Microdipodops pallidus, Merriam, 1901

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 : 222

46.

Pallid Kangaroo Mouse

Microdipodops pallidus

French: Souris-kangourou pale / German: Fahle Kangurumaus / Spanish: Raton canguro pélido

Other common names: Pale Kangaroo Mouse, Soda Spring Valley Kangaroo Mouse

Taxonomy. Microdipodops pallidus Merriam, 1901 ,

Mountain Well, Churchill Co., Nevada, USA.

Prior to 1979, the two recognized species of kangaroo mice were considered to be semi-species (in the process of diverging) based on morphological studies of the two in sympatry. Karyotypic and protein studies confirmed their full species status, and further mtDNA sequencing studies revealed that the two represent rather ancient lineages, diverging an estimated 8-1 million years ago. In their 2008 study of the phylogeography of M. pallidus based on sequencing of three mtDNA genes, J. C. Hafner and his colleagues determined that there were two major phylogroups within the species that appear to represent morphologically cryptic species: Western and Eastern clades. They preferred to delay taxonomic recognition of these clades until further karyological and nuclear sequence data are available. The Western Clade is composed of the subspecies pallidus and restrictus. Most ofthis clade has a 42-a karyotype (2n =42, FN = 70), except that populations on the north-western periphery of the species (on the southern end of Pyramid Lake) have a 42-y karyotype (2n = 42, FN = of 80) that is most similar to the 42-a karyotype (based mostly on small autosomes and autosomal marker chromosomes). Western Clade exhibitslittle geographical overlap with the distribution of M. megacephalus , occurring between Western and Central clades of that species. The Eastern Clade (subspecies ammophilus, purus, and ruficollaris) has the 42-8 karyotype (2n = 42, FN = 80), distinguished from both the 42-a and 42-y karyotypes on the basis of the two pairs of marker autosomes and the five smallest pairs of non-marker autosomes. The Eastern Clade geographically overlaps almost completely with the Central Clade of M. megacephalus . Border between the two clades of M. pallidus is closely coincident with the western margin of the main distribution of the Central Clade of M. megacephalus . Five subspecies recognized.

Subspecies and Distribution.

M.p.pallidusMerriam,1901—WUSA(lowerelevationGreatBasinofWNevadaandadisjunctpopulationinDeepSpringsValley,ECalifornia).

M.p.ammophilusHall,1941—WUSA(RailroadValley,GreatBasinofENevada).

M.p.purusHall,1941-WUSA(EmigrantandDesertvalleys,GreatBasinofSENevada).

M.p.restrictusJ.C.Hafner,1985—WUSA(knownonlyfromthetypelocalityattheSendofRhodesSaltMarshinSodaSpringsValley,WNevada).

M. p. ruficollaris Hall, 1941 — W USA (Great Basin of SC Nevada).

Descriptive notes. Head-body mean 66 mm, tail 74-99 mm, ear mean 10 mm, hindfoot 24-27 mm (mean 26 mm); weight 10-17 g. The Pallid Kangaroo Mouse has no significant secondary sexual dimorphism. Although much has been stated about the similarity between kangaroo mice and kangaroo rats, they more generally resemble small silky pocket mice but with a gigantic head (result of massively inflated auditory bullae), enlarged hindlegs and hindfeet (soles are densely haired), weak frontlegs, and a short tail that is not striped, crested, or tufted and is noticeably fatter in middle. Each ear has a conspicuous light spot. Compared with the Dark Kangaroo Mouse ( M. megacephalus ), the Pallid Kangaroo Mouseis lighter in color, with upper parts light pinkish cinnamon with a light overwash of buffy or blackish; post-auricular patch is pure white; ventral pelage is usually white at the base; and tail is the same color as dorsum and lacking black tip. It also hasa slightly longer hindfoot (usually more than 25 mm in length) and more-inflated auditory bullae. Chromosomal complement has 2n = 42 and FN = 70 or 80.

Habitat. Restricted to fine, loose, sandy soils with little or no gravel overlay in lower parts of the Upper Sonoran Life Zone of the south-western Great Basin. The Pallid Kangaroo Mouse occurs at elevations of1190-1830 m, usually below the sagebrush ( Artemisia , Asteraceae ) community, often associated with greasewood ( Sarcobatus , Sarcobataceae ) and saltbush ( Atriplex , Amaranthaceae ). The Western Clade inhabits the lowest elevation basins of the western Great Basin, whereas the Eastern Clade occurs at high elevations, geographically overlapping with the Central Clade of the Dark Kangaroo Mouse. The more ecologically restricted Pallid Kangaroo Mouse co-occurs with the Dark Kangaroo Mouse at only 13 localities. Burrows of Pallid Kangaroo Mice are simple, short, non-branched tunnels; no seed caches or nests were found in excavated burrows. Captive individuals have little tendency to build a nest, and they routinely plugged the burrow entrance with sand.

Food and Feeding. The Pallid Kangaroo Mouse is primarily granivorous and seeks out clumps of seeds instead of harvesting individual seeds; it also eats a variety of insects, particularly in summer. While foraging, food is packed into cheek pouches and returned to the burrow for eating and storage. One captured individual had a small centipede (Myriapoda) in its cheek pouch. Foraging kangaroo mice are predominantly quadrupedal, but at higher speeds, they are bipedal. As with most arid-adapted heteromyid rodents, the Pallid Kangaroo Mouse does not need to drink water and relies on metabolic water and moisture in food and conserves water by being active at night and retreating to the relatively moist burrow during the day. Contrary to earlier studies, fat stored in the thickened area in the middle ofthe tail increases prior to winter inactivity, is depleted during winter, and is related to overwinter survival.

