Correlated evolution between repertoire size and song plasticity predicts that sexual selection on song promotes open-ended learning.

Cristina M Robinson,Nicole Creanza,Kate T Snyder

doi:10.7554/elife.44454

Abstract

Some oscine songbird species modify their songs throughout their lives ('adult song plasticity' or 'open-ended learning'), while others crystallize their songs around sexual maturity. It remains unknown whether the strength of sexual selection on song characteristics, such as repertoire size, affects adult song plasticity, or whether adult song plasticity affects song evolution. Here, we compiled data about song plasticity, song characteristics, and mating system and then examined evolutionary interactions between these traits. Across 67 species, we found that lineages with adult song plasticity show directional evolution toward increased syllable and song repertoires, while several other song characteristics evolved faster, but in a non-directional manner. Song plasticity appears to drive bi-directional transitions between monogamous and polygynous social mating systems. Notably, our analysis of correlated evolution suggests that extreme syllable and song repertoire sizes drive the evolution of adult song plasticity or stability, providing novel evidence that sexual selection may indirectly influence open- versus closed-ended learning.

Highlights

Song is a learned behavior with a complex evolutionary history in the oscine songbirds
When possible, we reclassified the species into three categories: 1) those that stop changing their song before their first breeding season, 2) those that modify their songs during their first breeding season but not after, and 3) those that modify their songs after their first breeding season has ended
We examined the evolutionary patterns of adult song stability and plasticity, as well as their interactions with species-level song characteristics and mating behaviors

Summary

Introduction

Song is a learned behavior with a complex evolutionary history in the oscine songbirds. Still other species can continue to acquire new syllables or songs throughout their lives (AdretHausberger et al, 2010; Espmark and Lampe, 1993; Gil et al, 2001; Hausberger et al, 1991; Mountjoy and Lemon, 1995; Price and Yuan, 2011). This spectrum of variation in the timing of the sensitive period is simplified into a dichotomy of ‘open-ended learning’ and ‘closed-ended learning.’. Previous hypotheses have suggested that seasonal factors, such as environmental variation and breeding season length, play a role in shaping adult song learning (Nottebohm et al, 1986; Smith et al, 1997; Tramontin et al, 2001)

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