Sex differences in the disease resistance of red swamp crayfish (Procambarus clarkii)

Sexual size dimorphism is a common characteristic of aquatic animals. However, little is known regarding the differences in immunity that are caused by gender differences in red swamp crayfish (Procambarus clarkii). In this study, the differences in disease resistance between the two sexes of crayfish were assessed according to mortality, pathology within the intestinal tract, apoptosis, melanism, and reactive oxygen species (ROS) activity analyses in haemocytes. Transcriptome analyses were performed to identify novel immune genes that are involved in disease resistance in crayfish. The differentially expressed genes (DEGs) associated with disease resistance were further validated using quantitative real-time PCR. The results indicated significantly higher mortality in male crayfish compared to that in females under pathogen stress (p < 0.05). Meanwhile, the damage to the intestinal track in the infected male crayfish was more serious than was that in females, while the apoptosis rate, melanism concentration, and ROS within haemocytes in the infected female crayfish were all significantly higher than were those of males at 96 h post injection (p < 0.05). Additionally, 43 DEGs involved in immuneregulated pathways such as the p53 signaling pathway, the AMP-activated kinase (AMPK) signaling pathway, and the PI3K-Akt signaling pathway were examined between the two sexes of crayfish under pathogen stress. The expression patterns of immune genes, including crustin2 and proPO, are more conducive to disease resistance in female crayfish than they are in males. Together, these results indicate that female crayfish possess much stronger disease resistance than do male crayfish, and they suggest that mono-sex breeding (all female crayfish) represents an important strategy for crayfish breeding.