DNA barcodes effectively identify the morphologically similar Common Opossum (Didelphis marsupialis) and Virginia Opossum (Didelphis virginiana) from areas of sympatry in Mexico.

Two morphologically similar species of opossum from the genus Didelphis-Didelphis virginiana and Didelphis marsupialis-cooccur sympatrically in Mexico. High intraspecific variation complicates their morphological discrimination, under both field and museum conditions. This study aims to evaluate the utility and reliability of using DNA barcodes (short standardized genome fragments used for DNA-based identification) to distinguish these two species. Sequences of the cytochrome c oxidase subunit I (Cox1) mitochondrial gene were obtained from 12 D. marsupialis and 29 D. virginiana individuals and were compared using the neighbor-joining (NJ) algorithm with Kimura's two-parameter (K2P) model of nucleotide substitution. Average K2P distances were 1.56% within D. virginiana and 1.65% in D. marsupialis. Interspecific distances between D. virginiana and D. marsupialis varied from 7.8 to 9.3% and their barcode sequences formed distinct non-overlapping clusters on NJ trees. All sympatric specimens of both species were effectively discriminated, confirming the utility of Cox1 barcoding as a tool for taxonomic identification of these morphologically similar taxa.

A new species of Pelecitus (Filarioidea: Onchocercidae) from the endangered Tehuantepec jackrabbit Lepus flavigularis.

Pelecitus meridionaleporinus n. sp. from the Tehuantepec jackrabbit is described. The new species differs from Pelecitus helicinus (Molin, 1860) in having delicate transverse striations, a salient vulva, and a readily apparent preesophageal ring; P. helicinus has teardrop cells around the vulva, which are lacking in the species presently described. The new species is different from Pelecitus scapiceps (Leidy, 1886) in having the vulva anterior to the esophageal-intestinal junction and wider lateral alae. Pelecitus scapiceps is found in the tarsal bursa of the hind feet of lagomorphs, whereas P. helicinus is found around tendons of legs and feet of birds. Pelecitus meridionaleporinus n. sp. occurs in the subcutaneous tissue at the base of both ears. This is the second species in Pelecitus Railliet and Henry, 1910 that occurs in New World lagomorphs, and the third found infecting mammals.