Mechanisms and significance of physiological plasticity in winter-dormant fishes: a model to understand constraints on performance in cold environments

冬季的低温和随之而来的食物短缺，是鱼类在极向纬度持续生存的关键瓶颈，但鱼类冬季反应的详细机制仍然难以捉摸。鱼类越冬和冷适应的研究主要集中在冬季活动的物种（如。鲑鱼、鳕鱼）;对许多具有重要生态意义的物种进行冬季休眠的情况知之甚少（如温带濑鱼、太阳鱼）。冬季休眠是一种不活跃、遮蔽、不进食和低代谢的状态，以科普恶劣的冬季条件。了解冬季休眠是很重要的：这是一个关键的季节性事件，可以包括多达一半的鱼的寿命和活动和能量预算的温度限制可以对鱼类种群的健康和持久性产生重大影响。该基金的目的是揭示鱼类冬季休眠的意义和潜在机制。基于冬季休眠的进化模式，作者认为这是某些温适应鱼类向极地扩展地理范围的一种新策略，为研究冷适应的生理限制和地理限制提供了一个理想的模型。为了评估这个总体假设，我们将研究3个主要问题。(1)冬季休眠的生理和行为机制是什么？我们将使用一个综合的方法来阐明行为活动和细胞功能的作用，在设置低代谢率是冬季休眠鱼类的特点。(2)为什么会出现冬季休眠？首先，我们将测试冬季休眠鱼类的关键有氧（心肺和游泳）性能是否在寒冷中受到很大限制，从而可能因为无法觅食或逃避捕食者而进入休眠。然后，通过测量体内摄食率，生长过程，并在活跃和休眠的鱼喂可变的口粮或强制喂食的基本机制，我们还将测试冬季休眠是否是一种兼性行为，以避免能源效率低下的觅食时，食物是稀缺的，或强制性的后果，对食物同化的热限制。(3)如何有发展条件，表型可塑性，或适应当地环境设置不同的季节性温度阈值的冬季休眠纬度分离的人群之间，它是一个结果，种群间的变化，在热性能？拟议的研究将解决有关生态相关压力（如温度，食物）如何塑造鱼类的季节性生理和行为的基本知识差距。所获得的信息将提高我们对生理学如何设定物种分布的理解，并将有助于预测鱼类种群是否会随着气候变化而变化或扩大范围。

Low temperature in winter, and accompanying food scarcity, are key bottlenecks on the persistence of fishes at poleward latitudes, yet a detailed mechanistic understanding of winter responses in fishes remains elusive. Research on overwintering and cold adaptation of fishes has focused on winter-active species (eg. salmons, cods); much less is known about the many ecologically-important species that undergo winter dormancy (e.g. temperate wrasses, sunfishes). Winter dormancy is an inactive, sheltering, non-feeding, and low-metabolism state to cope with harsh winter conditions. Understanding winter dormancy is important: it is a key seasonal event that can comprise up to half the fish's lifespan and temperature constraints on activity and energy budgets can have major consequences for the health and persistence of fish populations. The objective of this grant is to reveal the significance and underlying mechanisms of winter dormancy in fishes. Based on the evolutionary patterns of winter dormancy, I propose that it is a novel strategy evolved by certain lineages of warm-adapted' fishes to extend their poleward geographic range, providing an ideal model to study physiological constraints on cold adaptation and geographic limits. To evaluate this overarching hypothesis, we will investigate 3 major questions. (1) What are the physiological & behavioural mechanisms underlying winter dormancy? We will use an integrative approach to elucidate the roles of behavioural activity and cellular function in setting the low metabolic rate that is characteristic of winter-dormant fishes. (2) Why does winter dormancy occur? First, we will test whether critical aerobic (cardiorespiratory & swimming) performance of winter dormant fishes is greatly constrained in the cold, thus obligating entry to dormancy possibly because of an inability to forage or flee predators. Then, by measuring in vivo feeding rates, growth processes, and underlying mechanisms in active and dormant fish fed variable ration or force-fed, we will also test whether winter dormancy is a facultative behaviour to avoid energetically-inefficient foraging when food is scarce, or an obligatory consequence of thermal limitations on food assimilation. (3) How have developmental conditions, phenotypic plasticity, or adaptation to the local environment set different seasonal temperature thresholds for winter dormancy among latitudinally-separated populations and is it a result of interpopulation variation in thermal performance? The proposed research will address fundamental knowledge gaps about how ecologically-relevant stressors (e.g. temperature, food) shape the seasonal physiology and behaviour of fishes. The information gained will improve our understanding of how physiology sets species distributions and will aid efforts to predict if fish populations will shift or expand ranges with climate change.