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Explaining the coexistence of asexuals with their sexual progenitors: no evidence for general-purpose genotypes in obligate parthenogens of the peach-potato aphid, Myzus persicae




In parthenogens, selection acts on entire genotypes rather than individual alleles. The general-purpose genotype hypothesis (GPG) predicts that temporally variable environments select for clones with broad ecological tolerances. These general-purpose genotypes should exhibit low fitness variance and high geometric mean fitness across environments. We tested this hypothesis by comparing the fitness of obligately and cyclically parthenogenetic genotypes of the peach-potato aphid, Myzus persicae, on three unrelated host plants. We found genetic variation for the relative performance on different hosts, but no difference in geometric mean fitness between obligate and cyclical parthenogens. Thus, for an environmental variable of major importance to aphids, the GPG hypothesis was not supported. In addition, the lack of an overall fitness difference between reproductive modes suggests that cyclical parthenogens incur no cost of polyphenism, but neither can they compensate for the cost of sex during the parthenogenetic phase of their life cycle.