Assortative pairing with respect to parasite load in the beetle Timarcha maritima (Chrysomelidae)

Because of their effects on host reproductive behaviour, parasites are theo retically expected to create sometimes assortative mating among hosts, with heavily parasitized individuals pairing together and lightly parasitized o nes pairing among themselves. We investigated the influence of protozoan gu t parasites on the pairing pattern of the chrysomelid beetle Timarcha marit ima. In the field, fecundity was negatively correlated with the parasite lo ad of females, unpaired males were significantly more heavily infected than paired ones and, among pairs, males and females were matched for parasite load. Mate choice experiments in the laboratory showed that males have some ability to avoid heavily infected partners when given the choice between t wo females. Male competitiveness, measured as their mobility, was also nega tively correlated with parasite load. These results indicate that parasite- related assortative pairing in this beetle could result from parasitized fe males being less fecund and parasitized males less competitive.