Low genetic differentiation in the populations of the Malabar carp Labeo dussumieri as revealed by allozymes, microsatellites and RAPD

The population structure of Labeo dussumieri, an endangered and endemic cyprinid from three riverine locationsin the Western Ghats, India wasinvestigated using allozyme, microsatellite and RAPD markers. L. dussumierisamples were obtained from Meenachil, Manimala and Pamba River basins, Kerala. Fourteen (46.7%) out of 30 allozyme loci, seven microsatellite loci and 12 RAPD Operon decamers gave polymorphic pattern. Six allozyme loci (AAT-2*, EST-4*, GLDH*, GPI-2*, G PDH* and LDH-2*) and three microsatellite loci (LdussG1, MFW19 and Bgon22) exhibited consistent significant deviation from Hardy-Weinberg Equilibrium expectations in different populations after probability level (P<0.05) was adjusted for sequential Bonferroni correction. All the three marker types demonstrated concordant results and various estimates revealed genetic variability within the subpopulations but surprisingly low level (θ = 0.0034 to 0.0081) of genetic differentiation among L. dussumieri from different river samples. AMOVA analysis also indicated low differentiation among subpopulations. No evidence for a recent genetic bottleneck was observed in L. dussumieri populations based on allozyme and microsatellite data set analysis. Meenachil, Manimala and Pamba Rivers open in to the southern end of Vembanad Lake in Kerala and are connected to each other in the lower reachesthrough an extensive network of natural canals. Common ancestry in the prehistoric period; and possible mixing of fish populations resulting in high gene flow across the rivers through the lake and interconnecting canals could have been responsible for the lack of significant allelic heterogeneity among the L. dussumieri populations. The stocks from the three rivers do not require different management strategies and for propagation assisted river ranching programme of this species, large effective breeding population can be developed by mixing individuals from three rivers.