Aphid wing dimorphisms: linking environmental and genetic control of trait variation

Abstract

Both genetic and environmental factors underlie phenotypic variation. While research at the interface of evolutionary and developmental biology has made excellent advances in understanding the contribution of genes to morphology, less well understood is the manner in which environmental cues are incorporated during development to influence the phenotype. Also virtually unexplored is how evolutionary transitions between environmental and genetic control of trait variation are achieved. Here, I review investigations into molecular mechanisms underlying phenotypic plasticity in the aphid wing dimorphism system. Among aphids, some species alternate between environmentally sensitive (polyphenic) and genetic (polymorphic) control of wing morph determination in their life cycle. Therefore, a traditional molecular genetic approach into understanding the genetically controlled polymorphism may provide a unique avenue into not only understanding the molecular basis of polyphenic variation in this group, but also the opportunity to compare and contrast the mechanistic basis of environmental and genetic control of similar dimorphisms.

Figure 1.

(a) Unwinged and winged females and (b) unwinged and winged males of the pea aphid. Note that the two morphs differ by more than whether they have wings. For example, the winged morphs have heavily muscled, well-defined thoraces relative to the unwinged individuals.

Figure 2.

Phylogeny of several aphid subfamilies, simplified from Ortiz-Rivas et al. (2004). To the right of the phylogeny are columns showing the presence of winged (W) and unwinged (UW) morphs during stages of the life cycle in each group. A checkmark indicates that at least one species in the subfamily is monomorphic if ‘W’ or ‘UW’ is marked, or at least one species is dimorphic if ‘W&UW’ is marked. Data compiled from multiple sources (Hille Ris Lambers 1966; Stroyan 1977; Heie , , , , , ; Blackman & Eastop 1994, 2000). See table S1 in the electronic supplementary material for a species-by-species listing.