A primer to the use of African ostracods in water quality assessment: taxonomy and ecology of non-marine Ostracoda (Crustacea) from Benin

Abstract

The systematic exploration of more than 200 wells across four Beninese catchment areas led to the discovery of a diverse assemblage of ostracods, comprising 60 species, including 36 stygobites species belonging to the family Candonidae. This taxonomic diversity resulted in the description of a new endemic subfamily, Benincandoninae Hotèkpo & Martens represented by the genus Benincandona Hotèkpo & Martens characterised by a unique combination of characters, such as a seven-segmented antennula and a caudal ramus with a fully developed ramus, a single apical (anterior) claw and three short setae; which includes at least 35 species, five of which were formally described. This represents the first report of such a significant radiation of subterranean ostracods across the African continent, comparable to previously documented radiations in Europe, America, and especially Northwest Australia. Ecological analyses identified environmental factors structuring these ostracod communities. By analysing the georeferenced database we identified several key variables influencing species distribution, including electrical conductivity, pH, temperature, and, notably, nitrite concentration. The differential sensitivity to nitrites between stygobites and non-stygobites species marks a significant advancement for the development of bioindication tools adapted to the West African context, where nitrogen pollution in general poses an increasing threat to groundwater resources. Molecular analyses of one representative genus of the (non-stygobite) Cyprididae, namely Strandesia Stuhlmann, 1888, integrated taxonomic and phylogenetic study and identified 14 15 genetic species in nine morphospecies, emphasising the importance of integrating morphological and molecular analyses for precise species delimitation in ostracods. The intercontinental history of Strandesia remained unresolved, but current evidence tentatively points to vicariance as one of the possible driving factors in its diversification, pending broader sampling and multi-locus molecular data. In parallel with the molecular study of Strandesia, a taxonomic atlas of most species of Cyprididae found in the present survey in wells in Benin documents the morphological diversity of the representative of this predominant ostracod family. The characterization of eight genera (and 22 species) in six subfamilies (Cyprettinae, Cypricercinae, Cypridinae, Cyprinotinae, Herpetocypridinae, and Cypridopsinae) and the identification of significant morphological variations, particularly within the genus Strandesia, naturally bridge to the molecular approaches. Cypridopsis vidua is the only cosmopolitan species, while others show circum-tropical, Afrotropical, or potentially West African endemic distributions. In addition, most taxonomic confusion exists in Cypricercinae, especially the genus Strandesia, due to homoeomorphy and the possi physical and chemical quality on valve morphology. There are at least three species new to science awaiting description. The present study lays the scientific foundation for developing biotic indices based on stygobitic ostracods, and tailors such indices to the environmental and socioeconomic realities in West Africa. The exceptional evolutionary radiation of Benincandoninae, combined with their differential environmental sensitivity, presents a unique opportunity to develop endemic bioindicator tools, potentially applicable at and beyond a regional scale for groundwater monitoring and protection, which are both crucial for millions of people.