THE GENUS MACROBRACHIUM (CRUSTACEA, CARIDEA, PALAEMONIDAE): A TAXONOMIC SYNOPSIS FROM THE CRADLE OF EVOLUTION IN AFRICA TO ASIA AND THE AMERICAS.

Abstract

The genus Macrobrachium like all other decapod groups is very speciose. This make its systematic fairly cumbersome especially because the major morphological organ used in the classication is dependent on the ambient environment and also very plastic. The congruence therefore between classication based on morphology and molecular markers is an essential new process for deducing valid systematics of members of the group. The 16S rRNA mitochondrial gene is perhaps the most frequently used molecular marker for the systematics of the group. For this research work, we sequenced the three major Macrobrachium species found in Nigeria, namely the Macrobrachium vollenhovenii, Macrobrachium dux and Macrobrachium macrobrahion and used the obtained sequences to mine other sequences that were 95% similar to our sequences to deduce the phylogenetic afnities in fourty four species of Macrobrachium species found in four continents namely Africa, Asia, North and South America. There was conict between morphological and molecular systematics in the Nigerian species as consistently the Macrobrachium dux and Macrobrachion macrobrachion were grouped together making them at best ecotypes of the same species. Very high afnities also existed between the Asian species as they grouped together consistently using three different methods of phylogenetic inference (maximum likelihood, minimum evolution and maximum parsimony). The African species also mapped closely with the north American species consistently. One very clear conclusion is that the genetic divergence between the grouping is small, evidence that the genus is just evolving. Further research need to include more African species as there is a dearth of sequences from African species in the Genebank.