Otomys simiensis Taylor et al. 2011

Mizerovská, Daniela, Martynov, Aleksey A., Mikula, Ondřej, Bryjová, Anna, Meheretu, Yonas, Lavrenchenko, Leonid A. & Bryja, Josef, 2023, Genomic diversity, evolutionary history, and species limits of the endemic Ethiopian laminate-toothed rats (genus Otomys, Rodentia: Muridae), Zoological Journal of the Linnean Society 199 (4), pp. 1059-1077 : 1072

Otomys simiensis Taylor et al. 2011

Simien Vlei Rat

Holotype: ZMMU 178757 ; adultmale, dryskinandskull, collector’s number 1338; collected by L.A. Lavrenchenko, 4 May 2005.

Type locality: Ethiopia, Simien Mountains NP, vicinity of Sankaber campsite, 3250 m a.s.l..

Taxonomic notes: Small species, like O. yaldeni , but still larger by external measurements, karyotype distinctive (2n = 54, NF = 56). Similarly as in O. yaldeni , the upper third molar possesses seven complete laminae and the double-layered dorsal fur, differentiating them from the Ethiopian species in the TYPUS group (see more details in: Taylor et al. 2011). The species had been known only from the type locality, i.e. the Simien Mts.. We genetically analysed the material from the type locality, including the holotype. Using additional genotyped material, we significantly expanded its known distribution, as genetically similar specimens were recorded in Tsibet, Aboye Gara, and Borena Saynt NP. The specimens from Borena Saynt NP (and partly also those from Aboye Gara) cluster with O. cf. yaldeni in sNMF analysis ( Fig. 4 ). The close relationship of O. simiensis and O. yaldeni is documented also by the InfoMap clustering ( Fig. 5 ). The only included skull of O. simiensis from Borena Saynt NP clusters with O. cf. yaldeni , suggesting that this population probably originated by recent hybridization between O. simiensis and O. yaldeni . No morphological data (i.e. skulls of adult animals) are available from Aboye Gara and Tsibet.

Ecological notes: This species occurs in tree-heather forest composed of trees such as Erica arborea , Hypericum revolutum , and the shrub Rosa abyssinica , with open grassy patches. In the higher altitudes of the Simien Mts. (and possibly also in other mountain ranges, e.g. Aboye Gara), this species is replaced by O. typus ( Taylor et al. 2011, Craig et al. 2020).

Distribution: Otomys simiensis is distributed in Afromontane habitats in the north-western part of the Ethiopian Highlands. Most records from the Simien Mts. are from its type locality (3250 m a.s.l.), but one record is from 3800 m a.s.l.. We documented the species (but see taxonomic notes above) in three additional mountain blocks in northern Ethiopia (Aboye Gara, Borena Saynt NP, and Tsibet) between 3500 and 3850 m a.s.l. (see Supporting Information, S1).

Figures

Figure 4. The result of sNMF analysis based on 80% occupancy dataset, i.e. 3141 biallelic SNPs (one SNP per locus).Vertical bars show individual genotypes as composed of ancestral population gene pools, whose proportional contributions are indicated by coloured segments. Horizontal lines at the boưom delimit clusters defined by the dominant ancestral contributions. The associated labels identify clusters with named species or their geographically restricted populations (B. S. = Borena Saynt, D. S. = Debre Sina).Note that specimens from the populations in Borena Saynt and Aboye Gara, identified as O. simiensis by mtDNA and concatenated ddÞD data, cluster with O. cf. yaldeni from Ankober (purple cluster).

Figure 5. Co-ancestry matrix and delimitation of gene pools by two different methods: fineSTRUCTURE (18 clusters shown by grey squares) and Infomap (three clusters shown by black squares). The intensity of the colour (from yellow to blue) indicates the level of co-ancestry among individual genomes.