Against the Flow: The Colonisation of the Lesotho Highlands by Freshwater Limpets

Abstract

To date, limited research has taken place on the evolutionary history of biodiversity in the high-altitude zones of southern Africa, particularly the Lesotho Highlands. The few studies that do exist point to similar high-altitude zones being either prolific museums (i.e., refugia and cradles) for cold-evolved species or sinks for temperate species post the Last Glacial Maximum, yet the role this zone has played for freshwater biodiversity is unknown for almost all freshwater taxa. In this study, we address this lack of knowledge by looking at the phylogeography of the freshwater limpet genus, Burnupia, across its southern and eastern African range, but particularly focusing on the Lesotho Highlands. We used COI data to reconstruct the evolutionary history of the genus, quantify phylogenetic species diversity, test both isolation by distance (IBD) and by elevation (IBE) and model ancestral area estimation “in” and “out” of the Highlands to determine: 1) The diversity and endemicity of Burnupia spp. in the Highlands in comparison to the broader southern African region and 2) when did the colonisation of the Highlands happen. Our results showed that at least two of the nine southern African phylogenetic species delimited occur in the Highlands (which appears average for the geographical extent of this area in comparison to the broader southern African region) and that the genus has been present in the Lesotho Highlands for somewhere between 1.38–0.23 million years. However, we found the endemicity of at least one of the two Highland species, supported by weak but significant IBD and IBE in Burnupia. Therefore we favour the notion that the Highlands are likely an important haven for cold-evolved species. As our results also generated a lot of data useful for Burnupia systematics, we discuss some taxonomic implications of our findings.

The fossil record of freshwater Gastropoda – a global review

“…No fossil‐only species are known for: ( i ) Acochlidimorpha, comprising 12 living freshwater species in the families Tantulidae and Acochlidiidae [although a Jurassic origin was suggested by Jörger et al . (2010, 2014) based on molecular clock dates]; ( ii ) the lymnaeoid family Burnupiidae, containing 22 extant species of the single genus Burnupia (molecular data indicate a Miocene age for the group; Sands et al ., 2022); ( iii ) the truncatelloid family Clenchiellidae, consisting today of four genera and 14 species (MolluscaBase eds, 2023). Until recently, the Helicostoidae would have been included in that list, containing the single enigmatic sessile (and probably recently extinct) species Helicostoa sinensis .…”

Let's get high: Cladogenesis in freshwater crabs (Decapoda: Potamonautidae: Potamonautes) supports the mountain gradient speciation hypothesis in the Cape Fold and Drakensberg Mountains, South Africa

“…In contrast to the CFM, the Drakensberg Mountains experienced marked Holocene temperature increases and more mesic periods, altering floral and faunal composition patterns during the Plio/Holocene. Dated phylogenies for the Drakensberg Mountain inhabiting taxa suggest that pulses of diversification are strongly linked to Plio/Pleistocene uplift and the subsequent erosion of the landscape (Bentley et al., 2014 ; Sands et al., 2022 ).…”