Penognathus longimembris (Caues, 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 : 202-203

17.

Little Pocket Mouse

Penognathus longimembris

French: Petite Souris-a-abajoues / German: Kleine Seidentaschenmaus / Spanish: Raton de abazones pequerio

Other common names: Los Angeles Little Pocket Mouse, Los Angeles Pocket Mouse

Taxonomy. Olognosis longimembris Coues, 1875 ,

Old Fort Tejon, Tehachapi Mountains, Kern Co., California, USA.

Based on detailed sequencing of nDNA and mtDNA genes, P. longimembris is a member of the longimembris species group ofsilky pocket mice along with P. inornatus and P. amplus . There has been a history of confusion about relationships and distributions of this species and P. inornatus . For example, P. inornatus subspecies psammophilus was previously allocated to P. longimembris , and P. longimembris subspecies longimembris was depicted as occurring along the western side of the San Joaquin Valley. Type locality of P. longimembris (at which no silky pocket mice have been collected in well over a century) is in a position where either species might occur or have occurred. Preliminary karyotypic, molecular, and morphometric analyses indicate that all populations of silky pocket mice from north of the Transverse Ranges are P. inornatus , as are populations in the extreme north-western corner of the Mojave Desert. The two species appear to be sympatric over ¢.50 km near the junction of Kern, Los Angeles, and San Bernardino counties. Molecular analyses have revealed 2-3 major clades within P. longimembris that are paraphyletic relative to P. inornatus . Separate clades representing the geographically restricted subspecies virginis (which was synonymized under arizonensis based on morphological similarity) and arizonensis are basal to the lineage containing all remaining subspecies of P. longimembris and P. inornatus . Sixteen subspecies recognized.

Subspecies and Distribution.

P. l. longimembris Coues, 1875 — SW USA (Mojave Desert and Transverse Ranges, SW California).

P. l. aestivus Huey, 1928 — NW Mexico (W base Sierra Juarez to Valle de la Trinidad, N Baja California).

P.l. arizonensis Goldman, 1931 — SW USA (SC Utah and NC Arizona to SE Nevada).

P. l.bangsi Mearns, 1898 — SW USA (W Colorado Desert of S California).

P. l. bombycinus Osgood, 1907 — SW USA and NW Mexico (lower Colorado River Valley of SE California, SW Arizona, NE Baja California, and NW Sonora).

P. l. brevinasus Osgood, 1900 — SW USA (arid coastal basins of SW California).

P. l. gulosus Hall, 1941 — W USA (along the W margin of former Pleistocene Lake Bonneville in the Great Basin of E Nevada and W Utah).

P. l. internationalis Huey, 1939 — SW USA and NW Mexico (SC California and adjacent NC Baja California).

P. l. kinoensis Huey, 1935 — NW Mexico (disjunct and geographically restricted population along Bahia Kino, W Sonora), but may be extinct.

P. l. nevadensis Merriam, 1894 — W USA (Great Basin of SE Oregon, NE California, and NC Nevada).

P. l. pacificus Mearns, 1898 — SW USA (coastal plains of SW California to the USA-Mexico border).

P. I. panamintinus Merriam, 1894 — SW USA (Great Basin of W Nevada and SE California).

P. l. pimensis Huey, 1937 — SW USA (disjunct distribution in SC Arizona).

P. l. salinensis Bole, 1937 — SW USA (restricted distribution in the Salinas Valley of SE California).

P. l. tularensis Richardson, 1937 — SW USA (restricted distribution in the upper valley of the Kern River, SC California).

P. l. venustus Huey, 1930 — NW Mexico (known only from the type locality of San Agustin, NC Baja California).

Descriptive notes. Head-body mean 58 mm, tail mean 74 mm, ear mean 7 mm, hindfoot mean 19; weight 7-12 g. There is no significant secondary sexual dimorphism. Pelage ofthe Little Pocket Mouse is soft and fine, with no hint of spines or stiff bristles; posterior one-half of sole of hindfoot has a sparse covering of short hairs; and tail is short and not tufted. The Little Pocket Mouse has short, rounded ears without lobed antitragus. It is small-sized for the genus. Dorsal pelage is pinkish buff to ocherous buff, overlaid with blackish hairs. The Little Pocket Mouse has an indistinct buffy postauricular patch, pale yellowish lateral line, and white under parts. Tail is longer than head-body length and nearly unicolored. Chromosomal complement has 2n = 56 and FN = 82-88. The Little Pocket Mouse is smaller, with relatively longer tail, than the San Joaquin Pocket Mouse ( P. inornatus ), and is smaller than the Arizona Pocket Mouse ( P. amplus ).