Breeding. The Pallid Kangaroo Mouse probably is polyestrous, with young being born in March-September. Litter sizes are 2-6 young (mean 3-5). Reproduction is reduced by lack of autumn and winter precipitation and consequent low germination of winter annuals.

Activity patterns. The Pallid Kangaroo Mouse is nocturnal, with peak of activity outside of the burrow occurring within the first two hours after sunset and then declining to sporadic foraging during the rest of the night. Low temperatures and rain inhibit activity. Avoidance of moonlight was reported at one site, but a more comprehensive study throughout the distribution of the genus showed no significant moonlight avoidance. Instead, kangaroo mice may be active on moonlit nights to take advantage of absence of larger, more dominant kangaroo rats, which avoid moonlight. The Pallid Kangaroo Mouse is generally inactive aboveground in November—February. Although the Pallid Kangaroo Rat may forage intermittently all winter,it enters torpor readily in the laboratory and likely is torpid for lengthy periods during colder months.

Movements, Home range and Social organization. The Pallid Kangaroo Mouseis probably solitary and asocial, like the Dark Kangaroo Mouse, which maintains a small territory around its burrow but a larger home range that overlaps considerably with those of conspecifics. Estimates of density are not available for the Pallid Kangaroo Mouse, but trap success is usually an order of magnitude less than that of the most common species in the same community (usually a kangaroo rat). Trap success is ¢.5% for each species in allopatry (average of 5-2% for the genus throughout the Great Basin) and for the genus in sympatry (5-2% and 5-3% for the two sites studied), suggesting that there may be a maximum environmental density for the genus. During four successive days of removal trapping on a plot of c.16 ha, trap success for kangaroo mice of both species declined from an initial 5% to 3% to 1% to 0-4% for a total of 37 mice for an estimated 2-3 ind/ha.

Status and Conservation. Classified as Least Concern on The IUCN Red List. Nevertheless, populations of the Pallid Kangaroo Mouse are likely already extinct at its type locality and at several other historical sites. Small, isolated populations face habitat alteration, fragmentation, and destruction from wild fires and invasive plants, but even more so from agricultural conversion and livestock grazing.

Bibliography. Eisenberg (1963), French (1993), Hafner, D.J. & Hafner (1998b), Hafner, D.J. et al. (1979), Hafner, J.C. (1981, 1993), Hafner, J.C., Hafner & Hafner (1996), Hafner, J.C., Light et al. (2007), Hafner, J.C., Upham et al. (2008), Hall (1941, 1946), Jones (1993), Light et al. (2013), Linzey & NatureServe (Hammerson & Morefield) (2008), O'Farrell (1999b), O'Farrell & Blaustein (1974b), Upham & Hafner (2013), Williams et al. (1993).

Figures

45. Dark Kangaroo Mouse (Microdipodops megacephalus), 46. Pallid Kangaroo Mouse (Microdipodops pallidus), 47. Desert Kangaroo Rat (Dipodomys deserti), 48. Banner-tailed Kangaroo Rat (Dipodomys spectabilis), 49. Nelson’s Kangaroo Rat (Dipodomys nelsoni), 50. Texas Kangaroo Rat (Dipodomys elator), 51. Plateau Kangaroo Rat (Dipodomys ornatus), 52. Phillips’s Kangaroo Rat (Dipodomys phillipsu), 53. San Quintin Kangaroo Rat (Dipodomys gravipes), 54. Merriam’s. 9 Kangaroo Rat. Dipodomys merriami (null), 55. Ord’s Kangaroo Rat (Dipodomys ordu), 56. Gulf Coast Kangaroo Rat (Dipodomys compactus), 57. California Kangaroo Rat (Dipodomys californicus), 58. Narrow-faced Kangaroo Rat (Dipodomys venustus), 59. Agile Kangaroo Rat (Dipodomys agilis), 60. Dulzura Kangaroo Rat (Dipodomys simulans), 61. Giant Kangaroo Rat (Dipodomys ingens), 62. Chisel-toothed Kangaroo Rat (Dipodomys microps), 63. San Joaquin Kangaroo Rat (Dipodomys nitratoides), 64. Stephens’s Kangaroo Rat (Dipodomys stephenst), 65. Heermann' ’ s Kangaroo Rat (Dipodomys heermanni), 66. Panamint Kangaroo Rat (Dipodomys panamintinus)

Subspecies and Distribution. M.p.pallidusMerriam,1901—WUSA(lowerelevationGreatBasinofWNevadaandadisjunctpopulationinDeepSpringsValley,ECalifornia). M.p.ammophilusHall,1941—WUSA(RailroadValley,GreatBasinofENevada). M.p.purusHall,1941-WUSA(EmigrantandDesertvalleys,GreatBasinofSENevada). M.p.restrictusJ.C.Hafner,1985—WUSA(knownonlyfromthetypelocalityattheSendofRhodesSaltMarshinSodaSpringsValley,WNevada). M. p. ruficollaris Hall, 1941 — W USA (Great Basin of SC Nevada).