Les effets des vagues de chaleur marines et de la pêche accidentelle sur la survie et le métabolome de la mye commune Mya arenaria (Linnaeus, 1758) et de la mye tronquée Mya truncata (Linnaeus, 1758)

RÉSUMÉ : La biodiversité mondiale subit une contraction sous l'effet des perturbations anthropiques, et les écosystèmes côtiers sont menacés par une gestion inadéquate des pêcheries et par les changements environnementaux qui comprennent l'augmentation des vagues de chaleur marines. Lorsqu'elles agissent conjointement, les perturbations multiples entraînent des effets complexes sur les organismes et sont difficiles à prédire. De plus, la tolérance des espèces d'invertébrés marins comme les palourdes est généralement méconnue, et leur vulnérabilité pourrait être aggravée en raison de leur susceptibilité aux variations thermiques et de leur capacité de dispersion limitée. Deux espèces de palourdes, la mye commune Mya arenaria (Linnaeus, 1758) et la mye tronquée Mya truncata (Linnaeus, 1758), ont été prélevées de l'estuaire du Saint-Laurent (Québec, Canada) là où leurs répartitions biogéographiques se recoupent. Afin d'évaluer leur tolérance aux vagues de chaleur marines et à la pêche accidentelle, ces espèces ont été assujetties à un design expérimental factoriel croisé comprenant sept températures (2, 7, 12, 17, 22, 27, 32 °C) ainsi que deux intensités de pêche accidentelle (présence, absence). La survie a été mesurée après une période de 12 jours et trois tissus (branchies, manteau, muscle adducteur postérieur) ont été récoltés pour caractériser leur profil métabolomique. La survie était principalement affectée par l'interaction significative entre l'espèce et la température sans effet de la pêche. La tolérance aux vagues de chaleur était nettement différente entre les espèces : 26,9 °C pour M. arenaria et 17,8 °C pour M. truncata. À la limite supérieure de tolérance de M. arenaria, les métabolites [acide a-aminoadipique], [histidine], [phénylalanine], [serine], [thréonine] et [valine] ont augmenté et [aspartate], [acide ß-aminoisobutyrique], [FAD], [glutamine], [acétyl-CoA], [ADP], [cis-aconitate], [citrate] et [oxaloacétate] ont diminué dans les trois tissus. Pour M. truncata, seul le métabolite [phénylalanine] a augmenté tandis que [glutamine], [glycine] et [succinate] ont diminué dans les trois tissus. Selon les analyses en composantes principales et les analyses discriminantes, le métabolome de chaque tissu changeait en réponse aux vagues de chaleur. Les analyses de réseau ont révélé que M. arenaria s'appuie sur un grand nombre de voies cellulaires et emploie principalement des voies d'expression et de réparation de l'ADN et des voies signalétiques. Notre étude a révélé des mécanismes physiologiques pouvant expliquer la survie des espèces d'invertébrés marins en conditions futures de vagues de chaleur marines. -- Mot(s) clé(s) en français : conservation, métabolomique, changements climatiques, physiologie, pêcheries, bivalves, biologie intégrative. -- ABSTRACT : Biodiversity is currently threatened by several anthropogenic global change stressors and coastal ecosystems are imperiled by both unsustainable fishing practices and changing environmental conditions such as marine heatwaves. The co-occurrence of multiple stressors may produce complex interactions that are difficult to predict without appropriate experimentation. Furthermore, the tolerance of marine invertebrate species such as clams to these stressors is poorly understood, yet their vulnerability may be high due to their acute sensitivity to temperature variations and limited dispersal abilities. Two species of clams, softshell clams Mya arenaria (Linnaeus, 1758) and blunt gapers Mya truncata (Linnaeus, 1758) were collected from the St-Lawrence Estuary (Québec, Canada) where their biogeographic distributions overlap. To test their tolerance to marine heatwaves and harvesting disturbance, these species were subjected to both stressors in a controlled experimental environment with a fully crossed design comprised of seven temperatures (2, 7, 12, 17, 22, 27, 32 °C) and two harvesting disturbance intensities (with, without). Survival was measured after a 12 d exposure period, and three tissues (gills, mantle, posterior adductor muscle) were collected from surviving individuals for metabolomic profiling. Breakpoint analysis for species survival revealed a significant interaction species x temperature, and no significant effect of harvesting disturbance. Heatwave tolerance differed between species: 26.9 °C for M. arenaria and 17.8 °C for M. truncata. At the upper thermal limit of M. arenaria, [a-aminoadipic acid], [histidine], [phenylalanine], [serine], [threonine], and [valine] consistently increased whereas [aspartate], [ß-aminoisobutyric acid], [FAD], [glutamine], [acetyl-CoA], [ADP], [cis-aconitate], [citrate], and [oxaloacetate] consistently decreased across tissues. At the upper thermal limit of M. truncata, only [phenylalanine] consistently increased whereas [glutamine], [glycine], and [succinate] consistently decreased across tissues. Entire metabolome profiles were most significantly impacted by the interactive effect of species × tissue. Individually, each species' tissue metabolome displayed a unique and gradated response to heatwaves as evidenced by the converging results of principal component analysis and discriminant analysis. Network analysis of species' individual tissues revealed striking differences in pathway utilization at the upper heatwave limit, with M. arenaria displaying more abundant pathways and a greater reliance on DNA repair and expression as well as cell signaling pathways. Our study offers an in-depth understanding of physiological underpinnings of survival in marine invertebrates exposed to intensified heatwaves. -- Mot(s) clé(s) en anglais : conservation, metabolomics, climate change, physiology, fisheries, bivalves, integrative biology

