Genotype-specific responses in Atlantic salmon (Salmo salar) subject to dietary fish oil replacement by vegetable oil: a liver transcriptomic analysis

<p>Abstract</p> <p>Background</p> <p>Expansion of aquaculture is seriously limited by reductions in fish oil (FO) supply for aquafeeds. Terrestrial alternatives such as vegetable oils (VO) have been investigated and recently a strategy combining genetic selection with changes in diet formulations has been proposed to meet growing demands for aquaculture products. This study investigates the influence of genotype on transcriptomic responses to sustainable feeds in Atlantic salmon.</p> <p>Results</p> <p>A microarray analysis was performed to investigate the liver transcriptome of two family groups selected according to their estimated breeding values (EBVs) for flesh lipid content, 'Lean' or 'Fat', fed diets containing either FO or a VO blend. Diet principally affected metabolism genes, mainly of lipid and carbohydrate, followed by immune response genes. Genotype had a much lower impact on metabolism-related genes and affected mostly signalling pathways. Replacement of dietary FO by VO caused an up-regulation of long-chain polyunsaturated fatty acid biosynthesis, but there was a clear genotype effect as fatty acyl elongase (elovl2) was only up-regulated and desaturases (Δ5 fad and Δ6 fad) showed a higher magnitude of response in Lean fish, which was reflected in liver fatty acid composition. Fatty acid synthase (FAS) was also up-regulated by VO and the effect was independent of genotype. Genetic background of the fish clearly affected regulation of lipid metabolism, as PPARα and PPARβ were down-regulated by the VO diet only in Lean fish, while in Fat salmon SREBP-1 expression was up-regulated by VO. In addition, all three genes had a lower expression in the Lean family group than in the Fat, when fed VO. Differences in muscle adiposity between family groups may have been caused by higher levels of hepatic fatty acid and glycerophospholipid synthesis in the Fat fish, as indicated by the expression of FAS, 1-acyl-sn-glycerol-3-phosphate acyltransferase and lipid phosphate phosphohydrolase 2.</p> <p>Conclusions</p> <p>This study has identified metabolic pathways and key regulators that may respond differently to alternative plant-based feeds depending on genotype. Further studies are required but data suggest that it will be possible to identify families better adapted to alternative diet formulations that might be appropriate for future genetic selection programmes.</p

Monogamous sperm storage and permanent worker sterility in a long-lived ambrosia beetle

The lifetime monogamy hypothesis claims that the evolution of permanently unmated worker castes always requires maximal full-sibling relatedness to be established first. The long-lived diploid ambrosia beetle Austroplatypus incompertus (Schedl) is known to be highly social, but whether it has lifetime sterile castes has remained unclear. Here we show that the gallery systems of this beetle inside the heartwood of live Eucalyptus trees are always inhabited by a single core family, consisting of a lifetime-inseminated mother, permanently unmated daughter workers, and immatures that are always full siblings to each other and their adult caretakers. Overall sex ratios are even. Males always disperse and only survive as stored sperm, but female offspring either disperse to mate and found their own colony or assume unmated worker roles, probably surviving for many years without any reproductive potential because tarsal loss precludes later dispersal. A well-supported Platypodinae phylogeny has allowed us to infer that parental monogamy evolved before a lifetime-unmated worker caste emerged, confirming the prediction that monogamy and full-sibling relatedness are necessary conditions for the evolution of such workers. The initially very challenging but ultimately long-term stable nesting habitat in live trees appears to have provided the crucial benefit/cost factor for maintaining selection for permanently sterile workers after strict monogamy and lifetime sperm storage had become established in this curculionid coleopteran lineage