REDESCRIPTION OF HASSALSTRONGYLUS ADUNCUS CHANDLER, 1932 (NEMATODA: HELIGMONELLIDAE), WITH THE DESCRIPTION OF A NEW SPECIES OF THE GENUS AND THEIR PHYLOGENETIC POSITION WITH OTHER HELIGMOSOMOIDEA TRAVASSOS, 1914.

ABSTRACT: Hassalstrongylus Durette-Desset, 1971 (Nematoda: Heligmonellidae), includes 19 species that are distributed from the southwestern United States to central-western Argentina. Hassalstrongylus aduncus is a parasitic nematode of rodents from the subfamilies Arvicolinae, Murinae, and Sigmodontinae, and has been recorded from southern Virginia and Oklahoma to Costa Rica. This species was described by Chandler in 1932; the morphology of the synlophe was not included. Subsequently, in 1972, Durette-Desset described only the synlophe of the middle region of the body in both sexes. Despite its wide geographical distribution, to date, there has been no redescription that includes information complementary to the morphology of the synlophe, such as a study of the body surface or a molecular phylogenetic analysis. We reevaluated the morphology of some specimens that were presumably similar to H. aduncus parasite of Sigmodon sp. from Jalisco, Mexico, and it was determined that these corresponded to an undescribed species of the genus. Herein, we present a redescription of H. aduncus parasite of Sigmodon toltecus from Hidalgo, Mexico, with morphological traits such as the excretory pore, deirids, and ovijector, and provide a description of the synlophe in the anterior and posterior regions of both sexes and include scanning electron microscopy images. Hassalstrongylus geolayarum n. sp. is differentiated from H. aduncus by the number of ridges in the middle region of the body (23 vs. 21), as well as proportions between some traits of males and females such as total length/spicule length, total length/gubernaculum length, total length/length of the esophagus and total length/distance of the vulva and the size of the eggs (42 vs. 58 µm). Phylogenetic analysis is based on partial sequences of the nuclear ribosomal internal transcribed spacer region (ITS1 + 5.8S + ITS2) of the rDNA, using the maximum-parsimony, maximum-likelihood, and Bayesian inference methods revealed the close relationship of H. aduncus + H. geolayarum n. sp. within the Heligmosomoidea and confirmed the placement of the Hassalstrongylus monophyletic clade well-supported within Heligmonellidae. The new species presented a genetic divergence of 3.4-3.8% relative to H. aduncus. This is the first species of the genus described in Mexico. Presumably, there are more species not yet described throughout the geographic range of H. aduncus. A taxonomic review and molecular phylogenetic analysis are required in which more species and genes are analyzed in Heligmosomoidea to confirm the status of the nonmonophyletic groups recovered here.

A NEW SPECIES OF CHIGGER MITE AND THE RECORD OF A GASTROINTESTINAL NEMATODE IN SCELOPORUS CAUTUS (SQUAMATA: PHRYNOSOMATIDAE) FROM THE CHIHUAHUAN DESERT PROVINCE IN COAHUILA, MEXICO.

The chigger species Acomatacarus coahuilensis n. sp. (Acariformes: Trombidiformes: Leeuwenhoekiidae) inhabiting the neck scales of the wary spiny lizard Sceloporus cautus Smith, 1938 (Squamata: Iguania: Phrynosomatidae), from Chihuahuan Desert Province, Coahuila, Mexico, is described herein. The new mite species is assigned to the genus AcomatacarusEwing, 1942, based on a palptarsus with 6 branched setae plus the tarsala (ω). This new species can be separated from the other species in this genus mainly based on the combination of the following characters: presence of mastisetae (MTa) on tarsus III and tibiala (φ) on tibia III, subterminala (ζ1), parasubterminala (z), and pretarsala (ζ2) on tarsus I, 2 genualae (σ1-2) on genu I, onychotriches and claw-like empodium of legs I-III, and absence of mastisetae on tibia III. In addition to the new species, the gastrointestinal nematode Skrjabinoptera phrynosoma (Ortlepp, 1922) Schulz, 1927 (Physalopteridae), was also found, which represents a new host record in the wary spiny lizard. This study reports the third species of the genus Acomatacarus recorded from Mexico and the first record of chigger mites and helminth parasites associated with Sc. cautus.

Signatures of the Evolution of Parthenogenesis and Cryptobiosis in the Genomes of Panagrolaimid Nematodes.

Most animal species reproduce sexually and fully parthenogenetic lineages are usually short lived in evolution. Still, parthenogenesis may be advantageous as it avoids the cost of sex and permits colonization by single individuals. Panagrolaimid nematodes have colonized environments ranging from arid deserts to Arctic and Antarctic biomes. Many are obligatory meiotic parthenogens, and most have cryptobiotic abilities, being able to survive repeated cycles of complete desiccation and freezing. To identify systems that may contribute to these striking abilities, we sequenced and compared the genomes and transcriptomes of parthenogenetic and outcrossing panagrolaimid species, including cryptobionts and non-cryptobionts. The parthenogens are triploids, most likely originating through hybridization. Adaptation to cryptobiosis shaped the genomes of panagrolaimid nematodes and is associated with the expansion of gene families and signatures of selection on genes involved in cryptobiosis. All panagrolaimids have acquired genes through horizontal gene transfer, some of which are likely to contribute to cryptobiosis.

