Extent of plasticity in the nuptial body coloration of the white ecotype of the threespine stickleback (Gasterosteus aculeatus)

Abstract

During mating, animals use both behavioural and morphological traits to compete for and attract mates. In some species, one of the sexes may exhibit nuptial colouration, a type of signal that is under sexual selection. This colouration may function in female choice to indicate mate quality, and/or male competition to assert possession of a territory to competitors. During their breeding season, male Threespine Stickleback build and defend a nest from competitors and actively court females. They display red and blue colouration in combination with these mating behaviours. Male white Threespine Stickleback, an ecotype endemic to Nova Scotia, display red and blue colour, and also turn a pearlescent white. However, whether this colouration functions in female choice or male-male competition (or neither) is not well understood. Therefore, the goal of this study was to determine the association between the phase of the breeding cycle and nuptial colouration of the white ecotype. Males were exposed to experimental conditions that mimicked the three main phases of the breeding cycle: nest-building, territory defense, and mate acquisition. The nest-building condition was used as a baseline to quantify the males’ colouration before being exposed to a competitor or a potential mate. Male colouration was recorded and quantified to determine the influence of the different experimental conditions. The intensity of red, blue and white colouration was lower in the nest-building phase than the other phases; however, there was little difference between the male competition and female choice phase. These results suggest that the white Threespine Sticklebacks’ nuptial colouration may be associated with both male-male competition and female choice.