Abstract
The freshwater isopod crustacean Asellus aquaticus has recently been developed as an emerging invertebrate cave model for studying evolutionary and developmental biology. Mostly morphological and genetic differences between cave and surface A. aquaticus populations have been described up to now, while scarce data are available on other aspects, including physiology. The purpose of this study was to advance our understanding of the physiological differences between cave A. aquaticus and its surface-dwelling counterparts. We sampled two surface populations from the surface section of the sinking Pivka River (central Slovenia, Europe), i.e. locality Pivka Polje, and locality Planina Polje, and one cave population from the subterranean section of the sinking Pivka River, i.e. locality Planina Cave. Animals were sampled in spring, summer and autumn. We measured the activities of acetylcholinesterase (AChE) and glutathione S-transferase (GST) in individuals snap-frozen in the field immediately after collection. Acetylcholinesterase is likely related to animals’ locomotor activity, while GST activity is related to the metabolic activity of an organism. Our study shows significantly lower AChE and GST activities in the cave population in comparison to both surface A. aquaticus populations. This confirms the assumption that cave A. aquaticus have lower locomotor and metabolic activity than surface A. aquaticus in their respective natural environments. In surface A. aquaticus populations, seasonal fluctuations in GST activity were observed, while these were less pronounced in individuals from the more stable cave environment. On the other hand, AChE activity was generally season-independent in all populations. To our knowledge, this is the first study of its kind conducted in A. aquaticus. Our results show that among closely related cave and surface A. aquaticus populations also physiological differences are present besides the morphological and genetic. These findings contribute to a better understanding of the biology of A. aquaticus and cave crustaceans in general.
Highlights
The freshwater isopod water louse, Asellus aquaticus (L.) (Isopoda: Crustacea), is a benthic crustacean with several important roles in freshwater ecosystems
The aim of this paper was to investigate whether AChE and glutathione S-transferase (GST) activities differ between the cave A. aquaticus and its surface-dwelling counterparts, both living in well-oxygenated water
Two-way robust ANOVA showed the same general pattern in AChE and GST: enzyme activities were noticeably lower in the cave population than in either surface population
Summary
The freshwater isopod water louse, Asellus aquaticus (L.) (Isopoda: Crustacea), is a benthic crustacean with several important roles in freshwater ecosystems It inhabits various freshwater habitats throughout most of Europe, including caves [1], [2]. Quite a few studies on presumable physiological adaptations of other cave crustaceans, such as different energy saving mechanisms, are available. These showed that many cave crustaceans have an amazing ability to endure starvation over prolonged periods of time due to their enhanced capacity for food storage [17], diminished locomotor activity [17], [18], and lower metabolic activity [16], [18], [26], [27], [28]
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