210.

Lowland Striped Shrew Rat

Chrotomys mindorensis

French: Chrotomys de Mindoro / German: Luzon-Flachlandstreifenratte / Spanish: Rata musarana listada de tierras bajas

Other common names: Lowland Chrotomys, Lowland Striped Rat, Mindoro Striped Rat, Mindoro Striped Shrew Rat

Taxonomy. Chrotomys mindorensis Kellogg, 1945,

“3 miles [= 5 km] south-southeast of San Jose (Central), Mindoro Island, [Mindoro Occidental Province], Philippine Islands. Altitude, 200 feet [= 61 m].”

Chrotomys and Rhynchomys of the Philippines were typically allied in the past with the Australo-Papuan water rats ( Hydromys etc.), mainly on account of dental similarities. Their closest phylogenetic affinities, as revealed by molecular studies, are with other, recently discovered Philippine shrew rats and mice of genera Archboldomys and Soricomys, and with theless specialized Philippine murines of genus Apomys . C. mindorensis was described as a subspecies of C. whitehead: but was elevated to species level by G. G. Musser and coworkers in 1982, an arrangement that has gained further support from subsequent molecular studies. Currently regarded as monotypic but in need of further assessment.

Distribution. Luzon and Mindoro Is, Philippines.

Descriptive notes. Head-body 155-186 mm,tail 99-123 mm, ear 19-23 mm, hindfoot 36-40 mm; weight 152-199 g. Chrotomys arestout-bodied, semi-fossorial murines with short, strong limbs, and thick tail considerably shorter than head-body length;relatively small eyes; rounded and relatively short ears; forefeet proportionally large and with strong digits and heavy, nearly straight claws on second to fourth digits; hindfeet long and narrow with small plantar pads and claws on all digits; cranium robust, with flaskshaped outline, forward-projecting upper incisors that are probably used for digging, short nasal bones that terminate well behind level of incisors, and small molars with occlusal pattern consisting of shallow “basins.” The Lowland Striped Shrew Rat, one of larger members of genus, has fur on upperparts dense, soft and sleek, 16-17 mm in length at mid-back, a broad yellowish-buff medial stripe from between eyes to base oftail, strongly defined black or blackish-brown lateralstripes, and pale yellowish buff suffused with gray on flanks and sides of head; underparts usually silvery gray, sometimes washed pale buff, transition from flanks to underparts moderately abrupt; no eye-ring; vibrissae reach just past ears; ears pale gray and sparsely furred. Feet have upper surfaces silvery gray, plantar surface with six well-formed pads. Tail is relatively short (57-76% of headbody length), skin brown or blackish brown above and nearly white below, scales small, in 16-19 rows per cm, each scale with three short, silvery hairs.Cranium has relatively narrow and deep braincase; three molars in each series,slightly larger overall than in the Montane Striped Shrew Rat (C. whiteheads), and the third strongly reduced. Females have two pairs of mammae, both inguinal. Chromosomal complement has 2n = 44 and FN = 52, and includes two pairs of small metacentric, one pair of large submetacentric, one pair of large subacrocentric, and 18 pairs of acrocentric chromosomes, the last grading from large to small. The X and Y chromosomes cannot be distinguished from the autosomes and must be among the acrocentric series. This karyotype is shared with the Isarog Striped Shrew Rat ( C. gonzalesi) and the Blazed Luzon Striped Shrew Rat ( C. silaceus). Spermatozoa with relatively short (8-5 pm) and broad (2:4 pm) head bearing an apical hook and lacking accessory ventral processes;tail, at 135 pm, is moderately long.

Habitat. Evergreen tropical rainforests, including both primary and secondary forest, and in Ifugao Province, NC Luzon, it commonly ventured into adjoining agricultural land, including irrigated rice fields. Across most ofits range it appears to be confined to lowland rainforest and derived secondary growth below ¢.500 m, but in Zambales Mountains, western Luzon, it extends upward into montane forest to 2050 m.

Food and Feeding. [.. R. Heaney and coworkers wrote in 2016 that Lowland Striped Shrew Rats “dig extensively through humus and soil, feeding on earthworms, insects and other invertebrates. Their presence is often conspicuous, due to the abundance of shallow pits and small piles ofdirt where they have dug for food.”

Breeding. No information.

Activity patterns. The Lowland Striped Shrew Ratis reported as being active by both day and night.

Movements, Home range and Social organization. No information.

Status and Conservation. Classified as Near Threatened on The IUCN Red List. L.. A. Ruedas encountered the Lowland Striped Shrew Rat at “very high population levels” in 1992 in lightly disturbed primary forest on flanks of Mount Halycon, on Mindoro, and it appears to be moderately common in irrigated rice fields in Laguna Province, where these abut areas of remnant forest.

Bibliography. Barbehenn et al. (1972), Heaney & Balete (2008b), Heaney, Balete, Dolar et al. (1998), Heaney, Balete & Rickart (2016), Joshi et al. (2004), Kellogg (1945b), Musser & Carleton (2005), Musser & Heaney (1992), Musseret al. (1982), Rickart & Heaney (1991), Ruedas (1995), femme (1974).