First molecular characterization and species validation of Toxocara alienata (Rudolphi 1819) (Nematoda: Ascarididae), from a crab-eating raccoon (Procyon cancrivorus)

Abstract

Toxocara alienata infects racoons and wild pigs in South America and its taxonomy is important to distinguish the species from closely related zoonotic congeners, such as T. canis. This study provides the first genetic characterization of T. alienata from the Brazilian Amazon, along with a comprehensive morphological description, to clarify its distinction from the closely related T. canis. Nematodes were observed using light and scanning electron microscopy and genetically characterized based on barcode COI mtDNA. A phylogeny was reconstructed using Bayesian inference and different species delimitation methods (PTP, bPTP, ASAP, GMYC) were performed for robust species validation. Specimens were identified as T. alienata based on a somewhat narrow cervical alae; male with equal, alate spicules, shorten than 1 mm, 28 pairs of caudal papillae (24 subventral precloacal pairs and 4 postcloacal pairs) and a protruded well-developed precloacal lip with an unpaired papilla on it, which was observed for the first time in the species. These morphological features can differentiate T. alienata from T. canis mainly regarding number and arrangement of postcloacal papillae, structure of precloacal lip and the presence of the unpaired papilla. In the phylogeny, T. alienata represented an independent lineage, sister to a clade formed by T. canis sequences. All species delimitation methods validated T. alienata as a specific entity, different from T. canis. The present results, including the first genetic characterization of T. alienata, reinforce its validation and provide crucial data for future taxonomic, epidemiological and ecological works on Toxocarinae.