Experimental manipulation of a signal trait reveals complex phenotype-behaviour coordination

Iris I Levin,Rebecca J Safran,Christine M Bergeon Burns,Toshi Tsunekage,Amanda K Hund,Bailey K Fosdick,Matthew A Aberle

doi:10.1038/s41598-018-33948-0

Abstract

Animals use morphological signals such as ornamental traits or weaponry to mediate social interactions, and the extent of signal trait elaboration is often positively associated with reproductive success. By demonstrating relationships between signal traits and fitness, researchers often make inferences about how behaviour operates to shape those outcomes. However, detailed information about fine-scale individual behaviour, and its physiological basis, can be difficult to obtain. Here we show that experimental manipulations to exaggerate a signal trait (plumage colour) and concomitant changes in testosterone and stress-induced corticosterone levels altered social interactivity between manipulated males and their social mates. On average, darkened males did not have higher levels of interactivity than unmanipulated males; however, males who experienced a greater shift in colour (pale to dark), a larger, positive change in testosterone levels, and a dampened stress-induced corticosterone response had a larger increase in the number of interactions with their social mate post-manipulation compared to pre-manipulation. This work provides new insights into the integration and real-time flexibility of multivariate phenotypes and direct evidence for the role of social interactions in pair bond maintenance.

Highlights

The need to react rapidly to a variety of social stimuli requires a highly coordinated and integrated phenotype
A separate correlational study using proximity tags to track social interactions revealed that females are more interactive with naturally dark males with stronger stress-induced corticosterone (CORT) responses[20]
To directly examine the role of social interactions in mate selection behaviour and phenotype integration, we investigated changes in social interactivity in response to experimental manipulation of male ventral plumage colour and associated natural changes in circulating testosterone levels and stress-induced CORT levels

Summary

Introduction

The need to react rapidly to a variety of social stimuli requires a highly coordinated and integrated phenotype. Research has focused on how animals react to environmental stressors, including extreme weather events[1], food shortages[2,3], and increased threats from predation[2,4]; individuals face additional challenges within their social environment, including competition for mates In this context, animals have evolved signal traits to mediate social interactions with conspecifics, such as advertising fighting[5] and foraging[6] ability. To directly examine the role of social interactions in mate selection behaviour and phenotype integration, we investigated changes in social interactivity (measured via proximity loggers21) in response to experimental manipulation of male ventral plumage colour and associated natural changes in circulating testosterone levels and stress-induced CORT levels. In addition to testing for a treatment effect corresponding to the plumage colour manipulation, we examined whether the degree of plumage colour change was related to changes in interactivity and hormone levels

Methods

Results

Conclusion