Aggressive calls improve leading callers' attractiveness in the treefrog Dendropsophus ebraccatus

In complex acoustic choruses, competitive call timing interactions are often important in female mate choice. In the treefrog Dendropsophus ebraccatus, neighboring males' advertisement calls tend to overlap and females prefer lagging calls. Males that produce leading advertisement calls are thus at a disadvantage relative to lagging males. In this study, I propose a novel strategy by which leading males may overcome this problem: the production of aggressive calls. Aggressive calls are longer than advertisement calls. Therefore, if a lagging male responds with an advertisement call to a leading aggressive call, the leading aggressive call may end after the lagging call. If females prefer calls that end last, then leading aggressive calls may be more attractive. I compared female preferences for advertisement and aggressive calls when they either overlapped, with the aggressive call leading, or alternated. Females preferred the advertisement call in alternation, but this preference was abolished when it overlapped with the aggressive call. I recorded interactions between pairs of males to determine whether leading males utilized aggressive calls as predicted. Among leading calls, aggressive calls were more likely to end after lagging calls than were advertisement calls. When switches to aggressive calling occurred after a bout of overlapping advertisement calls, it was more likely that the male that switched to aggressive calling had been in the leading position previously. These experiments suggest a strategy for leading males to reduce their disadvantage in call timing interactions and provide an explanation for this species' high levels of aggressive calling. Copyright 2011, Oxford University Press.