Mating system evolution in response to search costs in the speckled wood butterfly, Pararge aegeria

A general and intuitive prediction from models of mate preference is that w hen the cost of searching for mates increases, individuals should become le ss choosy. Here, we test this prediction by comparing the mating propensity of females in two populations of the butterfly Pararge aegeria. The popula tions originated from southern Sweden and Madeira and due to different adul t emergence patterns throughout the year, the average density of males per female is likely to be lower on Madeira. Therefore, we expected that the co st of searching should be greater on Madeira and, consequently, that the Ma deiran females should be less choosy. In line with predictions, the Madeira n females mated significantly sooner after the first interaction with males than did females from southern Sweden; This difference may reflect a weake r preference for territorial males over non-territorial patrollers in the M adeiran population, because of the greater costs of searching. The Madeiran females also showed a shorter time lag between mating and the start of ovi position. We discuss this unexpected result and propose that the same mecha nism could also explain this population difference, i.e. different costs of searching for suitable host plants. Both search processes are Fundamental for female reproductive success and we find it plausible that they can be g eneralised into the same theory of optimal search behaviour.