Eavesdroppers and Signal Evolution

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The most extravagant behaviors in the animal kingdom are used by males to attract females during courtship. These signals are favored by selection because males with more extravagant traits are preferred as mates by females. But eavesdroppers can use these signals to find their prey and hosts. Researchers will investigate this communication network in the tungara frog, Physalaemus pustulosus. Males produce a mating call to attract females. The call has two parts: the whine is always produced, and 1-7 chucks can be added. Males add chucks when in vocal competition with other males. Females are attracted to a simple whine but prefer a whine with chucks. The two spies that eavesdrop to find the frogs are frog-eating bats (Trachops cirrhosus), who devour the frogs, and blood-sucking flies (Corethrella spp.) who infect the frogs with protozoan trypanosomes. Both find the frogs by homing in on their calls, are attracted to whines, but prefer whines and chucks. The researchers ask why each of the three receivers is preferentially attracted to calls with chucks: are they easier to find, do they travel farther, do they indicate larger choruses? They then ask if males alter their calling behavior in response to the presence of the bats and flies. Finally, the relative costs (predation risk) and benefits (matings) of adding chucks are measured. This research will permit an understanding of why when males try to show off to females they do so at a great cost, and how these costs and benefits of male sexual displays interact to both promote and limit the extent of their evolution.This award is co-funded by the Office of Science and Engineering