Habitat change influences mate search behaviour in three-spined sticklebacks

Mate choice is one of the main mechanisms of sexual selection, with profound implications for individual fitness. Changes in environmental conditions can cause individuals to alter their mate search behaviour, with consequences for mate choice. Human-induced eutrophication of water bodies is a global problem that alters habitat structure and visibility in aquatic ecosystems. We investigated whether changes in habitat complexity and male cue modality, visual or olfactory, influence mate search behaviour of female three-spined sticklebacks, Gasterosteus aculeatus. We allowed gravid females to search for mates in experimental pools that contained two nesting males and one social female, under low and high structural complexity (created from green Plexiglas sheets), with access to either visual or olfactory cues of the individuals. We found increased habitat complexity reduced the number of visits to nesting males, while a switch from visual to olfactory cues reduced the time spent searching for males, the number of visits to nesting males, the time spent evaluating males, and the relative time spent associating with males rather than females. Thus, females decreased mate searching and mate evaluation in the absence of visual stimulation. This reduced the rate of mate encounters and probably also the opportunity for choice. Our results show that changes in habitat structure and visibility can alter female mate searching, with potential consequences for the opportunity for sexual selection.