Chaetodipus arenarius (Roth, 1976)

Álvarez-Castañeda, Sergio Ticul & Rios, Evelyn, 2011, Revision of Chaetodipus arenarius (Rodentia: Heteromyidae), Zoological Journal of the Linnean Society 161 (1), pp. 213-228 : 225

CHAETODIPUS ARENARIUS

Distribution: The range of C. arenarius includes all of the State of Baja California (northern half of the peninsula) and the northern 80% of the State of Baja California Sur (from La Paz northward, including the driest areas) and Magdalena Island (geographical group 25). It does not include the coastal areas as previously considered by Hall (1981) and Patton & Álvarez-Castañeda (1999). Chaetodipus arenarius is not found in any localities with foggy desert scrubland.

Diagnosis: This is a moderately small species within the genus, with tail longer than the head and body, small ears, and the pelage relatively soft and usually lacking stiff bristles or spines; the lateral stripe is not clearly developed. The skull is short and broad, with somewhat vaulted braincase, slender and parallel zygomatic arches, the interparietal is more than twice as broad as it is long and is strap shaped to slightly pentagonal with slender nasals ( Lackey, 1991).

In the field, the differences between C. arenarius and C. dalquesti were noted by simple comparisons. Chaetodipus arenarius is smaller, with a smaller, crested tail and is more light coloured dorsally. Rump spines are mainly absent in C. arenarius and present in C. dalquesti , but not as strongly developed as in C. spinatus . The fur is softer in C. arenarius than in C. dalquesti .

Subspecific taxonomy: Some of the subspecies previously considered as C. arenarius show genetic characteristics that are assigned to C. dalquesti . The only previous subspecies from the Cape Region that is still considered C. arenarius is Chaetodipus arenarius ramirezpulidoi ( Álvarez-Castañeda & Cortés-Calva, 2004) , which is restricted to El Mogote sand bar at the south-western end of Bahía de La Paz (geographical group 28). The population is surrounded by populations of C. dalquesti . Genetic analyses indicate that the population in the Loreto area (geographical group 17) is genetically different from all other specimens of C. arenarius .

Comments: Phylogenetic analyses show that the range of C. arenarius is separated into three geographical areas that could be related to discontinuous habitat characteristics: northern populations ( Fig. 1 , solid circles; Fig. 2D , subclade Ia); southern populations, including specimens from El Mogote ( Fig. 1 , open circles; Fig. 2D , subclade Ib); and Loreto ( Fig. 1 , grey circles; Fig. 2D , subclade Ic). The ranges of the subspecies follow Patton & Álvarez-Castañeda (1999).

The Loreto group (geographical group 17) is geographically isolated from other populations of C. arenarius and has a 3.6% genetic distance from specimens from the southern part of the peninsula; therefore, this group should be considered a different subspecies. However, because only a few specimens have been examined, there are no clear morphological characteristics to distinguish the Loreto population from other populations of C. arenarius .

The current subspecies included under C. arenarius are: C. a. arenarius ( Merriam, 1894) , which occurs in the inland areas of Baja California Sur from San Ignacio Lagoon (geographical group 12) southward to the north of the Isthmus of La Paz (geographical group 30). Chaetodipus a. albescens ( Huey, 1926) is found on sandy eastern lowlands of the San Pedro Mártir Range in the vicinity of San Felipe (geographical group 1) in the State of Baja California. Chaetodipus a. ambiguus ( Nelson & Goldman, 1929) is found in the south-central part of Baja California and northwestern part of the Vizcaino Desert in Baja California Sur. Chaetodipus a. mexicalis ( Huey, 1939) occurs on sandy eastern lowlands of the Sierra de Juárez, including the area of Laguna Salada and the northeastern coast of Baja California. Chaetodipus a. paralios ( Huey, 1964) is found in the eastern lowlands of the Sierra de La Giganta from Bahía de los Ángeles (geographical group 5) to El Barril (geographical group 7) in Baja California. Chaetodipus a. albulus ( Nelson & Goldman, 1923) is restricted to Magdalena Island (geographical group 25). Chaetodipus a. helleri ( Elliot, 1903) is found from the San Quintín Plains (geographical group 2) to the coastal area southward from El Rosario (geographical group 3) and C. a. ramirezpulidoi ( Álvarez-Castañeda & Cortés-Calva, 2004) is restricted to the El Mogote (geographical group 28) sand spit in the south-western end of Bahía de La Paz.

Figures

Figure 1. Location of Chaetodipus arenarius specimens examined for sequencing. Black-filled circles are the Northern subnetwork, open circles the Southern subnetwork, and grey-filled circles the Gulf of California subnetwork of C. arenarius. The localities with half-filled circles have specimens from all subnetworks. Rhomboids are the locations of Chaetodipus dalquesti and squares are the locations of Chaetodipus siccus. The distributions of the three species are shaded in different colours: white for C. arenarius, grey for C. dalquesti, and black for C. siccus. The specimens and geographical groups are listed in Table 1. The dashed line shows the hypothetical borders between species.

Figure 2. Phylogenetic relationships amongst 21 specimens of the concatenated cytochrome b and cytochrome c oxidase subunit III gene sequences of the Chaetodipus arenarius complex. The main topology was the same as the one used for the Bayesian inference analyses (A), maximum likelihood (B), maximum parsimony, consensus of four trees (C) and bootstrap of the neighbor-joining (D). The three groups are monophyletic. Clade I contains specimens of C. arenarius and has three subclades (indicated in D) with strong geographical relationships. (Ia) includes specimens northward to the Vizcaino Desert; (Ib) contains specimens southward to the Vizcaino Desert and Magdalena Island; and (Ic) contains specimens from the Loreto area bordering the Gulf of California. Clade II contains specimens of Chaetodipus dalquesti and Clade III contains specimens of Chaetodipus siccus. The acronym for each species is at the tip of each branch (A, C. arenarius; D, C. dalquesti; S, C. siccus), the locality numbers are as shown in Figure 1 and the haplotype (H) numbers listed in Table 1 are shown in parentheses. The values at the nodes are branch support for each of the analyses.