Spiny dogfish (Squalus acanthias) and smoothhound (Mustelus canis) sharks in the northwest Atlantic undergo seasonal migrations driven by changes in water temperature. However, the recognized thermal habitats of these regional populations are poorly described. Here, we report the thermal range, catch frequency with bottom temperature, and catch frequency with time of year for both shark species in Narragansett Bay, Rhode Island. Additionally, we describe levels of two thermal stress response indicators, heat-shock protein 70 and trimethylamine N-oxide, with an experimental increase in water temperature from 15 °C to 21 °C. Our results show that S. acanthias can be found in this region year-round and co-occurs with M. canis from June to November. Further, adult S. acanthias routinely inhabits colder waters than M. canis (highest catch frequencies at bottom temperatures of 10 °C and 21 °C, respectively), but both exhibit similar upper thermal ranges in this region (bottom temperatures of 22–23 °C). Additionally, acute exposure to a 6 °C increase in water temperature for 72 hours leads to a nearly threefold increase in heat-shock protein 70 levels in S. acanthias but not M. canis. Therefore, these species display differences in their thermal tolerance and stress response with experimental exposure to 21 °C, a common summer temperature in Narragansett Bay. Further, in temperature-stressed S. acanthias there is no accumulation of trimethylamine N-oxide. At the whole-organism level, elasmobranchs’ trimethylamine N-oxide regulatory capacity may be limited by other factors. Alternatively, elasmobranchs may not rely on trimethylamine N-oxide as a primary thermal protective mechanism under the conditions tested. Findings from this study are in contrast with previous research conducted with elasmobranch cells in vitro that showed accumulation of trimethylamine N-oxide after thermal stress and subsequent suppression of the heat-shock protein 70 response.

中文翻译：

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西北大西洋两种鲨鱼的温度范围和生理耐受机制

大西洋西北部的多刺角鲨（Squalus acanthias）和平滑猎犬（Mustelus canis）鲨鱼在水温变化的推动下进行季节性迁徙。然而，对这些区域种群公认的热栖息地的描述很差。在这里，我们报告了罗德岛纳拉甘西特湾两种鲨鱼物种的热范围、捕获频率与底部温度以及捕获频率与一年中的时间。此外，我们描述了两种热应激反应指标的水平，热休克蛋白 70 和三甲胺 N-氧化物，水温从 15 °C 增加到 21 °C。我们的结果表明，S. acanthias 全年都可以在该地区发现，并在 6 月至 11 月与 M. canis 共同发生。此外，成年 S.​​ acanthias 通常栖息在比 M. acanthias 更冷的水域。canis（底部温度分别为 10 °C 和 21 °C 时捕获频率最高），但两者在该区域（底部温度为 22–23 °C）表现出相似的高温范围。此外，急性暴露于水温升高 6 °C 72 小时会导致 S. acanthias 而不是 M. canis 中的热休克蛋白 70 水平增加近三倍。因此，这些物种在实验暴露于 21 °C（纳拉甘西特湾常见的夏季温度）时，其热耐受性和应激反应显示出差异。此外，在受温度胁迫的 S. acanthias 中，没有三甲胺 N-氧化物的积累。在整个生物体水平上，韧皮科的三甲胺 N-氧化物调节能力可能受到其他因素的限制。或者，在测试条件下，弹性枝条可能不依赖三甲胺 N-氧化物作为主要的热保护机制。这项研究的结果与之前在体外对弹鳃细胞进行的研究形成对比，该研究显示热应激后三甲胺 N-氧化物的积累和随后的热休克蛋白 70 反应的抑制。