Male morphological traits are heritable but do not predict reproductive success in a sexually-dimorphic primate

Clare M Kimock,James P Higham,Lauren J N Brent,Constance Dubuc

doi:10.1038/s41598-019-52633-4

Clare M Kimock, James P Higham + Show 2 more

Open Access

https://doi.org/10.1038/s41598-019-52633-4

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Journal: Scientific Reports	Publication Date: Dec 1, 2019
Citations: 15	License type: open-access

Affiliation: New York University, University of Exeter

Abstract

Sexual selection favours traits that increase reproductive success via increased competitive ability, attractiveness, or both. Male rhesus macaque (Macaca mulatta) morphological traits are likely to reflect the effects of multiple sexual selection pressures. Here, we use a quantitative genetic approach to investigate the production and maintenance of variation in male rhesus macaque morphometric traits which may be subject to sexual selection. We collected measurements of body size, canine length, and fat, from 125 male and 21 female free-ranging rhesus macaques on Cayo Santiago. We also collected testis volumes from males. We used a genetic pedigree to calculate trait heritability, to investigate potential trait trade-offs, and to estimate selection gradients. We found that variation in most male morphometric traits was heritable, but found no evidence of trait trade-offs nor that traits predicted reproductive success. Our results suggest that male rhesus macaque morphometric traits are either not under selection, or are under mechanisms of sexual selection that we could not test (e.g. balancing selection). In species subject to complex interacting mechanisms of selection, measures of body size, weaponry, and testis volume may not increase reproductive success via easily-testable mechanisms such as linear directional selection.

Highlights

Sexual selection favours traits that increase reproductive success via increased competitive ability, attractiveness, or both
Where direct male-male mating competition for access to fertile females is high, sexual selection promotes the evolution of traits such as large body size and weaponry[4,5]
We used a quantitative genetic approach to investigate the production and maintenance of variation in male rhesus macaque morphometric traits putatively associated with intrasexual competition

Summary

Introduction

Sexual selection favours traits that increase reproductive success via increased competitive ability, attractiveness, or both. In species subject to complex interacting mechanisms of selection, measures of body size, weaponry, and testis volume may not increase reproductive success via -testable mechanisms such as linear directional selection. Where direct male-male mating competition (intrasexual competition) for access to fertile females is high, sexual selection promotes the evolution of traits such as large body size and weaponry (horns, antlers, or large canine teeth)[4,5]. The evolution of exaggerated male traits such as ornaments, large body size, weaponry, and large testis volumes, has been linked to sexual selection pressures across many species. Sexual dimorphism in body and canine size[33,34,35] and relative testis volume[6] vary widely across species, suggesting variation in investment in both direct male-male competition and in sperm competition across the Order. There are multiple routes to reproductive success in rhesus males: some males engage in consortships while others employ alternative reproductive tactics, like sneaky matings, and both very passive and very aggressive males sire offspring[49,50,51,52]

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