Monnet Gauthier, Rosenfeld Jordan S, Richards Jeffrey G
Department of Zoology, The University of British Columbia, Vancouver, BC, Canada.
British Columbia Ministry of the Environment, Vancouver, BC, Canada.
J Anim Ecol. 2020 Nov;89(11):2717-2732. doi: 10.1111/1365-2656.13326. Epub 2020 Oct 12.
Adaptive trade-offs are fundamental mechanisms underlying phenotypic diversity, but the presence of generalizable patterns in multivariate adaptation and their mapping onto environmental gradients remain unclear. To understand how life history affects multivariate trait associations, we examined relationships among growth, metabolism, anatomy and behaviour in rainbow trout juveniles from piscivore versus insectivore ecotypes along an experimental gradient of food availability. We hypothesized that (a) selection for larger size in piscivorous adults would select for higher juvenile growth at the cost of lower active metabolism; (b) elevated growth of piscivores would be supported by a greater productivity of their natal stream and more proactive foraging behaviours and (c) general patterns of multivariate trait associations would match the predictions of the Pace-Of-Life Syndrome. Relative to insectivores, piscivorous fry showed a pattern of higher growth (+63%), maximum food intake (+33%), growth efficiency (+41%) and standard metabolic rate (SMR; +47%), but lower active metabolic capacity (maximum metabolic rate [MMR; -17%], aerobic scope [AS; -48%]), suggesting that faster piscivore growth is supported by greater food intake and digestive capacity but is traded-off against lower scope for active metabolism. A similar trade-off appeared among organ systems, with piscivorous fry exhibiting an 83% greater investment in average mass of organs associated with food consumption and processing (i.e. stomach and intestine), but an apparently smaller relative investment in organs involved in cardiovascular or cognitive activities (heart and brain, respectively). Higher invertebrate drift in their natal rearing habitat, quicker behavioural transition to a novel food source and lower anxiety after a frightening event in piscivorous fry suggest that faster growth requires both proactive foraging behaviours and higher prey availability in the environment. Finally, the sampling of replicate insectivore populations confirmed their lower juvenile growth (-73% on average) and reduced environmental productivity of their natal streams (-45% lower drift abundance) relative to the piscivore ecotype. Our results suggest that selection for large adult body size influences selection on high juvenile growth, high basal metabolism and proactive behaviours, and that the intense phenotypic divergence between piscivorous and insectivorous rainbow trout may be constrained by environmental productivity.
适应性权衡是表型多样性的基本机制，但多元适应中普遍模式的存在及其与环境梯度的映射关系仍不明确。为了解生活史如何影响多元性状关联，我们沿着食物可利用性的实验梯度，研究了食鱼型与食虫型生态型虹鳟幼鱼的生长、代谢、解剖结构和行为之间的关系。我们假设：(a) 对食鱼型成鱼较大体型的选择会以较低的活跃代谢为代价，选择较高的幼鱼生长速度；(b) 食鱼型幼鱼较高的生长速度将得到其出生溪流更高生产力以及更主动觅食行为的支持；(c) 多元性状关联的一般模式将与生活节奏综合征的预测相符。相对于食虫型幼鱼，食鱼型幼鱼表现出更高的生长速度（+63%）、最大食物摄入量（+33%）、生长效率（+41%）和标准代谢率（SMR；+47%），但活跃代谢能力较低（最大代谢率 [MMR；-17%]，有氧代谢范围 [AS；-48%]），这表明食鱼型幼鱼更快的生长速度是由更大的食物摄入量和消化能力支持的，但要以较低的活跃代谢范围为代价。类似的权衡也出现在器官系统之间，食鱼型幼鱼对与食物消耗和处理相关器官（即胃和肠道）的平均质量投资高出83%，但对参与心血管或认知活动的器官（分别为心脏和大脑）的相对投资明显较小。食鱼型幼鱼出生的育幼栖息地中更高的无脊椎动物漂流数量、更快地向新食物源的行为转变以及在受到惊吓事件后的较低焦虑水平表明，更快的生长既需要主动的觅食行为，也需要环境中更高的猎物可利用性。最后，对重复的食虫型种群的采样证实，相对于食鱼型生态型，它们的幼鱼生长速度较低（平均低73%），出生溪流的环境生产力也较低（漂流丰度低45%）。我们的结果表明，对成年个体大体型的选择会影响对高幼鱼生长速度、高基础代谢和主动行为的选择，并且食鱼型和食虫型虹鳟之间强烈的表型差异可能受到环境生产力的限制。
