Transcriptomic responses of the endangered freshwater mussel Margaritifera margaritifera to trace metal contamination in the Dronne River, France

Abstract

The freshwater pearl mussel Margaritifera margaritifera is one of the most threatened freshwater bivalves worldwide. In this study, we aimed (i) to study the processes by which water quality might affect freshwater mussels in situ and (ii) to provide insights into the ecotoxicological significance of water pollution to natural populations in order to provide necessary information to enhance conservation strategies. M. margaritifera specimens were sampled in two close sites located upstream or downstream from an illegal dumping site. The renal transcriptome of these animals was assembled and gene transcription determined by RNA-seq. Correlations between transcription levels of each single transcript and the bioaccumulation of nine trace metals, age (estimated by sclerochronology), and condition index were determined in order to identify genes likely to respond to a specific factor. Amongst the studied metals, Cr, Zn, Cd, and Ni were the main factors correlated with transcription levels, with effects on translation, apoptosis, immune response, response to stimulus, and transport pathways.However, the main factor explaining changes in gene transcription appeared to be the age of individuals with a negative correlation with the transcription of retrotransposon-related genes. To investigate this effect further, mussels were classified into three age classes. In young, middle-aged and old animals, transcription levels were mainly explained by Cu, Zn and age, respectively. This suggests differences in the molecular responses of this species to metals during its lifetime that must be better assessed in future ecotoxicology studies.

Population genetics of freshwater pearl mussel (Margaritifera margaritifera) in central Massachusetts and implications for conservation

“…Discriminant analysis of principal components (DAPC) and fastStructure analyses suggest the existence of a single panmictic population of Margaritifera margaritifera in Massachusetts. Population structure was inferred using a panel of 287 single nucleotide polymorphisms shared between 59 individuals from six sites in Massachusetts and 23 individuals from one site in France (Bertucci et al, 2017). DAPC suggests (a) one and (b) two populations when Massachusetts individuals are analysed and when Massachusetts and French individuals are analysed together respectively.…”

“…This bioinformatics pipeline is summarized in Figure 2. This process was repeated with transcriptome data from 23 French M. margaritifera isolates (Bertucci et al, 2017) in order to investigate global population structure and to compare population genetic metrics between North American and European populations using an identical set of markers.…”

A weight‐of‐evidence approach for defining thermal sensitivity in a federally endangered species

“…New and reliable methods for quantifying stress in mussels could include the use of custom intermittent flow respirometry systems, which may provide improved means for quantifying respiration and clearance rates (Steffensen, ; Sui et al, ; Svendsen, Bushnell, & Steffensen, ). Alternatively, molecular markers have been developed for assessing physiological responses to stressors in other aquatic taxa (Denslow, Garcia‐Reyero, & Barber, ); however, few studies have applied this technology to freshwater mussels (but see Bertucci et al, ; Luo et al, ; Robertson, Galbraith, Iwanowicz, Blakeslee, & Cornman, ). Carefully selected molecular markers have the added benefit of providing insight into the mechanism (pathway) of the physiological response (Denslow et al, ).…”

“…Alternatively, molecular markers have been developed for assessing physiological responses to stressors in other aquatic taxa (Denslow, Garcia-Reyero, & Barber, 2007); however, few studies have applied this technology to freshwater mussels (but see Bertucci et al, 2017;Luo et al, 2014;Robertson, Galbraith, Iwanowicz, Blakeslee, & Cornman, 2017). Carefully selected molecular markers have the added benefit of providing insight into the mechanism (pathway) of the physiological response (Denslow et al, 2007).…”

Exposure to Elevated Concentrations of Major Ions Decreases Condition Index of Freshwater Mussels: Comparison of Metrics

“…After testing three commonly used formulas, they recommended a standardized method, calculated as CI ¼ dry soft tissue weight (g) 3 1000/internal shell cavity capacity (g). However, review of recent literature for freshwater bivalves still shows wide variation in the methodology used to calculate CI, with soft tissue weight (wet or dry) divided by either shell length (Blaise et al 2017), shell length^3 (Spooner and Vaughn 2009), shell weight (Payton et al 2016;Bertucci et al 2017;Zhao et al 2017), shell cavity volume (Nobles and Zhang 2015;Otter et al 2015), total dry weight (Ganser et al 2015), or total wet weight (Michel et al 2013), with or without the use of scaling factors (310, 3100, etc. ).…”