Embryo Development Influences the Isotopic Signatures of Egg Components in Incubated Eggs

. Stable isotopes have become an accepted method to track resource acquisition and nutrient utilization by birds. Many studies have used these methods to examine nutrient allocation and utilization during egg formation. None, however, has addressed the potential influence of nutrient utilization and movement during embryo development on the isotopic signature of egg components or its implications for sampling protocols. Such fractionation would distort the isotopic signature in incubated eggs, resulting in conclusions based on eggs that may not reflect resource allocation during formation. Using incubated domestic chicken (Gallus gallus) eggs, we examined how embryo development influences &dgr;13C and &dgr;15N signatures in albumen, yolk protein, and yolk lipid. Embryo development significantly lowered &dgr;15N by 1.0‰ in yolk protein after day 15 and depleted &dgr;13C by 0.2‰ in albumen after just 3 days. Future studies examining resource allocation to eggs must control for the influence of embryonic development on isotopic signatures in eggs.