Identification of leopard frogs (Anura: Ranidae: Lithobates) distributed in some localities of the Southern Mexican Plateau using mitochondrial DNA sequences.

Species of the genus Lithobates are difficult to identify, especially on the 'Rana pipiens' complex, because the morphological differences among the species are often subtle. In this study, we used 12S ribosomal RNA gene partial sequences to identify specimens of leopard frogs from some new localities (not sampled on previous studies) of the Southern Mexican Plateau, to carry out a phylogenetic analysis, and also a morphometric analysis of some morphological features were analyzed to evaluate their morphological variation. A phylogenetic analysis using partial sequences of 12S rDNA mitochondrial gene for 31 samples was carried out using Bayesian Inference, Maximum Parsimony, and Maximum Likelihood. In addition, 20 morphological lineal measurements from 97 specimens were analyzed by principal component analysis (PCA) to evaluate if the frogs studied are conspecific. Partial sequences of the 12S rDNA obtained from frogs distributed in the Southern Mexican Plateau show two haplotypes with a divergence of 0.4%. Phylogenetic hypothesis shows an exclusive group with a previous sequence of Lithobates montezumae. The PCA indicates that variables are not linearly correlated and specimens belong to a single group. Evidence found, let us consider that specimens studied belong to one species of the Lithobates montezumae subgroup, distributed principally in the Southern Mexican Plateau.

A New Species of Morelacarus (Acariformes: Prostigmata: Leeuwenhoekiidae) Associated With Sceloporus grammicus (Squamata: Phrynosomatidae) From the Mexican Plateau, Zacatecas, Mexico.

A new species of chigger mites, Morelacarus uazi n. sp., parasitizing lizards of the species Sceloporus grammicus from Mazapil, Zacatecas, Mexico, is described and illustrated. This new taxon differs from other species of the genus by having a palpal claw with 4 subequal paired prongs, and it can be further distinguished by the combination of the following characters: presence of onychotriches and mastitarsala III, absence of mastitibiala III, subterminala I, and parasubterminala I, and the palpal setal formula B/B/BBb. Additionally, an identification key for the species of the genus Morelacarus is presented. The new species represents the seventh species assigned to the genus and the first species described from a Mexican lizard.

Cholinergic signaling plasticity maintains viscerosensory responses during Aspiculuris tetraptera infection in mice small intestine.

Intestinal parasites alter gastrointestinal (GI) functions like the cholinergic function. Aspiculuris tetraptera is a pinworm frequently observed in laboratory facilities, which infests the mice cecum and proximal colon. However, little is known about the impact of this infection on the GI sensitivity. Here, we investigated possible changes in spontaneous mesenteric nerve activity and on the mechanosensitivity function of worm-free regions of naturally infected mice with A. tetraptera. Infection increased the basal firing of mesenteric afferent nerves in jejunum. Our findings indicate that nicotinic but not muscarinic receptors, similarly affect spontaneous nerve firing in control and infected animals; these axons are mainly vagal. No difference between groups was observed on spontaneous activity after nicotinic receptor inhibition. However, and contrary to the control group, during infection, the muscarinic signaling was shown to be elevated during mechanosensory experiments. In conclusion, we showed for the first time that alterations induced by infection of the basal afferent activity were independent of the cholinergic function but changes in mechanosensitivity were mediated by muscarinic, but not nicotinic, receptors and specifically by high threshold nerve fibers (activated above 20mmHg), known to play a role in nociception. These plastic changes within the muscarinic signaling would function as a compensatory mechanism to maintain a full mechanosensory response and the excitability of nociceptors during infection. These changes indicate that pinworm colonic infection can target other tissues away from the colon.

Molecular Phylogenetic Analysis of Infidum similis, Including Morphological Data and Estimation of its Genome Size.

: Infidum similis Travassos, 1916 (Dicrocoeliidae: Leipertrematinae) was found in the gall bladder of Leptophis diplotropis Günther, 1872 from El Podrido, Acapulco, Guerrero, Mexico. A phylogenetic analysis based on partial sequences of the 28S ribosomal RNA using maximum likelihood (ML) and Bayesian inference (BI) analyses was carried out to assess its phylogenetic position within suborder Xiphidiata, alongside members of the superfamilies Gorgoderoidea and Plagiorchoidea. The phylogenetic trees showed that the genus is most-closely related to the Plagiorchoidea rather than to the Gorgoderoidea, in keeping with previous taxonomic designations. Phylogenies obtained from ML and BI analysis of the 28S rDNA gene revealed a well supported clade in which Choledocystus hepaticus (Lutz, 1928) Sullivan, 1977 is sister to I. similis. On the other hand, a tree obtained using a partial sequence of the cytochrome c oxidase subunit 1 (cox1) mtDNA gene (ML and BI analysis), with species supposed to be closely related to I. similis according to 28S, does not support this relatedness. Based on the independence of Infidum from the subfamily Leipertrematinae Yamaguti, 1958 , our results clearly demonstrated that the genus corresponds to a different family and with species closely related to C. hepaticus within Plagiorchoidea. New data are presented about the tegumental surface of I. similis by scanning electron microscopy as well as the estimation of its haploid genome size using Feulgen Image Analysis Densitometry of sperm nuclei as part of the characterization of this species. This is the first genome size estimated for a member of Plagiorchiida, and these data will provide a new source of knowledge on helminth diversity and evolutionary studies. This constitutes the first host record, and new geographical distribution, for this species in Mexico.

