Does competition allow male mate choosiness in threespine sticklebacks?

The theory of mate choice posits that intensified competition for mates can generate variation in either the strength or the direction of mate preferences within the competing sex. Here, we show that intensified male competition, manipulated through the operational sex ratio, induced differential mate choosiness among threespine stickleback males Gasterosteus aculeatus. In the absence of male competition, males were choosy independent of their condition when presented sequentially with a large and a small female. However, in a male-biased social setting, males in poor condition became indiscriminate, whereas good-condition males continued to be selective. Hence, competition induced condition-dependent mate choosiness. This was probably due to mating opportunities decreasing more for poor-condition than for good-condition males when competition intensified, resulting in condition-dependent cost of choice. Variation in condition and cost of choice could thus allow the persistence of male mate choosiness in populations experiencing intense male competition.