161.

Lesser Marmoset Rat

Hapalomys delacouri

French: Petit Hapalomys / German: Delacour-Seidenratte / Spanish: Rata titi menor

Other common names: Delacour’'s Marmoset Rat

Taxonomy. Hapalomys delacour Thomas, 1927,

“Dakto, S Vietnam” (= Dak To, Kon Tum Province, Vietnam).

There are relatively subtle morphological differences between populations of H. de-lacouri in southern Vietnam and northern Laos, with names delacouri and pasquieri by O. Thomas in 1927 available for use,if warranted. Recent studies of chromosomes of populations in southern Vietham and northern Thailand found clear of evidence of multiple species within delacour, resulting in the description of H. suntsoviin by A. V. Abramov and colleagues in 2017. The relation of the northern Thailand populations to other population within this probably species complex are still uncertain and a full scale revision is needed within this group to establish species limits. The name marmosa by G. M. Allen in 1927 is available from Hainan Island, but this population is poorly characterized. Monotypic.

Distribution. S China (S Yunnan, S Guangxi, and Hainan), N Laos, N Thailand (Loei Province), and C Vietnam.

Descriptive notes. Head—body 102-146 mm, tail 135-171 mm, ear 10-15 mm, hindfoot 22-24 mm. No specific data are available for body weight. The Lesser Marmoset Rat is stocky and highly arboreal, with thick, soft, and silky fur and ocherous brown upperparts, white below with no contrasting strip between the two. Head is broad with short snout; uppersurface and back are the same color; and white of belly extends onto throat, lower and upperlips cheeks, and onto cheeks. Ears are relatively large, brown, and conspicuously fringed by elongated brown hair. All vibrissae are black and long, and mystacial group folds back past ears. Forefeet and hindfeet are short and broad, clearly adapted to climbing, with large terminal and plantar pads. Hallux is wide and has a nail; all other digits have strong, curved claws. Tail is 20-30 mm longer than head-body length, dark, and finely scaled; tail hairs are conspicuous only toward tip; and terminal brush is longer on specimens from northern Laos than from central Vietham. Cranium is broad and compact, with strong incisors, large cuspidate molars, and inflated, rounded auditory bullae. Four mammae are on each side: one pectoral, one post-axillary, and two inguinal pairs. Chromosomal complement of individuals from central Vietnam is 2n = 38, FN = 48; there are six pairs of metacentric and twelve pairs of acrocentric autosomes, large metacentric X, and smaller metacentric Y. Chromosomal complement of individuals from northern Thailand is 2n = 48, FN = 92; all autosomes are metacentric or submetacentric, with very large metacentric X and small acrocentric Y. Chromosomes of northern Thailand population were mapped against karyotype of laboratory Brown Rat ( Rattus norvegicus) using cross-species fluorescence in situ hybridization and suggested that the Lesser Marmoset Rat is a representative of the most basal lineage within Murinae.

Habitat. Evergreen tropical forest in southern Vietnam and dry deciduous tropical forest with oaks ( Quercus) and chestnuts ( Castanea), both Fagaceae, in northern Laos at elevations of 1200-1500 m. All records of the species are associated with clumps of bamboo within regional forest habitat, and there are no records from highly modified habitats.

Food and Feeding. Dietis likely similar to that of the Greater Marmoset Rat (FH. longicaudatus), which appears to be exclusively herbivorous and heavily focused on growing tips of bamboo twigs and fruiting bamboos, although in captivity they will eat fruits and tubers.

Breeding. Similar to the Greater Marmoset Rat, the Lesser Marmoset Rat might nest in internodal cavities of dead or living bamboo culms.

Activity patterns. Body form of the Lesser Marmoset Rat suggests ahighly arboreal lifestyle, which is supported by the captured records.

Movements, Home range and Social organization. No information.

Status and Conservation. Classified as Vulnerable on The IUCN Red List, the Lesser Marmoset Rat is facing to ongoing loss ofits primary forest habitat with natural stands of bamboo.

Bibliography. Abramov, Aniskin & Rozhnov (2012), Abramov, Balakirev & Rozhnov (2017), Allen (1927), Badenhorst, Dobigny & Robinson (2012), Badenhorst, Herbreteau et al. (2009), Chaimanee (1998), Chen Gengjiao et al. (2012), Corbet & Hill (1992), Dang Huy Huynh et al. (1994), Ellerman (1941), Lunde & Aplin (2008c), Lunde & Nguyen Truong Son (2001), Misonne (1969), Musser (1972), Musser & Carleton (2005), Osgood (1932), Smith & Yan Xie (2008), Thomas (1927e), Wang Yingxiang (2003), Zhang Yongzu et al. (1997), Zheng Shaohua (1993).