Effects of sex on innate immunity characteristics in the Pacific white shrimp (Litopenaeus vannamei)

Sexual dimorphism is a common feature in all crustaceans. However, little information is available on the relationship between sex and disease resistance in Litopenaeus vannamei. This study aimed to evaluate the differences in innate immunity characteristics between male and female L. vannamei under stimulation with Vibrio parahaemolyticus causing acute hepatopancreatic necrosis disease (VpAHPND) or lipopolysaccharide (LPS). We found that the survival rates of female shrimp were significantly higher than those of males during VpAHPND stimulation (P < 0.05). In transcriptome analysis, we discovered obvious differences in the pathways activated for immune and metabolic responses between male and female shrimp after VpAHPND stimulation. Genes associated with immunity were downregulated in the VM (male stimulation group) vs. BM (male control group) comparison, whereas they were upregulated in the VF (female stimulation group) vs. BF (female control group) comparison. Furthermore, the transcriptome results showed that changes in processes such as carbohydrate metabolism and amino acid metabolism were also different between females and males. After LPS stimulation, the contents of semi-granular cells (SGCs) significantly decreased while those of granular cells (GCs) significantly increased in male shrimp, while the number of hyaline cells (HCs) decreased in female shrimp. The phagocytosis rate of hemocytes in male shrimp significantly decreased, while the catalase (CAT), peroxidase (POD), polyphenol oxidase (PPO), and glutathione S-transferase (GSH-ST) contents in the plasma of female shrimp were higher than those in males. These results collectively indicate that female shrimp have superior disease resistance compared to males, which provides an important reference for subsequent breeding efforts aimed at enhancing disease resistance in L. vannamei.