Microdipodops megacephalus Merriam 1891
Creators: name: Don E. Wilson
name: Thomas E. Lacher, Jr
name: Russell A. Mittermeier
Publisher: name: Lynx Edicions
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Mammalia
Rodentia
Heteromyidae
Microdipodops
Microdipodops megacephalus

description: 45.
Dark Kangaroo Mouse
Microdipodops megacephalus
French: Souris-kangourou foncée / German: Dunkle Kangurumaus / Spanish: Raton canguro oscuro
Other common names: Owyhee River Kangaroo Mouse
Taxonomy. Microdipodops megacephalus Merriam, 1891,
Halleck, Elko 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 2011 study of the phylogeography of M. megacephalus based on sequencing of three mtDNA genes, J. C. Hafner and N. S. Upham determined that there were four phylogenetic groups within the species that appear to represent morphologically cryptic species: Western, Idaho, Central, and Eastern clades. They preferred to delay taxonomic recognition of these clades until further karyological and nuclear sequence data are available. The Western Clade comprises subspecies ambiguus, californicus, medius, and oregonus. This clade grades from the subspecies oregonus (in the north) with the 40-a karyotype (2n = 40, FN = 74) and belly hairs that are gray (plumbeous) at the base, to californicus and medius (in the south) with the 40-f karyotype (2n = 40, FN = 76) and belly hairs that are pure white at the base. In between, appropriately named subspecies ambiguus resembles oregonus in karyotype throughout most ofits distribution, has somewhat intermediate-colored belly hairs (very light gray at the base), and resembles californicus in these characters on southern and eastern fringes. Karyotype of nexus (which is likely extinct) is not known, but specimens have belly hair gray at the base. To the north of that subspecies, the Idaho Clade (subspecies atrirelictus) is the only clade with the 40-B karyotype that has belly hairs gray at the base, and it may extend further south throughout the Nevada part of the Owyhee Basin, approaching the distribution of nexus. The Central Clade (subspecies megacephalus, polionotus, and sabulonis) has the 40-0. karyotype and gray-base belly hairs, whereas the neighboring Eastern Clade (subspecies albiventer, leucotis and paululus) has the 40-f karyotype and white-based belly hairs. In a larger geographical and phyletic sense, the four clades fall into two groups: north-western, including the Western (mostly 40-a karyotypes) and Idaho (40-8 karyotype) clades, and south-eastern, including the Central (40-a karyotypes) and Eastern (40-B karyotype) clades. The subspecies nasutus was placed in synonymy with polionotus in 2006 byJ. C. Hafner and colleagues. Twelve subspecies recognized.
Subspecies and Distribution.
M.m.megacephalusMerriam,1891—WUSA(GreatBasinDesertofCandNENevada).
M.m.albiventerHall&Durrant,1937—WUSA(restrictedtoDesertValley,GreatBasinDesertofSENevada).
M.m.ambiguusHall,1941—WUSA(SmokeCreekandBlackRockdeserts,lowerHum-boldtRiverValley,GreatBasinDesertofNWNevadaandadjacentNECalifornia).
M.m.atrivelictusJ.C.Hafner,1985—WUSA(knownonlyfromGreatBasinDesertofextremeSWIdaho).
M.m.californicusMerriam,1901—WUSA(GreatBasinDesertofWCNevadaandadjacentNECalifornia).
M.m.leucotisHall&Durrant,1941—WUSA(restrictedtoBonnevilleBasin,GreatBasinDesertofNWUtah).
M.m.mediusHall,1941—WUSA(GreatBasinDesertofNWNevada).
M.m.nexusHall,1941—WUSA(GreatBasinDesertofNCNevada),butmaybeextinct.
M.m.oregonusMerriam,1901—WUSA(ColumbiaPlateauofCOregontoGreatBasinDesertofNWNevadaandNECalifornia).
M.m.paululusHall&Durrant,1941—WUSA(Pine,White,andSnakevalleys,GreatBasinDesertofWCUtah).
M.m.polionotusGrinnell,1914—WUSA(MonoLakeBasinandheadofOwensValley,GreatBasinDesertofECalifornia).
M. m. sabulonis Hall, 1941 — W USA (Great Basin Desert of SC Nevada).
Descriptive notes. Head—body mean 66 mm, tail 67-103 mm, ear mean 10 mm, hindfoot 23-26 mm (mean 25 mm); weight 10-17 g. There is no significant secondary sexual dimorphism. Although much has been stated about similarity between kangaroo mice and kangaroo rats (Dipodomys), the Dark Kangaroo Mouse more generally resembles the small silky pocket mice but with gigantic head (result of massively inflated auditory bullae), enlarged hindlegs and hindfeet (soles are densely haired), weak frontlegs, and shorttails that are notstriped, crested, or tufted and are noticeably fatter in the middles. Each ear has a conspicuous light spot. Compared with the Pallid Kangaroo Mouse (M. pallidus), the Dark Kangaroo Mouse is generally darker, with upper parts dark brownish or buffy and an over wash of blackish; post-auricular patch is buffy; ventral pelageis usually gray at base; and tail is blackish distally and tipped in black. It also has a slightly smaller hindfoot (usually less than 25 mm in length) and less inflated auditory bullae. Chromosomal complement has 2n = 40 and FN = 74 or 76.
