Perognathus mollipilosus, Coues, 1875

Don E. Wilson, Thomas E. Lacher, Jr & Russell A. Mittermeier, 2016, Heteromyidae, Handbook of the Mammals of the World – Volume 6 Lagomorphs and Rodents I, Barcelona: Lynx Edicions, pp. 170-233 : 208

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Great Basin Pocket Mouse

Perognathus mollipilosus

French: Souris-a-abajoues de Coues / German: Great-Basin-Seidentaschenmaus / Spanish: Raton de abazones de la Gran Cuenca

Taxonomy. Perognathus mollipilosus Coues, 1875 ,

Fort Crook [about 2 mi NE of Burgettville], Shasta Co., California.

Based on detailed sequencing of nDNA and mtDNA genes, P. mollipilosus is a member of the parvus species group of silky pocket mice, along with P. alticola and P. parvus , and is sister-taxon to P. alticola , which may be only a subspecies ofthis species. Recent genetic studies revealed that P. mollipilosus 1s specifically distinct from P. parvus in which it had long been included; the two diverged an estimated eleven million years ago. The two species are known to co-occur at only one locality in northcentral Oregon. The species identity of subspecies on the central and eastern Snake River Plain (clarus and idahoensis) and north into south-western Montana is not yet fully established. They are included within P. mollipilosus here based on the karyotype of a population of clarus in north-eastern Utah and sequence data for a population of clarus in south-eastern Wyoming. It is equally possible that populations of the Snake River Plain and north into Montana (including the northern two-thirds of clarus) belong instead to P. parvus . Compared with the geographically nearest species, P. longimembris , P. mollipilosus is distinguished by its much larger size, lobed antitragus, and longer, darker hairs forming a slight crest on the distal part of tail. It was included as a subspecies of P. parvus until 2014. Seven subspecies recognized.

Subspecies and Distribution.

P.m.mollipilosusCoues,1875—WUSA(SCOregonWoftheColumbiaRiverandNECalifornia).

P.m.bullatusDurrant&Lee,1956—SWUSA(restricteddistributioninSEUtah).

P.m.clarusGoldman,1917—WUSA(SWMontana,SEIdaho,NEUtah,andSWWyoming).

P.m.idahoensisGoldman,1922—WUSA(KingsBowlandWapilavafields,SnakeRiverPlainofSCIdaho).

P.m.olivaceusMerriam,1889—WUSA(GreatBasininSCIdaho,Nevada,WUtah,andSECalifornia).

P.m.trumbullensisBenson,1937—SWUSA(SWUtahandNWArizona).

P. m. xanthanotus Grinnell, 1912 — SW USA (restricted distribution on the Mojave Desert slope of the Tehachapi Mts, S California).

Descriptive notes. There are no specific measurements available. Principal component analysis of external and cranial characters shows extensive overlap between the Great Basin Pocket Mouse and the Columbia Plateau Pocket Mouse (PF. parvus ), and the other memberof the parvus species group, the White-eared Pocket Mouse (PF. alticola ). Discriminant function analysis of external and cranial measurements was able to correctly distinguish all specimens of the White-eared Pocket Mouse, which is smaller overall with a wider skull, but was able to correctly assign only 86% of specimens of the other two species. Based on that analysis, the Great Basin Pocket Mouseis slightly larger than the Columbia Plateau Pocket Mouse in external measurements except tail length and has a slightly wider skull. In the combined external measurements for these two species, males are significantly larger than females; head—body mean 84 mm (males) and 78 mm (females), tail mean 95 mm (males) and 86 mm (females), ear mean 9 mm, hindfoot mean 24 mm (males) and 22 mm (females); weight 17-31 g. Pelage of both species is soft and fine, with no hint of spines orstiff bristles; posterior one-half of sole of hindfoot has a sparse covering of short hairs; and tail is short and not tufted. Unlike most other silky pocket mice, the Great Basin Pocket Mouse has lobed antitragus of ear pinna, and tail is slightly crested for distal one-third (with dark hairs). The Great Basin Pocket Mouse is the largestsized species of the genus. Hairs on inner surfaces of ear pinna are white or yellowish. Dorsal pelage is ocherous buff, overlain with blackish hair; lateral line is usually faint; and under parts are white. Tail is the same length or slightly longer than head-body length and bicolored. Chromosomal complement has 2n = 54 and FN = 70-76.

Habitat. Arid or semiarid situations on more or less sandy ground where sagebrush ( Artemisia tridentata, Asteraceae ) dominates and shrub-steppe habitat of open pinyon ( Pinus , Pinaceae )—juniper ( Juniperus , Cupressaceae ) woodland, saltbush ( Atriplex , Amaranthaceae ), and greasewood ( Sarcobatus , Sarcobataceae ). The Great Basin Pocket Mouse occupies nearly the entire Great Basin, and extends up central Oregon to the Columbia River. It has at least one isolated relict population in the Transverse Range of southern California (xanthonotus); isolated populations of the White-eared Pocket Mouse in the same area may represent a disjunct subspecies of the Great Basin Pocket Mouse. Burrows typically are constructed at bases of shrubs and include a permanent burrow with a nest chamber and more simple escape or refuge burrows with multiple entrances. Entrance to permanent burrow is plugged during the day.

