Characteristics of acoustic signals can be classified from static to dynamic based on their
coefficients of variation. In anuran amphibians, the amplitude variation of each characteristic
composing an acoustic signal normally increases according to the organizational scale of
analysis. Static traits (less variable individually), if they show greater variation between
populations, indicate a possible role in pre-mating isolation. Studies suggest that, through mate
choice, females can exert stabilizing selection over certain traits that become stereotyped
(static), while other selection pressures – or the absence of these – result in more variable
(dynamic) traits. In this project, we sought to find the potential of the spectral and temporal
acoustic signals of the advertisement call as indicators for discrimination between populations
by studying the stereotypy of acoustic signals in the Amazonian litter frogs Allobates tapajos
and Allobates sumtuosus at intra-individual, intrapopulation and interpopulation scales. To
avoid confusion with intrinsic (body size) and ecological (temperature) parameters, we also
tested the influence of these possible co-variates on call traits. As observed in previous studies
with congener species, none of the vocalization characteristics of both studied species stood out
as a potential discriminator among populations, reinforcing the idea that these, in isolation, do
not serve as cues for social recognition or sexual selection. Body size was relevant for acoustic
traits in only one of the species, A. sumtuosus. Unlike previous studies with Allobates and
anurans in general, temperature had little or no effect on the advertisement call of both species,
suggesting that the plasticity of advertisement call traits has little relation to this ecological
covariate. The idiosyncrasies detected in the group formed by this and other similar studies
make it difficult to detect general patterns and emphasize the importance of standardized
investigations involving multiple species to understand the variability and determinants of
variation in temporal and spectral acoustic parameters of the sexual signals of different species
of anurans.
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