Social interaction in males of the Amazon river prawn Macrobrachium amazonicum (Heller, 1862) (Decapoda, Palaemonidae)

Abstract

The large size variation of Macrobrachium amazonicum reflects a complex population structure that consists of four morphotypes, called TC (Translucent Claw), CC (Cinnamon Claw), GC1 (Green Claw 1), and GC2 (Green Claw 2). The effect of the largest morphotype (GC2) claws on development and behaviour of the smallest male morphotype (TC) was analysed through manipulations of the large prawn’s second pair of claws. TC males were paired for 75 days in aquaria with (a) an intact GC2, (b) a GC2 with immobilized dactyls, and (c) a GC2 without chelipeds. Isolated TC males served as a control. The maintenance activities of TC males and social interactions with the GC2 morphotype were monitored. Survival and growth of TC males was lower in relation to the control when they were paired with intact GC2 males. Aggressive interactions were carried out almost exclusively by GC2 and strongly affected the behaviour of the small prawns. The absence of chelipeds and immobilization of dactyls in GC2 prawns reduced the negative effect on the development of TC males and agonistic behaviour. The social interactions between GC2 and TC prawns reflect a stable dominance hierarchy. The large claw of the GC2 morphotype plays a major role in the social interaction.