Hylomys peguensis Blyth, 1859

Hinckley, Arlo, Camacho-Sanchez, Miguel, Chua, Marcus A. H., Ruedi, Manuel, Lunde, Darrin, Maldonado, Jesús E., Omar, Hasmahzaiti, Leonard, Jennifer A. & Hawkins, Melissa T. R., 2024, An intbgoativb taxonomic obvision of lbssbo gvmnuobs (Eulipotvphla: Hylomys) obvbals fivb nbw spbcibs and bmboging paưbons of local bndbmism in Toopical East Asia, Zoological Journal of the Linnean Society 202 (2), pp. 1-33 : 15-17

Hylomys peguensis Blyth, 1859

Hylomys peguensis Blyth, 1859: 294 . Original description.

Hylomys siamensis Kloss, 1916: 10 .

Hylomys suillus microtinus Thomas, 1925: 497 .

Hylomys suillus suillus Corbet, 1988: 122 (part).

Subspecific taxonomy

Hylomys peguensis peguensis Blyth, 1859: 294 .

Hylomys peguensis siamensis (Kloss), 1916: 10 .

Hylomys siamensis Kloss, 1916: 10 .

Hylomys peguensis microtinus (Thomas), 1925: 497 .

Hylomys suillus microtinus Thomas, 1925: 497 .

Holotype: The original description does not specify a reference number. Adult male and female collected by Major Berdmore and housed in the Indian Museum (Zoological Survey of India, National Zoological Collection), at Kolkata (syntypes). Preserved in spirit according to the description but one of the skulls was subsequently extracted ( Anderson 1874). Khajuria et al. (1977) revised the mammal types in this museum and did not cite these specimens. The staff at the Zoological Survey of India National Zoological Collection have stated that these syntypes are lost (Uttam Saikia pers. comm.).

Type locality: ‘Schwe Gyen, in the valley of the Sitang river, Tenasserim province’ (Shwegyin, valley of the Sittang river , Bago, Myanmar).

Paratypes: Non-existent.

Neotype designation: Given that the type series is lost and that there are no available topotypes, we here designate as a neotype the geographically closest specimen to the type locality that is available: USNM 583813 . This specimen is an adult male collected at ‘Kinmun, 5 Km N E Of, By Road, Yetagon Myaung, Kyaikhtiyo Wildlife Sanctuary, Mon, Myanmar’ (386 m a.s.l.; 17.4442, 97.0994) on 15 March 2002 by J.F. Jacobs. This locality is approximately 58 km away from the type locality and there are no geographical barriers in between. The neotype specimen morphology matches the species description and Anderson (1874) redescription of H. peguensis (venter coloration, nasals extend to the level of the antorbital rim, strongly developed cingulum in P4) and it is unlikely to represent any other species, given that the other two mainland Asian Hylomys species allopatric distribution ranges do not span this region. The specimen consists of a museum study skin with accompanying cranium and mandible, remaining body in fluid, and frozen tissue samples; skin has retained the phallus and all four limbs and is in a perfect condition; skull has a small area of the palate, posterior to the right incisive foramen, broken, but is otherwise in a good condition. Total length 172 mm, tail 20 mm (13% HB), hindfoot 26 mm, ear length 19 mm, weight 73 g. Skull measurements in Supporting information, Table S2. 3D surface scans of this neotype skull are available at MorphoSource: https://doi.org/10.17602/M2/M560027 (cranium); https:// doi.org/10.17602/M2/M560031 (mandible). Pictures of this holotype skin and skull are shown in Figures 7A and 8A . DNA sequences associated with this neotype have been deposited in GenBank: OR554485 , OR554506 , OR554522 , OR554414 , OR554417 , OR554461 .

Emended diagnosis: A medium-sized Hylomys (average HB = 129 mm, W = 54.2 g, GLS = 34.4 mm) characterized by a brown dorsum fur with a yellow tinge and relatively lighter coloured appearance than Sundaic relatives (except at the southern tip of its range), silvery tinged with buff venter coloration, bicoloured and relatively long tail (average T = 21.3 mm, T / HB = 17%), light brown feet, short hindfoot (average HF = 22.5 mm, HF + nail = 24.8 mm), relatively short ears (average E = 16.4 mm, E/ GLS = 50%) with a whitish/light brown rim (except in one Cambodian specimen). Its skull is short (average GLS = 34.4 mm) and has a relatively short rostrum (average ROL = 14.6 mm). It can be distinguished from all other relatives by the combination of the following characters: obtuse-angled notch on anterior side of premaxilla; nasals generally extend to the level of the antorbital rim (9/11 specimens); highly to moderately developed supraorbital processes; antorbital ridge/flange poorly developed; relatively shallow antorbital fossa; anterior side of the antorbital rim is anterior or in line with M1 second cusp; lacks posteriorly extended horizontal crest in maxillary, behind infraorbital canal; long alisphenoid canal (average ASC = 1 mm); ectotympanic anterior process is robust and thickens dorsoventrally towards the tip, interior side of ectotympanic anterior process is not elongated and expanded anteriorly; I2 is oriented posteriorly; flat braincase at the occipitum (average BD = 9.3 mm); relatively gracile mandibular ramus (average LAP = 9.1 mm) with narrow coronoid process; average sized upper first incisor (average I1 = 2.6 mm) not projected towards lingual side, so that space between incisors does not narrow towards the tip; labial cingulum in P4.

