Genetic diversity of the rainbow shell (Villosa iris (Lea 1829)) in the South Fork of the Spring and Spring Rivers, Arkansas

Genetic structuring of the freshwater mussel Villosa iris was investigated at four populations in the Spring River drainage [Spring River (SR) and South Fork Spring River (SFR)] in Arkansas. For freshwater mussels, gene flow occurs through migration of glochidia via host fish and genetic distance corresponds with geographic distance. We sampled two populations (n= 11 and 56) in SR and two populations (n= 17 and 82) from SFR. We used 7 polymorphic microsatellite primers previously designed for Lampsilis abrupta.  Number of alleles per locus ranged from 9 to 32, with an average of 23 alleles per locus.  Population structuring was low between all populations (F_st= 0.028).  We observed lower genetic diversity in the SFR (F_st= 0.012) than in the SR (F_st= 0.022).  Four loci were not in Hardy-Weinberg equilibrium in at least one population, while two loci were not in equilibrium in any population. Genetic diversity did not increase with geographic distance. Low overall diversity values and variable and low sample size in two populations could explain the lack of increased diversity with geographic distance.  The high gene flow observed in this study could be explained by V. iris being known to use highly mobile host fish.