Department of Biological Sciences, North Carolina State University, Raleigh, NC, 27607, USA.
Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, Raleigh, NC, 27607, USA.
Environ Pollut. 2021 Oct 1;286:117221. doi: 10.1016/j.envpol.2021.117221. Epub 2021 May 4.
Freshwater salinization is a rapidly emerging ecological issue and is correlated with significant declines in aquatic biodiversity. It remains unclear how changing salinity regimes affect the physiology of sensitive aquatic insects. We used the parthenogenetic mayfly, Neocloeon triangulifer, to ask how ionic exposure history alters physiological processes and responses to subsequent major ion exposures. Using radiotracers (Na, SO, and Ca), we observed that mayflies chronically reared in elevated sodium or sulfate (157 mg L Na or 667 mg L SO) had 2-fold (p < 0.0001) and 8-fold (p < 0.0001) lower ion uptake rates than mayflies reared in dilute control water (16 mg L Na and 23 mg L SO) and subsequently transferred to elevated salinities, respectively. These acclimatory ion transport changes provided protection in 96-h toxicity bioassays for sodium, but not sulfate. Interestingly, calcium uptake was uniformly much lower and minimally influenced by exposure history, but was poorly tolerated in the toxicity bioassays. With qRT-PCR, we observed that the expression of many ion transporter genes in mayflies was influenced by elevated salinity in an ion-specific manner (general upregulation in response to sulfate, downregulation in response to calcium). Elevated sodium exposure had minimal influence on the same genes. Finally, we provide novel light microscopic evidence of histomorphological changes within the epithelium of the Malpighian tubules (insect primary excretory system) that undergoes cellular degeneration and necrosis secondary to calcium toxicity. We conclude that physiological plasticity to salinity stress is ion-specific and provide evidence for ion-specific toxicity mechanisms in N. triangulifer.
淡水盐化是一个迅速出现的生态问题，与水生生物多样性的显著下降有关。目前尚不清楚盐度变化如何影响敏感水生昆虫的生理机能。我们利用孤雌生殖的石蝇 Neocloeon triangulifer，研究了离子暴露史如何改变生理过程以及对随后主要离子暴露的反应。我们使用放射性示踪剂（Na、SO 和 Ca），观察到长期在高钠或高硫酸盐（157mg/L Na 或 667mg/L SO）中饲养的石蝇的离子摄取率比在低浓度对照水中（16mg/L Na 和 23mg/L SO）饲养的石蝇低 2 倍（p<0.0001）和 8 倍（p<0.0001），然后分别转移到高盐度环境中。这些适应离子转运的变化在针对钠的 96 小时毒性生物测定中提供了保护，但对硫酸盐没有保护作用。有趣的是，钙摄取率普遍较低，受暴露史的影响较小，但在毒性生物测定中耐受性较差。通过 qRT-PCR，我们观察到石蝇中许多离子转运基因的表达受离子特异性影响（对硫酸盐的一般上调，对钙的下调）。高钠暴露对相同基因的影响最小。最后，我们提供了新的光镜证据，证明了 Malpighian 管（昆虫初级排泄系统）上皮内的组织形态学变化，这些变化是由于钙毒性导致的细胞退化和坏死。我们得出结论，对盐度胁迫的生理可塑性是离子特异性的，并为 N. triangulifer 的离子特异性毒性机制提供了证据。
