Carotenoids in the eggs of American coots : associations with size of eggs, local environment and diet

I studied carotenoids in the eggs of American coots (Fulica americana) from 3 study sites in Saskatchewan, Canada. I supplemented two diet types designed to reduce carotenoids in the diet of laying coots to investigate the relationship of carotenoids and the size of eggs and to examine the allocation of carotenoids into eggs.In chapter 2, I examined influences of local environment, food quantity and food quality on egg size. Carotenoid content and stable nitrogen and carbon isotopes in yolk were measured and used to elucidate whether variation in type of food eaten contributes to egg size. By analyzing isotopes in coot tissues, I confirmed that coots use endogenous lipid reserves for egg formation but not endogenous protein reserves, and the size of eggs is more dependent on exogenous sources of nutrients. My data demonstrate that carotenoids are not causal in egg size, but are components of natural, high quality diets. Carotenoids are obtained through the diet and deposited into egg yolk. It has been hypothesized that concentrations and percentages of individual carotenoids can be labile and dependent on diets or maintained in an optimal balance to meet requirements of embryos. In chapter 3, I investigate deposition of carotenoids in egg yolk among nesting locales, among hens within a site and among treatments in a diet manipulation experiment. My data show maintenance in the percent composition of a suite of 3 important carotenoids, lutein, zeaxanthin and â–carotene, independent of scale of investigation and in contrast to other individual carotenoids that appear to vary in proportions based on diet. These results suggest that birds can maintain nutritional balances in their eggs despite variation in diets.In chapter 4, I tested 3 hypotheses regarding the apportionment of carotenoids into egg yolk over the laying sequence. Without exception, concentrations of these nutrients have previously been shown to decline with egg sequence. In contrast to these findings, coots actually increased the carotenoid concentration in yolks over the laying sequence. My experimental evidence supports the explanation that this pattern of deposition depends on carotenoid availability to the laying female