Can. J. Zool. 87(11): 1044–1051 (2009)  |  doi:10.1139/Z09-097  |  Published by NRC Research Press / Publié par les Presses scientifiques du CNRC  

No evidence for developmental plasticity of color patterns in response to rearing substrate in pygmy grasshoppers

M. Karlsson, J. Johansson, S. Caesar, and A. Forsman

Abstract: Color polymorphisms in animals may result from genetic polymorphisms, developmental plasticity, or a combination where some phenotypic components are under strong genetic control and other aspects are influenced by developmental plasticity. Understanding how color polymorphisms evolve demands knowledge of how genetic and epigenetic environmental cues influence the development and phenotypic expression of organisms. Pygmy grasshoppers (Orthoptera, Tetrigidae) vary in color pattern within and among populations. Color morphs differ in morphology, behavior, and life history, suggesting that they represent alternative ecological strategies. Pygmy grasshoppers also show fire melanism, a rapid increase in the frequency of black and dark-colored phenotypes in populations inhabiting fire-ravaged areas. We examined the influence of plasticity on color polymorphism in the pygmy grasshopper Tetrix subulata (L., 1761) using a split-brood design. Individuals were experimentally raised in solitude on either crushed charcoal or white aquarium gravel. Our analyses uncovered no plasticity of either color pattern or overall darkness of coloration in response to rearing substrate. Instead, we find a strong resemblance between maternal and offspring color patterns. We conclude that pygmy grasshopper color morphs are strongly influenced by genetic cues or maternal effects, and that there is no evidence for developmental plasticity of coloration in response to rearing conditions in these insects.

Résumé : Le polymorphisme de la coloration chez les animaux peut résulter de polymorphismes génétiques, de plasticité au cours du développement ou d’une combinaison dans laquelle certaines composantes phénotypiques sont sous un fort contrôle génétique, alors que d’autres aspects sont influencés par la plasticité du développement. Une compréhension du développement des polymorphismes de la coloration exige une connaissance de l’influence des signaux environnementaux génétiques et épigénétiques sur le développement et l’expression phénotypique des organismes. Les tétrix (Orthoptera, Tetrigidae) ont des patrons de coloration qui varient au sein des populations et entre les populations. Les différents morphes de couleur diffèrent par leur morphologie, leur comportement et leur cycle biologique, indiquant qu’il s’agit de stratégies écologiques de rechange. Les tétrix possèdent aussi un mélanisme relié au feu, soit une augmentation rapide de la fréquence des phénotypes noirs et de couleur foncée dans les populations qui vivent dans des zones ravagées par le feu. Nous examinons l’influence de la plasticité sur le polymorphisme de la coloration chez des criquets granulés, Tetrix subulata (L., 1761), qui utilisent une stratégie de couvain divisé. Nous avons élevé expérimentalement des individus solitaires sur du charbon de bois écrasé ou sur du gravier blanc d’aquarium. Nos analyses ne décèlent aucune plasticité dans le patron de coloration, ni dans la noirceur globale de la coloration en réaction au substrat d’élevage. Nous observons plutôt une forte ressemblance entre les patrons de coloration de la mère et de ses petits. Nous en concluons que les morphes de couleur des tétrix sont fortement influencés par les signaux génétiques ou les effets maternels et qu’il n’existe aucune indication de plasticité de la coloration durant le développement en réaction aux conditions d’élevage chez ces insectes.

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