Olfactory perception of mates in ecologically divergent stickleback: population parallels and differences

Background: The independent evolution of sympatric species pairs of threespine sticklebacks has provided a natural system to explore how divergent ecologies shape mating preferences. Research has shown that both limnetic and benthic females discriminate against heterospecific males, but not against populations of the same species from different lakes, at least when visual cues are available (Rundle et al., 2000). It is known that olfaction is used in species discrimination by benthic but not limnetic sticklebacks in one of the species pairs (Rafferty and Boughman, 2006), but differences across populations are unknown. Hypotheses: Females from benthic habitats make use of olfactory cues to distinguish between species but not lakes of potential mates. Limnetic females will not show preferences for males of different species or lakes when limited to only olfactory cues. Organisms: Benthic and limnetic populations of threespine stickleback (Gasterosteus aculeatus) from Paxton and Priest Lakes, British Columbia. Methods: We exposed gravid females from each population to chemical stimuli from nesting males in a Y-maze, and recorded which stimulus a female chose and how much time was taken to make a decision. Results: We did not find significant differences between female populations in the preference for conspecific over heterospecific male odours. There was also no preference for odours of males from the same or a different lake. In all populations of females, the preference for male odours of different lakes differed between the two species of male odours: benthic male odours from a different lake were selected over limnetic male odours. The amount of time taken to make a decision differed between female populations, but only when benthic females ultimately chose a limnetic male odour over a benthic one. Conclusions: The preference for conspecific over heterospecific odours, although not strong, may still contribute to reproductive isolation in sympatric sticklebacks, particularly through interactions with other senses and environmental properties.