The ecological significance of lipid/fatty acid synthesis in developing eggs and newly hatched larvae of Pacific cod (Gadus macrocephalus)

The lipid/fatty acid composition of marine fish eggs and larvae is linked with buoyancy regulation, but our understanding of such processes is largely restricted to species with pelagic eggs. In this study, we examined developmental changes in the lipid/fatty acids of eggs and embryos of Pacific cod (Gadus macrocephalus), a species that spawns demersal eggs along coastal shelf edges, but as larvae must make a rapid transition to the upper reaches of the water column. Adult Pacific cod were collected in the Gulf of Alaska during the spawning season and eggs of two females were artificially fertilized with sperm from three males for each female. The eggs were subsequently reared in the laboratory to determine (1) how lipids/fatty acids were catabolized during egg and larval development, and (2) whether lipid/fatty acid catabolism had measurable effects on egg/embryo density. Eggs incubated at 4°C began hatching after 3-weeks and continued to hatch over a 10-day period, during which there was a distinct shift in lipid classes (phospholipids (PL), triacyglycerols (TAG), and sterols (ST)) and essential fatty acids (EFAs: 22:6n-3 (DHA), 20:5n-3 (EPA), and 20:4n-6 (AA)). In the egg stage, total lipid content steadily decreased during the first 60% of development, but just prior to hatch we observed an unexpected 2–3-fold lipid increase (~6–9 μg individual⁻¹) and a significant drop in egg density. The increase in lipids was largely driven by PL, with evidence of long-chained fatty acid synthesis. Late-hatching larvae had progressively decreasing lipid and fatty acid reserves, suggesting a shift from lipogenesis to lipid catabolism with continued larval development. Egg density measures suggest that lipid/fatty acid composition is linked to buoyancy regulation as larvae shift from a demersal to a pelagic existence following hatch. The biochemical pathway by which Pacific cod are apparently able to synthesize EFAs is unknown, therefore representing a remarkable finding meriting further investigation.     

Production of food-associated calls in wild male chimpanzees is dependent on the composition of the audience

Chimpanzees produce acoustically distinct calls when encountering food. Previous research on a number of species has indicated that food-associated calls are relatively widespread in animal communication, and the production of these calls can be influenced by both ecological and social factors. Here, we investigate the factors influencing the production of food-associated calls in wild chimpanzees and examine whether male chimpanzees produce food-associated calls selectively in the presence of important social partners. Male chimpanzees form stable long-term social relationships with each other, and these social bonds are vital in enabling a range of cooperative activities, such as group hunting and territory defence. Our data show that males were significantly more likely to produce food-associated calls if an important social partner was nearby, regardless of the size of the audience or the presence of oestrus females. Call production was also mediated by the size of the food patch and by whether or not the food could be monopolised. The presence of important social partners explained most of the variation in male calling behaviour, indicating that food-associated calls are socially directed and serve a bonding function.