Differences in Agonistic Behavior and Energy Metabolism between Male and Female Swimming Crab Portunus trituberculatus Based on the Analysis of Boldness.

Individual differences in metabolism and agonistic behavior have been a key research area in evolution and ecology recently. In this study, we investigated the boldness of swimming crabs Portunus trituberculatus and explored the agonistic behavior between female and male crabs, specifically examining competitions between bold females vs. bold males (BF-BM), bold females vs. shy males (BF-SM), shy females vs. shy males (SF-SM), and shy females vs. bold males (SF_BM) and its relationship with energy metabolism. The main results revealed the following: There was no significant difference in boldness between females and males, while there were more bold individuals than shy in both females and males. Bold individuals initiated significantly more fights than shy individuals, and male initiators won significantly more fights than female initiators. The duration and intensity of fight between bold individuals was significantly higher than fights between shy individuals. For males, the concentration of glucose in the hemolymph was significantly higher in shy crabs than bold crabs, while there was no significant difference between shy and bold individuals in females. After fighting, the concentration of glycogen in claws was lower than that before fighting, and the concentrations of glucose and lactate in hemolymph were significantly higher after fighting than before. We found that the fighting willingness and ability were higher in male crabs than females and higher in bold crabs than shy. Fighting ability varied between sexes and was influenced by boldness and energy state.

What Forms, Maintains, and Changes the Boldness of Swimming Crabs (Portunus trituberculatus)?

Boldness of personality is an important theme in animal behavior and has significant ecological and evolutionary consequences. Studies on boldness in crustaceans typically focus on their behavior, while relatively few studies have focused on the formation and maintenance of and change in boldness, such as energy metabolism and neurotransmission. In this study, we measured the boldness of swimming crabs (Portunus trituberculatus) and analyzed the relationship between boldness and oxygen consumption rate, energy concentration, and the relative expression of energy-metabolism-related and 5-HT genes in mRNA. The results showed that boldness remained stable across repeated tests but changed under dangerous conditions. Swimming crabs could be divided into bold and shy individuals. Bold individuals consumed oxygen at a significantly higher rate than shy individuals. Lactate and glucose concentrations in hemolymph were significantly lower in bold individuals than in shy individuals, and mRNA relative expression of Na+/K+-ATPase and 5-HT genes was significantly higher in bold than in shy individuals. Preliminary results indicate that energy metabolism and neurotransmitters may underlie the formation and maintenance of personality characteristics of swimming crabs. Swimming crabs also exhibit behavioral flexibility in order to cope with risks. This may be an adaptation to their complex environments.

Agonistic behaviour and energy metabolism of bold and shy swimming crabs Portunus trituberculatus.

The metabolism and behaviour of crustaceans are highly flexible, and the inter-individual variation in these traits is evolutionarily and ecologically significant. We analysed the relationships among personality traits (boldness, activity and hesitancy), agonistic behaviour and energy status (glycogen, glucose and lactate) in the swimming crab Portunus trituberculatus The main results were as follows. (1) Boldness was significantly correlated with activity and hesitancy. Bold crabs were more likely to initiate and win a fight. In bold individuals, the frequencies of 'move to', 'cheliped display', 'grasp' and 'contact' were significantly higher than those of shy individuals, whereas the frequency of 'move away' was significantly lower than that of shy individuals. (2) Before fighting, the glucose concentrations in the haemolymph of bold individuals were significantly lower than those of shy individuals, whereas the concentrations of lactate showed the opposite trend. There were no significant differences in glycogen and lactate concentrations in the claw muscle between bold and shy individuals. (3) After fighting, the glucose and lactate concentrations in the haemolymph of both bold and shy individuals were significantly higher than those before fighting. The glucose concentrations in the haemolymph were significantly higher in bold individuals than shy individuals. In addition, bold individuals showed a larger increase in glucose in the haemolymph but a smaller increase in lactate compared with shy individuals. (4) After fighting, the glycogen concentrations in the claw muscle were significantly lower than those before fighting; however, there were no significant differences in the concentrations of lactate in the claw muscle. These results indicated that the agonistic behaviour of the swimming crab is related to its behavioural type. Energy reserves may be one of the factors affecting the personality traits and agonistic behaviour in crabs. These results should lay a foundation for in-depth understanding of the relationships among crustacean personality, agonistic behaviour and metabolic physiology.