Comparisons: It is currently thought to have an allopatric distribution with Sumatran and mainland Asian H. maxi , from which it can be distinguished based on its generally lighter dorsum (brown with yellowish tinge vs. without), venter (buff vs. greybrown) and feet coloration (light vs. dark brown), particularly on its forefeet (light brown vs. dark brown/black), presence of whitish/pale brown in ear rim (except in Cambodian population), longer tail and shorter hindfoot (Supporting information, File S1, Fig. S6 ), shorter skull length (32.3–36.0 vs. 35.5–38.4 mm), shorter rostrum length ( RL: 13.1–15.8 vs. 16.1–18.2 mm), shorter upper and lower toothrows ( IM 3 SA: 15.8–18.3 vs. 18.3–19.7 mm, IM 3I: 15.1–17.4 vs. 17.6–18.9 mm), flatter braincase at occipitum ( BD: 9.0–9.6 vs. 9.3–10.5 mm), and longer alisphenoid canal (0.7–1.2 vs. 0.1–0.4 mm). Posterior end of nasals generally extends to the level of the antorbital rim but it does not in H. maxi . It has similar sized supraorbital processes to H. maxi despite its much smaller skull size. Antorbital flange is thinner in H. peguensis giving a shallower appearance to the antorbital and nasolabilis fossa than H. maxi . Anterior side of the antorbital rim is anterior or in line with M1 second cusp, while it is posterior in H. maxi . Its robust ectotympanic process thickens dorsoventrally towards the tip, while it is generally more gracile and dorsoventrally even in H. maxi . Its P4 labial cingulum is generally thinner/less prominent than H. maxi .

Comparisons with additional species have been included in the following accounts, after such species have been formally defined.

Distribution, habitat, and natural history: Distributed across most of Indochina’s hills and mountains, except the Da Lat and Dak Lak Plateaus and surrounding lowlands. Its southern distribution limit seems to be in Perlis (Malaysia), possibly at the K-P vegetation transition, mirroring the distribution of other small mammals ( Hinckley et al. 2023). In southern Myanmar, specimens were caught at c. 400 m a.s.l. along a fast-running stream with boulders in a heavily cut secondary forest (Jacobs field notes, USNM Mammal Division archives). In northern Myanmar, it was collected dead on a path on a thickly wooded hillside at c. 900 m a.s.l ( Anderson 1874). In central and north Thailand confined to hilly and mountain areas, with dense undergrowth (Lekagul and McNeely 1977), and under logs in a grove of wild bananas ( Allen and Coolidge 1940). In Huai Kha Khaeng Wildlife Sanctuary, central Thailand, H. peguensis has been recorded in dry evergreen and mixed deciduous forests with a relatively closed canopy (>60%), and a variable, but reduced ground cover (<60%) at an altitude of 550–650 m a.s.l., but not in a mixture of dry mixed deciduous forest and dry dipterocarp forest at an elevation of 400–500 m a.s.l., and a relatively open canopy (<60%) with thick ground cover (>60%; Walker and Rabinowitz 1992). In northern Lao P.D. R. it was recorded in a small, vegetated gully with a small running stream, in a secondary and highly degraded semi-deciduous forest (authors’ unpublished data). In northern Viet Nam the species has been recorded from c. 100–1000 m a.s.l., but it is most abundant at higher elevations (900–1000 m a.s.l.) in habitats with plentiful logs ( Abramov et al. 2013, this study), and on stream banks with wild bananas and reeds in open spaces near forest ( Van Sung 1976). In Kiri Rom Plateau, Cambodia it has been recorded at 700 m a.s.l., in the grass at the edge of a pine forest (Bernard Feinstein’s field notes, USNM Mammal Division archives).

In the north-west of its distribution, H. peguensis appears to be parapatric with Neotetracus sinensis , which occurs at higher elevations (1500–2700 m) ( Van Sung 1976, Corbet 1988).

