Embryonic environment impacts adult traits and phenotypic integration in the pea aphid

Understanding how the embryonic environment affects adult phenotype is critical in the context of both human health and the increasing variance of environmental conditions due to climate change. Here we consider this topic within the framework of phenotypic integration, i.e., the pattern of correlations among elements of functionally robust trait suites. We investigated the life-long consequences of alternative embryonic environments on phenotypic integration in the pea aphid (Acyrthosiphon pisum). We exposed live-bearing pea aphid mothers to an adverse, high-density environment or a benign, low-density environment and measured morphological traits, fecundity, and transcriptional profiles in the resulting winged and wingless adult offspring. We observe that morphological integration decreases in both morphs in response to the adverse maternal environment. Transcriptional integration, on the other hand, shows a morph-specific response: integration increases in wingless offspring but decreases in winged offspring in response to the adverse maternal environment. Our results show the remarkable phenotypic diversity that a single genotype can express in response to environmental variation; that maternal environmental conditions can have strong effects on offspring trait variation and trait integration; and that these effects differ at the morphological and transcriptional levels.