Mus harennensis, Krásová & Mikula & Lavrenchenko & Šumbera & Meheretu & Bryja, 2022

Krásová, Jarmila, Mikula, Ondřej, Lavrenchenko, Leonid A., Šumbera, Radim, Meheretu, Yonas & Bryja, Josef, 2022, A new rodent species of the genus Mus (Rodentia: Muridae) confirms the biogeographical uniqueness of the isolated forests of southern Ethiopia, Organisms Diversity & Evolution (New York, N. Y.) 22 (2), pp. 491-509 : 501-504

publication ID	https://doi.org/ 10.1007/s13127-022-00539-x
persistent identifier	https://treatment.plazi.org/id/EF42E002-5610-760F-FCC7-FD6DFD59FA52
treatment provided by	Felipe
scientific name	Mus harennensis
status	sp. nov.

Treatment

Description of Mus harennensis , sp. nov.

Mus (Nannomys) harennensis Lavrenchenko & Bryja , sp. nov.

Mus sp. nov. ( Rupp, 1980).

Mus triton View in CoL ( Yalden, 1988; Yalden et al., 1996).

Mus sp. A View in CoL ( Aniskin et al., 1998).

Mus cf. triton ( Lavrenchenko, 2000) View in CoL .

Mus sp. “Harenna View in CoL ” (MOTU 3) ( Bryja et al., 2014; Krásová et al., 2019).

Mus sp. “Harena” ( Bryja et al., 2019).

Holotype: ZMMU S-164895; adult male; skull and dry skin; collected by L.A. Lavrenchenko and A.A. Warshavsky (18 January 1996); collecting number 504. Tissue samples (spleen in 96% ethanol) of the holotype and all paratypes were taken and they are stored in the collections of the A. N. Severtsov Institute of Ecology and Evolution of the Russian Academy of Sciences in Moscow ( Russia) and the Institute of Vertebrate Biology of the Czech Academy of Sciences (Czechia).

Type locality: The upper belt of the Harenna forest , Bale Mountains National Park (06°45' N 39°44' E, 2760 m a.s.l.), Ethiopia GoogleMaps .

Paratypes: ZMMU S-164896 (adult female; skull and dry skin; collector's number 506); collected from the type locality by L.A. Lavrenchenko and A.A. Warshavsky on 18 January 1996 . ZMMU S-192757 (adult female; skull and dry skin; collector's number 2256); ZMMU S-192758 (adult male; skull and dry skin; collector's number 2274); ZMMU S-192759 (adult male; skull and dry skin; collector's number 2283); all three specimens collected by L.A. Lavrenchenko at the Kacha area of the Harenna forest (06°43′01.9'' N; 39°43′37.4'' E; 2380 m a.s.l.) between 01 and 05 April 2013 GoogleMaps . ZMMU S-192756 (adult male; skull and dry skin; collector's number 2335); ZMMU S-192754 (adult male; skull and dry skin; collector's number 2336); two specimens collected by L.A. Lavrenchenko in the Erica arborea shrub on the southern slope of Sanetti Plateau (06°47′19″N, 39°46′01″E, 3730 m a.s.l.) between 11 and 12 April 2013 GoogleMaps . NMP 97301 View Materials (adult female; skull and dry skin; collector’s number ETH0211 View Materials ); a specimen collected in the Kacha area of the Harenna forest (6°41′27.2′′ N; 39°43′39.7′′ E; 2123 m a.s.l.) by J. Bryja GoogleMaps , R. Šumbera and Y. Meheretu on 7 November 2012 . NMP 97302 View Materials (adult male; skull and dry skin; collector’s number ETH1528 View Materials ); a specimen collected in the Chingawa forest (7°25′15.9′′ N; 35°23′59.7′′ E; 2333 m a.s.l.) by J. Bryja, J. Krásová, M. Lövy and Y. Meheretu on 12 November 2017 GoogleMaps ).

Etymology: The name harennensis refers to the Harenna forest , which is the type locality of this new species. The suggested English vernacular name is Harenna Mouse.

Diagnosis: A typical large-sized representative of the Nannomys subgenus, similar in fur colour and skull shape to Mus triton , but with relatively larger body and skull size, longer tail and hind foot length, relatively short incisive foramens that end in front of the first cusp row of the first upper molars, relatively narrow zygomatic plate with a straight anterior margin, karyotype distinctive (2n = 34, NFa = 32). It can be easily diagnosed also by DNA sequences, at both mitochondrial ( Fig. 2 View Fig ) and nuclear ( Fig. 3 View Fig ) markers.

