Historical Drainage Evolution and Water Level Fluctuations in the African Great Lakes Shaped Phylogeny and Biogeography of Freshwater Gastropods

Abstract

Aim: The role of historical drainage connectivity and the influence of water level fluctuations in African lakes on the evolution and distribution of macroinvertebrates remain poorly understood. This is partly because evolutionary biology research has largely focused on mobile vertebrates, such as cichlids. Here, we studied an African freshwater snail genus and assessed its phylogenetic relationships and phylogeographic patterns, and determined its colonisation history in African waters. Location: African Great Lakes (AGL). Taxon: Gabbiella (Gastropoda: Bithyniidae). Methods: We applied a multi- locus molecular phylogenetic approach combining two mitochondrial DNA markers (COI and 16S) and two nuclear DNA markers (H3 and 28S) based on samples covering six AGL, their major connected rivers, and two crater lakes in western Uganda. Using maximum likelihood (ML) and Bayesian inference (BI) approaches, we inferred a dated phylogeny of Gabbiella and estimated the ancestral areas of the Gabbiella humerosa subspecies using BioGeoBEARS. We used statistical parsimony haplotype networks and genetic p- distances to investigate phylogeography and quantify genetic divergence within and between Gabbiella clades. Results: The ML and BI analyses yielded nearly identical topologies. Our BEAST analysis suggests that Gabbiella probably originally diversified in the Miocene and later in the Pliocene and Pleistocene, too. We found high genetic distance among Gabbiella species and typical intraspecific genetic distance among G. humerosa subspecies. Phylogenetic inferences suggest that the most recent common ancestor (MRCA) of all G. humerosa subspecies originated in the Kivu–Tanganyika region during the Late Pleistocene. The MRCA of the Nilotic G. humerosa subspecies was most likely distributed in the Lake Kivu and Lake Albert regions. Main Conclusions: The timing of diversification of Gabbiella coincides with significant geological events, such as rifting, historical drainage changes and lake- level fluctuations. These events suggest that the tectonic and climatic history of the region plays an intergral role in diversification. Following each episode of vicariance, dispersal rather than extinction seems to determine the distribution patterns, underlining the high ecological tolerance of G. humerosa. The spatial diversification patterns of Gabbiella show similarities with those of other African molluscs and several fish taxa, suggesting that diversification is influenced by common underlying factors.