Food and Feeding. Diet of the Great Basin Pocket Mouse consists largely of seeds of shrubs, annuals, and grasses, butit also includes smaller amounts of green vegetation and insects; insects are eaten more commonly in the spring before grass seeds ripen. Food items are collected in external, furlined cheek pouches and transported back to burrows, where they are stored in burrow caches. As in other heteromyids, the volume of seeds jammed into the cheek pouches is equivalent to the daily energy requirement. The Great Basin Pocket Mouse does not need to drink water, subsisting entirely on water from its food and water produced as a byproduct of metabolism.

Breeding. Breeding season of the Great Basin Pocket Mouse begins in April-May and extends into autumn. Females have 1-2, rarely three, litters per year, except in dry years when one or no litters are produced. Number of littersis correlated closely with precipitation and production of winter annuals. If precipitation is adequate, juveniles born early in the breeding season may produce a litter in autumn of the same year. Gestation is 21-28 days, and mean litter sizes are 4-5 young (range 2-8).

Activity patterns. The Great Basin Pocket Mouse is nocturnal and terrestrial, and like others in the genus, it enters torpor for various periods in all seasons, particularly winter. Torpor may result from cold temperatures or low foraging success. During longer periods of winter torpor, individuals wake periodically to eat from seed caches.

Movements, Home range and Social organization. The Great Basin Pocket Mouse appears to be asocial. In paired encounters in the laboratory, it was agonistic and dominant over kangaroo mice ( Microdipodops ), the Little Pocket Mouse ( P. longimembris ), and the North American Deermouse (Peromyscus maniculatus). Estimates of home ranges vary widely (0-01-4 ha), but male home ranges appear to be larger than those of females. Studies disagree on the extent of overlapping of home ranges. Estimates of density average 28-5 ind/ha, but it may be greater than 80 ind/ha during years with precipitation is above average. The Great Basin Pocket Mouse frequently is numerically dominant in small mammal communities of the Great Basin.

Status and Conservation. The Great Basin Pocket Mouse has not been assessed on The IUCN Red List.

Bibliography. Aquino & Neiswenter (2014), Kirkland (1999), Linzey & NatureServe (Hammerson) (2008l), Riddle et al. (2014), Verts & Kirkland (1988), Williams (1978a), Williams et al. (1993).

Figures

1. Salvin’s Spiny Pocket Mouse (Heteromys salvini), 2. Panamanian Spiny Pocket Mouse (Heteromys adspersus), 3. Mexican Spiny Pocket Mouse (Heteromys irroratus), 4. Jaliscan Spiny Pocket Mouse (Heteromys spectabilis), 5. Painted Spiny Pocket Mouse (Heteromys pictus), 6. Nelson's Spiny Pocket Mouse (Heteromys nelsoni), 7. Trinidad Spiny Pocket Mouse (Heteromys anomalus), 8. Overlook Spiny Pocket Mouse (Heteromys catopterius), 9. Paraguana Spiny Pocket Mouse (Heteromys oasicus), 10. Southern Spiny Pocket Mouse (Heteromys australis), 11. Ecuadorean Spiny Pocket Mouse (Heteromys teleus), 12. Gaumer’s Spiny Pocket Mouse (Heteromys gaumeri), 13. Desmarest’s Spiny Pocket Mouse (Heteromys desmarestianus), 14. Goldman’s Spiny Pocket Mouse (Heteromys goldmani), 15. Cloud-dwelling Spiny Pocket Mouse (Heteromys nubicolens), 16. Mountain Spiny Pocket Mouse (Heteromys oresterus)

Subspecies and Distribution. P.m.mollipilosusCoues,1875—WUSA(SCOregonWoftheColumbiaRiverandNECalifornia). P.m.bullatusDurrant&Lee,1956—SWUSA(restricteddistributioninSEUtah). P.m.clarusGoldman,1917—WUSA(SWMontana,SEIdaho,NEUtah,andSWWyoming). P.m.idahoensisGoldman,1922—WUSA(KingsBowlandWapilavafields,SnakeRiverPlainofSCIdaho). P.m.olivaceusMerriam,1889—WUSA(GreatBasininSCIdaho,Nevada,WUtah,andSECalifornia). P.m.trumbullensisBenson,1937—SWUSA(SWUtahandNWArizona). P. m. xanthanotus Grinnell, 1912 — SW USA (restricted distribution on the Mojave Desert slope of the Tehachapi Mts, S California).