Data from: Thermal limits in native and alien freshwater peracarid Crustacea: the role of habitat use and oxygen limitation

1. In order to predict which species can successfully cope with global warming and how other environmental stressors modulate their vulnerability to climate related environmental factors, an understanding of the ecophysiology underpinning thermal limits is essential for both conservation biology a nd invasion biology. 2. Heat tolerance and the extent to which heat tolerance differed with oxygen availability were examined for four native and four alien freshwater peracarid crustacean species, with differences in habitat use across species. Three hypotheses were tested: 1) Heat and lack of oxygen synergistically reduce survival of species; 2) Patterns in heat tolerance and the modulation thereof by oxygen differs between alien and native species, and between species with different habitat use; 3) small animals can better tolerate heat than large animals and this difference is more pronounced under hypoxia. 3. To assess heat tolerances under different oxygen levels, animal survival was monitored in experimental chambers in which the water temperature was ramped up (0.25 ˚C min-1). Heat tolerance (CTmax) was scored as the cessation of all pleopod movement, and heating trials were performed under hypoxia (5kPa Oxygen), normoxia (20 kPa) and hyperoxia (60 kPa). 4. Heat tolerance differed across species as did the extent by which heat tolerance was affected by oxygen conditions. Heat tolerant species, e.g., Asellus aquaticus and Crangonyx pseudogracilis, showed little response to oxygen conditions in their CTmax, whereas the CTmax of heat sensitive species, e.g., Dikerogammarus villosus and Gammarus fossarum, was more plastic, being increased by hyperoxia and reduced by hypoxia. 5. In contrast to other studies on crustaceans, alien species were not more heat tolerant than native species. Instead, differences in heat tolerance were best explained by habitat use, with species from standing waters being heat tolerant and species from running waters being heat sensitive. In addition, larger animals displayed lower CTmax, but only under hypoxia. An analysis of data available in the literature on metabolic responses of the study species to temperature and oxygen conditions suggests that oxygen conformers and species whose oxygen demand rapidly increases with temperature (low activation energy) may be more heat sensitive. 6. The alien species D. villosus appeared most susceptible to hypoxia and heat stress. This may explain why this species is very successful in colonizing new areas in littoral zones with rocky substrate which are well aerated due to continuous wave action generated by passing ships or prevailing winds. This species is less capable of spreading to other waters which are poorly oxygenated and where C. pseudogracilis is the more likely dominant alien species.

1. 为预测哪些物种可成功适应全球变暖，以及其他环境胁迫因子如何调控其对气候相关环境因素的脆弱性，阐明支撑热耐受极限的生理生态学（ecophysiology）机制，对于保护生物学（conservation biology）与入侵生物学（invasion biology）均具有核心意义。
2. 本研究针对4种本地淡水囊虾类甲壳动物（peracarid crustacean）与4种外来淡水囊虾类甲壳动物，在不同生境利用模式下的热耐受能力，以及热耐受能力随氧气可获得性变化的幅度展开了探究，并检验了3项假说：① 高温与缺氧会协同降低物种存活率；② 热耐受能力模式及其受氧气的调控效应，在外来物种与本地物种之间、以及不同生境利用模式的物种之间存在差异；③ 小型动物的热耐受能力强于大型动物，且该差异在低氧（hypoxia）条件下更为显著。
3. 为评估不同氧水平下的热耐受能力，本研究在水温以0.25℃/min速率逐步升高的实验舱中监测动物存活率。以所有腹肢（pleopod）运动停止作为临界高温（CTmax）的判定标准，并分别在低氧（5kPa氧气）、常氧（normoxia，20kPa氧气）与高氧（hyperoxia，60kPa氧气）条件下开展加热实验。
4. 不同物种的热耐受能力存在差异，其热耐受能力受氧气条件影响的幅度也各不相同。热耐受能力较强的物种，如水虱（Asellus aquaticus）与假细钩虾（Crangonyx pseudogracilis），其CTmax对氧气条件几乎无响应；而热敏感物种，如壮肢钩虾（Dikerogammarus villosus）与河钩虾（Gammarus fossarum），其CTmax具有更高的可塑性：高氧条件可提升其CTmax，低氧条件则会降低其CTmax。
5. 与其他甲壳动物相关研究不同的是，本研究中外来物种的热耐受能力并未显著高于本地物种。相反，热耐受能力的差异最适合用生境利用模式来解释：静水水体中的物种热耐受能力较强，流水水体中的物种则热敏感。此外，体型更大的动物CTmax更低，但该现象仅在低氧条件下出现。对现有文献中本研究物种对温度与氧气条件的代谢响应数据进行分析后发现，氧顺应型物种以及随温度升高其氧气需求快速上升（活化能（activation energy）较低）的物种，可能具有更高的热敏感性。
6. 外来物种壮肢钩虾（D. villosus）对低氧与热胁迫的敏感性最高。这或许可以解释该物种为何能成功定殖于由船舶通行或盛行风产生持续波浪作用、因而溶氧充足的岩石底质沿岸带新生水域；而该物种难以扩散至溶氧较低的其他水体，在这类水体中假细钩虾（C. pseudogracilis）更有可能成为优势外来物种。