It seems to have a parapatric or allopatric distribution with Neohylomys hainanensis , which has recently been recorded in Viet Nam, in evergreen mixed forest north of the Red river (Cao Bang, Vinh Phuc, and Bak Kan provinces) at elevations of 300 to c. 850 m a.s.l, but not at higher elevations of 1500– 1800 m a.s.l. ( Abramov et al. 2018, this study). Although both species might overlap in their elevation ranges, they have not been recorded in sympatry; in fact, H. peguensis has been recorded in the Red River valley (Lao Cai province) but not north of it. In Kyaikhtiyo Wildlife Sanctuary, Myanmar, H. peguensis shares its habitat with Crocidura cf. fuliginosa , Tupaia belangeri , Cannomys badius , Maxomys surifer , Mus cookii , Rattus andamanensis , and Callosciurus phayrei (Jacobs field notes, USNM Mammal Division archives). In Huai Kha Khaeng Wildlife Sanctuary, central Thailand, it shares its habitat with Tupaia belangeri , Cannomys badius , Maxomys surifer , Leopoldamys herberti, Niviventer sp. , Menetes berdmorei , and Rattus rattus ( Walker and Rabinowitz 1992) . In Phu Lom Lo, northern Thailand, it shares habitat with Berylmys berdmorei , Cannomys badius , Leopoldamys herberti , Maxomys surifer, Niviventer mekongis , Rattus nitidus , Rattus rattus , Dremomys rufigenis , and Menetes berdmorei (Robert Elbel’s field notes, USNM Mammal Division archives). In Kiri Rom Plateau, Cambodia, it shares its habitat with Tupaia belangeri , Maxomys surifer , Mus shortridgei , Rattus rattus , and Rattus andamanensis (Feinstein’s field notes, USNM Mammal Division archives).

Earthworms, snails, ants, beetles, butterfly caterpillars, and fruits of Ficus and Melastoma have been recorded in specimen stomachs ( Van Sung 1976). Males had larger testicles in March (13 × 6 mm) than in December (7–8 × 3 mm) suggesting this species might breed in spring or summer in northern Viet Nam ( Van Sung 1976). Gravid females have been recorded in late-February on the Myanmar– China border, and in mid-May in Ba Vi National Park, Viet Nam. Litter size was 2 (N = 1) and 4 (N = 2), respectively (AMNHM-44272; Abramov et al. 2013). An adult male and female specimen were caught in the same trap during consecutive days suggesting the species might form pair bonds or males may mate guard, and that male and female territories must overlap (perhaps just when breeding; Jacobs field notes, USNM Mammal Division archives).

Conservation: Recorded in Thung Yai Naresuan, Huai Kha Khaeng and Kyaikhtiyo wildlife sanctuaries, Mae Wong, Ba Vi, Xuan Son, and Preah Monivong Bokor National Parks ( Walker and Rabinowitz 1992, Robinson et al. 1995, Abramov et al. 2013, Pavlova et al. 2018; Supporting information, Table S1 ). Recorded in Khasia pine plantations with native undergrowth vegetation, and in margin between evergreen forest and short-term agriculture but not in Khasia pine plantations with coffee or macadamia plantations ( Chaiyarat et al. 2020, THNHM field notes). To evaluate the conservation status of H. peguensis , additional research is necessary to ascertain population trends within protected areas and to understand the species tolerance to environmental degradation in anthropized landscapes. Additional field surveys and habitat suitability modelling is necessary to predict future trends. Some of the described subspecies of H. peguensis may deserve species-level recognition (see below), and as such we suggest each is treated as an independent conservation unit by regional government agencies.

Comments: This species exhibits higher levels of genetic structure than other relatives but the craniodental morphospace of these lineages ( peguensis , siamensis , and microtinus ) overlaps, and sample size is low. Thus, further geographic sampling will be required to assess if these populations might deserve specific status. In the meantime, we suggest retaining siamensis and microtinus as subspecies of H. peguensis . The literature regarding the distribution limits of H. peguensis and H. maxi is somewhat confusing. Lekagul and Mcneely (1977) stated that only H. s. siamensis is present in Thailand, indirectly suggesting that H. peguensis distribution should at least extend to the K-P. Chasen (1940) recorded the lighter coloured H. s. siamensis ( H. peguensis ) as far south as Tapli (Ranong) in the Isthmus of Kra based on specimen ZRC 4.5033 and only a few miles north of the Malaysian boundary. However, Hill (1960) describes this supposedly ‘light coloured’ specimen as very brown with a strong reddish tinge and a clear grey underside (features that resemble more H. maxi ). Hill (1960) states that H. maxi distribution extends to Tasan (Chumphon) and is present in Pelarit (Perlis). Ruedi et al. (1994) followed Hill (1960). The only molecular evidence we have (two short nuclear fragments of specimen MZUM-M 00057, Kaki Bukit, Perlis), along with diagnostic craniodental (e.g. rostrum length) and selected external measurement bivariate plots, seem to support Chasen (1940), suggesting that H. peguensis distribution extends to the Malaysian boundary, possibly at the K-P.

Figures

Figure 6. Bivariate plot of rostrum length (ROL) and rostrum breadth (ROB) measurements.

Figure 7. Dorsal and ventral views of the skins of (A) Hylomys peguensis (USNM583813, neotype), and (B) Hylomys macarong(USNM 320500, holotype). Photo credits:Katie Sayers.

Figure 8. Skulls of (A) Hylomys peguensis (USNM583813, neotype) and (B) Hylomys macarong (USNM 320500, holotype).All images are at the same scale.Photo credits: Katie Sayers.