Mate choice is not consistent with short-term effects of intraspecific admixture in woodlice

Abstract

Theory posits that individuals should exhibit mate preferences partly based on genetic relatedness such that fitness is maximized. Intraspecific genetic admixture can have different effects depending on the genetic characteristics and evolutionary histories of the individuals and populations involved. We investigated whether female mate choice behaviour in the common rough woodlouse (Porcellio scaber) matched the fitness consequences of genetic admixture. Most females from two populations that were introduced in sequence to one male from each of the populations were found to mate with both males and, furthermore, monandrous females (i.e. females that only mated with one male) predominantly mated with males from their own population. To test for the effects of genetic admixture, females from four populations were divided into two replicate pairs and assigned to mate either with a male from the same population as the female (pure) or with a male from the other population (admixed). The effect of mating treatment on the proportion of females that produced eggs and hatched young, as well as on the number and viability of offspring, depended on female source population. Mating treatment had opposing effects in two of the populations, whereas there were no detectable effects in the other two populations. By contrast to expectations, the mating patterns did not match the observed effects of genetic admixture. We discuss alternative adaptive and non-adaptive explanations for the observed patterns.