Molecular mechanisms underlying the effects of temperature increase on Mytilus sp. and their hybrids at early larval stages.

The present work aims to investigate the effects of water temperature increase on Mytilus galloprovincilis and Mytilus edulis pure larvae (PG, PE) and their hybrids (HFG, HFE). D-larvae were maintained at 18 °C or exposed to a higher temperature of 22 °C for 48 h. Initially, Embryotoxicity test was evaluated. Second, a transcriptomic analysis using a recently developed microarray platform was applied to determine the main biological processes involved in early life stages responses to temperature increase. Finally, an immunofluorescence investigation was performed to bridge the gap between transcriptomic regulation and the real changes at cellular/tissue levels. Embryotoxicity test revealed a higher sensitivity of M. edulis (PE) D-larvae as well as hybrids from females M. edulis (HFE) to temperature increase, with the highest rate of larval malformations. Transcriptomic results indicated a lack of an adequate heat shock protein (Hsp) response in PE and HFE larvae (the high expression was observed in PG larvae); the differential expression of gene involved in translation, energy metabolism and oxidative stress response may contribute to explain the observed complex alterations in the studied conditions. As revealed by immunohistochemistry, cytoskeleton proteins changes associated with a drastic decrease of Histidine-Rich Glycoprotein (HRG) may elucidate the larval abnormalities in shell development observed for PE and HFE larvae. Overall, the results indicate that each type of pure larva (PG and PE) and their respective female hybrid (HFG and HFE) react similarly to the temperature increase. Our data should be carefully considered in view of the water temperature increase in marine ecosystems and especially for the mussel's species in confluence zones.