Environment rather than character displacement explains call evolution in glassfrogs

The Acoustic Adaptation Hypothesis (AAH) and Ecological Character
Displacement (ECD) are two potential mechanisms shaping call evolution
that can predict opposite trends for the differentiation of signals. Under
AAH, signals evolve to minimize environmental degradation and maximize
detection against background noise, predicting call homogenization in
similar habitats due to environmental constraints on signals. In contrast,
ECD predicts greater differences in call traits of closely-related taxa in
sympatry because of selection against acoustic interference. We used
comparative phylogenetic analyses to test the strength of these two
selective mechanisms on the evolution of advertisement calls in
glassfrogs, a highly diverse family of neotropical anurans. We found that,
overall, acoustic adaptation to the environment may outweigh effects of
species interactions. As expected under the AAH, temporal call parameters
are correlated with vegetation density, but spectral call parameters had
an unexpected inverse correlation with vegetation density, as well as an
unexpected correlation with temperature. We detected call convergence
among co-occurring species and also across multiple populations from the
same species in different glassfrogs communities. Our results indicate
that call convergence is common in glassfrogs, likely due to habitat
filtering, while character displacement is relatively rare, suggesting
that costs of signal similarity among related species may not drive
divergent selection in all systems.