Phylogenetic position of Sri Lankan freshwater prawn Macrobrachium rosenbergii (Decapoda: Palaemonidae)

Abstract

The giant freshwater prawn, Macrobrachium rosenbergii is the largest known palaemonid in the world. It is one of the most economically important freshwater crustaceans around the world including Sri Lanka. Its natural range extends from south to southeast Asia including Papua New guinea, Australia and around pacific islands. The availability of two geographically distinct groups has been revealed in past studies and is suggested to recognize and re-name eastern and western groups as M. rosenbergii and M. dacqueti, respectively. The present study examined the phylogenetic position of Sri Lankan M. rosenbergii using mitochondrial 16S rRNA partial sequences. Sequences from 13 geographically separated populations were used in this analysis. Results supported the division of two clades indicating geographically separated genetically different western and eastern groups. Between two clades the nucleotide divergence level ranged from 4.89% - 5.96%. The degree of nucleotide divergence within western clade ranged from 0.00% to-0.64% and within eastern clade it varied from 0.21%-0.85%. Presence of two haplotypes was indicated (nucleotide divergence level 0.21%) within Sri Lankan populations and they grouped within the western clade. Between two haplotypes found, haplotype II is common among six other populations. This evidence suggests that further studies are needed to confirm whether giant freshwater prawn in Sri Lanka is different from hototype of M. rosenbergii and could be treated as the recently designated lectotype, M. dacqueti.