Male morphotypes and alternative mating tactics in freshwater prawns of the genus Macrobrachium: a review

Abstract

The discontinuous variation in male mating behaviour is termed alternative mating tactics. A distinction is commonly made between alternative mating tactics that are fixed for life or flexible with simultaneous or sequential switches between tactics over the sexually mature life. Freshwater species of the genus Macrobrachium demonstrate flexible tactics with sequential (i.e. developmental) switch between tactics. Sexually mature populations of the commercially important giant freshwater prawn M. rosenbergii consist of three morphologically and behaviourally distinct male morphotypes: small males, orange claw and blue claw males, representing (respectively) successive stages in the developmental pathway of sexually mature males. The dominant blue claw males secure mating by guarding receptive soft-shelled females with their long chelipeds while the subordinate SM use an alternative tactic of sneak mating to fertilize females. Current knowledge of the mating behaviour and reproductive success of these male morphotypes, including male competition over females, female mate choice and the involvement of pheromones, is reviewed. So far, the occurrence of distinct sexually mature male morphotypes has been described in 24 species within the genus Macrobrachium. The prevalence of distinct male morphotypes and alternative mating tactics among Macrobrachium species is discussed in view of the phylogeny of the genus, based on molecular markers. The environmental and genetic determination of the male morphotypes is discussed, as well as the evolution of the developmental alternative mating tactics in the genus Macrobrachium. Possible implications for prawns' aquaculture and future research are suggested.

Male morphotypes of the freshwater prawn Macrobrachium brasiliense (Decapoda: Caridea: Palaemonidae)

“…These observations reinforce the importance of chelipeds during the adult phase, when they play a fundamental role in the reproduction and social structure of the population. As emphasized by Karplus and Barki (), studies on various species of Macrobrachium suggest that these appendages are extremely important in the reproductive success of individuals. The presence of morphotype differences directly influences the abundance of the largest individuals due to the high aggressiveness displayed during the agonistic conflicts between dominant or submissive individuals (Karplus & Barki, ; Karplus et al, ).…”

“…As emphasized by Karplus and Barki (), studies on various species of Macrobrachium suggest that these appendages are extremely important in the reproductive success of individuals. The presence of morphotype differences directly influences the abundance of the largest individuals due to the high aggressiveness displayed during the agonistic conflicts between dominant or submissive individuals (Karplus & Barki, ; Karplus et al, ). Interestingly, unlike in other species that have multiple morphotypes, we did not observe individuals with injuries to the body or chelipeds, or with chelipeds under regeneration (see Rojas et al for details).…”

“…Possibly, the chelipeds have a remarkable importance in the social hierarchy of populations of Macrobrachium . The chelipeds probably serve as a behavioral display of dominance and submission, and influence the reproductive success of the males (Karplus & Barki, ).…”

“…The main evidence for two morphotypes was the development and morphology of the chelipeds. Besides the features we used to distinguish the morphotypes (morphometry and morphology), it is possible that there are other differences between these morphotypes, such as in behavior, sperm count, or histological patterns, similar to what is known in other species of Macrobrachium (Karplus & Barki, ; Paschoal & Zara, , ). Our contribution to the knowledge of the biology of M. brasiliense can clarify some questions raised by earlier studies that focused on their population structure, and contribute to future studies that focus on the contribution of morphotype differences to population structure.…”

Should only females of giant freshwater prawn Macrobrachium rosenbergii be selected in genetic improvement programmes?

“…However, this requires further study to ascertain advantages of OC male selection because in practical breeding programmes for GFP, to reduce generation time BC male is often selected. BC provided better breeding rate than other male GFP morphotypes (Karplus & Barki, ; Thanh et al, ). Based on these results and the close to one genetic correlation between male morphotypes, there is no need to run separate breeding programmes for each female and male morphotypes.…”