Transcriptomic analysis of the effects of reproduction on immunity in the clam Meretrix petechialisn during the breeding season

Immune defense and reproduction are both physiologically demanding processes, therefore the trade-off is expected between them in breeding season. Although this balance strategy has been extensively studied in many species, it remains rare in the mollusc. Moreover, summer mortality of marine bivalve often occurs during breeding season and reproduction is suspected to play a significant role for the mass death. To address if spawning affects immunity to cause clam death, we performed transcriptome and gene expression analyses on the hepatopancreas of clam Meretrix petechialis at pre-/post-spawning. DEGs enrichment analysis revealed important immune signaling pathways and key genes changed before and after spawning. The results showed females up-regulated genes involved in apoptosis, TLR signal pathway and heat shock, whereas males down-regulated complement-related genes after spawning. Additionally, under vibrio challenged, the changes of four immune-related DEGs showed both genders up-regulate their immunocompetence more drastically to against pathogen infection after spawning. Our study provides a new insight into the understanding of molecular mechanisms underlying reproduction-influenced immune differences in M. petechialis and offers some clues to explain the possible reason for clam summer mortality.