Chaetodipus, DALQUESTI

Álvarez-Castañeda, Sergio Ticul & Rios, Evelyn, 2011, Revision of Chaetodipus arenarius (Rodentia: Heteromyidae), Zoological Journal of the Linnean Society 161 (1), pp. 213-228 : 226

CHAETODIPUS DALQUESTI

Distribution: The original distribution of C. dalquesti was limited to the south-western tip of the Baja California Peninsula ( Roth, 1976). The examined specimens placed the range of C. dalquesti from López Mateos (geographical group 20) on the Pacific side and the La Paz region (geographical group 30) on the Gulf side and southward to the Cape Region, with the exception of the El Mogote (geographical group 28) sand spit and the Los Planes Basin. The range of C. dalquesti also includes Margarita Island (geographical group 27) on the Pacific side of the peninsula.

Diagnosis: Following Roth (1976: 562), C. dalquesti is similar to C. arenarius ; however, C. dalquesti is larger; the tail is longer, darker, and distinctly crested; has numerous somewhat weakly developed rump spines; ears are large and edged with white fur; pelage is grizzled; males are slightly larger than females. The bulla is moderately inflated; posterior palatal pits are small; nasal bones are long.

Subspecific taxonomy: The genetic analysis of specimens from different areas shows that the range of C. dalquesti includes some populations previously considered to be C. arenarius .

Comments: Analysis of genetic data of specimens from different localities on the peninsula shows that the species’ range is larger than previously reported, including coastal areas on both sides of the peninsula and an island population ( Fig. 1 ).

In the La Paz region (geographical group 30), C. dalquesti and C. arenarius are apparently present; for that reason the position of C. a. sublucidus ( Nelson & Goldman, 1929) is not easy. However, C. arenarius occurs on the El Mogote sand spit and in the western coastal zone surrounding the Laguna de La Paz. By contrast, C. dalquesti is widely spread in the La Paz area, south and east of the Laguna de La Paz. The original vegetation of the La Paz area was palm and mesquite trees that are more closely related to the habitat characteristics of C. dalquesti . For those reasons, we tentatively assign C. sublucidus as a subspecies of C. dalquesti . However, a final assignment of this subspecies can only be made by an appropriate comparison of sequenced DNA from the holotype of C. sublucidus .

The range of C. dalquesti is restricted to moister areas on the coastal plain of the southern part of the Baja California Peninsula. These areas have some characteristics that make it a very particular habitat. The vegetation is a desert scrubland in an area subject to coastal fog and contains epiphytes, mainly Rocella and Tillandsia recurvata . Along the Pacific coast, these characteristics are special, containing many endemic plant species: Gongylocarpus sp. , Opuntia pycnacantha , Ferocactus santa-maria , Stenocereus eruca , Cyrtocarpa edulis var. glabra , and Harfordia macroptera ( Turner, Bowers & Burgess, 1995) . The climate in the foggy desert scrubland is moister and cooler than inland areas of the peninsula.

The range of C. dalquesti seems to be discontinuous, probably related to the disjunctive characteristics of the habitats in the three areas: (1) the Pacific coastal area from López Mateos (geographical group 20) to Migriño (geographical group 34); (2) La Paz (geographical group 30); and (3) Margarita Island (geographical group 27, Fig. 1 ). Each group is considered a different subspecies. Between the Pacific coast and La Paz, the relatively narrow isthmus, mostly a rolling plain of geological origin, acts as a pathway that brings more moister and cooler breezes across the isthmus from the Pacific, for at least part of the year. During the Pleistocene, the lowland connection probably brought even more pronounced cool and moist air across the peninsula.

The current C. dalquesti subspecies include: C. d. dalquesti ( Roth, 1976) , which occupies the Pacific coastal area from López Mateos to all of the Cape Region of the State of Baja California Sur; C. d. ammophilus ( Osgood, 1907), which is restricted to Margarita Island on the Pacific side of the Baja California Peninsula; and C. d. sublucidus ( Nelson & Goldman, 1929) , which occupies the coastal area near the Bahía de La Paz, with the exception of the El Mogote sand spit.

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.