Sexuality and the Components of Environmental Uncertainty: Clues from Geographic Parthenogenesis in Terrestrial Animals

Abstract

When parthenogenetic populations of terrestrial animals have different geographic distributions than closely related bisexual populations, the sexual forms tend to occupy regions of higher biotically imposed stress, generally being found at lower latitudes and altitudes, in mesic rather than xeric areas, on the mainland as opposed to islands, and in undisturbed as opposed to disturbed habitats. If sexual reproduction is favored by unpredictably changed conditions, then it would appear that regions of greater biotic stress are more unpredictable than those where abiotic factors are a major source of stress. This greater unpredictability probably stems from interspecific interactions (competition, predation). The changing genotypes of the organisms with which an individual interacts may be the major source of this biotic uncertainty; once evolved, sex in one population may lead to the spread and persistence of sex in a community of highly interacting individuals.