All animals require a diverse suite of elemental nutrients and organic compounds in order to survive and reproduce, but nutrients vary widely in their availability both among and within ecosystems. Theory predicts an inverse relationship between availabilitv of organic
animal's diet and its abilitv to make or svnthesize. these nutrients from simpler compounds. Across the tree of lite. organisms feeding on nutritionallv-poor foods tvpicallv have a greater capacitv for synthesis than those feeding on nutritionallv-rich foods. However, the question of how this ability evolves evolves remains unresolved. When species encounter new landscapes with new foods, tor example during range expansion, they may be confronted with lower quality foods as well as competition for these resources with other species. To establish in such environments species: can evolve the capacity to synthesize a greater diversity of important organic compounds internally, and/or change their diet by evolving new traits that enable them to use either new foods that help them meet their nutritional needs.
The omega-3 long-chain polyunsaturated fatty acids (n-3 LCPUFAs) are a particularly important group of organic nutrients that animals need for both early life and reproduction. The availability of these fats can be an important determinant of a consumer's fitness, and affect the evolution of both dietarv and metabolic traits. Organisms in oceans are rich in the n-3 LCPUFAs docosahexaenoic acid (DHA; 22:6n-3) and eicosapentaenoic acid (EPA; 20:5n03), as well as alpha linolenic acid (ALA; 18:3n-3) their n-3 precursor. In contrast,
freshwater primarv producers and consumer typically contain only PA and ALA. This stark nutritional contrast between ecosystems present a significant challenge tor animals expanding their range into treshwater ecosystems, presenting an opportunity tor adaptation. Animals can adapt to a novel nutritional distribution of resource: through different combinations or metabolic traits and behavioral traits.
This project examined how fish from DHA-rich oceans have changed their diet and/ or metabolic synthesis capacity when establishing in freshwaters. In freshwater habitats, we might expected fish to have better ability to store and/or synthesize n-3 LCPUrAs. Functional fatty acid desaturase gene 2 (FADS2) is a key gene in involved in the synthesis of ALA to both EPA and DHA. FADS2 gene duplication is associated with an increased rates of LCPUFA synthesis. Behavioral dietary traits (i.e. eating prey richer in n-3 LCPUFA) associated with the acquisition of n-3 LCPUFA might also evolve in nutritionally-poor freshwaters.
We studied how populations from multiple populations of threespine stickleback (Gasterosteus aculeatus) throughout Europe from multiple geneticallv- and ecologicallv-differentiated populations have evolved the ability to survive in freshwaters. Our obiectives were to understand: 1) Is there evidence of population-specific diet variation in the wild? 2) Is there evidence of population-specific variation in FADS2 copy numbers in the wild and DHA synthesis ability in captivity on controlled diets? 3) Does population-specific diet and/or metabolic variation lead to variation in performance in terms of growth, condition, and survival?
