FADSEVOL · Metabolic and behavioral solutions to the nutritional challenges of life in freshwater

When invading nutritionally-poor environments, species can expand their functional metabolic niche, by evolving the capacity to synthesize essential compounds, and/or their dietary niche, by evolving new behavioral or morphological traits that enable them to use either novel or rare resources. The relative value of behavioral versus metabolic means for resolving mismatches remains unresolved because these have not been examined concurrently. Omega-3 long-chain polyunsaturated fatty acids (n-3 LCPUFA) are important for consumers, but are scarce in freshwaters compared to marine ecosystems, presenting a challenge for species invading freshwaters. The proposed study will be the first to examine both metabolic and behavioral means for regulating nutritional composition and fitness when invading freshwaters from marine ecosystems. We will examine the dietary niche of threespine stickleback (Gasterosteus aculeatus) in terms of diet variation and foraging preferences, and the metabolic functional niche in terms of genotypes and n-3 LCPUFA synthesis ability. FADSEVOL will be especially innovative by building upon the recently-identified genetic basis of variation in stickleback fatty acid metabolism: FADS2 copy number variation. We will characterize the fatty-acid composition of prey and tissues of lineages that vary widely in their FADS2 copy numbers and history of adaption to freshwater (WP1). Next, we will examine foraging preferences of common garden fish for prey that vary in nutritional composition (WP2). Finally, we will evaluate n-3 LCPUFA synthesis ability, FADS2 expression, and life history traits of lineages in common-garden conditions with high or low dietary n-3 LCPUFA availability (WP3). These approaches will allow us to understand variation in both the functional metabolic niche and the dietary niche, providing insights into how foraging behavior and metabolic evolution can enable consumers to invade nutritionally-challenging ecosystems.