Diversity and systematics of three freshwater bivalve families from South Africa

Abstract

Bivalves play an important role in the environment as they are filter feeders and contribute to the biogenic transfer of particles in the water column. Additionally, they can increase the oxygen level in sediment as they are burrowers. Freshwater bivalves, specifically in the Sphaeriidae, Iridinidae, and Unionidae families are understudied in South Africa. This study aimed to revise the species that occur in South Africa and update the distribution to ultimately contribute to the molecular, morphological, and distribution data. Sampling sites were determined based on previous distribution records and consisted of 78 sites in the northern provinces of South Africa. The bivalves that were found were morphologically identified based on existing keys considering key morphological characteristics as Euglesa sp., Euepra ferruginea, Chambardia wahlbergi, and Unio caffer. Molecular methods were used to generate sequences for each species, where possible, whereafter GenBank and BOLD sequences were aligned with the novel sequences to determine their phylogenetic relationships. In total, 35 COI and 47 16S sequences were generated and identified as the following species: Euglesa costulosa, Euglesa viridaria, Eupera ferruginea, Chambardia wahlbergi, and Unio caffer. The study found that intraspecific variations are more prevalent than interspecific variations, with morphological differences observed within species that are phylogenetically identical. This suggests that there may be fewer species than previously proposed in the literature. The current distribution of these species, as observed in this study, was compared to data from GBIF and the NWU Snail Collection, leading to the conclusion that species richness and diversity have declined for sphaeriids, iridinids, and unionids. Further research is needed to address conservation concerns for these bivalves, particularly in relation to identified research gaps, such as the lack of distribution records and molecular data.