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Variation in shell shape and mitochondrial DNA of two species of freshwater mussels in the Kiamichi River, Oklahoma, USA

Moore, Elisabeth1; Vaughn, Caryn1; Franzen, Alex12

Published Jul 06, 2026 on Dryad. https://doi.org/10.5061/dryad.h44j0zq2h

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Abstract

Numerous freshwater mussel species possess highly variable shell morphologies, though it remains unclear what major factors drive shell morphology patterns in many species. Therefore, basic research of the interactions between mussels and their environment is a pressing research priority. We investigated the shell shape of two mussel species found in the Kiamichi River, USA, to test the hypothesis that river hydrology gradients have an influence on shell traits rather than the alternative that shell trait variation is strictly a product of evolutionary processes. We measured shell length, height, and width of Amblema plicata and Pustulosa pustulosa individuals in the river at four sites, then extracted and sequenced mitochondrial DNA (mtDNA) from each individual to assess genetic variation. After controlling for shell size, we tested whether shell traits varied between sites and varied with hydrological attributes. We constructed phylogenies and generated TCS haplotype networks from mtDNA sequences to examine the distribution of genetic diversity of A. plicata and P. pustulosa in the river and used Mantel tests to test for isolation-by-distance patterns. We found little difference in A. plicata shell shape across sites, whereas P. pustulosa individuals were more compressed in the upper river, likely due to higher stream velocity, and P. pustulosa at downriver sites were more inflated, likely due to increased flow rate. Haplotype networks indicated extensive sharing of mtDNA haplotypes between sites for both species. Our phylogenies showed no indication Kiamichi River A. plicata and P. pustulosa populations are genetically unique, nor did we find evidence of isolation by distance, which suggests shell shape is unlikely to be driven by genetic distinctiveness. Our results show that hydrology likely has a strong influence on shell shape in some mussels, and considering increases in extreme droughts and floods, this study highlights the importance of basic ecological research for informing conservation.