Sex allocation and mate choice of selfed and outcrossed Schistocephalus solidus (Cestoda)

Abstract

Animals that inbreed regularly under natural conditions may provide valuable information about the evolutionary response of mate choice to an increase in a population's rate of inbreeding. I studied how an individual's inbreeding status affects its criteria of mate choice, as well as its own attractiveness, in a parasite, the hermaphroditic cestode Schistocephalus solidus, which inbreeds under natural conditions. Specifically, I tested whether a cestode's inbreeding status and allocation to reproductive tissue affect its attractiveness to selfed and outcrossed individuals. In a simultaneous choice situation, outcrossed cestodes strongly preferred an outcrossed mating partner over a selfed one, whereas selfed cestodes showed no preference with respect to the partner's inbreeding status. Both selfed and outcrossed cestodes were attracted to partners with a large combined amount of male and female reproductive tissue and with the potential to produce large eggs. I discuss how assortative mating with respect to inbreeding status may have consequences for the maintenance of a genetic load in the population as well as for the maintenance of selfing.