Dietary fat supplements influence weight gain and egg production but not offspring sex ratios in Japanese quail

Sex ratio theory suggests that females should bias offspring sex ratios
based on maternal condition and the availability of critical food
resources. Work in birds indicates that females do, indeed, bias sex
ratios according to maternal condition and food quality and quantity. Yet
it is unknown whether these sex ratio skews occur due to fluctuations in
particular micro- or macro-nutrients, caloric content overall, or even the
perception of food availability. We hypothesized that dietary fats may
drive biases in offspring sex ratios, because measures of maternal
condition often reflect fat reserves, and fats are critical for the
process of egg-laying in birds. To test this, we provided breeding
Japanese quail, a species that biases sex ratios in response to maternal
condition, with either a control breeding diet or a diet supplemented with
two oils (safflower oil and flaxseed oil). These oils were chosen for
their high omega-3 and omega-6 fatty acid content as well as their
importance in mammalian sex allocation. We then measured influences of
these diets on the sex ratio of offspring, the change in maternal weight,
and the laying rates of female quail. The dietary oil supplements
increased weight gains in quail but decreased the number of eggs laid
during the experiment. There was no influence of the oil supplements on
offspring sex ratios. This indicates that fat may not be a macro-nutrient
involved in the process of sex ratio adjustment in quail.