Description: Mus harennensis sp. nov. is a large-sized representative of the subgenus Nannomys . The dorsal pelage is dark olive-brownish. The bristles are grey with black tips; the guard hairs are grey at the base with rufous subterminal bands and black tips. Ventral pelage is greyish, the individual hairs grey at the base and tipped with white. The transition between dorsal and ventral coloration is conspicuous. Dorsal surface of the forefeet is brownish with sparse and short brown fur; digits are covering by longer whitish hairs; claws are white. Dorsal surface of the long hindfeet (longer than 15.8 mm) is greyish with sparse and short grey hairs with light tips; digits are long and slender with ungual tufts of hairs, which are grey basally and white in the terminal half, that exceed the white claws in length. The ears are blackish, inner surface with sparse and short dark hairs. The bicoloured tail is relatively long (longer than 54 mm), the dorsal caudal hairs are blackish in contrast to the nearly white ventral hairs. The skull is similar in shape to M. triton but with somewhat larger overall size, relatively shorter incisive foramens that end in front of the first cusp row of the first upper molars and narrower zygomatic plate with a straight (not convex) anterior margin. The chromosomal set of Mus harennensis sp. nov. (2n = 34, NFa = 32) comprises 16 pairs of gradually decreasing acrocentric autosomes. The X-chromosome is medium-sized acrocentric; the Ychromosome is small acrocentric ( Aniskin et al., 1998).

Comparisons: Mus harennensis sp. nov. differs from its sister species M. triton in: longer hindfeet and tail, relatively shorter incisive foramens that end in front of the first cusp row of the first upper molars and narrower zygomatic plate with a straight (not convex) anterior margin. The karyotype (2n= 34, NF = 34; Aniskin et al., 1998) is distinct from described chromosomal sets of M. triton (Clade A: 2n= 32, NF = 34; Clades C and D: 2n = 20–22, NF = 32 (female) or 34 (male); see Jotterand, 1972; names of clades according Krásová et al., 2019). Mus harennensis sp. nov. differs from sympatric species M. mahomet (and also from M. proconodon , which prefers very different habitat, however; Fig. 1A View Fig ) in significantly larger general size, distinct coloration (olive-brownish dorsally and greyish ventrally), incisive foramens ending in front of the first cusp row of the first upper molars, zygomatic plate possessing a straight (not convex) anterior margin protruding forward in its lower part ( Tables 2, 3; Figs. 8 View Fig , 9 View Fig ).

Distribution: The species has been found in two regions of southern and southwestern Ethiopia: Bale Mts. (with most records from the Harenna forest ) and the Chingawa forest ( Fig.1 View Fig ). Both places represent the most humid forests in Ethiopian highlands, but it remains possible that the new species inhabits other forested areas between these distant (ca. 500 km) regions.

Ecology: All known specimens of Mus harennensis sp. nov. were collected in forest clearings and moorland areas between 1950 and 3730 m a.s.l. The holotype and five paratypes were captured in the upper vegetation belt of Harenna forest dominated by Hagenia abyssinica , Schefflera abyssinica , S. volkensii , Aningeria adolfi-friederici , Hypericum revolutum . Two paratypes were captured in the Erica arborea shrub on the southern slope of Sanetti Plateau. Yalden (1988) reported it to be also commensal in Rira village at 3000 m a.s.l. The new species might occur together with at least following rodent species in the Bale Mts.: Lophiomys imhausii Milne-Edwards 1867 , Megadendromus nikolausi Dieterlen and Rupp 1978 , Tachyoryctes splendens (Rüppel 1835) , Lophuromys chrysopus Osgood 1936 , L. brevicaudus Osgood 1936 , Otomys helleri Frick 1914 , Mus mahomet Rhoads 1896 , Stenocephalemys albipes (Ruppell 1842) , S. griseicauda Petter 1972 and S. albocaudatus Frick 1914 . One paratype was captured in the very moist Afromontane Chingawa forest with notable abundance of epiphytic and tree ferns. The following rodent species were also collected at the same trapping site: Lophuromys chrysopus , L. brunneus Thomas 1906 , Otomys fortior Thomas 1906 , Stenocephalemys albipes , S. ruppi (Van der Straeten & Dieterlen 1983) and Chingawaemys rarus Lavrenchenko, Mikula & Bryja 2021. It should be mentioned that both disjunct areas of moist evergreen montane forests, where M. harennensis sp. nov. is distributed, are floristically very similar ( Friis et al., 2010).

Biogeographical importance of Ethiopian rainforests and conservation implications

Even though subjected to the intensive anthropogenic disturbances, the humid Harenna forest stands as the largest relic moist forest in Ethiopia ( Tesfaye et al., 2002). Intensive past research revealed that it is very rich in the diversity of fauna and flora and discoveries of paleo-endemic species with a limited range of distribution like Mus harennensis sp. nov. are not exceptional. Indeed, several Ethiopian endemic species have been described from this forest, including the small tree ( Maytenus harenensis ), Harenna Forest Grass Frog ( Ptychadena harenna ), viperid snake ( Bitis harenna ), Bale Monkey ( Cercopithecus djamdjamensis ) and Harenna Shrew ( Crocidura harenna ) (see Largen, 1997; Lavrenchenko, 2000; Gower et al., 2016).

