POPULATION GENETICS AND TAXONOMIC SIGNATURES OF WILD TILAPIA IN JAPAN, BASED ON MITOCHONDRIAL DNA CONTROL REGION ANALYSIS

The successful introduction of tilapia to Asian and South American countries was because of its adaptiveness to new environments under different environmental conditions to foster outstanding ecological and physiological variations making successful invaders of ecosystems throughout the tropical and subtropical regions. However, the cohabitation of other tilapia species with the Nile tilapia (Oreochromis niloticus) causes the reduction in population sizes, genetic diversity, and perturbation of the other species. This study aimed to establish the level of genetic integrity, population diversity, and population biogeography of wild tilapia species found in Japan. The mtDNA control region sequences generated fifty-two distinct haplotypes indicating significant differences of genetic variability in the entire data set for which 78.87% and 21.13% respectively represent the shared and singleton or private haplotypes.

The analysis of molecular variance (Table 1) showe d  high variation  within populations except for taxonomic units indicating a significant genetic structure among the 11 populations analyzed.

Our results indicated that the introduction of O. niloticus contribute d significantly  to genetic differentiation among populations in only a few generations showing signals of mtDNA introgression across the species boundary of O.  niloticus subjecting  the  genetic integrity of previously introduced species to jeopardy . The presence of private alleles, restricted gene flow among populations,  and  low  levels of genetic exchange between species indicated that the taxonomic signatures captured in our data is represented by a network of relatively  same genetic units that are geographically restricted .

However, clustering of biogeographic regional populations restricted by distance and the Pacific Ocean allowed us to define the population genetic structure as a mapping of taxonomic and genetic diversity rather than distance, therefore,  for  genetic conservation purposes, we propose an urgent  need for  a countrywide  genetic assessment of tilapia species thriving in Japan  as  some populations indicated minimal or no genetic pollution of some taxonomic signatures .