Morphological and molecular characterization of a new Trichuris species (Nematoda- Trichuridae), and phylogenetic relationships of Trichuris species of Cricetid rodents from Argentina.

María Del Rosario Robles,Cristina Cutillas,Carlos Javier Panei,Rocío Callejón,Philippe Castagnone-Sereno

doi:10.1371/journal.pone.0112069

Abstract

Populations of Trichuris spp. isolated from six species of sigmodontine rodents from Argentina were analyzed based on morphological characteristics and ITS2 (rDNA) region sequences. Molecular data provided an opportunity to discuss the phylogenetic relationships among the Trichuris spp. from Noth and South America (mainly from Argentina). Trichuris specimens were identified morphologically as Trichuris pardinasi, T. navonae, Trichuris sp. and Trichuris new species, described in this paper. Sequences analyzed by Maximum Parsimony, Maximum Likelihood and Bayesian inference methods showed four main clades corresponding with the four different species regardless of geographical origin and host species. These four species from sigmodontine rodents clustered together and separated from Trichuris species isolated from murine and arvicoline rodents (outgroup). Different genetic lineages observed among Trichuris species from sigmodontine rodents which supported the proposal of a new species. Moreover, host distribution showed correspondence with the different tribes within the subfamily Sigmodontinae.

Highlights

Species of Trichuris Roederer, 1761 (Nematoda: Trichuridae) have a cosmopolitan distribution and parasitize a broad range of mammalian hosts, such as ruminants, marsupials, rodents, and primates, including humans [1,2]
The specimens found in Phyllotis bonariensis Crespo, 1964 and P. xanthopygus Waterhouse, 1837 were identified as Trichuris pardinasi; and those found in Akodon montensis Thomas, 1913 and Thaptomys nigrita (Lichtenstein, 1829) as T. navonae
Identification of closely related species is very difficult. This is due in part to the phenotypic plasticity of the organisms themselves, host-induced variation, the paucity of morphological features, and the extensive overlap in morphometric characteristics that occur among species e.g. [8,18,15,22]

Summary

Introduction

Species of Trichuris Roederer, 1761 (Nematoda: Trichuridae) have a cosmopolitan distribution and parasitize a broad range of mammalian hosts, such as ruminants, marsupials, rodents, and primates, including humans [1,2]. To discriminate between the alternative hypotheses of co-speciation (host-parasite) versus geographical differentiation, it is necessary to integrate studies of both morphological and molecular analysis [4]. Several features, such as the presence/absence of the spicular tube, the shape and distribution of the spines of the spicular sheath, length of the spicule and the cloacal tube, the shape of the proximal and distal cloacal tube, and the vulvar morphology, along with classic morphometric characteristics have been used as characteristics with high discriminatory value to differenciate the species of Trichuris i.e. Different populations with overlapping morphometrical features [8] result in taxonomic and nomenclatorial problems, e.g. individuals of the same species recognized as different species (under different names: synonyms), and different species referred as the same species (sibling species) [20,21]

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