Do Neighbors Matter? The Influence of Call-Based Quality of Nearby Signalers on Relative Attractiveness of Male Gray Treefrogs (Hyla versicolor) to Females

Aggregations of males advertising for a mate are typically comprised of individuals that vary in their perceived attractiveness to females. Using Gray Treefrogs, Hyla versicolor, we tested the hypothesis that the preference of females for high-quality male calls is influenced by the characteristics of acoustic stimuli provided by the calls broadcast by neighboring groups of males rather than just those of an individual male that females might or might not prefer. Using five-speaker choice experiments with synthetic male calls of different durations and female Gray Treefrogs, H. versicolor, we tested whether the choice of a simulated male giving the more attractive (longest) calls was influenced by the signal-based quality of a simulated pair of neighbors. In half of the experimental tests, the speaker broadcasting the longest calls was flanked by two speakers broadcasting relatively unattractive short calls, while two speakers, on the opposite side of a choice arena, broadcast calls of intermediate attractiveness. In other experimental tests, neighbors were good (giving longer calls) rather than bad (giving short calls), and the two flanking speakers simulated good males broadcasting calls of intermediate quality. We employed two call-timing arrangements and used either 30- or 36-pulse calls as the longest calls in separate sets of tests. In control tests, four speakers broadcast calls of average duration, and a fifth flanked speaker broadcast either 30- or 36-pulse calls. We predicted that the preference of females for the longest call would not be influenced by neighbor quality, possibly because stronger attraction to the side of the arena with good neighbors than bad neighbors would be counterbalanced by a smaller difference in relative attractiveness between the simulated longest caller and the good neighbors. We usually observed an increasing proportion of females choosing calls with greater duration, as well as greater than expected by chance discrimination in favor of the longest call type broadcast. Females also exhibited a significant differential in their tendency to move to the side of the arena broadcasting the longest call, regardless of whether the neighbors were good or bad. However, we did not observe a significant effect of neighbor quality on choice for the longest call as this was independent of the nature of the adjacent call sources and similar to results obtained during control tests. Our results add to a growing body of information demonstrating how the sonic and spatial structure of the chorus environment impacts the details of female mate choice and the realization of female preferences that are exhibited under unnaturally simplified conditions.