Abstract
Variation in diet can influence the timing of major life‐history events and can drive population diversification and ultimately speciation. Proximate responses of life histories to diet have been well studied. However, there are scant experimental data on how organisms adapt to divergent diets over the longer term. We focused on this omission by testing the responses of a global pest, the Mediterranean fruitfly, to divergent selection on larval diets of different nutritional profiles. Tests conducted before and after 30 generations of nutritional selection revealed a complex interplay between the effects of novel larval dietary conditions on both plastic and evolved responses. There were proximate‐only responses to the larval diet in adult male courtship and the frequency of copulation. Males on higher calorie larval diets consistently engaged in more bouts of energetic courtship. In contrast, following selection, larval development time, and egg to adult survival showed evidence of evolved divergence between diet regimes. Adult body size showed evidence for adaptation, with flies being significantly heavier when reared on their “own” diet. The results show the multifaceted responses of individuals to dietary selection and are important in understanding the extreme generalism exhibited by the medfly.
Highlights
The responses of individuals to dietary nutrients represent an important driver for natural selection (Raubenheimer et al 2009)
Quantitative and qualitative variations in dietary nutrients significantly influence the timing of major life history events such as reproduction (Simpson and Raubenheimer 1993) and can direct allocation decisions and trade-offs (Stearns 1992)
Egg to adult survival We found that the number of individuals surviving development from egg to adult eclosion was affected by a significant interaction
Summary
We conducted replicated experimental evolution under two divergent larval diet regimes: ASG, “A” (a high calorie diet with a mix of simple and complex carbohydrates) and Starch, “S” (a lower calorie diet comprising complex carbohydrates) (details below). To measure the effect of larval diet and experimental adaptation on body mass, the dry weights of males and females from the development tests were taken by freezing individuals posteclosion at –20°C for 24 h, followed by desiccation at 25°C for 24 h and weighing samples of 100 flies from each replicate/treatment on a BDH DE-100A micro-balance. Data from early and late generations were analyzed together with generations, selection regime, and proximate larval diet designated as discrete factors and included in the models as fixed effects. Replicate lines were nested as a random effect within selection regime These data were split and the dietary responses of flies at early versus late generations were analyzed separately. No-choice mating tests The success of males in securing copulations during 30-minute no choice mating tests was recorded as success or failure, and analyzed using a Chi-Square test for equality of proportions (Wilson 1927)
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