Habitat. Open desert dominated by creosote bush ( Larrea , Zygophyllaceae ), rabbitbrush ( Chrysothamnus , Asteraceae ) and sagebrush ( Artemisia , Asteraceae ), and arid open grassland, shrub-steppe, and coastal sage habitats in the Colorado, Mojave, and Great Basin deserts. The Little Pocket Mouse lives on sandy and gravelly soils, often in terrain that is rolling or broken by ravines and rocks.

Food and Feeding. Diet of the Little Pocket Mouse consists largely of seeds of shrubs, annuals, and grasses, but it also includes smaller amounts of green vegetation and insects. It prefers smaller seeds, such as the minute seeds of grasses. Food items are collected in external, furlined cheek pouches and transported back to burrows, where they are stored in burrow caches. Like all small species of silky pocket mice, it tends to husk seeds or separate seeds from seed-heads before stuffing them in its cheek pouches. The Little Pocket Mouse does not need to drink water, subsisting entirely on water from its food and water produced as a byproduct of metabolism.

Breeding. The Little Pocket Mouse begins breeding soon after it emerges from winter dormancy, usually producing a single litter averaging 3-3 young (range 2-6). In drought years, when few annuals germinate, it may not breed; when productivity is high, females may produce multiple litters, and young-of-the-year may breed later in the same season.

Activity patterns. The Little Pocket Mouse is nocturnal and terrestrial, spending the day belowground in its burrow and foraging on the surface at night. It appears to enter torporfor varying periods in response to cold surface temperatures or low food supply, and it may be absent from the surface for up to nine months of the year.

Movements, Home range and Social organization. There is no specific information available for this species, but the Little Pocket Mouse is often extremely abundant.

Status and Conservation. Classified as Least Concern on The IUCN Red List. Efforts to capture specimens of the disjunct subspecies along the margin of Bahia Kino (kinoensis) at the only known locality were unsuccessful. Most of the narrow (0-25 x 3 km) sandy peninsula on which they were previously found has been developed for homes. Traps placed on a small remaining patch ofrelatively undisturbed dunes on a Mexican naval base yielded only numerous darkling beetles (Eleodes); numerous tracks and scat of feral cats (Felis catus) were evident in the sand. This disjunct subspecies of the Little Pocket Mouse may be extinct.

Bibliography. Alvarez-Castafieda et al. (2001), Aquino & Neiswenter (2014), Best (1993a), French (1999), Hoffmeister (1986), Linzey (2008a), McKnight (1995, 2005), Patton & Alvarez-Castafeda (1999), Williams (1978a), Williams et al. (1993).

Figures

Subspecies and Distribution. P. l. longimembris Coues, 1875 — SW USA (Mojave Desert and Transverse Ranges, SW California). P. l. aestivus Huey, 1928 — NW Mexico (W base Sierra Juarez to Valle de la Trinidad, N Baja California). P.l. arizonensis Goldman, 1931 — SW USA (SC Utah and NC Arizona to SE Nevada). P. l.bangsi Mearns, 1898 — SW USA (W Colorado Desert of S California). P. l. bombycinus Osgood, 1907 — SW USA and NW Mexico (lower Colorado River Valley of SE California, SW Arizona, NE Baja California, and NW Sonora). P. l. brevinasus Osgood, 1900 — SW USA (arid coastal basins of SW California). P. l. gulosus Hall, 1941 — W USA (along the W margin of former Pleistocene Lake Bonneville in the Great Basin of E Nevada and W Utah). P. l. internationalis Huey, 1939 — SW USA and NW Mexico (SC California and adjacent NC Baja California). P. l. kinoensis Huey, 1935 — NW Mexico (disjunct and geographically restricted population along Bahia Kino, W Sonora), but may be extinct. P. l. nevadensis Merriam, 1894 — W USA (Great Basin of SE Oregon, NE California, and NC Nevada). P. l. pacificus Mearns, 1898 — SW USA (coastal plains of SW California to the USA-Mexico border). P. I. panamintinus Merriam, 1894 — SW USA (Great Basin of W Nevada and SE California). P. l. pimensis Huey, 1937 — SW USA (disjunct distribution in SC Arizona). P. l. salinensis Bole, 1937 — SW USA (restricted distribution in the Salinas Valley of SE California). P. l. tularensis Richardson, 1937 — SW USA (restricted distribution in the upper valley of the Kern River, SC California). P. l. venustus Huey, 1930 — NW Mexico (known only from the type locality of San Agustin, NC Baja California).