Brzek Paweł, Kohl Kevin, Caviedes-Vidal Enrique, Karasov William H
Department of Forest and Wildlife Ecology, University of Wisconsin, Madison, WI 53706, USA.
J Exp Biol. 2009 May;212(Pt 9):1284-93. doi: 10.1242/jeb.023911.
House sparrow nestlings are fed primarily on insects during the first 3 days of their life, and seeds become gradually more important afterwards. We tested whether developmental changes in size and functional capacity of the digestive tract in young house sparrows are genetically hard-wired and independent of diet, or can be modified by food type. Under laboratory conditions, we hand-fed young house sparrows with either a starch-free insect-like diet, based mainly on protein and fat, or a starch-containing diet with a mix of substrates similar to that offered to older nestlings in natural nests when they are gradually weaned from an insect to a seed diet. Patterns of overall development in body size and thermoregulatory ability, and in alimentary organ size increase, were relatively similar in house sparrow nestlings developing on both diets. However, total intestinal maltase activity, important in carbohydrate breakdown, was at least twice as high in house sparrow nestlings fed the starch-containing diet (P<0.001). The change in maltase activity of nestlings was specific, as no change occurred in aminopeptidase-N activity in the same tissues. There was no significant diet effect on digesta retention time, but assimilation efficiency for radiolabeled starch tended to be higher (P=0.054) in nestlings raised on starch-containing diet. Future studies must test whether the diet-dependent increase in maltase activity during development is irreversible or reversible, reflecting, respectively, a developmental plasticity or a phenotypic flexibility.
家麻雀雏鸟在出生后的头3天主要以昆虫为食，之后种子的重要性逐渐增加。我们测试了家麻雀幼鸟消化道大小和功能能力的发育变化是由基因决定且与饮食无关，还是会受到食物类型的影响。在实验室条件下，我们用两种食物人工喂养家麻雀幼鸟：一种是不含淀粉的类似昆虫的食物，主要由蛋白质和脂肪组成；另一种是含淀粉的食物，其底物组合类似于自然巢穴中较大雏鸟逐渐从昆虫饮食过渡到种子饮食时所提供的食物。两种饮食喂养下的家麻雀雏鸟，其身体大小和体温调节能力的总体发育模式以及消化器官大小的增加模式相对相似。然而，在分解碳水化合物方面起重要作用的肠麦芽糖酶总活性，在喂食含淀粉食物的家麻雀雏鸟中至少高出两倍（P<0.001）。雏鸟麦芽糖酶活性的变化是特异性的，因为相同组织中的氨肽酶-N活性没有变化。饮食对消化物保留时间没有显著影响，但在含淀粉饮食喂养下的雏鸟中，放射性标记淀粉的同化效率往往更高（P=0.054）。未来的研究必须测试发育过程中依赖饮食的麦芽糖酶活性增加是不可逆的还是可逆的，这分别反映了发育可塑性或表型灵活性。
