Epilogue

Abstract

Cyclical parthenogenesis, which developed early in the evolution of aphids, has been a major factor shaping their ecology. It led to the evolution of the telescoping of generations and prodigious rates of population increase. The latter they fuel by efficiently extracting all the amino nitrogen they need from large quantities of low quality phloem sap and utilizing their symbionts to upgrade and recycle nitrogen. Their short generation times enable aphids to track very closely the seasonal trend in resources. By anticipating this trend and by means of phenotypic plasticity they develop forms that are close to optimal for the conditions they each experience. In this context the function of sex is to reset the biological clocks that enable them to anticipate the trends. Accepting that there is a species specific minimum size at birth determined by the depth of phloem within the plant parts fed on by aphids, then the optimum adult size for maximizing r _m is 15 times the birth size, which for most aphids is relatively small.