Physiological plasticity and acclimatory responses to salinity stress are ion-specific in the mayfly, Neocloeon triangulifer. (1st October 2021)

• Record Type: Journal Article
• Authors: Orr, Sarah E.; Negrão Watanabe, Tatiane Terumi; Buchwalter, David B.
• Is Part Of: Environmental pollution. Volume 286(2021)
• Publication Date: 2021-10-01
• Subjects: Salinity -- Osmoregulation -- Aquatic insects -- Acclimation -- Major ions; Pollution -- Periodicals; Pollution -- Environmental aspects -- Periodicals; Environmental Pollution -- Periodicals; Pollution -- Périodiques; Pollution -- Aspect de l'environnement -- Périodiques; Pollution -- Effets physiologiques -- Périodiques; Pollution; Pollution -- Environmental aspects; Periodicals; Electronic journals; 363.73
• DOI: 10.1016/j.envpol.2021.117221
• Languages: English
• ISSNs: 0269-7491

Abstract

Abstract: 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 ( 22 Na, 35 SO4, and 45 Ca), we observed that mayflies chronically reared in elevated sodium or sulfate (157 mg L −1 Na or 667 mg L −1 SO4 ) 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 −1 Na and 23 mg L −1 SO4 ) 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 . Graphical abstract: Image 1 Highlights: Pre-exposure to elevated sodium or sulfate reduced ion uptake rates. Pre-exposure to sodium reduced toxicity. Exposure to calcium caused tissue degeneration in the Malpighian tubules. There appears to be ion-specific mechanisms of toxicity.