Department of Biology, Kalamazoo College, Kalamazoo, MI 49006, USA.
Comp Biochem Physiol A Mol Integr Physiol. 2010 Sep;157(1):19-27. doi: 10.1016/j.cbpa.2010.05.010. Epub 2010 Jun 1.
Maternal investment by oviparous amniotes, in the form of yolk and albumen, and the mechanisms by which embryos use available energy and nutrients have a profound effect on embryo and, consequently, hatchling phenotype. Nutrient provisioning and uptake vary within and among oviparous taxa, avian and non-avian reptiles, due to differences and similarities in environment, behavior, and phylogeny. Eggs of crocodilians, the closest extant relatives to modern birds, are ideal models for examining modes of embryonic development, especially with regard to nutrient uptake, in non-avian reptiles and comparing them with those of birds. In this study, we investigated egg composition, embryo growth, and nutrient use in the domestic chicken (Gallus gallus) and American alligator (Alligator mississippiensis). We explored egg composition by separating and weighing components of fresh eggs. We measured embryo growth and nutrient usage by dissecting embryos and by obtaining samples of liquid from the amnion, digestive tract, and yolk sac throughout the last half of incubation. Variation in albumen mass contributed most to egg mass variation in chicken eggs, whereas alligator eggs were composed almost equally of yolk and albumen, although larger eggs contained proportionally more albumen and less yolk than smaller eggs. Both chicken and alligator albumen were mostly water (87% and 96%, respectively) although chicken albumen contained over three times more solid mass per gram than alligator albumen. In both species, yolk contained a high proportion of solids. Larger eggs produced larger hatchlings in both chickens and alligators, but albumen solids contributed to embryo mass only in chicken embryos. However, intact albumen proteins appeared in the stomach in embryos of both species. While the final disposition of albumen in alligators is unclear, variation in maternal investment of yolk at oviposition was responsible for nearly all of the variation in alligator hatchling phenotype, while both yolk and albumen contributed to chicken hatchling mass.
卵生羊膜动物的母体投资以卵黄和蛋清的形式存在，胚胎利用可用能量和营养物质的机制对胚胎产生深远影响，进而影响幼体表型。由于环境、行为和系统发育的差异，卵生动物、鸟类和非鸟类爬行动物之间的营养供应和吸收存在差异。鳄鱼是现生鸟类最接近的亲缘动物，其卵是研究非鸟类爬行动物胚胎发育模式的理想模型，特别是在营养吸收方面，并将其与鸟类进行比较。在这项研究中，我们研究了家鸡（Gallus gallus）和美洲鳄（Alligator mississippiensis）的卵成分、胚胎生长和营养利用。我们通过分离和称重新鲜卵的成分来研究卵成分。我们通过解剖胚胎和在孵化后期从羊膜、消化道和卵黄囊获得液体样本来测量胚胎生长和营养利用。蛋清质量的变化对鸡卵的卵质量变化贡献最大，而鳄卵几乎由卵黄和蛋清组成，尽管较大的卵比较小的卵含有更多的蛋清和更少的卵黄。鸡和鳄的蛋清主要由水组成（分别为 87%和 96%），尽管鸡蛋清每克固体质量是鳄蛋清的三倍多。在这两个物种中，蛋黄含有很高比例的固体。较大的卵在鸡和鳄中都产生较大的幼体，但只有鸡胚胎中蛋清固体对胚胎质量有贡献。然而，在两个物种的胚胎中，完整的蛋清蛋白都出现在胃中。虽然鳄的蛋清最终去向尚不清楚，但卵母投资在产卵时的差异几乎决定了鳄的幼体表型的所有变化，而蛋黄和蛋清都对鸡的幼体质量有贡献。
