Data from: Convergence in organ size but not energy metabolism enzyme activities among wild Lake Whitefish (Coregonus clupeaformis) species-pairs

The repeated evolution of similar phenotypes by similar mechanisms can be indicative of local adaptation, constraints or biases in the evolutionary process. Little is known about the incidence of physiological convergence in natural populations, so here we test if energy metabolism in ‘dwarf’ and ‘normal’ Lake Whitefish evolves by similar mechanisms. Prior genomic and transcriptomic studies have found that divergence in energy metabolism is key to local adaptation in whitefish species-pairs, but that distinct genetic and transcriptomic changes often underlie phenotypic evolution among lakes. Here, we predicted that traits at higher levels of biological organization, including the activities of energy metabolism enzymes (the product of enzyme concentration and turnover rate) and the relative proportions of metabolically active tissues (heart, liver, skeletal muscle) would show greater convergence than genetic and transcriptomic variation. We compared four whitefish species-pairs and found convergence in organ size whereby all dwarf whitefish populations have a higher proportion of red skeletal muscle, three have relatively larger livers and two have relatively larger ventricles than normal fish. On the other hand, hepatic and muscle enzyme activities showed little convergence and were largely dependent on lake of origin. Only the most genetically divergent species-pair (Cliff Lake) displayed white muscle enzyme activities matching results from lab-reared normal and dwarf whitefish. Overall, these data show convergence in the evolution of organ size, but not in the activities of candidate enzymes of energy metabolism, which may have evolved mainly as a consequence of demographic or ecological differences among lakes.

通过相似演化机制反复产生相似表型（phenotype）的现象，往往可反映演化过程中的局部适应、演化限制与演化偏向。目前学界对自然种群中生理趋同（physiological convergence）现象的发生频率尚缺乏深入认知，因此本研究旨在验证「矮型」与「正常型」湖白鱼（Lake Whitefish）的能量代谢是否通过相似机制完成演化。此前的基因组学（genomics）与转录组学（transcriptomics）研究已证实，能量代谢通路的分化是白鱼物种对本地适应的核心驱动因素，但不同湖泊间的白鱼表型演化往往由差异化的遗传与转录组改变所支撑。基于此，本研究推测：相较于遗传与转录组变异，生物学组织层级更高的性状——包括能量代谢酶活性（由酶浓度与周转率共同决定）以及代谢活跃组织（心脏、肝脏、骨骼肌）的相对占比——会表现出更强的趋同性。本研究对比了四组白鱼物种对（whitefish species-pairs），结果发现器官大小存在趋同演化特征：相较于正常型个体，所有矮型白鱼种群的红色骨骼肌占比更高，其中3个种群的肝脏相对更大，另有2个种群的心室相对更大。但肝脏与肌肉的酶活性则几乎未表现出趋同性，且在很大程度上取决于其来源湖泊的环境特征。仅遗传分化程度最高的物种对（克利夫湖（Cliff Lake）种群）的白肌酶活性，与实验室饲养的正常型及矮型白鱼的相关实验结果相符。综上，本研究数据表明，湖白鱼的器官大小演化存在趋同性，但能量代谢候选酶的活性并未表现出趋同；这类酶活性的演化主要源于不同湖泊间的种群动态与生态环境差异。