Relative growth, shell morphology and genetic relationships between freshwater mussels of the genus Unio (Mollusca: Bivalvia: Unionidae) from rivers of the Ichkeul watershed (Tunisia)

ABSTRACT

Unio, a freshwater mussel genus, has a low number of species in Tunisia, among them U. durieui, which is categorised as Endangered for conservation in IUCN Red List. The purpose of the study was to investigate morphological similarity and genetic relationships between samples of the genus Unio collected from rivers of the Ichkeul watershed. The collection includes three samples of U. ravoisieri, a single sample of U. durieui and a sample morphologically distinct from the first two, which could be a new ‘species’ discovered in the sampling area. Principal components analysis, based on eight morphological traits, separated the samples into three groups according to the ‘species’ and the variant form was found morphologically closer to U. ravoisieri than U. durieui. Analysis of genetic diversity has defined an extensive allozyme monomorphism. The Nei’s standard genetic distance between U. ravoisieri and U. durieui, ranges from 0.5330 to 0.5881 and F_ST values vary between 0.93 and 0.98 and are highly significant. However, the genetic comparison between the variant form and U. ravoisieri samples showed no significant difference in allele and genotype frequencies, which supports the hypothesis that the new form is a phenotype of U. ravoisieri and not a separate species.

KEYWORDS:

• Endangered species
• isozymes
• shell shape indices
• biochemical systematics
• diagnostic loci
• allometric growth
• species identification
• population assignment
• phenotypic plasticity

Acknowledgements

The authors gratefully acknowledge Dr. Karl-Otto Nagel and Dr. Rafael Araujo for their critical reading that substantially improved the manuscript. We would like to express our sincere gratitude to the anonymous referee who definitely helped to improve the readability and quality of the paper. Many thanks to our support staff for assistance in obtaining specimens and to the teams from Research Unit Ecosystems & Aquatic Resources (UR13AGRO1, INAT/University of Carthage) for their valuable support and advice.

Disclosure Statement

No potential conflict of interest was reported by the authors.

ORCID

Chiheb Fassatoui http://orcid.org/0000-0003-2624-4081

Additional information

Funding

This work was jointly funded by the Institution of Agricultural Research and Higher Education, and the Ministry of Higher Education and Scientific Research of the Tunisian Republic.