Morphological and chromosomal taxonomic assessment of Sylvilagus brasiliensis gabbi (Leporidae)

The cottontail rabbit species, Sylvilagus brasiliensis, is currently understood to be constituted by 18 subspecies ranging from east central Mexico to northern Argentina, and from sea level to at least 4800 m in altitude. This hypothesis of a single widespread polytypic species remains to be critically tested. In other species groups of Sylvilagus from other geographic areas, the use of chromosomal information has been important in delineating taxonomic boundaries. To date, however, no chromosomal data are available for Sylvilagus south of Mexico. Here we report the chromosomal complement of two individuals (a male and a female) putatively ascribed to Sylvilagus brasiliensis on the basis of morphological characters and collected from southern Península del Azuero in Panama. The diploid number (2n) of these two individuals was 38 and the fundamental number (autosomal arms, aFN) was 72. Karyotypes of S. brasiliensis from southern Mexico have reported two chromosomal forms: 2n=36, FN=68 and 2n=40, FN=76. We complement the chromosomal data with a morphological examination of the Panama specimens and of holotype materials pertinent to the taxonomic identity of Mesoamerican taxa of Sylvilagus. These findings, in association with others regarding the phylogenetic relationships of Sylvilagus from the Neotropics, reinforce the idea that the current taxonomic treatment of the species merits critical scrutiny. In particular, we excise Sylvilagus gabbi from subspecific synonymy with S. brasiliensis and remove the subspecies truei from brasiliensis to gabbi.