Male–male interactions select for conspicuous male coloration in damselflies

Abstract

Male ornamentation, such as conspicuous male coloration, can evolve through female mate choice. Alternatively, in species without overt female mate preference, conspicuous male coloration can evolve as a badge of status via intrasexual selection to avoid costly fights or prevent mating attempts with other males. Here, we investigated the drivers of conspicuous male coloration in an ontogenetic colour-changing damselfly, Xanthagrion erythroneurum, where the juvenile males are yellow and change colour to red upon sexual maturity. We first showed that red males were chromatically and achromatically more conspicuous than the yellow males. We then quantified the condition of the males: red males were larger and in better condition than yellow males. We tested female preference in a choice experiment where we artificially manipulated male colour and found that females did not choose mates based on male coloration. We further tested whether the male coloration affected male–male interactions. We presented red and yellow males at the breeding site and measured behavioural responses from conspecific males and heterospecific ( Ischnura heterosticta ) males. Red males received less aggression from conspecifics and heterospecifics than yellow males. Our study experimentally showed that male conspicuousness is not a target of female mate choice in damselflies. Instead, intra- and interspecific male–male interactions appear to be the driver of its evolution. • X. erythroneurum changes colour from yellow to red during ontogeny. • Red males are more conspicuous and in better condition than yellow males. • Females do not prefer more conspicuous red males to yellow males. • Red males incur less within- and across-species aggression. • Males' conspicuous colour appears to have evolved to reduce male-male interactions.