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

sought from two alternative approaches, a parsimony analysis of endemicity and a biotic ele- ment analysis. Materials and methods Study area & operational geographic units The study area is southern Africa, south-east of 22˚S and 23˚E and south-west of 31˚S and 23˚E (Fig 1). This includes the MPA hotspot, the greater MPA region of vertebrate endemism as well as the SEA zoogeographical dominion for vertebrates [24]. Furthermore, the entire Cape Floristic Region (CFR) biodiversity hotspot was also included in order to clarify the uncertain western limits of the SEA dominion. Land snail distribution data for the area could still be too incomplete for a numerical zoo- geographical analysis at a fine-grain such as the quarter-degree-squares (QDSs) scale. There- fore, a set of coarse-scale eco-geographical units (zoogeographical units for SEA [22], redrawn according to QDS borders; see Fig 1) were used as the operational geographic units (OGUs) for the present analyses. The use of these natural OGUs (delimited through qualitative overlay- ing or range maps in identification of biochoria for endemic vertebrates; see Perera et al. [22] for more details) for recording the incidence of selected land snail genera (a) avoids the caveats of incompleteness of distribution data at a finer grain of analysis, and (b) retains the natural geographical boundaries of the resulting zoogeographic entities that would have been distorted had a coarse equal-area OGU (e.g. 1˚ or 2˚ grid cells) been used. The OGUs for the western

section of the study area, beyond Knysna were defined based on the CFR and Succulent Karoo biodiversity hotspots [5, 6], and the bioregions of SA [25], resulting in a total of 40 a priori OGUs. Species incidence data matrix Twelve genera (monophyletic lineages) of land snails and slugs were selected for the study, all of which have recent species-level taxonomic revisions [2, 27–37]. We included all species described to date in each genus from the study area, with a few exceptions as detailed below. Hence the analysis included 73 taxa, comprising 70 species and three species complexes of two species each. These genera were selected due to, (a) their high endemicity within the study area, (b) they are comparatively well sampled and collected within the study area, and (c) they have a relatively recent well resolved and robust taxonomy. The selected genera represent three families, viz. Bothriembryontidae, Rhytididae and Urocyclidae. All genera occurring within the study area were included from the first two families, while the family Urocyclidae, was represented by the most speciose monophyletic clade of the family Sheldonia sensu lato [13, 27, 28], of which the taxonomy was recently resolved with morphological and molecular support recognising five genera from the study area; viz. Kerkophorus, Microkerkus, Ptilo- totheca, Selatodryas and Sheldonia sensu stricto [28, 29]. The family Bothriembryontidae is rep- resented in the area by three species in the genus Prestonella of the newly validated subfamily

Prestonellinae, of which only two species were included in this analysis, excluding P. quadin- gensis due to the unavailability of distribution data except the type locality and absence of any specimens or recent observations; [30–33, DGH pers. obs.]. Land snails and slugs of the family Rhytididae are represented in the area by nine species of the hunter slug genus Chlamyde- phorus [13], three genera of larger cannibal snails: Afrorhytida, Capitina, Natalina (four, two and six species, respectively) [34, 35] and two genera of dwarf cannibal snails: Nata (six spe- cies) and the monotypic genus Natella [36, 37], of which all species were included in the cur- rent analysis except for treating Nata erugata and N. vernicosa as a single entity. While the delimitation of these two species relied heavily on molecular data, Nata erugata-vernicosa 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 3 / 26