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

distributed over more than half of the centre’s extent, hence whose range edges roughly coin- cide with the boundary of the centre, while the narrow endemics occupy much narrower ranges within the COE. Areas of endemism and biotic elements. Areas of endemism (AOEs: areas with congru- ent distribution of at least two species of restricted range) [55, 58] (see Perera et al. [24] for a discussion on AOEs and COEs) were identified through the parsimony analysis of endemicity (PAE) [59]. However, we did not attempt a regionalisation based on the PAE as done is some studies [24, 60, 61] as the resulting area cladogram revealed only five clusters, although not hierarchically structured into larger AOEs, among which only four harboured at least two endemic species with sympatry, in addition to two terminal OGUs each with two narrow endemics with congruent ranges. The PAE was conducted using PAUP� 4.0b10 [62], where a full heuristic search was per- formed with tree bisection-reconnection (TBR) branch swapping, after the species present or absent in all OGUs (similar to constant characters in phylogenetics) and species found only in a single OGUs (i.e. parsimony uninformative characters; autapomorphies in phylogenetics) were excluded. A strict consensus tree was constructed from 1000 most parsimonious trees. Geographically contiguous clusters of OGUs in the strict consensus tree harbouring at least two endemic species with sympatry were recognized as AOEs. In the description of PAE meth- odology Morrone [59] recommends to “draw quadrats on a map of the region to be analysed,

considering quadrats only where at least one locality of one species exists” (p. 438), i.e. to remove any OGUs with zero presence of species in our dataset, and as such these OGUs are similar to outgroups and the parsimony analysis effectively remove multiple outgroups. Fur- thermore, during the parsimony analysis in phylogenetics, autapomorphies are removed from the dataset as these are considered uninformative. Similarly, during the PAE in biogeography, parsimony uninformative species (which are restricted to a single OGU) are removed from the analysis. However, such narrowly endemic species that are of conservation importance were included and considered in the delimitation of COEs. However, the PAE area cladogram did not show hierarchical structuring so we further tested our AOEs for consensus and congruency with those recovered from a biotic element analysis (BEA). The BEA proposed by Hausdorf & Hennig [63] is an alternative to AOEs, in identification of vicariant events during the history of an area. We performed a BEA which included a parametric bootstrap test for clustering of distribution areas [64] using the pro- gramme PRABCLUS in R studio [65]. Spatial patterns of land snail richness and endemism. The following spatially-based quantitative measures of land snail richness and endemism were calculated for each OGU using the species incidence matrix: (a) land snail species richness, (b) SEA dominion ende- mism, (c) narrow endemism, and (d) weighted endemism (WE). The measure (a) was calcu-

lated for the entire study area, while the latter parameters (b–d) were calculated only for the SEA dominion, delineated by the regionalisation above. Here a narrow endemic species was defined as one restricted to a single OGU, a CONE or occupying less than half the range of a COE recognized above. Based on this definition, Prestonella nuptialis, Afrorhytida trimeni and Selatodryas luteosoma-roseosoma were considered narrow endemic even though they occupy two OGUs each, on the basis that the OGUs concerned are narrow in extent and they each occupy less than half the area of the OGUs combined. On the other hand, Afrorhytida kraussi and Sheldonia phytostylus although present only in the Knysna OGU were not considered as narrow endemics on the basis that the Knysna OGU was too broad and the species are distrib- uted in more than half of its extent. The WE of each OGU was calculated as the sum of the reciprocals of the total number of OGUs in which each species of the respective OGU was found [56]. Further, the WE was corrected for the species richness in respective OGUs (= 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 6 / 26