Introduction: Globally, the prawns of the genus Macrobrachium comprises of about 243 species across the tropical and sub-tropical regions. This includes about 8 species reported in Kenya. Macrobrachium are important human food sources and also play many ecological roles although there is little information documented about their population genetics and the life history traits of M. lepidactylus and M. rude in Kenya including divergent lineages en route to form new species and test in each lineage whether or not larval development require marine conditions. Lineages that do not rely on saltwater for larval development would provide a great advantage in aquaculture.
Methods: All the population genetics analysis was carried out in the laboratory at Johann Wolfgang Goethe- University of Frankfurt/Main, Germany between year 2015-2018. Mitochondrial DNA (COX1) gene sequences were analysed using ARLEQUIN software ve 3.5.1.
Results and discussion: The results of this study based on analysis of the haplotype networks, pairwise FST and Analysis of Molecular variance (AMOVA), genealogical tree and the genetic divergence differences between the upstream and coastal populations of M. lepidactylus showed similar patterns of groupings suggesting genetic similarity although with a reduced gene flow. This suggest an ongoing incipient speciation event although it is difficult to state clearly at this moment that there is a clear evidence for independently evolving— and thus, potentially sympatrically speciating—divergent mitochondrial lineages. The results on the egg size differences indicated significantly larger eggs for the upstream than coastal populations which is consistent with evolution to a completely freshwater existence. On the contrary, the haplotypes of the individuals with larger egg sizes did not appear in the exclusive upstream diverging population suggesting that hololimnetic evolution is an independent evolutionary event.
Conclusions and recommendations: Therefore with caution, the two populations (upstream and coastal) of M. lepidactylus should be managed as distinct genetic stocks and the population which appears to be adapted to freshwater conditions can be highly suitable for aquaculture. On the other hand, the populations of M. rude revealed no population genetic structure suggesting gene flow and should be managed as a single genetic stock. Both species showed high genetic diversity suggesting good survival and breeding potential. Thus, the genetic definition of prawn stock structure is important in understanding of fisheries resources for informed conservation and to ensure the sustainability of prawn fisheries in aquaculture.
Key words: Macrobrachium, hololimnetic evolution, genetic stock, haplotypes, sympatric speciation, aquaculture