Induction and Function of Polyphenic Morphs: Proximate Regulatory Mechanisms and Evolutionary Implications

The wing polyphenism of pea aphids is a compelling laboratory model with which to study the molecular mechanisms underlying phenotypic plasticity. In this polyphenism, environmental stressors such as high aphid density cause asexual, viviparous adult female aphids to alter the developmental fate of their embryos from wingless to winged morphs. This polyphenism is transgenerational, in that the pea aphid mother experiences the environmental signals, but it is her offspring that are affected. Previous research suggested that the steroid hormone ecdysone may play a role in this polyphenism. Here, we analyzed ecdysone-related gene expression patterns and found that they were consistent with a down-regulation of the ecdysone pathway being involved in the production of winged offspring. We therefore predicted that reduced ecdysone signaling would result in more winged offspring. Experimental injections of ecdysone or its analog resulted in a decreased production of winged offspring. Conversely, interfering with ecdysone signaling using an ecdysone receptor antagonist or knocking down the ecdysone receptor gene with RNAi resulted in an increased production of winged offspring. Our results are therefore consistent with the idea that ecdysone plays a causative role in the regulation of the proportion of winged offspring produced in response to crowding in this polyphenism. Our results also show that an environmentally regulated maternal hormone can mediate phenotype production in the next generation, as well as provide significant insight into the molecular mechanisms underlying the functioning of transgenerational phenotypic plasticity.

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Ecdysone signaling underlies the pea aphid transgenerational wing polyphenism

Vellichirammal

Gupta

Hall

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

123

102

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Seasonal differences in body mass and circulating metabolites in a wing‐dimorphic pygmy grasshopper: implications for life history?

Lehmann

Marco

Lehmann

et al. 2018

Ecological Entomology

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1. Functional wing polymorphism in insects is an intriguing topic, especially with respect to the adaptive advantage of each wing morph. The common pygmy grasshopper in Germany, Tetrix subulata, displays wing polymorphism skewed towards macropterous (LW) individuals capable of flight. Furthermore, T. subulata is known to undergo adult diapause in winter and reproduce in spring.2. Morphometric and biochemical parameters were examined in field‐collected grasshoppers during autumn and spring to obtain a ‘snapshot’ from the same/one cohort of grasshoppers in the wild.3. Flight muscles are largely reduced in brachypterous (SW) specimens, whereas they are well developed in LW individuals. Body mass measurements indicated gain in female T. subulata in spring, especially in LW morphs, which could be attributed to increased reproductive activity (egg production).4. Metabolic fuel in haemolymph is differentially distributed in autumn: the concentration of lipids is highest in males, while carbohydrates are most abundant in LW specimens. The metabolic data imply that dispersal in T. subulata is predominantly in autumn, by flight in the case of LW specimens and by hopping/walking in males.5. The season seems to be an important factor for the reproductive versus dispersal trade‐off in this species. Moreover, this study shows that morphological differences in T. subulata individuals are reflected in physiological differences that may ultimately affect behaviour and ecology.

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Induction and Function of Polyphenic Morphs: Proximate Regulatory Mechanisms and Evolutionary Implications

Cited by 2 publications

References 86 publications

Ecdysone signaling underlies the pea aphid transgenerational wing polyphenism

Ecdysone signaling underlies the pea aphid transgenerational wing polyphenism

Seasonal differences in body mass and circulating metabolites in a wing‐dimorphic pygmy grasshopper: implications for life history?

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