A key metabolic gene for recurrent freshwater colonization and radiation in fishes

Abstract

Colonization of new ecological niches has triggered large adaptive radiations. Although some lineages have made use of such opportunities, not all do so. The factors causing this variation among lineages are largely unknown. Here, we show that deficiency in docosahexaenoic acid (DHA), an essential ω-3 fatty acid, can constrain freshwater colonization by marine fishes. Our genomic analyses revealed multiple independent duplications of the fatty acid desaturase gene Fads2 in stickleback lineages that subsequently colonized and radiated in freshwater habitats, but not in close relatives that failed to colonize. Transgenic manipulation of Fads2 in marine stickleback increased their ability to synthesize DHA and survive on DHA-deficient diets. Multiple freshwater ray-finned fishes also show a convergent increase in Fads2 copies, indicating its key role in freshwater colonization.

Comparative transcriptomics reveals domestication‐associated features of Atlantic salmon lipid metabolism

“…Finally, under dietary shortage of LC‐PUFAs, domesticated salmon respond with a compensatory increase in gene expression of fads2d5 and fads2d6a , which encode rate‐limiting enzymes for endogenous synthesis of LC‐PUFAs (Figure 5). Parallel to this finding, marine stickleback that colonize freshwater environments with lower levels of available dietary DHA evolve a greater endogenous LC‐PUFA synthesis ability through increased copy number of the same gene ( fads2 ) (Ishikawa et al., 2019). As the ability to perform endogenous synthesis of LC‐PUFAs is heritable in salmon (Horn, Ruyter, Meuwissen, Hillestad, & Sonesson, 2018), it is likely that the VO‐based diets in the domestic environment have unintendedly selected for improved ability of LC‐PUFA synthesis in domesticated salmon.…”

One Hundred Pressing Questions on the Future of Global Fish Migration Science, Conservation, and Policy

“…Partial migration theory (Chapman et al, 2012a,b;Secor, 2015a), which draws on studies of birds and fishes to explain a latent capacity for all taxa to exhibit phenotypic variation in their migration behaviors, may help encapsulate the many different forms that migration can take in fishes. Physiological research, such as the genetics of seawater tolerance, will also contribute to an evolutionary perspective on the origins of fish migration (Ishikawa et al, 2019). Recent discoveries of diverse modes of seasonal and lifetime migrations within populations fit well with the theory of partial migration, and aligns well with recent research agendas on population connectivity (Cowen and Sponaugle, 2008), biocomplexity (Ruzzante et al, 2006), and resilience (Hilborn et al, 2003;Kerr et al, 2010).…”

Assessment of Fatty Acid Desaturase (Fads2) Structure-Function Properties in Fish in the Context of Environmental Adaptations and as a Target for Genetic Engineering

“…The best was yet to come regarding studying marine vs. freshwater fish dealing with LC-PUFA poor food sources. Just a few months ago, Science released an exciting paper from Ishikawa et al [65]. In this comprehensive study, the authors compared three-spined stickleback (Gasterosteus aculeatus species complex) which successfully colonized newly emerged freshwater bodies after glacial retreat with closely related marine Japan Sea stickleback (G. nipponicus) which had failed to colonize freshwater.…”