Evolution of vocal performance and song complexity in island birds

Aloïs Robert,Martim Melo,Claire Doutrelant,Thierry Lengagne,Doris Gomez

doi:10.1111/jav.02726

Abstract

Oceanic islands share distinctive characteristics thought to underlie a set of parallel evolutionary trends across islands and taxonomic groups – including life‐history traits, morphology and visual signals. To which extent acoustic signals also change in parallel on islands is less clear. Some important processes associated with insularity, such as founder effects and reduced sexual selection, could lead to a decrease in vocal performance and song complexity on islands. In a field‐based study, we recorded 11 insular species and their closest mainland relatives. Out of the 11 species pairs, 6 live in the tropics (São Tomé/Mount Cameroon) and 5 in the temperate region (Madeira/southern France). For each species, we measured two proxies of vocal performance (song duration and syllable rate) and one proxy of song complexity (syllable diversity). This study did not recover a clear relationship between the island environment and song traits. If as expected, syllable rate was lower in island species than in their mainland counterparts, the two other proxies showed no clear island–mainland pattern of divergence. Several factors may explain the absence of reduction for song duration and syllable diversity. Among those, relaxation of interspecific competition on islands may have led to an increase in syllable diversity, or correlations between song variables may have constrained song evolution. More studies on island species are needed to draw a better picture of divergence patterns and go beyond the confounding ecological factors that could explain peculiar song characteristics in islands.

Highlights

The small area and isolation of oceanic islands make them amenable natural laboratories for the study of ecology and evolution (Whittaker et al 2017)
When we looked at each species independently, four tropical pairs out of six showed lower syllable rates on the island, thereby driving the insularity × latitude effect
Bayesian phylogenetic mixed model (BPMM) found a positive effect of insularity on syllable rate which was lower on islands

Summary

Introduction

The small area and isolation of oceanic islands make them amenable natural laboratories for the study of ecology and evolution (Whittaker et al 2017). (Adler and Levins 1994, Covas 2012, Novosolov et al 2013), body size (dwarfism and gigantism of animals and plants: Lomolino 2005, Clegg and Owens 2002; but see Meiri et al 2008), brain size (Sayol et al 2018) and ecological niche expansion (Grant 1998, Blondel 2000, Scott et al 2003, Eloy de Amorim et al 2017) Such convergences across diverse traits under insular conditions are grouped under the name ‘insularity syndrome’ and could include convergent evolution in communication signals (Figuerola and Green 2000, Baker 2006, Morinay et al 2013, Doutrelant et al 2016, Robert et al 2021b). Large-scale studies controlling these variations are needed to test whether vocal performance and song complexity are different on islands compared to the mainland

Methods

Results

Discussion

Conclusion