Does environmental stress affect cortisol biodistribution in freshwater mussels?

A Ronja D Binder,Felix Hiltwein,Sebastian Beggel,Michael W Pfaffl,Juergen Geist,Steven Cooke

doi:10.1093/conphys/coz101

A Ronja D Binder, Felix Hiltwein + Show 4 more

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https://doi.org/10.1093/conphys/coz101

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Abstract

As of today, regulation and physiological purpose of steroid hormones in invertebrates such as mussels are not completely understood. Many studies were able to show their presence, but their origin and genesis are not clear. Nevertheless, knowledge about changes in steroid hormone biodistribution in reaction to treatments could improve our understanding of their physiological functions in these species. Cortisol is a corticosteroid, which is frequently used as a stress biomarker in vertebrates, like fish or higher organisms. The aim of the study was to optimize cortisol extraction from various tissues of mussels, to develop a quantitative ELISA test system, and to study changes in biodistribution of cortisol in reaction to negative and positive stimulation treatments. As model organism, we used Anodonta anatina, a widespread freshwater mussel species native to Europe. We quantified cortisol concentrations in hepatopancreas, mantle, gills, gonads and the foot muscle. Tissue-specific reactions to environmental influences, simulated with the chemical stressors copper (II) chloride and sodium chloride, were assessed. During the 24-hours treatment, we additionally observed changes in cortisol regulation in response to feeding activity of the mussels. Besides, we found highly significant variations in the biodistribution of cortisol in different tissues, with a peak in the hepatopancreas. Whole body cortisol did not increase in the treated groups. However, balancing of all measured tissues showed redistribution of more than 10% of total body cortisol from the hepatopancreas to all other tissues during copper (II) chloride stressor treatment, but also when mussels ingested feed, compared to the non-fed control group. No redistribution was observed during sodium chloride treatment. We conclude that there can be a redistribution of cortisol in mussels, depending on external influences.

Highlights

Freshwater unionoid mussels rank among the most endangered taxonomic groups worldwide (Lydeard et al, 2004; Dudgeon et al, 2006; Lopes-Lima et al, 2017) and are considered target species of conservation (Geist, 2010, 2015)
A range of physiological stress biomarkers have been identified in marine bivalves (Liu et al, 2004; Li et al, 2007); information on freshwater mussels remains scarce (Fritts et al, 2015)
It is assumed that steroid hormones are environmentally accumulated substances, which do not fulfil hormone roles in invertebrates (Lafont and Mathieu, 2007; Fernandes et al, 2011)

Summary

Introduction

Freshwater unionoid mussels rank among the most endangered taxonomic groups worldwide (Lydeard et al, 2004; Dudgeon et al, 2006; Lopes-Lima et al, 2017) and are considered target species of conservation (Geist, 2010, 2015). Mainly vertebrate, species, a frequently used biomarker for environmental effects and stress-induced effects is the corticosteroid cortisol (Hellhammer et al, 2009; Yeh et al, 2013; Gong et al, 2015) The regulation of this glucocorticoid is well understood for vertebrates such as mammals and fish, but little is known about its role in invertebrates. If any changes in the cortisol level during a model treatment are measureable, it could improve the application of cortisol as a stress biomarker within these species as well, regardless of cortisol genesis This would improve the value of mussels as environmental bioindicator organisms (Hooper et al, 2007)

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