Developmental stability reflects the ability of a genotype to undergo stable development of a phenotype under given environmental conditions. Deviations from developmental stability arise from the disruptive effects of a wide range of environmental and genetic stresses, and such deviations are usually measured in terms of fluctuating asymmetry and phenodeviants. In this review, evidence is presented for a general relationship between health and developmental stability since the prevalence and the intensity of infections with parasites generally are associated with elevated developmental instability. The only exception is developmental stability in secondary sexual characters sometimes being positively associated with an increased frequency of venereal disease. Four studies have reported an elevated susceptibility to parasites among individuals with high levels of developmental instability. The cause of the positive relationships between parasitism and developmental instability may be either the generally poor condition of developmentally unstable individuals, or such individuals having genetically determined poor resistance to parasites as also reflected in an elevated level of developmental instability. The general relationship between parasitism and developmental instability has important implications for studies of parasite-host relationships in general and for conservation biology in particular.
