Porter Marianne E, Hernandez Andrea V, Gervais Connor R, Rummer Jodie L
Department of Biological Sciences, Florida Atlantic University, 777 Glades Road, Boca Raton, FL 33431, USA.
ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, QLD 4811, Australia.
Integr Comp Biol. 2022 Dec 30;62(6):1710-1724. doi: 10.1093/icb/icac127.
The epaulette shark, Hemiscyllium ocellatum, is a small, reef-dwelling, benthic shark that-using its paired fins-can walk, both in and out of water. Within the reef flats, this species experiences short periods of elevated CO2 and hypoxia as well as fluctuating temperatures as reef flats become isolated with the outgoing tide. Past studies have shown that this species is robust (i.e., respiratory and metabolic performance, behavior) to climate change-relevant elevated CO2 levels as well as hypoxia and anoxia tolerant. However, epaulette shark embryos reared under ocean warming conditions hatch earlier and smaller, with altered patterns and coloration, and with higher metabolic costs than their current-day counterparts. Findings to date suggest that this species has adaptations to tolerate some, but perhaps not all, of the challenging conditions predicted for the 21st century. As such, the epaulette shark is emerging as a model system to understand vertebrate physiology in changing oceans. Yet, few studies have investigated the kinematics of walking and swimming, which may be vital to their biological fitness, considering their habitat and propensity for challenging environmental conditions. Given that neonates retain embryonic nutrition via an internalized yolk sac, resulting in a bulbous abdomen, while juveniles actively forage for worms, crustaceans, and small fishes, we hypothesized that difference in body shape over early ontogeny would affect locomotor performance. To test this, we examined neonate and juvenile locomotor kinematics during the three aquatic gaits they utilize-slow-to-medium walking, fast walking, and swimming-using 13 anatomical landmarks along the fins, girdles, and body midline. We found that differences in body shape did not alter kinematics between neonates and juveniles. Overall velocity, fin rotation, axial bending, and tail beat frequency and amplitude were consistent between early life stages. Data suggest that the locomotor kinematics are maintained between neonate and juvenile epaulette sharks, even as their feeding strategy changes. Studying epaulette shark locomotion allows us to understand this-and perhaps related-species' ability to move within and away from challenging conditions in their habitats. Such locomotor traits may not only be key to survival, in general, as a small, benthic mesopredator (i.e., movements required to maneuver into small reef crevices to avoid aerial and aquatic predators), but also be related to their sustained physiological performance under challenging environmental conditions, including those associated with climate change-a topic worthy of future investigation.
肩章鲨（学名：Hemiscyllium ocellatum）是一种小型的、栖息于珊瑚礁的底栖鲨鱼，它能够利用其成对的鳍在水中和离开水后行走。在珊瑚礁浅滩中，随着潮水退去珊瑚礁浅滩与外界隔绝，该物种会经历短时间的二氧化碳浓度升高、缺氧以及温度波动。过去的研究表明，该物种对与气候变化相关的二氧化碳浓度升高具有较强的适应能力（即呼吸和代谢性能、行为方面），并且耐缺氧和缺氧环境。然而，在海洋变暖条件下饲养的肩章鲨胚胎孵化时间更早、体型更小，斑纹和颜色也有所改变，且代谢成本比它们的当代同类更高。迄今为止的研究结果表明，该物种具有一定的适应能力，能够耐受21世纪预测的一些但可能不是全部具有挑战性的环境条件。因此，肩章鲨正逐渐成为一个用于理解不断变化的海洋中脊椎动物生理学的模型系统。然而，很少有研究调查其行走和游泳的运动学，鉴于它们的栖息地和面临挑战性环境条件的倾向，这可能对它们的生物适应性至关重要。鉴于新生幼鲨通过内化的卵黄囊保留胚胎营养，导致腹部呈球状，而幼鲨则积极觅食蠕虫、甲壳类动物和小鱼类，我们推测早期个体发育过程中体型的差异会影响运动性能。为了验证这一点，我们沿着鳍、肩带和身体中线使用13个解剖学标志，研究了新生幼鲨和幼鲨在它们所采用的三种水生步态（慢至中等速度行走、快速行走和游泳）过程中的运动学。我们发现体型差异并没有改变新生幼鲨和幼鲨之间的运动学特征。早期生命阶段之间的整体速度、鳍的旋转、轴向弯曲以及尾鳍摆动频率和幅度是一致的。数据表明，即使它们的摄食策略发生变化，新生幼鲨和幼鲨的运动学特征仍保持一致。研究肩章鲨的运动使我们能够了解这种以及可能相关物种在其栖息地内应对挑战性环境条件并从中离开的移动能力。一般来说，作为一种小型的底栖中型食肉动物，这样的运动特征不仅可能是生存的关键（例如，为了躲避空中和水生捕食者而进入小珊瑚礁缝隙所需的移动），而且还与它们在具有挑战性的环境条件下（包括与气候变化相关的条件）的持续生理性能有关，这是一个值得未来研究的课题。
