A molecular approach to reveal the genetic identity of parrot mussel and other sympatric mussel species distributed along the Kerala coast

Abstract

Two commercially important mussel species are recorded from the Indian coast: green mussel Perna viridis (Linnaeus, 1758) and brown mussel P. indica (Kuriakose and Nair, 1976). Apart from this, a third type referred to as parrot mussel, which has shell shape of brown mussel, but with green shell colouration and suspected to be the hybrid of the above two species has also been reported from Kollam coast of Kerala, where both the species co-occur. In the present work, genetic identity of parrot and sympatric mussel species was determined using protein and genomic DNA markers. Protein markers viz. Sodium Dodecyl Sulphate Polyacrylamide Gel Electrophoresis (SDS-PAGE) and allozymes and the genomic DNA marker Random Amplified Polymorphic DNA (RAPD) were used for determining genetic identity of the three mussel groups. The green and brown mussels could be clearly differentiated using SDS PAGE. The parrot mussel protein pattern was similar to that of brown mussel, except for an additional band of molecular weight 48.7 Kda which is unique to brown mussel. Genus specific protein bands for Perna viz. 66 Kda, 43 Kda and 14.3 Kda, were detected in this study. Allozyme electrophoresis also followed a similar pattern. Of the 10 allozyme loci studied, seven revealed speciesspecific diagnostic differences between P.viridis and P.indica. They were AAT-1* (Aspartate Amino Transferase-1*), AAT-2*, ME (Malic Enzyme)*, PGM-2*(Phospo Gluco Mutase-2*), EST-1* (Esterase- 1*), EST-2*, IcDH* (Isocitrate Dehydrogenase)*. Parrot mussel shared all the alleles of brown mussel, and no hybrid pattern was observed. Species-specific alleles clearly differentiated green mussel from both brown and parrot mussel. The genetic distance of green mussel from brown mussel, estimated from allozyme data was 1.1145 and with parrot mussel it was 1.105. The genetic distance between parrot mussel and brown mussel was negligibly low (0.0005). Using allozyme and RAPD data, the Nei’s Unbiased Measures of genetic distance were calculated and the dendograms prepared based on these values clearly depicted the separation of parrot mussel from green mussel as well as the close resemblance of parrot mussel with brown mussel. The higher gene flow (1.1539) determined using RAPD marker also hints that brown and parrot mussel may be acting as single interbreeding population. Hence this study using molecular tools to test the genetic identity of parrot mussel has helped to conclude that parrot mussel is only a morphotype of brown mussel and not a true hybrid of the two.