Late-stage Chicken (Gallus domesticus) Embryo Growth Patterns and Albumen Consumption
Groth, Kevin D.
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Maternal investment of energy and nutrients, in the form of yolk and albumen contained in each bird egg, has a profound effect on hatchling phenotype. Composition of the egg and mechanisms by which nutrients are utilized match th e needs of the organism developing inside an eggshell. We used the natural variation in the mass and composition of chicken (Gallus domesticus) eggs to examine consequences of variation in yolk and albumen mass on hatchling mass in a precocial bird. The eggs we examined contained 68% albumen and 32% yolk and ranged in mass from 45 to 75 g. Variation in egg mass arose from changes in both albumen and yolk mass, but changes in albumen mass explained most of the variation in egg mass. We found a positive correlation between initial egg mass and wet body mass as embryos approached hatching, suggesting that embryos in larger eggs utilized additional albumen and yolk to increase embryonic growth. SDS-P AGE revealed that albumen was ingested by embryos and transported via the gut into the yolk sac during incubation. Variation in quantity of albumen added to the yolk sac during the latter half of incubation probably contributes to variation in structural growth (tibiotarsus and culmen length) and body mass of embryos. Although the exact means by which egg albumen is translocated into the amnion of bird embryos has yet to be identified, our findings suggest that albumen is a major contributor to variation in hatchling phenotype.