Data from: The mayfly nymph Austrophlebioides pusillus Harker defies common osmoregulatory assumptions

Osmoregulation is a key physiological function, critical for homeostasis. The basic physiological mechanisms of osmoregulation are thought to be well established. However through series of experiments exposing the freshwater mayfly nymph Austrophlebioides pusillus (Ephemeroptera) to increasing salinities, we present research that challenges the extent of current understanding of the relationship between osmoregulation and mortality. A. pusillus had modeled 96 hour LC10, LC50 and LC99 of 2.4, 4.8 and 10 g/L, respectively. They were strong osmoregulators. At aquarium water osmolality of 256 ± 3.12 mmol/kg (±SE), (equivalent to 10 g/L added synthetic marine salt), the haemolymph osmolality of A. pusillus was a much higher 401± 4.18mmol/kg (±SE). The osmoregulatory capacity of A. pusillus did not break down, even at the salinity corresponding to their LC99, thus their mortality at this concentration is due to factors other than directly to external salinity. No freshwater invertebrate has been previously reported as suffering mortality from rises in salinity that are well below the iso-osmotic point. Recently studies have reported reduced abundance/richness of Ephemeroptera with slightly elevated salinity. Given that salinisation is an increasing global threat to freshwaters, there is an urgent need for studies into the osmo-physiology of the Ephemeroptera to determine if their loss at locations with slightly elevated salinity is a direct result of external salinity, or other, possibly physiological, causes.渗透压调节（osmoregulation）是一项关键的生理功能，对维持体内稳态（homeostasis）至关重要。目前学界普遍认为，渗透压调节的核心生理机制已得到充分阐明。然而，本研究通过一系列将淡水蜉蝣若虫*Austrophlebioides pusillus*（蜉蝣目（Ephemeroptera））暴露于逐步升高的盐度环境中的实验，对当前关于渗透压调节与死亡率之间关联的认知边界提出了挑战。该物种的96小时最低致死浓度（LC10）、半致死浓度（LC50）与最高致死浓度（LC99）的模型估算值分别为2.4、4.8和10 g/L。它们属于高效渗透压调节者：当养殖水体渗透压为256±3.12 mmol/kg（±标准误（SE）），对应添加10 g/L人工合成海盐的盐度时，该蜉蝣若虫的血淋巴（haemolymph）渗透压高达401±4.18 mmol/kg（±标准误（SE））。即便在与其LC99对应的盐度条件下，*A. pusillus*的渗透压调节能力也未出现崩溃，因此该浓度下的死亡率并非由外部盐度直接引发。此前尚无淡水无脊椎动物在远低于等渗点的盐度升高条件下出现死亡的相关报道。近期研究显示，随着盐度轻度升高，蜉蝣目的种群丰度与物种丰富度均出现下降。鉴于盐化（salinisation）正日益成为全球淡水生态系统的重大威胁，亟需开展针对蜉蝣目物种渗透生理学的研究，以明确其在盐度轻度升高的生境中种群消失的原因，究竟是外部盐度的直接作用，还是其他潜在的生理因素所致。