DOI: 10.5061/dryad.3tx95x6ts
title: Population genetic data for freshwater mussels: <em>Unio crassus</em> and <em>Unio nanus</em> in Europe

description: Historically, the thick-shelled river mussel (Unio crassus agg. complex)
 was considered a single, widespread species across Europe. However, recent
 phylogenetic taxonomic revisions have delineated 12 species from this
 complex, including Unio crassus (s. str. Philipsson in Retzius, 1788),
 Unio nanus (Lamarck, 1819 stat. rev.), which exhibit substantial range
 overlap and broad European distributions. Understanding their fine-scale
 genetic diversity, population structure, and potential for recent or
 ancient hybridization is critical for effective conservation planning.
 This study investigated the genetic diversity and structure of U. crassus
 and U. nanus across Europe, examining the influence of glacial disturbance
 history and host fish associations. Using mitochondrial (COI) and nuclear
 (microsatellite) markers on 60 populations, we revealed a discordance
 between mitochondrial and nuclear structuring, suggesting ancient
 introgression. Crucially, no evidence of recent hybridization was detected
 between U. crassus and U. nanus. We found significantly higher nuclear
 genetic diversity in U. crassus compared to U. nanus. Our findings
 indicate an older Black Sea–Caspian Sea divergence and ancient
 introgression between U. nanus and U. crassus, as well as distinct
 postglacial colonization routes: a Western route for U. nanus and an
 Eastern route for U. crassus, converging in a secondary contact zone. Our
 results highlight the strong influence of host fish associations and
 glacial history in shaping the genetic patterns of these mussels,
 underscoring the need to incorporate intraspecific genetic diversity into
 conservation strategies. As shell morphology proved unreliable for species
 identification, we recommend DNA barcoding for reliable species
 recognition and suggest further research into host-fish preferences to
 improve conservation efforts.
description: # Population genetic data for freshwater mussels: *Unio crassus* and *Unio
 nanus* in Europe ## 1. Dataset Overview This dataset contains raw and
 processed genetic data used in the study investigating the population
 structure, genetic diversity, and evolutionary history of two European
 freshwater mussel species, *Unio crassus* (the thick-shelled river mussel)
 and *Unio nanus*. The data comprises mitochondrial cytochrome c oxidase
 subunit I (COI) sequences and nuclear microsatellite genotypes. This
 research aims to understand historical gene flow, identify instances of
 ancient introgression, and provide insights for conservation management of
 these often threatened species across their European ranges. ## 2. Data
 Files This directory contains the primary genetic data files. *
 `1_Individual_Microsatellite_Data.xlsx`: Excel table containing raw
 microsatellite genotypes for all individuals across all loci. *
 `2_Individual_Sequence_Data.fas`: FASTA file containing all aligned
 mitochondrial COI sequences. ### 3. Methods **Microsatellite data**
 Microsatellite genotyping was performed on 1531 specimens using a set of
 eight loci (Uc5, Uc15, Uc16, Uc19, Uc25, Uc39, Uc69, Uc77). For initial
 input file preparation of Microsatellite raw data the EXCEL MICROSATELLITE
 TOOLKIT 3.1 was used. **COI sequence data** Mitochondrial DNA (mtDNA)
 analysis was conducted on a subset of 300 specimens. Sequences were
 aligned and trimmed to a standardized length of 442 bp using MEGA11
 software. #### 4. Metadata Detailed metadata is available in the
 Supporting Information Table S1 of the associated publication. Table S1
 contains the sampling characteristics of 60 populations: population code
 (POPID), species, river name, drainage system, country, geographic
 coordinates (WGS84), sample material (TS: tissue, HL: hemolymph),
 reference to used microsatellite data, sample size used for microsatellite
 analysis (NMs), for cytochrome c oxidase subunit I analysis (NCOI) and for
 shell outline analysis (NEFD).