Phenotype fixation and genotypic diversity in the complex life cycle of the aphid Pemphigus betae

Abstract

Pemphigus betae typically shows a complex life cycle, with annual alternation between cottonwood trees, where it forms leaf galls, and herbaceous plants, where it lives on roots. Distinct phenotypes are associated with each phase. In a population in Utah, aphid clones vary in their tendencies to undergo the cottonwood phase of the life cycle, with certain clones rarely producing the winged migrants that initiate the cottonwood phase. Performances of 35 aphid clones were compared on root hosts by quantifying size (a correlate of fecundity), developmental time, and mortality for clonal sublines. Clones that tend to delete the cottonwood phase and remain on roots developed faster, showed lower mortality, and were larger compared to clones that tend to undergo an annual migration to cottonwood. The set of clones not previously subjected to selection on root hosts showed higher variance than clones isolated following selection in the root-inhabiting phase. -from Author