Cowan Zara-Louise, Andreassen Anna H, De Bonville Jeremy, Green Leon, Binning Sandra A, Silva-Garay Lorena, Jutfelt Fredrik, Sundin Josefin
Department of Biology, Faculty of Natural Sciences, Norwegian University of Science and Technology, Høgskoleringen 5, Trondheim, 7491, Norway.
Groupe de Recherche Interuniversitaire en Limnologie et en Environnement Aquatique (GRIL), Département de Sciences Biologiques, Université de Montréal, 1375 Av. Théres̀e-Lavoie-Roux, Montréal, H2V 0B3, Canada.
Conserv Physiol. 2023 Aug 8;11(1):coad061. doi: 10.1093/conphys/coad061. eCollection 2023.
Aquatic ectotherms are vulnerable to thermal stress, with embryos predicted to be more sensitive than juveniles and adults. When examining the vulnerability of species and life stages to warming, comparable methodology must be used to obtain robust conclusions. Critical thermal methodology is commonly used to characterize acute thermal tolerances in fishes, with critical thermal maximum (CT) referring to the acute upper thermal tolerance limit. At this temperature, fish exhibit loss of controlled locomotion due to a temperature-induced collapse of vital physiological functions. While it is relatively easy to monitor behavioural responses and measure CT in larval and adult fish, this is more challenging in embryos, leading to a lack of data on this life stage, or that studies rely on potentially incomparable metrics. Here, we present a novel method for measuring CT in fish embryos, defined by the temperature at which embryos stop moving. Additionally, we compare this measurement with the temperature of the embryos' last heartbeat, which has previously been proposed as a method for measuring embryonic CT. We found that, like other life stages, late-stage embryos exhibited a period of increased activity, peaking approximately 2-3°C before CT. Measurements of CT based on last movement are more conservative and easier to record in later developmental stages than measurements based on last heartbeat, and they also work well with large and small embryos. Importantly, CT measurements based on last movement in embryos are similar to measurements from larvae and adults based on loss of locomotory control. Using last heartbeat as CT in embryos likely overestimates acute thermal tolerance, as the heart is still beating when loss of response/equilibrium is reached in larvae/adults. The last movement technique described here allows for comparisons of acute thermal tolerance of embryos between species and across life stages, and as a response variable to treatments.
水生变温动物易受热应激影响，预计胚胎比幼体和成体更敏感。在研究物种和生命阶段对变暖的脆弱性时，必须使用可比的方法来得出可靠的结论。临界热方法通常用于表征鱼类的急性热耐受性，临界热最大值（CT）指的是急性热耐受性上限。在这个温度下，由于重要生理功能因温度诱导而崩溃，鱼类会出现运动控制丧失。虽然在幼鱼和成鱼中监测行为反应和测量CT相对容易，但在胚胎中则更具挑战性，导致该生命阶段缺乏数据，或者研究依赖于可能不可比的指标。在这里，我们提出了一种测量鱼类胚胎CT的新方法，该方法由胚胎停止移动时的温度定义。此外，我们将此测量结果与胚胎最后心跳的温度进行比较，此前曾有人提出将其作为测量胚胎CT的一种方法。我们发现，与其他生命阶段一样，晚期胚胎表现出一段活动增加的时期，在CT前约2 - 3°C达到峰值。基于最后一次移动的CT测量比基于最后心跳的测量在后期发育阶段更保守且更容易记录，并且对大小胚胎都适用。重要的是，基于胚胎最后一次移动的CT测量与基于运动控制丧失的幼体和成体测量结果相似。在胚胎中使用最后心跳作为CT可能会高估急性热耐受性，因为在幼体/成体达到反应/平衡丧失时心脏仍在跳动。这里描述的最后移动技术允许比较不同物种之间以及不同生命阶段胚胎的急性热耐受性，并作为对处理的反应变量。
