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Common genome-wide patterns of transcript accumulation underlying the wing polyphenism and polymorphism in the pea aphid

ABSTRACT: The pea aphid, Acyrthosiphon pisum, exhibits several environmentally cued polyphenisms, in which discrete, alternative phenotypes are produced. At low density parthenogenetic females produce unwinged female progeny, but at high density females produce progeny that develop with wings. These alternative phenotypes represent a solution to the competing demands of dispersal and reproduction. Males also develop as either winged or unwinged, but these alternatives are determined by a genetic polymorphism. Winged and unwinged males are morphologically less distinct from each other than winged and unwinged females, possibly because males experience fewer trade-offs between dispersal and reproduction. To assess whether shared physiological differences mirror the shared morphological differences that characterize the wing polyphenism and polymorphism, we used a cDNA microarray representing an estimated 10% of the coding genome (1734 genes) to examine differential transcript accumulation between winged and unwinged females and males. We identified several transcripts that differentially accumulate between winged and unwinged morphs in both sexes, the majority of which are involved in energy production. Unexpectedly, the extent of differential transcript accumulation between winged and unwinged morphs was greater for adult males than for adult females. Together, these results suggest not only that similar physiological differences underlie the polyphenism and polymorphism, but that male morphs, like females, are subject to trade-offs between reproduction and dispersal that are reflected in levels of transcript accumulation and possibly genome-wide patterns of gene regulation. These data also provide a baseline for future studies of the molecular and physiological basis of life history trade-offs. Keywords: Transcript levels were compared between winged and unwinged male and female pea aphids, for both nymphs and adults.

ORGANISM(S): Escherichia coli Buchnera aphidicola Acyrthosiphon pisum

PROVIDER: GSE8008 | GEO | 2007/06/05

SECONDARY ACCESSION(S): PRJNA100799

REPOSITORIES: GEO

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Project description:Developmental mechanisms play an important role in determining the costs, limits, and evolutionary consequences of phenotypic plasticity. One issue central to these claims is the metaphor of developmental “decoupling,” where alternate morphs result from evolutionarily independent developmental pathways. We test this assumption through a microarray study that explores differences in gene expression between alternate morphs relative to differences between sexes, a classic example of developmental decoupling. We then examine whether morph-biased genes are less conserved, relative to morph-shared genes, as predicted if developmental decoupling relaxes pleiotropic constraints on divergence. We focus on the developing horns and brains of two species of horned beetles with spectacular sexual- and morph-dimorphism in the expression of horns and fighting behavior. We find that patterns of gene expression were as divergent between morphs as they were between sexes. However, overall patterns of gene expression were also highly correlated across morphs and sexes. Morph-biased genes were more evolutionarily divergent, suggesting a role of relaxed pleiotropic constraints or relaxed selection. Together these results suggest that alternate morphs are somewhat developmentally decoupled, and that this decoupling has significant evolutionary consequences. However, alternative morphs may not be as developmentally decoupled as sometimes assumed and such hypotheses of development should be revisited and refined. We compared gene expression in three focal epidermal tissues (head, prothorax, legs) relative to a "control" tissue (dorsal abdominal epidermis) without any outgrowths. We also surveyed gene expression in the brain, relative to ganglionic neural tissue. We compared such patterns of gene expression between two male morphs (horned, fighter and hornless, sneaker males) and between males and females. We focused our array analyses (N = 48 arrays) on Onthophagus taurus (the species for which the array was designed), but also ran 19 arrays on thoracic tissue of Onthophagus nigriventris, a species which expresses thoracic horns as adults (O. taurus expresses head horns). Finally, we included a small subset of arrays (N = 4) directly hybridizing head epidermis tissue of O. taurus male morphs to validate our overall estimates of morph-biased expression. For more detail, refer to Snell-Rood et al. 2010, Evolution.

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Common genome-wide patterns of transcript accumulation underlying the wing polyphenism and polymorphism in the pea aphid

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