Contrasting impacts of competition on ecological and social trait evolution in songbirds.

Jonathan P Drury,Hélène Morlon,Allison J Shultz,Kevin J Burns,Nicholas A Mason,Joseph A Tobias,Craig Moritz

doi:10.1371/journal.pbio.2003563

Abstract

Competition between closely related species has long been viewed as a powerful selective force that drives trait diversification, thereby generating phenotypic diversity over macroevolutionary timescales. However, although the impact of interspecific competition has been documented in a handful of iconic insular radiations, most previous studies have focused on traits involved in resource use, and few have examined the role of competition across large, continental radiations. Thus, the extent to which broad-scale patterns of phenotypic diversity are shaped by competition remain largely unclear, particularly for social traits. Here, we estimate the effect of competition between interacting lineages by applying new phylogenetic models that account for such interactions to an exceptionally complete dataset of resource-use traits and social signaling traits for the entire radiation of tanagers (Aves, Thraupidae), the largest family of songbirds. We find that interspecific competition strongly influences the evolution of traits involved in resource use, with a weaker effect on plumage signals, and very little effect on song. Our results provide compelling evidence that interspecific exploitative competition contributes to ecological trait diversification among coexisting species, even in a large continental radiation. In comparison, signal traits mediating mate choice and social competition seem to diversify under different evolutionary models, including rapid diversification in the allopatric stage of speciation.

Highlights

Many explanations for how phenotypic diversity accumulates over macroevolutionary timescales assign a central role to competition between species because, in theory, such competition is expected to generate interspecific trait divergence [1,2,3]
Whereas previous research in several iconic island clades has documented the key role of competition in adaptive radiations, our research provides robust empirical evidence that interspecific competition can structure ecological trait evolution in radiations that occur on continental scales
This view is most often applied to traits associated with resource use [2,12], but similar effects may extend to an array of signal traits mediating inter- and intraspecific social interactions such as mate recognition, mate attraction, and territory defense [13]

Summary

Introduction

Many explanations for how phenotypic diversity accumulates over macroevolutionary timescales assign a central role to competition between species because, in theory, such competition is expected to generate interspecific trait divergence [1,2,3]. The classic theory of character displacement predicts that competition between species with similar phenotypes will result in selection acting against intermediate phenotypes, resulting in interspecific trait divergence [2]. This view is most often applied to traits associated with resource use [2,12], but similar effects may extend to an array of signal traits mediating inter- and intraspecific social interactions such as mate recognition, mate attraction, and territory defense [13]. In addition to character displacement, competition can speed up phenotypic evolution as a response to selection pressure in the presence of many competitors, leaving a pattern of positive diversitydependence (DD) [18], or instead slow down phenotypic evolution as niches fill and ecological opportunity decreases, leaving a pattern of negative DD [19,20]

Methods

Results

Conclusion