calls relative to advertisement calls adjacent to a source of such aggressive calls. In a final test, we simulated an aggressive exchange with a winner and a retreating loser. Females allowed to eavesdrop failed to discriminate. Thus, there may be no cost to moving away and a potential gain in terms of reduced acoustic interference. Loud calls or physical intrusions by conspecific males may cause male frogs to give aggressive calls. Although acoustic features of aggressive vocalizations may be well-described, we are largely ignorant of their utility and potential costs to producing and nearby males. We investigated whether the production of aggressive calls would compromise the attractiveness of male gray treefrogs to potential mates. Choruses of frogs may be especially suitable venues for eavesdropping, a phenomenon also ripe for investigation. Accordingly, we tested whether females exposed to simulated aggressive vocal exchanges would discriminate in favor of putative winners. We found that aggressive calling can reduce the signaler’s attractiveness but, lacking acoustic interference, not that of a neighbor. Females failed to discriminate between a simulated retreating loser and winner suggesting that such outcomes are irrelevant to females or that their ability to eavesdrop is limited.