244.

Elegant Water Rat

Leptomys elegans

French: Leptomys élégant / German: Elegante Neuguinea-Wasserratte / Spanish: Rata de agua elegante

Other common names: Elegant Leptomys, Large Leptomys, Long-footed Rat, Long-footed Water Rat

Taxonomy. Leptomys elegans Thomas, 1897,

“British [= Papua] New Guinea — exact locality not known.”

The name elegans has been broadly applied to many or even all populations of Leptomys, sometimes with recognition of multiple subspecies. The current, mulispecies arrangement was proposed in 2008 by G. G.Musser and colleagues, following detailed review of majority of available specimens. Monotypic.

Distribution. Known from scattered localities in two areas in E New Guinea: Kikori and Strickland river catchments, and SE Papuan Peninsula.

Descriptive notes. Head-body 142-194 mm, tail 125-164 mm, ear 18-26 mm, hindfoot 36-43 mm; weight 66-120 g. Leptomys are unmistakable medium-sized terrestrial rats with short, dense, and silky or velvetlike fur, buff gray to orange brown on upperparts, cream or white below; black-tipped guard hairs barely project through general pelage; head with long, slender snout and long vibrissae that extend well past ears, latter being moderately large and thinly furred; upper surfaces of feet white, long and narrow hindfeet having all digits with claws, plantar pads relatively small; tail slender, finely scaled, and with three short hairs per scale, basal portion dark above and white or mottled below, distal portion entirely white, no terminal brush or prehensile pad. Cranium is relatively narrow and delicate, relatively robust incisors bearing orange enamel and forward-projecting lower incisors with paler yellow enamel; three molars, initially cuspidate but basined when worn, posterior molars very reduced. Mammae two on each side, both inguinal. The Elegant Water Rat, largest member of genus, has fur on upperparts moderately long, tawny brown onmid-back and flanks; underparts

pure white from chin to base oftail; head lacks dark mask around eyes, but some individuals have pale spot on crown;tail (66-110% of head—body length) is shorter than in all congeners.It differs from other Leptomys also in poor development of hypothenar pad on each hindfoot and in details of cranial and dental morphology. Karyotype with 2n = 48, autosomes predominantly acrocentric but one pair submetacentric. C-banding restricted to centromeric regions on most autosomes but extra interstitial bands on two largest pairs. Spermatozoa with long tail, sperm head with long apical hook and two shorter ventral hooks,tail long.

Habitat. All records of the Elegant Water Rat are associated with tropical evergreen rainforest. It has been found at elevations of 490-1500 m in Kikori and Strickland river catchments and at 20-800 m in south-eastern Papuan Peninsula; elevational range spans lowland rainforest, hill forest, and lower montane forest. At 1400-1500 m on south-west slopes of Mount Sisa (upper Strickland River catchment) it occurs in lower montane forest and in secondary forests with more than ten years of regeneration following shifting subsistence agriculture. It is absent from active gardens cut into mature forest, and from initial successional stages of regeneration with dense ground cover of grasses and weeds, followed by scrubby thickets.

Food and Feeding. Strong dietary focus on animal prey indicated by morphology of skull and teeth. P. Dwyer witnessed captive individuals killing and consuming grasshoppers and a praying mantis, and consuming both cooked and raw meat from bones and a rat carcass. Stomach contents of one individual included insect remains. Some individuals were caught at traps baited with meat and beetle larvae (“sago grubs”).

Breeding. The low mammary formula (two pairs) indicates smalllitter size. This is supported by Dwyer’s report of a mean litter size of 1-7 based on four pregnant females from Mount Sisa, and birth of a single young to a captive female as reported by T. Leary and L. Seri.

Activity patterns. Recorded captures of the Elegant Water Rat are exclusively on the ground. Recent camera-trapping effort at ¢.1100 m in Kikori River catchment suggests that this murid is active solely at night.

Movements, Home range and Social organization. The Elegant Water Ratis solitary, as indicated by camera-trapping results. Parental care presumably ends at time when young are weaned and leave the maternal nest. Dwyer’s field notes on a captive individual suggest an unusual “digitigrade” mode of locomotion with most of the plantar surfaces off the ground; tail was arched, with tip pointing downwards. Camera-trap images demonstrate same posture. H. M. Van Deusen made another interesting observation of an individual “hopping on the forest floor.” Camera-trap images often show Leptomys leaping or springing, presumably as a startle response to the camera flash, and perhaps a regular part of behavioral repertoire ofthis species. The narrow, elongate hindfeet also indicate significant saltatorial capability.

Status and Conservation. Classified as Least Concern on The IUCN Red List. Cameratrap imaging rates for this species suggest moderately high local abundancesin primary lower montane forests of the upper Kikori River catchment. The Elegant Water Rat appears to be absent from the Purari River catchment (immediately east of the Kikori River catchment) which has been intensive surveyed from sea level to 1500 m, most recently including camera trapping and analysis of large owl pellet accumulations. The apparent elevationalshift between eastern and western populations might reflect contrasting patterns of competition—on the south-eastern Papuan Peninsula the Elegant Water Rat is replaced at higher elevations by the Small Water Rat ( L. paulus) but there is no other species at lower elevation; in the Kikori and Strickland River catchments the elevational limits of the Elegant Water Rat are bracketed below, by records of the Fly River Water Rat ( L. signatus) and above, by records of Ernst Mayr’s Water Rat ( L. ernstmayri). There are no known instances of local sympatry of two species of Leptomys .

Bibliography. Breed & Aplin (1995), Cole et al. (1997), Donnellan (1989), Dwyer (1984), Flannery (1995b), Hide et al. (1984), Leary & Seri (1997), Leary, Singadan, Menzies, Helgen et al. (2016d), Musser & Carleton (1993, 2005), Musser, Helgen & Lunde (2008), Rimmler (1938).