Stenocephalemys, Frick, 1914

Kostin, Danila S., Kasso, Mohammed, Komarova, Valeria A., Martynov, Alexey A., Gromov, Anton R., Alexandrov, Dmitry Y., Bekele, Afework, Zewdie, Chemere, Bryja, Josef & Lavrenchenko, Leonid A., 2019, Taxonomic and genetic diversity of rodents from the Arsi Mountains (Ethiopia), Mammalia (Warsaw, Poland) 83 (3), pp. 237-247 : 243-244

Genus Stenocephalemys

As shown by previous studies (e.g. Lavrenchenko and Verheyen 2006, Bryja et al. 2018), the BM are characterised by a well-developed elevational gradient of ecological conditions and clear separation between adjacent altitudinal belts, which are inhabited by different narrow-headed rat species of the genus Stenocephalemys . Specifically, Stenocephalemys albipes (Rüppell, 1842) occupies forest habitats at altitudes of 800 to 3100 m a.s.l., Stenocephalemys griseicauda is common in Erica bush and mountain meadow at approximately 3300 to 3700 m a.s.l. and Stenocephalemys albocaudata is restricted to the Afroalpine zone above 3700 m a.s.l. ( Bryja et al. 2018). During our survey in the AM, we trapped all three Stenocephalemys species, though their spatial distribution was slightly different due to differences in altitudinal zonation (Table 2). In the Shirka region (site 1), we observed a local inversion of altitudinal belts, along with the species inhabiting them, i.e. S. griseicauda occupied hills covered with Erica bush, whereas S. albocaudata inhabited open swampy areas below these hills. On top of the Galama Ridge (3800 m a.s.l. and above) in the Badda region (site 5), a mosaic of both Ericaceous and Afroalpine habitats resulted in virtually sympatric populations of S. griseicauda and S. albocaudata , though the latter was more abundant. We performed chromosomal analysis in order to assess whether the sympatric occurrence of these generally parapatric sister species (see Bryja et al. 2018) was accompanied by ongoing hybridisation. As both species differ in the fundamental number of autosomal arms (NFa = 62 in S. albocaudata and NFa = 58 in S. griseicauda ; Lavrenchenko et al. 1997, 1999), one would expect the karyotype of the putative hybrid to have an intermediate fundamental number. Though karyotyped 20 individuals of both species, including three intermediate between the two species colour variants, we failed to find evidence of hybridisation, all karyotyped individuals having typical NFa for the species, corresponding with their mtDNA genotypes ( Bryja et al. 2018).

Stenocephalemys albipes was captured in forest habitats on both Mount Chilalo and the Galama ridge (sites 2, 3 and 6). A recent phylogenetic analysis of the genus Stenocephalemys revealed a clear phylogeographic structure for

S. albipes ( Bryja et al. 2018) . As all three mitochondrial haplogroups identified from the Southeastern plateau were also found in S. albipes , inhabiting Mount Chilalo (i.e. ap_1a, ap_1b, ap_1d; sensu Bryja et al. 2018), the Mount Chilalo population clearly shows high genetic diversity. This can be explained in two ways: either the AM acts as a centre of S. albipes diversification, with a long-term refugium in the Southeastern plateau, or different lineages diversified through lineage sorting in other regions (e.g. the BM and Chercher Mts. in the Eastern Ethiopian Highlands; see Bryja et al. 2018) and came into secondary contact in the AM. In our study, genetic analysis showed that all three AM Stenocephalemys species shared most haplotypes with their conspecifics from the BM (Table 2).