Development of the Jejunum in Embryos and Neonates of the Chicken (Gallus domesticus) and American Alligator (Alligator mississippiensis)
Stewart, Sarah E.
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Development of oviparous amniotes requires vast developmental changes to prepare organisms for the transition from in ovo life as an embryo to ex ovo life as a neonate. Whereas embryos of these vertebrates rely on maternally supplied nutrients in the yolk and albumen (absorbed via the yolk sac and, to some extent, the intestine), neonates ingest, digest, and absorb exogenous nutrients via the digestive system. While much is known about growth and development of the intestine in birds, especially the domestic chicken (Gallus domesticus), much less is known about intestine development in non-avian archosaurs, like the American alligator (Alligator mississippiensis), the closest extant relative to birds. In this comparative study, we investigated development of the jejunum, the primary site of absorption in the small intestine, of late-stage embryos and early-stage neonates of chickens and alligators. Specifically, we quantified villus count, shape, pattern, height, and other features characterizing development of the jejunum. As villus height in the chicken jejunum increased during the final 20% of incubation, villus count decreased. Neither the number nor the shape of villi in the alligator jejunum changed throughout the last 18% of development before hatch. Whereas chicken villi appear less mature at the beginning of this final stage of embryonic development and become more mature through the neonate stage, alligator villi appear to be more mature at the outset and remain that way through hatching. These observations should provide helpful insights into how these species process albumen ingested during the latter half of incubation.