Habitat. Variety of sandy substrates and floral associations of the Upper Sonoran Life Zone throughout the Great Basin, USA,at elevations of 1190-2318 m. The Dark Kangaroo Mouse is found in shadscale scrub, sagebrush scrub, and alkali-sink plant communities but is usually associated with the sagebrush (Artemisia, Asteraceae) floral community in upper parts of the life zone. Western and Eastern clades are distributed in the general vicinity of the two largest pluvial lakes of the Pleistocene (Lahontan and Bonneville, respectively) and seem to occur primarily in fine sands at somewhat lowelevation habitats. Central and Idaho clades occur at higher elevations in the species’ distribution, typically on sandy soils with a gravel overlay. This represents a broadersoil tolerance that that of the low-elevation, sand-obligate Pallid Kangaroo Mouse, which is found with the Dark Kangaroo Mouse at only 13 localities. Burrows of Dark Kangaroo Mice are simple, short, non-branched tunnels. There is field evidence for burrow seed caches; captive individuals use seed caches, construct elaborate nests, and routinely plugged the burrow entrance with sand.
Food and Feeding. The Dark Kangaroo Mouse is primarily granivorous;it seeks out clumps of seeds instead of harvesting individual seeds but also eats a variety of insects, particularly during summer. While foraging, food is packed into cheek pouches and returned to burrow for eating and storage. One captured specimen had fragments of a long-nosed leopard lizard (Gambelia wislizenii) in its cheek pouches. Foraging kangaroo mice are predominantly quadrupedal, but they are bipedal at higher speeds. As with most arid-adapted heteromyid rodents, the Dark 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 its relatively moist burrow during the day. Contrary to earlier studies, fat stored in the thickened area in the middle of the tail increases prior to winter inactivity, is depleted during winter, and is related to overwinter survival.
Breeding. The Dark Kangaroo Mouse might be polyestrous, with young born in April— September and a peak in May-June. There may be two periods of estrus (April and July). Litter sizes are 2-7 young (mean 4-5). Reproduction is reduced by lack of autumn and winter precipitation and consequent low germination of winter annuals.
Activity patterns. The Dark Kangaroo Mouse is nocturnal, with peak of activity outside the burrow in the first two hours after sunset, then declining to sporadic foraging during the rest of the night and ceasing (in spring and autumn) two hours before sunrise. In summer, there is a second peak of activity just prior to sunrise. 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 Dark Kangaroo Rat is generally inactive aboveground in November-February. Although it may forage intermittently all winter, it enters torpor readily in the laboratory and likely is torpid for lengthy periods during cold months.
Movements, Home range and Social organization. The Dark Kangaroo Mouse is apparently solitary and asocial. In one population studied, male-female sex ratio was 2:1. A small territory was maintained around the burrow, while a larger home range overlapped considerably with those of conspecifics. Home ranges were larger for males (0-07 ha) than for females (0-04 ha). Estimates of densities are not available for this species, 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 successis ¢.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 both species of kangaroo mice declined from an initial 5% to 3% to 1% to 0-4% for a total of 37 mice and an estimated 2-3 ind/ha.
Status and Conservation. Classified as Least Concern on The IUCN Red List. Nevertheless, populations of the Dark Kangaroo Mouse in the northern part of its distribution have suffered severe habitat alteration, fragmentation, and loss due to wild fires and invasive plants, particularly cheat grass (Bromus tectorum, Poaceae) and Russian thistle (Salsola tragus, Amaranthaceae). This habitat destruction has become particularly advanced in the past 30 years. It is likely that many northern populations are already extinct such as the subspecies nexus from north-central Nevada). Livestock grazing and agricultural conversion (especially alfalfa farming) also pose major threats to small, isolated populations of the Dark Kangaroo Mouse. Thus, populations in low elevations (e.g. basins and valleys) face habitat destruction from wild fires, invasive plants, agricultural conversion, and livestock grazing, while those at high elevations and in more northern latitudes suffer loss of sagebrush habitat through those factors and replacement by pinyon-juniper woodland.
Bibliography. Eisenberg (1963), French (1993), Hafner, D.J. & Hafner (1998a), Hafner, D.J. et al. (1979), Hafner, J.C. (1981, 1993), Hafner, J.C. & Upham (2011), Hafner, J.C., Hafner & Hafner (1996), Hafner, J.C., Light et al. (2007), Hafner, J.C., Reddington & Craig (2006), Hall (1941, 1946), Jones (1993), Light et al. (2013), Linzey & NatureServe (Hammerson) (2008h), O'Farrell (1999a), O'Farrell & Blaustein (1974a), Upham & Hafner (2013), Williams et al. (1993).
description: Published as part of Don E. Wilson, Thomas E. Lacher, Jr & Russell A. Mittermeier, 2016, Heteromyidae, pp. 170-233 in Handbook of the Mammals of the World – Volume 6 Lagomorphs and Rodents I, Barcelona :Lynx Edicions on pages 220-222, DOI: 10.5281/zenodo.6611160