209.

Isarog Striped Shrew Rat

Chrotomys gonzalesi

French: Chrotomys de |'lsarog / German: Isarog-Streifenratte / Spanish: Rata musarana listada de Isarog

Other common names: sarog Chrotomys, Isarog Striped Rat, Mount Isarog Striped Rat

Taxonomy. Chrotomys gonzales Rickart & Heaney, 1991,

“Western slope of Mount Isarog, 4 km N, 21 km E Naga, Camarines Sur Province, Luzon Island, Philippines, 1350 m elevation, 13°40’N, 123°22°E.”

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 the less specialized Philippine murines of genus Apomys . C. gonzales appears to be most closely related to C. whiteheadi and C. mindorensis . It is geographically isolated from other Chrotomys . Monotypic.

Distribution. Slopes of Mt Isarog, SE Luzon I, Philippines; recently collected specimen from Saddle Peak, S Sierra Madre, and a photographic record from Mt Malinao, SE Luzon, suggest possibility of two addtional populations.

Descriptive notes. Head-body 160-190 mm, tail 83-105 mm, ear 20-23 mm, hindfoot 34-39 mm; weight 70-190 g. According to L.. R. Heaney and coworkers, adult males are probably larger, on average, than females. Chrotomys species are stout-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 molars small, with occlusal pattern consisting of shallow “basins.” The Isarog Striped Shrew Rat is one of the larger members of genus and has fur on upperparts soft, dense, and fluffy, hair length 17-18 mm on middle of back; mid-dorsalstripe pale yellowish buff (individual hairs blackish brown, tipped with buff), narrow, typically running from forehead to base of tail but sometimes confined to head and upper back; lateral zone is blackish brown, merging into yellowish buff on flanks, and underparts are dark gray withfaint grayish-buff wash; transitions between lateral zone, flank, and underparts all gradual; white blaze sometimes present on chest or upper abdomen; top of head is blackish to snout,lipssilvery gray and merging with yellowish buff on cheeks and side of head; no eye-ring; vibrissae blackish gray, reaching just past ears; ears pale gray and sparsely furred. Feet have upper surface dark gray and well furred, except for digits that are unpigmented and nearly naked, palmar surface unpigmented; plantar surface of hindfeet pigmented pale gray to base of digits, usually with five pads,less often with six (addition ofvery small inner posterior pad). Tail is relatively short (55-60% of head-body length), skin pale gray above and nearly white below, sometimes with short all-white tip, scales small, in 16-18 rows per cm, each scale with three short, dark hairs. Cranium has relatively broad, low braincase, relatively narrow rostrum, and three molars in each series, the last 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 theLowland Striped Shrew Rat ( C. mindorensis) and the Blazed Luzon Striped Shrew Rat ( C. silaceus).

Habitat. Evergreen tropical forest, including montane and mossy forest types distinguished by ecologists in Philippines. Recorded elevational range of 1350-1750 m.

Food and Feeding. The Isarog Striped Shrew Rat is reported as foraging for earthworms and other soil invertebrates by digging in leaf litter and humus. Individuals consumed earthworms when kept briefly in captivity. Large forefeet and heavy claws are consistent with foraging mode that involves frequent digging in humus and soil.

Breeding. Little is known, but one adult female had two embryos.

Activity patterns. Heaney and coworkers reported that the Isarog Striped Shrew Rat it is active primarily during day but also at night.

Movements, Home range and Social organization. Heaney and coworkers reported that Isarog Striped Shrew Rats kept briefly in captivity were docile.

Status and Conservation. Classified as Near Threatened on The IUCN Red List. At the time of its discovery, in 1988, primary forest was present on Mount Isarog down to ¢.900 m elevation; extensive trapping effort at each of 475 m, 900 m, and 1125 m failed to yield captures ofthe Isarog Striped Shrew Rat. At higher elevations it was not common, with only eight captures out of 4900 trap-nights at or above 1350 m.

Bibliography. Balete, Heaney, Alviola & Rickart (2013), Balete, Rickart et al. (2012), Rickart & Heaney (1991).