Land snail biogeography and endemism in south-eastern Africa: Implications for the Maputaland-Pondoland-Albany biodiversity hotspot

Introduction Terrestrial molluscs (Mollusca: Gastropoda; hereafter land snails) with a global species rich- ness estimated at over 25,000 [1, 2] are not distributed evenly across the globe. Although sev- eral island land snail faunas are reported to have exceptional species richness and high degrees of endemism [3, 4], and are thus recognized as hotspots for molluscan conservation, similar continental hotspots are not widely recognized. Global biodiversity hotspots [5, 6] have been delimited based on floristic endemism, often with the assumption of congruent distribution patterns for animals, but such congruence of endemism between plants and land snails is yet to be well established. Invertebrates in general have long been underrepresented in studies on biodiversity, biogeography and conservation, primarily because much of their diversity is still to be documented, while their taxonomy is often not sufficiently robust and the knowledge on their distribution is incomplete [5, 7–11]. Sub-Saharan Africa has a rich terrestrial malaco- fauna with an estimated 6,000 species [12]. Land snails in South Africa (SA) are taxonomically better resolved and distributionally better understood compared to many other groups of invertebrates, at least in eastern SA [13]. Over 650 land snail species are recorded for southern Africa [14], while 525 species (with c. 90% endemism) occur in SA alone [15]. However, their biogeography has never been systematically studied in southern Africa, except for qualitative

studies [13, 14]. The terrestrial malacofauna of eastern SA includes relict Gondwanan lineages and speciose radiations of more recent origin exhibiting high levels of local endemicity [13]. The indigenous land snail fauna of eastern SA includes well over 270 species, with at least 173 (63%) species being endemic or near-endemic [13]. With high levels of diversity and ende- mism, land snails make an excellent indicator group to start exploring the invertebrate zooge- ography of south-eastern Africa (SEA). Narrow-range distribution patterns commonly observed in land snails, stemming from their low dispersal ability, make them a suitable candi- date group to study regional endemicity and historical biogeography [4, 16, 17], and to deter- mine priority areas for conservation [18, 19], at least for the best studied groups. Boundaries of biodiversity hotspots have seldom been empirically tested on actual species distribution ranges and not for endemic invertebrate fauna. The Maputaland-Pondoland- Albany (MPA) biodiversity hotspot of SEA has been delimited based on intuitive phytogeo- graphical units such as the Maputaland-Pondoland region and the Albany centre of floristic endemism [20]. Possessing more than 1,900 species of endemic higher plants, this hotspot spans the eastern coast of southern Africa from Maputo in Mozambique to Port Elizabeth in Eastern Cape province of SA and extends inland to reach an altitude of 1,800 m a.s.l. along the south-eastern portion of the Great Escarpment [21]. The MPA hotspot has recently been fur-

ther explored in terms of its vertebrate endemism, documenting 62 endemic and 60 near- endemic species, and further recognizing a greater MPA region of vertebrate endemism [22– 24]. The greater MPA region with 166 endemic vertebrate species is an expansion of the MPA hotspot’s area by 59%, to include 168% more endemic species, indicating a higher animal endemicity in areas adjacent to the original flora-based hotspot [24]. Here we numerically analyse the zoogeography of the terrestrial malacofauna in SEA for the first time, also assessing the importance and the delimitation of the MPA biodiversity hot- spot for land snail conservation. This is achieved through numerical biogeographical analyses and mapping of species richness and endemism patterns followed by comparison of the results with the current boundary of the MPA hotspot. Biogeographical analyses are presented with three numerical approaches, our primary objective being a phenetic agglomerative hierarchical clustering of incidence data to propose a land snail-based biogeographical regionalisation and secondly to identify centres of land snail endemism, for which consensus and congruency is PLOS ONE Land snail endemism in the Maputaland-Pondoland-Albany biodiversity hotspot PLOS ONE | https://doi.org/10.1371/journal.pone.0248040 March 4, 2021 2 / 26 post-doctoral scholarship (2013). SJP received study leave and a travel grant from the University Grants Commission and the Sabaragamuwa University of Sri Lanka to conduct this study in South Africa and a travel grant from Unitas

Malacologica to attend the World Congress of Malacology 2013 in Azores, where an early version of this work was presented. DGH’s work on the terrestrial molluscs of South Africa was funded by the NRF (South African Biosystematics Initiative – GUN 61261; http://www.sassb.co.za/sabi.htm). SR acknowledges the UKZN for research support. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist.