Morphological and molecular diversity of Unionidae (Mollusca, Bivalvia) from Portugal

Abstract

J. Reis, A. Machordom & R. Araujo. 2013. Morphological and molecular diversity of Unionidae (Mollusca, Bivalvia) from Portugal. Graellsia, 69(1): 17-36. Freshwater mussels from the family Unionidae are known to exhibit a high level of ecological phenotypic plasticity that is reflected in their shell shape. This variation has caused uncertainty on systematics and taxonomy of the group. Several naiad populations from nine river basins from Portugal were analyzed genetically, using two mitochondrial gene fragments (16SrRNA and Cytochrome Oxidase I) and morphologically, using ANOVA analyses of shell dimensions. Molecular phylogenetic analyses were used to revise the systematics and to infer an evolutionary hypothesis for the family at the westernmost Atlantic Iberian Peninsula. Genetic and morphological data were in agreement and supported the occurrence of 5 species in the region: Anodonta anatina, Anodonta cygnea, Potomida littoralis, Unio tumidiformis and Unio delphinus. The differentiation of all these species, except A. cygnea, is thought to have taken place during the isolation of the Iberian Peninsula and formation of the current river basins in the Tertiary. The possibility of A. cygnea being a relatively recent introduction is discussed. Basic morphometric measures of the shell proved to be useful to separate Unio species, but also seem to be strongly affected by environmental conditions. The high intraspecific morphologic variation was partially related to the species’ high level of phenotypic plasticity, but seems to have an important role in evolutionary processes.