Life-history traits display strong associations to genome size in annelids

Genome size, known also as the C-value, has been proposed as an important determinant of life-history variation in numerous animal taxa. We assessed the relationships between genome size and fitness-related life-history traits in six species of interstitial marine annelids of the genus Ophryotrocha. Life-history traits and genome size data obtained from 18 additional annelid species were included in our analyses to have a broader phylogenetic scope. Unexpectedly, genome sizes assessed here by flow cytometry in four Ophryotrocha species were three times larger than previously reported values obtained using Feulgen densitometry. This has implications for the hypothesis that harsh interstitial habitats select for small genomes in meiofaunal annelids. Within the genus Ophryotrocha, significant and positive relationships were found between genome size and nucleus size, and between genome size, age at first egg mass deposition, body size and lifespan. These relationships held up in the broader phylogenetic comparison. Our study provides evidence for the important role played by genome size in the evolution of life-history traits in annelids. -- Keywords : C-value ; Flow cytometry ; Ophryotrocha ; Body size ; Developmental rate ; Lifespan

Extensive gene rearrangements in the mitogenomes of congeneric annelid species and insights on the evolutionary history of the genus Ophryotrocha

Background Annelids are one the most speciose and ecologically diverse groups of metazoans. Although a significant effort has been recently invested in sequencing genomes of a wide array of metazoans, many orders and families within the phylum Annelida are still represented by a single specimen of a single species. The genus of interstitial annelids Ophryotrocha (Dorvilleidae, Errantia, Annelida) is among these neglected groups, despite its extensive use as model organism in numerous studies on the evolution of life history, physiological and ecological traits. To compensate for the paucity of genomic information in this genus, we here obtained novel complete mitochondrial genomes of six Ophryotrocha species using next generation sequencing. In addition, we investigated the evolution of the reproductive mode in the Ophryotrocha genus using a phylogeny based on two mitochondrial markers (COXI and 16S rDNA) and one nuclear fragment (Histone H3). Results Surprisingly, gene order was not conserved among the six Ophryotrocha species investigated, and varied greatly as compared to those found in other annelid species within the class Errantia. The mitogenome phylogeny for the six Ophryotrocha species displayed a separation of gonochoric and hermaphroditic species. However, this separation was not observed in the phylogeny based on the COX1, 16S rDNA, and H3 genes. Parsimony and Bayesian ancestral trait reconstruction indicated that gonochorism was the most parsimonious ancestral reproductive mode in Ophryotrocha spp. Conclusions Our results highlight the remarkably high level of gene order variation among congeneric species, even in annelids. This encourages the need for additional mitogenome sequencing of annelid taxa in order to properly understand its mtDNA evolution, high biodiversity and phylogenetic relationships. -- Keywords : Molecular phylogeny ; Dorvilleidae ; Mitogenome ; Next generation sequencing ; Model species ; Reproductive mode