Male red throat coloration, pelvic spine coloration, and courtship behaviours in threespine stickleback

Background: In addition to exhibiting red nuptial throat coloration, male threespine sticklebacks (Gasterosteus aculeatus) often possess red coloration on their pelvic spines. Although variation in throat colour has been shown to be associated with male reproductive behaviour, limited research has been devoted to the behavioural correlates of red spine colour. Like the red throat, spine colour might correlate with components of male reproductive behaviour and may also be androgen dependent, with important implications for a potential signalling function. Hypothesis: Spine coloration, like throat coloration, is correlated with components of courtship behaviour, and also with the fish androgen 11-ketotestosterone (11KT). Methods: To examine the role of male throat and spine colour expression in a mating context, we measured the behavioural response of nesting males to conspecific females. We analysed the relationships between throat and spine colours with reproductive behaviours as well as with 11KT. Results: Males with more intensely red throats courted females more vigorously, whereas males with redder spines displayed relatively more aggressive behaviour during courtship. An initial analysis of a subsample of males showed that 11KT was positively associated with spine colour intensity, but not with red throats or any behaviours. Hence throat and spine colour may reflect different components of male reproductive behaviour, and 11KT is a potential mediator of spine coloration in males.