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

S. aloicola [2, DGH pers. obs.]. The genus Kerkophorus was represented in the area by 20 spe- cies and is included in the analysis as 18 definitive species plus the Kerkophorus piperatus-vit- tarubra complex, while K. phaedimus was considered to be a synonym of K. corneus [2]. The K. piperatus-vittarubra complex was treated as such due to the difficulty in morphologically separating taxa at some locations due to their close relatedness and even a possible hybrid pop- ulation in Nkandla [28]. The genus Selatodryas being an endemic lineage in the study area with a narrow geographical range and represented by two morphologically similar species that can only be reliably identified through dissection of the genital tract was also included in the analysis as the Selatodryas luteosoma-roseosoma complex. These three species complexes, with the known localities for the two described species in each combined, are treated as three spe- cies hereafter (given with their specific epithets combined by a hyphen). The species incidence matrix was prepared for the 73 species above by scoring their pres- ence/absence (1/0) in 40 a priori OGUs (S1 Appendix). A species was recorded as present for a given OGU, even with a single occupied QDS, as long as this QDS was not along the margin of the OGU. A species occupying only marginal QDSs for a given OGU was scored as present only if the species occupied more than 10% of the OGU. A species occupying marginal QDSs with <10% coverage of the OGU was considered present only when the species was absent in

the neighbouring OGU, or the relevant QDS was in the coastal margin of its range. Species dis- tribution data were sourced from the KwaZulu-Natal Museum Mollusca database (more than 2300 records, with field visits to all OGUs), after removal of dubious records. Data analyses Zoogeographical regionalisation. Numerical analysis of the land snail incidence matrix, following the phenetic approach [38] of agglomerative hierarchical clustering of OGUs was used to fulfil the primary objective of the study, i.e. to propose a land snail based biogeographi- cal regionalisation (see Kreft & Jetz [39] and Morrone [40] for recent reviews on methods). The Jaccard’s coefficient of similarity was used to compare each OGU with every other based on their respective species assemblages [41–44], while the unweighted pair-group method using arithmetic averages (UPGMA) algorithm was used to convert the similarity matrix into a distance based dendrogram [39, 43–46]. Mouillot et al. [47] and Perera et al. [24] provides a discussion on the above methods. The analyses were conducted using FreeTree ver. 0.9.1.50 [48]. The resulting dendrograms were visualised using TreeView ver. 1.6.6. [49]. The subre- gional hierarchy of zoogeographical entities i.e., dominions, subdominions, provinces, subpro- vinces and districts [40, 50–52] (see Perera et al [24] for more details) were determined based on phenon lines [38, 53] placed on the dendrogram in order to generate geographically contig- uous clusters of OGUs, while OGUs that were not placed in such geographically contiguous

clusters were dissolved in to the geographically nearest and ecologically closest biogeographical entity derived from the same dendrogram [23, 24]. Centres of endemism. Centres of endemism (COEs: areas where endemic species con- centrate, usually having more endemics in comparison to the surrounding areas) [54–56], were also derived from the UPGMA cluster dendrogram. The COEs and centres of narrow endemism (CONEs) are presented based on decreasing range size and number of endemics: (a) COEs: clusters identified above as biogeographical districts that harbour four or more endemic land snail species and (b) CONEs: single OGUs or geographically narrow clusters of OGUs defined by a higher similarity than the districts, harbouring two or more narrowly endemic species. Characteristic and narrow endemics for each COE were identified following Williams et al. [54], Crisp et al. [57] and Procheş & Ramdhani [43]. Characteristic endemics are defined here as species occupying more than two-thirds of OGUs in the centre, and/or 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 5 / 26