A small set of differentially expressed genes was associated with two color morphs in natural populations of the pea aphid Acyrthosiphon pisum.

Color polymorphism is an ecologically important trait, which is related to local adaptation and ecological speciation. The pea aphid Acyrthosiphon pisum shows color polymorphism: the red and green color morphs where differences in ecological adaptation have been observed. Here, we measured genome-wide gene expression profiles of two color morphs in natural populations of A. pisum to explore the genetic basis of differentiated ecological adaptation. The results showed that only 32 genes were significantly differentially expressed between the two morphs, of which 18 had functional annotations. Among them, 13 genes were up-regulated [e.g. genes encoding protoheme IX farnesyltransferase (LOC100570971), carotene dehydrogenase (tor) and V-type proton ATPase subunit B (LOC100169462)] and 5 genes were down-regulated in the red morph (e.g. genes encoding transcription factors and heat shock proteins). To assess the functional importance of these differentially expressed genes (DEGs), we selected three highly expressed DEGs (LOC100169462, LOC100570971 and tor) with functional annotations and analyzed their expression levels in the red morph under three low temperatures (1 °C, 4 °C, and 8 °C) for 24 h. These three DEGs showed an interesting expression response to the cold acclimating conditions which resulted in an obvious phenotypic change of the red individuals to be greenish variants. This study suggests a link between gene expressions and body color polymorphisms in the pea aphid and provides important clues for further studying molecular mechanisms of ecological adaptation in aphids.