Genetic and Morphological Divergence in the Freshwater Pearl Mussel, Margaritifera laevis (Bivalvia: Margaritiferidae), with Reference to the Existence of Two Distinct Species

Abstract

Genetic and morphological divergence in the endangered freshwater pearl mussel Margaritifera laevis from Nagano Prefecture is investigated. We reveal the existence of two genetically divergent forms within the mussels. The two forms occurred sympatrically in one of four sampling locations and displayed complete allelic substitutions at four allozyme loci, suggesting an absence of hybridization between them. Their shell morphometries were also different. These findings strongly suggest they are two distinct species. A conservation program should be designed for each of the two forms.