Neither convergence nor divergence in the advertisement call of sympatric congeneric Neotropical treefrogs

Abstract

Sympatric species communicating by means of sounds share the same acoustic space, which may cause masking interference affecting the signal recognition processes. This should be especially problematic in congeneric species that tend to exhibit similar acoustic signals and behavioural traits. Thus, congeneric species in sympatry would presumably experience diversification pressures that lead to more intense call divergences than in congeneric species in allopatry. However, recent studies showed cases of signal convergence in sympatry, presenting opposite hypotheses such as convergence by adaptation to a common habitat. Therefore, to test these hypotheses, we analysed the advertisement calls and geographic distribution of 10 species of Sphaenorhynchus (i.e. a monophyletic genus of Neotropical hylids), which occur in sympatry with at least one congeneric species. Using two similarity analyses: multivariate comparison [unweighted pair group method with arithmetic mean (UPGMA)] and spectrogram cross-correlation (SPCC), and two thresholds of grouping (high and low), we searched for association between species distribution (sympatric and allopatric) and call similarity (grouped and ungrouped). Although assuming different principles, both UPGMA and SPCC methods provided extremely similar results. Sympatric species tend to be less often grouped by call similarity than allopatric species, with 0–15% of sympatric species grouped for both similarity methods. However, associations between variables were not confirmed by frequency distributions in contingency tables or by similarity values in the pairs of sympatric and allopatric species. Consequently, neither call divergence nor convergence in sympatry was supported by these results, fostering further investigation about other potential mechanisms underlying anuran call evolution, and suggesting a possible random distribution of call variables in the acoustic space.