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Keywords:

  • Aphid;
  • complex life cycle;
  • genotype-environment interaction;
  • heteroecy;
  • host alternation;
  • Pemphigus;
  • plasticity;
  • polyphenism;
  • sexupara

Abstract

In a Utah canyon, the aphid Pemphigus betae shows both a complex life cycle, with alternation between a gall-forming phase on cottonwood leaves and a root-feeding phase on herbs, and a simple life cycle, with year-round residence on roots. In order to determine the extent of clonal variation in life cycle, experiments using multiple sublines of individual clones were carried out in the laboratory and in the field. Previous studies suggested that both genetic and environmental factors underlie life cycle differences among subpopulations of aphids from different sites and different life cycle phases. The current study is the first assessment of clonal variation in propensity for host alternation within a natural population of aphids. In the laboratory experiment, clones showed highly significant differences in reproductive rates and in production of the host-alternating migrants. In agreement with previous findings, clones originating from lineages that had alternated to cotton-wood hosts in the previous year had lower average density and produced more migrants than clones originating from lineages that had remained on roots during the previous year.

In order to ascertain how clonal variation and site-specific environmental factors affect life cycle variation under natural conditions, clones from laboratory cultures were used to establish experimental colonies at two elevational sites within the canyon. Production of the host-alternating migrants was affected strongly by clone-x-site interaction and was affected slightly by site.

Results from both experiments indicate that loss of host alternation in P. betae could be effected through genetic change, environmental change, or both.