Biomes, geology and past climate drive speciation of laminate-toothed rats on South African mountains (Murinae: Otomys)

Abstract

Mitochondrial DNA sequences (1137 bp) of the cytochrome b gene and craniodental and craniometric data were used to investigate the evolutionary relationships of six putative rodent taxa of Otomys (family Muridae: subfamily Murinae: tribe Otomyini) co-occurring in the Western Cape and Eastern Cape provinces of South Africa. Phylogenetic analysis of 20 new sequences together with craniodental and craniometric characters of 94 adult skulls reveal the existence of a unique lineage of Otomys cf. karoensis (named herein Otomys willani sp. nov.) from the Sneeuberg Centre of Floristic Endemism in the southern Drakensberg Mountain Range. Craniometric analysis distinguished O. karoensis from O. willani and identified a further four localities in the range of the latter species. We document southern range extensions of both Sloggett’s ice rat, Otomys sloggetti, and the vlei rat Otomys auratus to the Sneeuberg Mountain Range, in addition to appreciable genetic divergence between Sneeuberg and southern and central Drakensberg populations of O. sloggetti. Our results demonstrate parallel patterns of cryptic speciation in two co-occurring species complexes (Otomys irroratus s.l. and O. karoensis s.l.) associated closely with the boundaries of biomes (fynbos vs. grassland biomes) and geological formations (Cape Fold Belt vs. Great Escarpment).

The cryptic case of Otomys sloggetti (Sloggett’s vlei rat): Interpreting murid molar morphology in the fossil record

“…1 The exact number of extant Otomys species is contentious and a number of cryptic species have been identified, while others await further elucidation. [2][3][4][5] Some studies suggest that speciation has occurred along biomes, with phenotypic and genotypic divergent lineages corresponding to the Fynbos/Albany Thicket and Grassland biomes in the case of Otomys irroratus and Otomys karoensis. 2,3 Geometric morphometric analyses carried out on the crania of Otomys unisulcatus also failed to support the genetic groupings, but rather followed biome boundaries, indicating previous environmental adaptations.…”

“…[2][3][4][5] Some studies suggest that speciation has occurred along biomes, with phenotypic and genotypic divergent lineages corresponding to the Fynbos/Albany Thicket and Grassland biomes in the case of Otomys irroratus and Otomys karoensis. 2,3 Geometric morphometric analyses carried out on the crania of Otomys unisulcatus also failed to support the genetic groupings, but rather followed biome boundaries, indicating previous environmental adaptations. 6 This, together with the adaptability observed in fossil Otomys communities when faced with environmental and climatic change on the south coast of South Africa 7 , as well as the fact that up to three or more Otomys species may live sympatrically in an area 1,2,7 , indicates the flexibility and plasticity of this murid subfamily.…”

“…The phylogeny of Otomys sloggetti, and the number of lineages and species present, as is the case with many of the other otomyine species, is currently unresolved. 1,2 In a study that looked at mitochondrial and nuclear genes, as well as morphological characteristics, specimens previously identified as Otomys sloggetti were found to represent two clades, and three lineages. 8 A cladistic analysis of 45 morphological (craniodental) and 46 binary allozyme characters indicated that Otomys sloggetti was basal to a 'mesic clade' of southern and eastern African species 9 , and the idea that Otomys sloggetti represents a basal lineage has been reiterated elsewhere 10 .…”

Mammals in the mountains: An historical review and updated checklist of the mammals of the Mountain Zebra National Park

“…Cryptic speciation amongst the laminate toothed rats (family Muridae: subfamily Murinae: tribe Otomyini), to which the vlei (Otomys irroratus), bush Karoo (O. unisulcatus) and Sloggett's ice rat (O. sloggetti) belong, is common, especially in mountainous habitats (Taylor et al 2019). In fact, recent taxonomic work has demonstrated that O. irroratus senso lato can be confused morphologically with at least one other cooccurring species O. karoensis (Taylor et al 2019). As such, I recommend that the specific assignment of the three laminate toothed rats putatively present in MZNP be verified through the collection of specimens for morphological and genetic analyses.…”

“…the introduction of passive infra-red camera traps) are likely to have improved the detectability of some species that other more traditional techniques failed to detect in the past (De Bondi et al 2010). Moreover, the nomenclature (and, effectively, the number) of individual mammal species may change over time as new knowledge about the evolutionary history of a species or group of species becomes available and they are either divided or synonymised (Taylor et al 2019). Thus, the aims of this study were to provide an historical review of the mammal species of the MZNP and to update the mammal checklist for the park.…”