Monnet Gauthier, Rosenfeld Jordan S, Richards Jeffrey G
Department of Zoology The University of British Columbia Vancouver British Columbia Canada.
British Columbia Ministry of the Environment Vancouver British Columbia Canada.
Ecol Evol. 2022 Sep 11;12(9):e9280. doi: 10.1002/ece3.9280. eCollection 2022 Sep.
Divergent energy acquisition and processing strategies associated with using different microhabitats may allow phenotypes to specialize and coexist at small spatial scales. To understand how ecological specialization affects differentiation in energy acquisition and processing strategies, we examined relationships among digestive physiology, growth, and energetics by performing captive experiments on juveniles of wild coho salmon () and steelhead trout () that exploit adjacent habitats along natural low-to-high energy flux gradients (i.e., pools versus riffles) in coastal streams. We predicted that: (i) the specialization of steelhead trout to high-velocity, high-energy habitats would result in elevated food intake and growth at the cost of lower growth efficiency relative to coho salmon; (ii) the two species would differentiate along a rate-maximizing (steelhead trout) versus efficiency-maximizing (coho salmon) axis of digestive strategies matching their ecological lifestyle; and (iii) the higher postprandial metabolic demand (i.e., specific dynamic action, SDA) associated with elevated food intake would occupy a greater fraction of the steelhead trout aerobic budget. Relative to coho salmon, steelhead trout presented a pattern of faster growth and higher food intake but lower growth efficiency, supporting the existence of a major growth versus growth efficiency trade-off between species. After accounting for differences in ration size between species, steelhead trout also presented higher SDA than coho salmon, but similar intestinal transit time and lower assimilation efficiency. Both species presented similar aerobic budgets since the elevated SDA of steelhead trout was largely compensated by their higher aerobic scope relative to coho salmon. Our results illustrate the key contribution of digestive physiology to the adaptive differentiation of juvenile growth, energetics, and overall performance of taxa with divergent habitat specializations along a natural productivity gradient.
与利用不同微生境相关的不同能量获取和处理策略，可能使表型在小空间尺度上实现特化并共存。为了解生态特化如何影响能量获取和处理策略的分化，我们通过对野生银大麻哈鱼（）和虹鳟（）的幼鱼进行圈养实验，研究了消化生理学、生长和能量学之间的关系。这两种鱼在沿海溪流中沿着自然的低到高能量通量梯度（即水塘与浅滩）利用相邻的栖息地。我们预测：（i）虹鳟对高速、高能量栖息地的特化将导致其食物摄入量和生长增加，但相对于银大麻哈鱼，生长效率较低；（ii）这两个物种将沿着与它们的生态生活方式相匹配的消化策略的速率最大化（虹鳟）与效率最大化（银大麻哈鱼）轴进行分化；（iii）与食物摄入量增加相关的更高的餐后代谢需求（即特殊动力作用，SDA）将占据虹鳟有氧预算的更大比例。相对于银大麻哈鱼，虹鳟呈现出生长更快、食物摄入量更高但生长效率更低的模式，这支持了物种之间存在主要的生长与生长效率权衡。在考虑了物种之间摄食量的差异后，虹鳟也比银大麻哈鱼具有更高的SDA，但肠道转运时间相似且同化效率较低。由于虹鳟较高的SDA在很大程度上被其相对于银大麻哈鱼更高的有氧范围所补偿，因此两个物种呈现出相似的有氧预算。我们的结果说明了消化生理学对具有不同栖息地特化的类群沿着自然生产力梯度在幼鱼生长、能量学和整体性能的适应性分化中的关键贡献。
