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Abstract

Olfactory cues play an important role in the process of mate choice in the three-spined stickleback. It has been shown that females take the MHC-genetic make-up of males into account for their choice; however, it seems unlikely that the highly diverse MHC can signal the reproductive condition of the male. We followed 17 individual males for up to 17 weeks through different seasons (winter to summer) and reproductive conditions (non-nesting, nesting, no longer nesting) and measured their olfactory attractiveness for females independent of the olfactory MHC signal. We kept the level of female choice constant throughout the experiment by desynchronising their seasonality from that of the males. Our results confirm that the MHC signal by itself is not sufficient to elicit any female response; it needs an additional olfactory cue. We show here that this additional cue renders males highly attractive during nest maintenance. This attractiveness drops significantly as soon as the nest is abandoned. We discuss possible candidates for this pheromone.