Department of Forest and Wildlife Ecology, University of Wisconsin, 1630 Linden Drive, Madison, WI 53706, USA.
J Exp Biol. 2011 Aug 15;214(Pt 16):2755-60. doi: 10.1242/jeb.058727.
Feeding conditions during the nestling period may significantly affect whole-life fitness in altricial birds but little is known about the physiological mechanisms responsible for these effects. Permanent changes (irreversible developmental plasticity) in digestive physiology caused by the neonatal diet may form such a mechanism. We previously showed that the lack of starch in the diet of house sparrow (Passer domesticus) nestlings between 3 and 12 days post-hatching significantly decreased the activity of intestinal maltase, an enzyme essential for starch digestion. To check whether diet-induced variation in maltase activity in young house sparrows is reversible, we raised them under laboratory conditions from 3 until 30 days of age on diets with either 0% starch or 25% starch, with some individuals experiencing a switch in their assigned diet at 12 days of age. We found evidence for the presence of an internal, presumably genetic, program for changes in the activity of maltase and sucrase, which was, however, significantly affected by diet composition (i.e. environmental factor). Digestive enzyme activity in 30 day old birds was not influenced by diet composition prior to day 12 but instead depended only on diet that was fed between days 12 and 30. We conclude that plasticity in the activity of intestinal disaccharidases in house sparrow nestlings represents completely reversible phenotypic flexibility that can help young sparrows to cope with unpredictable variation in food composition during ontogeny without long-term effects on their digestive system. However, comparison with other species suggests that the magnitude of digestive flexibility in young passerines may be evolutionarily matched to species-specific variation in feeding conditions.
育雏期的饲养条件可能会对晚成性鸟类的终生适应度产生显著影响，但我们对于导致这些影响的生理机制知之甚少。由新生期饮食引起的消化生理学的永久性变化（不可逆的发育可塑性）可能就是这样一种机制。我们之前曾表明，在孵化后 3 至 12 天期间，麻雀雏鸟饮食中缺乏淀粉会显著降低肠道麦芽糖酶的活性，而麦芽糖酶是消化淀粉所必需的酶。为了检查年轻麻雀中麦芽糖酶活性的饮食诱导变化是否具有可逆性，我们在实验室条件下饲养麻雀，从 3 日龄饲养到 30 日龄，饮食中分别含有 0%淀粉或 25%淀粉，其中一些个体在 12 日龄时经历了饮食的转变。我们发现了存在一种内部的、推测为基因的、用于麦芽糖酶和蔗糖酶活性变化的程序的证据，然而，这种程序受到饮食组成（即环境因素）的显著影响。30 日龄鸟的消化酶活性在 12 日龄之前不受饮食组成的影响，而只取决于 12 日龄至 30 日龄之间所喂食的饮食。我们得出的结论是，麻雀雏鸟肠道二糖酶活性的可塑性代表了完全可逆的表型灵活性，这种灵活性可以帮助幼鸟应对个体发育过程中食物组成的不可预测变化，而不会对其消化系统产生长期影响。然而，与其他物种的比较表明，幼 passerines 的消化灵活性的幅度可能与特定物种的喂养条件的变化相匹配。
