New species of Trichuris (Nematoda: Trichuridae) parasitizing Heteromys salvini (Rodentia: Heteromyidae) from Costa Rica, with a key to Trichuris species described from Heteromyidae

(Rodentia


Introduction
Heteromyidae is a family of rodents distributed from southern Canada to northern Colombia and Venezuela; the family includes 50 species belonging to five genera (Chaetodipus, Dipodomys, Heteromys, Microdipodops and Perognathus) that inhabit different ecoregions (Alexander & Riddle, 2005;Fernández et al., 2014;Hafner et al., 2007). In particular, Heteromys comprises 13 species, 7 of which [H. anomalus (Thompson), H. australis Thomas, H. desmarestianus Gray, H. gaumeri Allen, H. irroratus (Gray), H. pictus (Thomas) and H. salvini (Thomas)] have been studied from a parasitological perspective. In Costa Rica, this genus has been poorly studied; helminth species have only been reported in two (H. desmarestianus and H. salvini) of the four species distributed in the country (Falcón-Ordaz et al., 2019;Rodríguez-Herrera et al., 2014). In order to increase the knowledge of the nematode parasites of Heteromyidae rodents in this Central American country, we describe a new species of Trichuris collected from H. salvini. Twenty-nine species in this nematode genus have been recorded in American rodents belonging to the families Caviidae, Cricetidae, Ctenomyidae, Dasyproctidae, Echimyidae, Geomyidae, Heteromyidae, Myocastoridae, Octodontidae and Sciuridae (Eberhardt et al., 2019;Robles et al., 2018). The main morphological traits used to distinguish among them include the presence/ absence of a spicular tube (which contains the spicula), the length of the spicule, the shape of proximal cloacal tube (formed by the junction of the intestine and the ejaculatory tube) and distal cloacal tube (which in turn is originated by the junction of the proximal cloacal tube with the spicular tube) and vulvar morphology. Based on these features, we erected the new species and presented a taxonomic key for the species that parasitize American heteromyids.

Materials and Methods
Thirty-four individuals of H. salvini were collected by Sherman traps in February, 1996 from Área de Conservación Guanacaste, Costa Rica, and were examined for parasites. Nematodes were obtained from the caeca of the hosts and placed in 0.85% saline, fixed in glacial acetic acid and stored in 70% ethanol. Specimens were cleared for study with a solution of glycerol and 70% ethanol (2:1). Drawings, micrographs and measurements were made with a Zeiss microscope equipped with a drawing tube and Axiocam ERc5s camera. Measurements are given in millimeters unless otherwise indicated. The range of measurements is presented at the beginning, followed by the mean, standard deviation and holotype or allotype measurements in parentheses. Specimens processed for scanning electron microscopy (SEM) were dehydrated through a graded series of ethanol, critical point dried with CO 2 and sputter-coated with a mixture of gold-palladium; for SEM study were mounted on metal stubs with silver paste, and examined under a Hitachi Stereoscan S-2469 N at 15 kV at Laboratorio Nacional de Biodiversidad (LANABIO), Instituto de Biología, Universidad Nacional Autónoma de México (IBUNAM), Mexico City, Mexico. Type material was deposited in the Colección Nacional de Helmintos (CNHE), IBUNAM, Mexico City, Mexico.

Results
Family Trichuridae (Ransom, 1911) Railliet, 1915 Genus Trichuris Roederer, 1761 Trichuris guanacastei n. sp. (17 males and 30 females) General: Based on the holotype, allotype and paratypes. Cuticle with fine transverse striations. Anterior end of body long, narrow and sharp. Posterior end of body wide, diminishing towards the end ( Figure 1A). Stichosome with a single row of stichocytes, and 1 pair of conspicuous cells at the esophagus-intestinal junction level. Nuclei of stichosome single with 1 nucleus per every 1 to 2 subdivisions; at the esophagus-intestinal junction level, they may present numerous nuclei within the stichosome ( Figure 1B).   Bacillary band begins in the anterior region of the body, extending at its midpoint and fading gradually prior to the esophagus-intestinal junction. Bacillary band has cuticular inflations of different sizes and shapes bordering the band at the anterior end of the body; visible bacillary glands with conspicuous pore ( Figure 3D).
Finally, the total length of males (13.31-22.7) and females (31.43-36.21) of T. guanacastei n. sp. is smaller than the total length of males (25.0-30.0) and females (46.0-47.0) of T. perognathi, the final species of the genus with a spicular tube; moreover, the eggs size of the new species (0.03-0.05) and the cloacal tube length (0.72-1.36) clearly distinguish it from T. perognathi, in which these structures measure 0.065-0.067 and 2.00 mm, respectively.

Discussion
Trichuris guanacastei n. sp. is the first species of Trichuris described in Costa Rica and the fifth species described in the Americas that parasitizes Heteromyidae (Chandler, 1945;Read, 1956;Pfaffenberger & Best, 1989;Panti-May & Robles, 2016). The new species was compared with 29 known species of Trichuris that infect rodents in the Trichuris from heteromyds rodents in Costa Rica Americas and separated from these species based on a combination of various morphological characteristics in both males and females, mainly the presence of a spicular tube, the spicule size, vulvar morphology, and the length of the eggs. However, the identification of the Costa Rican specimens was difficult because some of their morphometric characteristics overlap, particularly with species that parasitize host included in the same family (T. silviae, T. perognathi, T. elatoris and T. dipodomis, see Robles, 2008). In addition, as Panti-May & Robles (2016) noted, the descriptions of some species are incomplete (e.g., T. dipodomis, T. perognathi, T. stransburyi, T. madisonensis and T. fossor), and the nomenclature of several traits should be clarified, especially those related to vulvar morphology as well as the spicular sheath. Authors such as Panti-May & Robles (2016) and Hasegawa & Dewi (2017) have analyzed the taxonomic value that features such as the presence/absence of a cephalic stylet, the characteristics of the bacillary band and accompanying structures, and the number and shape of nuclei in the stichocytes could have for the identification of Trichuris species. Further, DNA sequencing analysis of Trichuris species will be a key element for their differentiation in the future.