Chaetodipus spinatus (Merriam, 1889)

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 : 213

31.

Spiny Pocket Mouse

Chaetodipus spinatus

French: Souris-a-abajoues épineuse / German: Stachel-Rauhaartaschenmaus / Spanish: Raton de abazones espinoso

Taxonomy. Perognathus spinatus Merriam, 1889 ,

“Lower Colorado River, California, 25 miles below [S] the Needles,” San Bernardino Co., California, USA.

Based on detailed sequencing of nDNA and mtDNA genes, C. spinatus is the basal member of the Baja California Peninsula lineage of the “modern” clade of coarsehaired pocket mice. In addition to this species, the clade includes two closely related, chaparral-adapted coarse-haired species ( C. californicus and C. fallax ) and three closely related, sand-obligate smooth-haired species (C. ammophilus, C. arenarius , and C. siccus ). Analysis of geographical variation in mtDNA throughoutthe distribution of C. spinatus , including eleven of the 13 known island populations (excluding evermanni on Mejia Island and guardiae on Isla Angel de la Guarda), revealed only three clades: a basal clade of occultus from Isla del Carmen; the Cape Region subspecies peninsulae and lamb: of Espiritu Santo Island; and all other peninsular and insular populations sampled, at least to south-eastern California, including the nominate subspecies. Based on the very low levels of genetic divergence indicated between and within the three clades, a subspecific revision would likely result in recognition of only three subspecies: occultus, peninsulae, and spinatus .

Eighteen subspecies recognized.

Subspecies and Distribution.

C.s.spinatusMerriam,1889—SWUSAandNWMexico(SNevada,SECalifornia,andNEBajaCalifornia).

C.s.broccusHuey,1960—NWMexico(N&CBajaCaliforniaSur).

C.s.bryantiMerriam,1894—NWMexico(SanJoséI,GulfofCalifornia,BajaCali-forniaSur).

C.s.evermanniNelson&Goldman,1929—NWMexico(MejiaI,GulfofCalifornia,BajaCalifornia).

C.s.guardiaeBurt,1932—NWMexico(IAngeldelaGuarda,GulfofCalifornia,BajaCalifornia).

C.s.lambiBenson,1930—NWMexico(EspirituSantoI,GulfofCalifornia,BajaCalifornia).

C.s.latijugularisBurt,1932—NWMexico(SanFranciscoI,GulfofCalifornia,BajaCaliforniaSur).

C.s.lorenziBanks,1967—NWMexico(SanLorenzoNorte[=LasAnimas]andSanLorenzoSurIs,GulfofCalifornia,BajaCalifornia).

C.s.macrosensisBurt,1932—NWMexico(SanMarcosI,GulfofCalifornia,BajaCali-forniaSur).

C.s.magdalenaeOsgood,1907—NWMexico(MagdalenaI,PacificOcean,BajaCali-forniaSur).

C.s.margaritaeMerriam,1894—NWMexico(SantaMargaritaI,PacificOcean,BajaCaliforniaSur).

C.s.occultusNelson,1912—NWMexico(IdelCarmen,GulfofCalifornia,BajaCali-forniaSur).

C.s.oribatesHuey,1960—NWMexico(NCBajaCalifornia).

C.s.peninsulaeMerriam,1894—NWMexico(SBajaCaliforniaSur).

C.s.prietaeHuey,1930—NWMexico(SEBajaCalifornia).

C.s.pullusBurt,1932—NWMexico(CoronadoI,GulfofCalifornia,BajaCaliforniaSur).

C.s.rufescensHuey,1930—SWUSA(SCCalifornia).

C. s. seorsus Burt, 1932 — NW Mexico (I Danzante, Gulf of California, Baja California Sur).

Descriptive notes. Head—body 75-95 mm, tail 89-128 mm, ear mean 10 mm, hindfoot mean 24 mm; weight 13-18 g. There is no significant secondary sexual dimorphism.

The Spiny Pocket Mouse is coarse-haired and medium-sized for the genus, with crested and tufted tail that is longer than head-body length and bicolored. Pelage is quite hispid, with numerous large and conspicuous spines on rump, scattered on flanks, and often extending to shoulders. Dorsal pelage is drab grayish brown, with no lateral stripe, and under parts are buffy white. Chromosomal complement has 2n = 44 and FN = 54. The Spiny Pocket Mouse ranges throughout the Peninsular Desert of the Baja California peninsula, north along interior margins of Peninsular Ranges of south-western California and along the lower canyon of the Colorado River north into southern Nevada. It is found variously along with six other species of the genus. Only the two chaparral-associated forms (the California Pocket Mouse, C. californicus , and the San Diego Pocket Mouse, C. fallax ) have rump spines, but they are not nearly as numerous as in the Spiny Pocket Mouse, and they also have clearly defined lateral stripes. The other species lack rump spines: the Long-tailed Pocket Mouse (C. formosus ), which occursin gravelly and also sandy soils; the Peninsular Pocket Mouse ( C. rudinoris ), which favors more open areas of pebbly soils that mark transitions from sandy flats to rocky alluvial slopes or “bajadas”; and two sand obligates, the Little Desert Pocket Mouse ( C. arenarius ) and the Desert Pocket Mouse ( C. penicillatus ).

