Male-Male Competition as a Force in Evolutionary Diversification: Evidence in Haplochromine Cichlid Fish

Peter D Dijkstra,Ton G G Groothuis

doi:10.4061/2011/689254

Abstract

It has been suggested that intrasexual competition can be a source of negative frequency-dependent selection, causing agonistic character displacement and facilitating speciation and coexistence of (sibling) species. In this paper we synthesise the evidence that male-male and female-female competition contributes to cichlid diversification, showing that competition is stronger among same-coloured individuals than those with different colours. We argue that intrasexual selection is more complex because there are several examples where males do not bias aggression towards their own type. In addition, sibling species or colour morphs often show asymmetric dominance relationships. We briefly discuss potential mechanisms that might promote the maintenance of covariance between colour and aggression-related traits even in the face of gene-flow. We close by proposing several avenues for future studies that might shed more light on the role of intrasexual competition in cichlid diversification.

Highlights

The cichlid fish in East African lakes are emerging as one of the potentially most powerful model systems in speciation and adaptive radiation research [1,2,3,4]
The inference is that sexual selection by female mate choice on male colour plays a central role in the evolution and maintenance of haplochromine species richness (e.g., [1, 2, 8, 9])
Haplochromine females can behave aggressively [49], and we showed in the Lake Victoria cichlid species with a female colour polymorphism Neochromis omnicaeruleus that females bias aggression towards their own morph [50]

Summary

Introduction

The cichlid fish in East African lakes are emerging as one of the potentially most powerful model systems in speciation and adaptive radiation research [1,2,3,4]. Within genera, sibling species tend to be ecologically more similar, yet strikingly different in male nuptial coloration [5,6,7]. This interspecific colour variation resembles intraspecific colour variation between hybridising incipient species or colour morphs. Aggressive competition over territory sites is intense and is likely to affect sexual selection. Male-male competition can serve as a source of negative frequency-dependent selection in haplochromine cichlid fish due to stronger competition among same-coloured males than those with different colours [13,14,15]. We show that negative frequency-dependent selection is often not symmetric and that selection arising from malemale competition is often more complex than previously thought

Relevance of Male-Male Competition in Evolutionary Diversification

Pleiotropy between Colour and Aggression?