The Chingawa forest likewise is probably the most humid part of forests in southwestern Ethiopia, but also the most understudied despite recent indications that it is likely rich in narrowly endemic species (see, e.g. Mizerovská et al., 2020 and this study, for examples of small mammals). The unique character of this forest is further documented by the recent discovery of a new paleo-endemic monospecific genus of murine rodents, Chingawaemys ( Nicolas et al., 2021). This rare mammalian species, known only from the holotype collected in the Chingawa forest, split from their closest relatives in late Miocene, ca. 7 Ma, which corresponds with the beginning of fragmentation of pan-African forests due to overall climate aridification at the end of Miocene (see Nicolas et al., 2021 and references therein). Overall, the forests in southwestern Ethiopia harbour a rich concentration of evolutionarily unique endemic taxa (e.g. Herkt et al., 2016; Mairal et al., 2017; Shumi et al., 2019). If we focus again of mammals, a number of murine ( Otomys fortior , Stenocephalemys ruppi , Desmomys yaldeni , Lophuromys pseudosikapusi ) and deomyine (undescribed species of Dendromus ) rodents, and shrews ( Crocidura similiturba and C. macmillani ) are currently known only from rain forests of southwestern Ethiopia ( Lavrenchenko & Bekele, 2017; Bryja et al., 2019; Konečný et al., 2020; Mizerovská et al., 2020; Komarova et al., 2021; Meheretu et al., 2022). Recent studies of their evolutionary history suggest that such high endemic biodiversity evolved by three different processes. First, paleo-endemics are the results of old pre-Pleistocene vicariance of forests and their fauna (e.g. this study or Nicolas et al., 2021). Neo-endemics are of much younger origin and they diverged either by more recent Pleistocene colonization from the forests in the southern part of EAMBH, e.g. Albertine Rift or Kenyan highlands, followed by allopatric diversification in drier climatic periods ( Bannikova et al., 2021; Konečný et al., 2020), or by recent (Pleistocene) adaptive shifts of once widespread ancestors in Ethiopian highlands to specific forest habitats in lower elevation ( Bryja et al., 2018; Komarova et al., 2021; Voelker et al., 2021).

Notwithstanding the intensity in biodiversity research between the forests (Harenna being much more intensively studied than southwestern forests), a growing number of studies is providing evidence of a past connection between the two forest blocks. For instance, C. harenna and M. harennensis sp. nov., both considered until very recently to be endemic to Harenna forest , also occur in forests of southwestern Ethiopia ( Konečný et al., 2020; this study). Similarly, other more common forest specialist species are known to be distributed on both sides of the Great Rift Valley (see, e.g. Freilich et al., 2014 and 2016 for examples in frogs; Mizerovská et al., 2020 and Komarova et al., 2021 for rodents). Even if genetic lineages on both sides of the rift are moderately distinct in all these taxa, they evidence the ability of forest species to cross the rift valley in the past, probably in humid Pleistocene periods through the isolated montane forests in its southern Ethiopian part (Bonke or Bulcha, now mostly disappeared) that likely have worked as colonization stepping stones.

Consequently, even though they are yet to be formally tested against the hypotheses and categorical analysis of neo- and paleo-endemism ( CANAPE) ( Dagallier et al., 2020; Mishler et al., 2014), available data on small mammals diversity and endemism suggest that the forest blocks in southern and southwestern Ethiopia would make a suitable candidate area for centre of mixed-endemism, because they host a mixture of neo-endemic and paleo-endemic taxa (see Mishler et al., 2014; Dagallier et al., 2020 and the references therein). At the same time, both forests exemplify complex climatic history (Pleistocene climatic cycles) of the EAMBH and the intersections of rich biodiversity, sharp human population surge and accelerated environmental degradation from rapid land use changes. Hence, they represent a blueprint for future study of the impacts of proximate human-induced land use and climate changes on montane endemism, glacial refugia and glacial-source populations ( Perrigo et al., 2020). As far as conservation is concerned, in resource-poor countries like Ethiopia, areas with extreme/ highest paleo-endemism, such as these forests, should be top in conservation priority to prevent endangered evolutionarily unique taxa (“living fossils”) from extinction driven by human activities. The description of such taxa, diverged early in evolution in the forests, should make part of the incentives to embark on urgent conservation action for formal protection of these unique forests within the EAMBH.