Data from: Cardiac plasticity influences aerobic performance and thermal tolerance in a tropical, freshwater fish at elevated temperatures

Fishes faced with novel thermal conditions often modify physiological functioning to compensate for elevated temperatures. This physiological plasticity (thermal acclimation) has been shown to improve metabolic performance and extend thermal limits in many species. Adjustments in cardiorespiratory function are often invoked as mechanisms underlying thermal plasticity because limitations in oxygen supply have been predicted to define thermal optima in fishes, however few studies have explicitly linked cardiorespiratory plasticity to metabolic compensation. Here we quantify thermal acclimation capacity in the commercially harvested Nile perch (Lates niloticus) of East Africa, and investigate mechanisms underlying observed changes. We reared juvenile Nile perch for 3 months under two temperature regimes, and then measured a series of metabolic traits (e.g., aerobic scope, AS) and critical thermal maximum (CTmax) upon acute exposure to a range of experimental temperatures. We also measured morphological traits of heart ventricles, gills, and brains to identify potential mechanisms for compensation. We found that long-term (3-months) exposure to elevated temperature induced compensation in upper thermal tolerance (CTmax) and metabolic performance (SMR, MMR and AS), and induced cardiac remodeling in Nile perch. Furthermore, variation in heart morphology influenced variations in metabolic function and thermal tolerance. These results indicate that plastic changes enacted over longer exposures lead to differences in metabolic flexibility when acutely exposed to temperature variation. Furthermore, we established functional links between cardiac plasticity, metabolic performance, and thermal tolerance, providing evidence that plasticity in cardiac capacity may be one mechanism for coping with climate change.

鱼类遭遇新型热环境时，往往会调整自身生理机能以代偿温度升高带来的影响。这种生理可塑性（thermal acclimation，热驯化）已被证实可提升诸多物种的代谢性能并拓宽其热耐受上限。心肺功能的调整常被视作热可塑性的潜在机制，因为学界此前已提出，氧气供给限制是决定鱼类热适宜范围的核心因素，但目前鲜有研究明确将心肺可塑性与代谢补偿直接关联起来。本研究以东非商业化捕捞的尼罗河尖吻鲈（Lates niloticus）为研究对象，量化其热驯化能力，并探究其观测到的生理变化背后的机制。我们将幼年尼罗河尖吻鲈在两种温度条件下饲养3个月，随后在其急性暴露于一系列实验温度时，测定了一系列代谢指标（如有氧代谢范围（aerobic scope, AS）及临界最高温（critical thermal maximum, CTmax））。此外，我们还测定了心室、鳃及脑组织的形态学特征，以识别潜在的代谢补偿机制。研究发现，长期（3个月）暴露于高温环境可诱导尼罗河尖吻鲈的高温耐受上限（以CTmax表征）与代谢性能（标准代谢率（standard metabolic rate, SMR）、最大代谢率（maximum metabolic rate, MMR）及有氧代谢范围（aerobic scope, AS））产生补偿效应，并引发心脏重构。此外，心脏形态的差异会对代谢功能与热耐受水平产生显著影响。上述结果表明，长期暴露过程中产生的可塑性变化，会使得鱼类在急性暴露于温度波动时的代谢灵活性出现差异。此外，本研究明确了心脏可塑性、代谢性能与热耐受之间的功能关联，为心脏容量可塑性可能是应对气候变化的潜在机制之一提供了实验证据。