Seasonal variation of transcriptomic and biochemical parameters of cockles (Cerastoderma edule) related to their infection by trematode parasites.

Bivalve populations are controlled by several biotic and abiotic factors. Parasitism is among the biotic factors but is often neglected. In the present study, we focused on the transcriptomic and biochemical responses of Cerastoderma edule when parasitized as first intermediate host by the trematode Bucephalus minimus (sporocyst, the most damaging stage), and taking into account seasonal patterns. In order to test the hypothesis that the presence of B. minimus compromises cockle regular gene expression and biochemical performance and increases their vulnerability to other parasite species infection, cockles were sampled every other month during one year in Arcachon Bay (French Atlantic coast). Overall, results showed that B. minimus induced its first intermediate host defence mechanism against oxidative stress (mainly at gene level), increased host metabolism and energy demand especially in summer (revealed at both gene and biochemical level, although without significant differences) and was accompanied by a higher metacercariae abundance. Results allowed to accept the posted hypothesis and to conclude that transcriptomic and biochemical markers can provide additional and ecologically relevant information about parasite effects on their hosts, reflecting the invasion effects of pathogens but also the environmental conditions that animals experience.