Acoustic interference and recognition space within a complex assemblage of dendrobatid frogs

Abstract

In species-rich assemblages of acoustically communicating animals, heterospecific sounds may constrain not only the evolution of signal traits but also the much less-studied signal-processing mechanisms that define the recognition space of a signal. To test the hypothesis that the recognition space is optimally designed, i.e., that it is narrower toward the species that represent the higher potential for acoustic interference, we studied an acoustic assemblage of 10 diurnally active frog species. We characterized their calls, estimated pairwise correlations in calling activity, and, to model the recognition spaces of five species, conducted playback experiments with 577 synthetic signals on 531 males. Acoustic co-occurrence was not related to multivariate distance in call parameters, suggesting a minor role for spectral or temporal segregation among species uttering similar calls. In most cases, the recognition space overlapped but was greater than the signal space, indicating that signal-processing traits do not act as strictly matched filters against sounds other than homospecific calls. Indeed, the range of the recognition space was strongly predicted by the acoustic distance to neighboring species in the signal space. Thus, our data provide compelling evidence of a role of heterospecific calls in evolutionarily shaping the frogs' recognition space within a complex acoustic assemblage without obvious concomitant effects on the signal.

Fig. 1.

Four hypotheses on the shape of the recognition space (dotted lines) and its relationship with the signal space defined by individual signals (filled circles) of three hypothetically co-occurring species (colored circles).

Fig. 2.

Oscillogram (lower, blue) and sonogram (upper, gray) of the advertisement calls of 10 acoustically co-occurring frog species at Panguana, Peru. A1, Allobates sp. 1; A2, Allobates sp. 2; A3, Allobates sp. 3; Af, Allobates femoralis; Ah, Ameerega hahneli; Ape, Ameerega petersi; Api, Ameerega picta; At, Ameerega trivittata; La, Leptodactylus andreae; RI, Ranitomeya lamasi.

Fig. 3.

Discriminant plot summarizing between individuals’ (dots) and species’ (colors) differences in five parameters of the advertisement calls. The first discriminant function (DF1; 66.2%) is correlated with high values of low (r = 0.86), peak (r = 0.76), and high (r = 0.73) frequency, whereas the second (DF2; 25.8%) is mainly correlated with note duration (r = 0.69). The discriminant axes were switched to improve data visualization and comparison with Figs. 1 and 5. Species abbreviations are as described in Fig. 2.

Fig. 4.

Recognition space of five co-occurring frog species as estimated by a GAM on the phonotactic reaction of males to the playback of synthetic advertisement calls. The variables were manipulated beyond the natural range of variation (expressed as SD) until most individuals failed to react to the corresponding stimulus call.

Fig. 5.

Communication space depicting the relationships between the recognition space (5 species shown) and the signal space (10 species shown) as defined by two call parameters in an assemblage of diurnal frogs. Each dot represent average values of call parameters for a single frog. The line delimitates the call parameter values at which the probability of male reaction was estimated as 0.99 by a GAM.

Fig. 6.

Relationship between the projection of the recognition space (recognition distance) and pairwise differences in call traits (acoustic distance) while controlling for the degree of species co-occurrence in an acoustic community of diurnal frogs.