Condition-dependent signaling and adoption of mating tactics in an amphibian with energetic displays

Most alternative reproductive phenotypes are interpreted as alternative tactics within a conditional strategy: all individuals are predicted to choose among behavioral tactics based on some measure of their physiological condition or competitive status. The factors determining a male’s tactic at any particular time are generally unknown. Thus, most researchers have measured potential correlates of competitive ability (such as male body size) rather than directly measuring fighting ability, for example, in males adopting alternative mating tactics. In species in which sexual competition primarily involves production of acoustic signals, an individual’s choice of mating tactic may largely depend on physical characteristics, such as age, strength, or condition, which determine its ability to compete acoustically by producing attractive calls. Male green tree frogs (Hyla cinerea) often switch tactics (caller or satellite), but body size changes very little during the breeding season. I tested the hypothesis that mating-tactic switches are mediated via the effects of changing body condition on advertisement call characteristics. My field study shows that the switch between tactics is predicted by condition but not by size. Moreover, short-term changes in body weight result in condition-dependent changes in several properties of the advertisement call. The demonstration of condition-dependent advertisement calling and tactic adoption links a physical characteristic correlated with mating-tactic adoption with actual competitive status (calling performance). Vocal fatigue may constrain males to produce relatively unattractive advertisement calls, thus increasing the potential fitness payoffs associated with adoption of the satellite tactic.