Helminth parasites of Pseudacris hypochondriaca (Anura: Hylidae) from Baja California, Mexico, with the description of two new species of nematodes.

The helminth parasite fauna of the hylid frog Pseudacris hypochondriaca in several localities along the Baja California Peninsula in northwestern Mexico is presented. The helminth fauna consists of 4 species of nematodes (Oswaldocruzia pipiens, a larval form of an Ascaridid, 2 new species belonging to the genera Rhabdias and Cosmocercoides), and 1 species of digenean ( Gorgoderina sp.). The new species of Rhabdias represents the 88th species assigned to the genus and the third species described from Mexican anurans. Also, the species of Cosmocercoides represents the 20th species assigned to the genus and the first representative of this genus described from Mexico.

Molecular evidence that Langeronia macrocirra and Langeronia cf. parva (Trematoda: Pleurogenidae) parasites of anurans from Mexico are conspecific.

The genus Langeronia parasitizing the intestine of several species of anurans is distributed from North to Central America. We identified Langeronia macrocirra and Langeronia cf. parva from the same host and localities, and present here new data not applicable about their tegumental surface by scanning electron microscopy. We compared sequences of the rDNA ITS2 region and mtDNA cox1 gene for the two morphotypes. ITS2 exhibited a high degree of conservation. Phylogenetic reconstruction using cox1 revealed three clades (I, II, and III), which did not correspond to a previous identification or host. Little divergence was found within clades: sequences were identical in clade I, whereas clade II had 0.27% and clade III had 1.08%. Inter-clade divergence reached 8.69% (I vs. III). This pattern of genetic divergence indicated that both taxa probably belong to the same species, so we posit that the morphological changes could be correlated with development. Increasing sample size and geographical coverage will contribute to the taxonomy of the genus based on morphological and molecular evidence, and will open tracks toward the use of DNA barcodes to the genus in Mexico.

New species of Rhabdias (Nematoda: Rhabdiasidae) from Bufo occidentalis (Anura: Bufonidae) from Sierra Madre del Sur, Mexico.

Rhabdias kuzmini n. sp., a parasite of the lungs of Bufo occidentalis, is described and illustrated. This Mexican taxon differs from the related species in the genus by the possession of 4 lips (2 subdorsal and 2 subventral) and 2 lateral pseudolabia, corpus not inflated, a larger barrel-shaped buccal capsule, equatorial vulva, and the presence of a slightly swollen cuticle in the anterior and posterior ends of the body. This is the 16th species described in the Neotropical Realm and the first species of Rhabdias described from endemic anurans in México.

A new rhabdiasid species from Norops megapholidotus (Sauria: Polychrotidae) from Mexico.

Rhabdias leonae n. sp., a parasite of the lungs of Norops megapholidotus, is described and illustrated. The Mexican taxon differs from the other species in the genus by a combination of characters: possession of 4 lips, corpus slightly inflated, slightly postequatorial vulva, and presence of swollen cuticle of anterior and posterior ends. This is the 12th species described in the Neotropical realm and the first species of Rhabdias described from an endemic Mexican lizard.

Confirmation of Gnathostoma binucleatum Almeyda-Artigas, 1991, advanced third-stage larvae in Tres Palos Lagoon, Mexico, by morphological and molecular data.

Advanced third-stage larvae of Gnathostoma sp. corresponding to 6 morphotypes, distinguished on the basis of the shape of the cephalic hooklets, were collected from the muscle tissue of 5 species of freshwater fish (i.e., Dormitator latifrons, Eleotris picta, Gobiomorus maculatus, Ariopsis guatemalensis, and Cichlasoma trimaculatum) in Tres Palos Lagoon, Guerrero, Mexico. Principal components analysis of 4 morphological characters cluster all samples in a single taxonomic group. A minimum amount of variation was observed among ITS2 sequences of 3 morphotypes and Gnathostoma binucleatum obtained from GenBank (0-0.84%). The observed variation among morphotypes 1, 2, and 3 is the result of intraspecific variability of G. binucleatum supported by morphology and DNA. Morphotypes 4, 5, and 6 belong to the same taxon on the basis of morphology of the hooklets only. For an accurate morphological diagnosis of the causative agent of gnathostomiasis, it is necessary to develop similar studies with other species of the genus.