Abstract
Selection arising from social competition over non-mating resources, i.e. resources that do not directly and immediately affect mating success, offers a powerful alternative to sexual selection to explain the evolution of conspicuous ornaments, particularly in females. Here, we address the hypothesis that competition associated with the territoriality exhibited by both males and females in the cichlid fish Tropheus selects for the display of a conspicuous colour pattern in both sexes. The investigated pattern consists of a vertical carotenoid-coloured bar on a black body. Bar width affected the probability of winning in size-matched female–female, but not male–male, contests for territory possession. Our results support the idea that the emergence of female territoriality contributed to the evolution of sexual monomorphism from a dimorphic ancestor, in that females acquired the same conspicuous coloration as males to communicate in contest competition.
Highlights
The evolution of sexually monomorphic ornaments and armaments is often explained by mutual mate choice or competition for mating opportunities in both sexes [1]
Our results support the idea that the emergence of female territoriality contributed to the evolution of sexual monomorphism from a dimorphic ancestor, in that females acquired the same conspicuous coloration as males to communicate in contest competition
Wider bars increased the likelihood of winning in female–female contests when controlling for Relative differences in body size (RSD) and condition factor differences (CFD)
Summary
The evolution of sexually monomorphic ornaments and armaments is often explained by mutual mate choice or competition for mating opportunities in both sexes [1]. It has been argued that in comparison to sexual selection, competition over non-sexual resources (i.e. other than mates) is more likely to affect both sexes and underlie monomorphism in competitive traits [2,3]. Competition in non-sexual situations, such as during dominance interactions, can still directly influence mating success [7,8,10,11]. One solution to reduce the ambiguity over the types of benefits gained from competitive success is to study competition outside the breeding season [12]. If no discrete breeding seasons exist for a given taxon, as in the current study, another solution is to examine female competition over resources that do not confer reproductive benefits immediately or over the short-term
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