Three hundred and fifty generations of extreme food specialisation: testing predictions of nutritional ecology |
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Authors: | James Warbrick-Smith David Raubenheimer Stephen J Simpson & Spencer T Behmer |
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Institution: | Zoology Department, University of Oxford, South Parks Road, Oxford, OX1 4AU, UK;, Institute of Natural Sciences, Massey University, Private Bag 102 904, North Shore Mail, Auckland, New Zealand;, School of Biological Sciences, Heydon-Laurence Building, A08, University of Sydney, NSW 2006, Australia;, and Department of Entomology, Texas A&M University, College Station, TX 77843-2475, USA |
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Abstract: | We used a strain of diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), that had been reared for approximately 350 generations in a precisely characterised environment to test hypotheses regarding the influence of nutritional heterogeneity on the evolution of nutrient regulatory responses. Caterpillars were maintained with ad libitum access to a diet that emulated that of an extreme nutritional specialist, comprising a homogeneous food of fixed nutrient composition. We measured performance (survival, development rate, and pupal mass), as well as the protein and carbohydrate intake of individual caterpillars confined to one of a range of single foods differing in their protein, carbohydrate, and water content. In a separate experiment, we measured the amount and balance of protein and carbohydrate self-selected by caterpillars presented with nutritionally complementary foods. Results showed a close fit with three of four predictions about the nutritional responses of 'nutrient specialist' feeders: (1) survival, development rate, and pupal mass were highest for animals given diets with the protein:carbohydrate composition of the ancestral culture diet, and dropped off sharply with higher and lower protein:carbohydrate balance, (2) caterpillars coped poorly with dietary dilution by water, irrespective of the macronutrient balance, and (3) the self-selected intake point corresponded with the macronutrient balance that gave peak performance (i.e., that of the ancestral culture diet). The fourth prediction, that caterpillars would be disinclined to over-ingest nutrients on imbalanced diets, was at best weakly met. We hypothesise that the evolution and maintenance of the specialist strategy might, paradoxically, require some degree of environmental heterogeneity. |
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Keywords: | diet breadth foraging theory nutrient balance nutritional heterogeneity nutritional regulation diamondback moth Plutella xylostella Lepidoptera Plutellidae |
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