Habitat. Rocky and gravelly soils and rocky slopes and arroyos up to elevations of c.900 m. Desert vegetation in these areas is sparsely distributed xerophilous shrubs. The Spiny Pocket Mouseis rarely captured in the same trap line as another saxicolous, coarse-haired species, and only narrowly overlaps in distribution with the San Diego Pocket Mouse, which has a similar habitat. Burrows are inconspicuous and are usually located near or under rocks. Presence of the Spiny Pocket Mouse on numerousislands in the Gulf of California and off of the Pacific coast attests to its ability to invade and survive on islands with often-hostile arid and rocky environments. Although pelage color of the Spiny Pocket Mouse varies geographically, the population on one of these islands (guardiae on Isla Angel de la Guarda) is polymorphic, with one pelage color a yellowish agouti and the other a grizzled gray. Only yellowish agouti specimens were captured in 1932, whereas in 1981 both colors were captured, perhaps indicating a secondary dispersal from the mainland.

Food and Feeding. Diet of the Spiny Pocket Mouse consists largely of seeds of shrubs, annuals, and grasses, but it also includes smaller amounts of green vegetation and insects. Food items are collected in external, fur-lined cheek pouches and transported back to burrows, where they are stored in burrow caches. It does not need to drink water, subsisting entirely on water from its food and water produced as a byproduct of metabolism.

Breeding. Female Spiny Pocket Mice have been reported with embryos and placental scars in April, August, and October. Averagelitter size is five young (range 4-5).

Activity patterns. The Spiny Pocket Mouse is nocturnal and terrestrial, and it is probably active throughout the year, although it likely is torpid during particularly cold nights or when food is scarce.

Movements, Home range and Social organization. There is no information is available for this species.

Status and Conservation. Classified as Least Concern on The IUCN Red List. Some populations on islands are likely threatened by predation and extirpation by feral cats (Felis catus).

Bibliography. Alvarez-Castafieda & Murphy (2014), Aquino & Neiswenter (2014), Best (1993a), Ceballos & Oliva (2005), Lackey (1991b, 1999), Linzey, Timm, Alvarez-Castafieda, Castro-Arellano & Lacher (2008r), Williams et al. (1993).

Figures

27. Hispid Pocket Mouse (Chaetodipus hispidus), 28. Long-tailed Pocket Mouse (Chacetodipus formosus), 29. Bailey's Pocket Mouse (Chaetodipus bailey), 30. Peninsular Pocket Mouse (Chaetodipus rudinoris), 31. Spiny Pocket Mouse (Chaetodipus spinatus), 32. California Pocket Mouse (Chaetodipus californicus), 33. San Diego Pocket Mouse (Chaetodipus fallax), 34. Little Desert Pocket Mouse (Chaetodipus arenarius), 35. Dalquest’s Pocket Mouse (Chaetodipus ammophilus), 36. Cerralvo Island Pocket Mouse (Chaetodipus siccus), 37. Desert Pocket Mouse (Chaetodipus penicillatus), 38. Chihuahuan Desert Pocket Mouse (Chaetodipus eremicus), 39. Sinaloan Pocket Mouse (Chaetodipus pernix), 40. Rock Pocket Mouse (Chaetodipus intermedius), 41. Nelson’s Pocket Mouse (Chaetodipus nelsoni), 42. Lined Pocket Mouse (Chaetodipus lineatus), 43. Goldman’s Pocket Mouse (Chaetodipus goldmani), 44. Narrow-skulled Pocket Mouse (Chaetodipus artus)

Subspecies and Distribution. C.s.spinatusMerriam,1889—SWUSAandNWMexico(SNevada,SECalifornia,andNEBajaCalifornia). C.s.broccusHuey,1960—NWMexico(N&CBajaCaliforniaSur). C.s.bryantiMerriam,1894—NWMexico(SanJoséI,GulfofCalifornia,BajaCali-forniaSur). C.s.evermanniNelson&Goldman,1929—NWMexico(MejiaI,GulfofCalifornia,BajaCalifornia). C.s.guardiaeBurt,1932—NWMexico(IAngeldelaGuarda,GulfofCalifornia,BajaCalifornia). C.s.lambiBenson,1930—NWMexico(EspirituSantoI,GulfofCalifornia,BajaCalifornia). C.s.latijugularisBurt,1932—NWMexico(SanFranciscoI,GulfofCalifornia,BajaCaliforniaSur). C.s.lorenziBanks,1967—NWMexico(SanLorenzoNorte[=LasAnimas]andSanLorenzoSurIs,GulfofCalifornia,BajaCalifornia). C.s.macrosensisBurt,1932—NWMexico(SanMarcosI,GulfofCalifornia,BajaCali-forniaSur). C.s.magdalenaeOsgood,1907—NWMexico(MagdalenaI,PacificOcean,BajaCali-forniaSur). C.s.margaritaeMerriam,1894—NWMexico(SantaMargaritaI,PacificOcean,BajaCaliforniaSur). C.s.occultusNelson,1912—NWMexico(IdelCarmen,GulfofCalifornia,BajaCali-forniaSur). C.s.oribatesHuey,1960—NWMexico(NCBajaCalifornia). C.s.peninsulaeMerriam,1894—NWMexico(SBajaCaliforniaSur). C.s.prietaeHuey,1930—NWMexico(SEBajaCalifornia). C.s.pullusBurt,1932—NWMexico(CoronadoI,GulfofCalifornia,BajaCaliforniaSur). C.s.rufescensHuey,1930—SWUSA(SCCalifornia). C. s. seorsus Burt, 1932 — NW Mexico (I Danzante, Gulf of California, Baja California Sur).