Effects of acoustic environment on male calling activity and timing in Neotropical forest katydids

Abstract

Many characteristics of signals can convey information, but the exact timing of the signal often matters as well. The timing of signals is shaped by selective pressures including mate preferences, predation, and competition. In many insect communities, male calling to attract females is persistent and pervasive, and signal timing interactions among individuals are relatively common. In Neotropical forests, many katydid species are represented in the acoustic environment, but calls are usually short (<40 ms) and infrequent (<10 s of sound per individual per night), characteristics that have likely evolved in response to intense predation by insectivorous bats. We test two alternative hypotheses about signal timing in environments where signaling is rare and costly, either that timing is absent due to the unpredictable nature of the signals or that the rarity of signals places a premium on signal timing and attention to the acoustic environment. We tested these hypotheses by broadcasting conspecific calls, heterospecific calls, and silence to eight species of katydids and measuring calling activity and call timing in each playback treatment. All species changed the amount or timing of calling (or both) as a result of the playbacks, but species responded differently to playbacks, with some calling more or less during specific treatments and some showing differences in the timing of calls relative to playbacks. Although short latency signal timing was not observed, this study shows that Neotropical forest katydids are responsive to their acoustic environment despite an exceptionally low rate of signaling.

Significance statement

In many species, males produce signals to attract females, and studies show that the timing of these signals relative to other stimuli can play an important role in mate attraction and predator avoidance. Most of these studies have investigated species that are prolific signalers, due to the ease of collecting data. Here, we extend these theories and test them in Neotropical forest katydids, which produce very short and sporadic acoustic signals. We find that these insects do not display the fast competitive interactions seen in more prolific signalers, but still adjust both the timing and amount of calling in response to what they hear. These findings reveal that insects that signal rarely are still attending to the signaling of others and that their behavior can be strongly affected by the signals of other insects, including insects of other species.