Range-wide spatial mapping reveals convergent character displacement of bird song

Abstract

A long-held view in evolutionary biology is that character displacement generates divergent phenotypes in closely related coexisting species to avoid the costs of hybridization or ecological competition, whereas an alternative possibility is that signals of dominance or aggression may instead converge to facilitate coexistence among ecological competitors. Although this counterintuitive process—termed convergent agonistic character displacement—is supported by recent theoretical and empirical studies, the extent to which it drives spatial patterns of trait evolution at continental scales remains unclear. By modelling the variation in song structure of two ecologically similar species of Hypocnemis antbird across western Amazonia, we show that their territorial signals converge such that trait similarity peaks in the sympatric zone, where intense interspecific territoriality between these taxa has previously been demonstrated. We also use remote sensing data to show that signal convergence is not explained by environmental gradients and is thus unlikely to evolve by sensory drive (i.e. acoustic adaptation to the sound transmission properties of habitats). Our results suggest that agonistic character displacement driven by interspecific competition can generate spatial patterns opposite to those predicted by classic character displacement theory, and highlight the potential role of social selection in shaping geographical variation in signal phenotypes of ecological competitors.

Sharing sound: Avian acoustic niches in the Brazilian Atlantic Forest

“…Theories of interactive communication networks predict the prevalence of cross-species vocal interaction for mutual benefit over acoustic partitioning. In dense, biodiverse environments, communication between species in a shared bandwidth may be evolutionary advantageous in helping to mediate territorial defense and aggression (Cardoso & Price, 2010;Keen et al, 2020;Kirschel et al, 2019;Malavasi & Farina, 2013;Tobias et al, 2014 S1). The similarity between the distributions of song in 3D PCA space between them was nonetheless striking, as there was minimal overlap in species makeup (only five species were present at both sites).…”

Predicting evolutionary responses to interspecific interference in the wild

“…Traditionally, character displacement is studied by documenting a geographic pattern of trait variation consistent with character displacement (e.g., divergence or convergence in sympatry) and then attempting to rule out alternative explanations for the pattern, such as chance, genetic drift, hybridisation and species sorting, while also testing assumptions of the character displacement hypothesis (Schluter ; Pfennig & Pfennig ). This approach has been applied to several putative examples of both convergent and divergent ACD (Grether et al , ), and some new case studies are particularly compelling (e.g., darters, Moran & Fuller ,b; antbirds, Tobias & Seddon , Kirschel et al ; nightingales, Reif et al ; Souriau et al ; singing mice, Pasch et al ; damselflies, Anderson & Grether ,b; Drury & Grether ). However, while the traditional approach can provide strong evidence that character displacement has occurred in particular cases, it provides little information about its prevalence or predictability (Germain et al ).…”

Competition and hybridization drive interspecific territoriality in birds

“…I nterspecific territoriality is among the most common forms of interference competition in animals (1)(2)(3)(4), and has been shown to affect species range (5)(6)(7)(8) and drive phenotypic evolution, particularly of traits involved in competitor recognition (9)(10)(11)(12)(13)(14). Yet, interspecific territoriality itself remains poorly studied.…”