Life cycle strategies and genotypic variability in populations of aphids

Abstract

Populations of the rose aphid (Macrosiphum rosae) from various latitudes show differences in their life cycles. In warm climates they are exclusively parthenogenetic, whereas in cold climates sexual reproduction allows the aphid to overwinter in the egg stage. In temperate zones both holocyclic and anholocyclic clones occur within the same population. It is assumed that the reproductive mode has consequences for the genotypic structure of the populations. Continuous parthenogenesis results in low genogypic variability caused by selection and/or random genetic drift. The greater genotypic variability of holocyclic populations is due to recombination during the sexual phase. This yiew is supported by the study of populations which revealed high genotypic variability and homogeneity between populations in areas with harsh winters (e.g. Norway). In temperate countries (e.g. England) the genotypic variability was lower but the uniformity between populations still high, and in warm climates (e.g. the Canary Isles) the variability was lowest and heterogeneity between populations largest.