Parasites and the ontogeny of sexual size dimorphism in a passerine bird
Abstract
Explanations of sexual size dimorphism in animals have generally relied on theoretical predictions of sexual selection, niche differentiation, and sex ratio theories, whereas proximate influences on size dimorphisms are undescribed in wild populations. We describe the differential effects of mite nest ectoparasites on the growth of the tarsus, a measure of skeletal size, in nestling pied flycatchers, Ficedula hypoleuca, depending on sex. The detrimental effects of mites were suffered by males to a higher degree than females. It is proposed that parasites may interact with both host hormones and the host immune system to cause sexual size dimorphisms in young animals.