Heat shocks during eggs incubation lead to development, morphological and behavioural differentiation in Arctic charr (<i>Salvelinus alpinus</i>)

Temperature variation is affecting fish biodiversity worldwide, causing changes in geographic distribution, phenotypic structure and even species extinction. Incubation is a critical stage for stenothermic species, which are vulnerable to large temperature fluctuations, and its effects on the phenotype at later developmental stages are understudied, despite phenotype is essential for organism ecology and evolution. In this study, we tested the effects heat shocks during the embryonic period on the phenotype of Arctic charr (<i>Salvelinus alpinus</i>). We repeatedly quantified multiple phenotypic traits, including morphology, development and behaviour, over a period of 4 months, from hatching to juvenile stage on individuals having experienced heat shocks (+ 5°C on 24h, seven times) during their embryonic stage or not. We found that heat shocks led to smaller body size at hatching, and a lower sociability. Interestingly, these effects weakened throughout the development of individuals, and even reversed in the case of body size. We also found accelerated growth rate and higher body condition in the presence of heat shocks. Our study provides evidence that heat shocks experienced during incubation can have long-lasting effects on an individual's phenotype. This highlights the importance of the incubation phase for the development of ectothermic organisms, and suggests that temperature fluctuations may have significant ecological and evolutionary implications for Arctic charr. Given the predicted increase in extreme events and unpredictability of temperature fluctuations, it is critical to further investigate their effects on development by examining fluctuations that vary in frequency and intensity.全球范围内的温度变化正影响鱼类生物多样性，引发地理分布、表型（phenotype）结构的改变，甚至导致物种灭绝。孵化期是狭温性物种（stenothermic species）的关键发育阶段，此类物种极易受温度大幅波动影响；尽管表型（phenotype）对生物的生态与演化至关重要，但目前针对该阶段温度变化对个体后续发育阶段表型的影响仍研究不足。本研究以北极红点鲑（Arctic charr，<i>Salvelinus alpinus</i>）为研究对象，探究胚胎期热激（heat shocks）对其表型的影响。研究从孵化至幼鱼阶段，对经历过胚胎期热激（24小时内升温5℃，共7次）与未经历热激的个体，开展了为期4个月的重复量化分析，涵盖形态学、发育状态与行为学在内的多项表型性状（phenotypic traits）。结果显示，胚胎期热激会导致个体孵化时体型更小，社交性也更低。值得注意的是，此类影响会随着个体发育逐渐减弱，甚至在体型指标上出现逆转。此外，热激处理组个体的生长速率更快，躯体状况也更为优良。本研究证实，胚胎孵化期经历的热激会对个体的表型产生长期影响。这凸显了孵化阶段对变温生物（ectothermic organisms）发育的重要性，同时表明温度波动可能对北极红点鲑产生不容忽视的生态与演化层面的影响。鉴于未来极端温度事件频发且温度波动更具不可预测性，亟需通过探究不同频率与强度的温度波动对发育的影响，进一步深入研究此类效应。