Nematode third stage larvae of the genus Physaloptera (Nematoda: Physalopteridae) were recovered from the stomach of Lithobates montezumae (Anura: Ranidae) collected in the Pedregal de San Angel Ecological Reserve in Mexico D. F. (19º11’6.50” N, 99º11’41.42” W; 2 312 m asl). The morphology of the larvae is briefly described and a list of previously recorded localities and hosts in Mexico is given. This study is the first record of Physaloptera sp. parasitizing L. montezumae, and also represents the first helminthological record for anurans in this locality, as well as a new locality record for the nematode genus.
Se aislaron larvas de tercer estadio de Physaloptera (Nematoda: Physalopteridae) del estómago de Lithobates montezumae (Anura: Ranidae) capturados en la Reserva Ecológica del Pedregal de San Ángel en la Ciudad de México (19º11’6.50” N, 99º11’41.42” O; 2 312 m snm). La morfología de las larvas se describe brevemente y se proporciona un listado de los registros del género en México con localidad y hospedero. Este estudio es el primer registro de Physaloptera spp. como parásito de L. montezumae y también representa el primer registro helmintológico para anuros en esta localidad, así como un nuevo registro de localidad para este género de nemátodos.
Lithobates montezumae Blaird 1854 (=Rana montezumae) (Anura: Ranidae) occurs in the center of Mexico through the states of Jalisco, Michoacán, Puebla, Mexico State, Tlaxcala, México D. F., San Luis Potosí, Hidalgo and Querétaro. It breeds in lakes and large bodies of water of pine-oak or oak forest above 2 000 m asl (AmphibiaWeb). Although L. montezumae is the amphibian species that has been most extensively studied for helminths in Mexico (Pérez-Ponce de León et al., 2002) there are no previous records of the nematode Physaloptera spp. parasitizing this host. Adults of Physaloptera occur in the stomach of mammals, snakes, and a few species of lizards and amphibians. The hosts acquire the infection through the ingestion of insects containing infective larvae. Larvae are common in amphibians and some lizards, which are considered as paratenic hosts (Anderson, 2000). Only 2 species of Physaloptera have been recorded as adults in anurans: P. amphibia Linstow 1899 described from Limnonectes macrodon (=Rana macrodon) from the Philippines and P. tigrinae Ali and Farooqui 1969 from Hoplobatrachus tigrinus (=Rana tigrina) in India (Baker, 1987). There is also a record of an adult female of Physaloptera sp. from Lithobates brownorum in Mexico (Terán-Juárez, 2011). In addition to the present record, Physaloptera third stage larvae have been recorded in 12 Mexican anurans from the families Bufonidae, Hylidae, and Ranidae from 13 localities in 9 states of Mexico (Table 1).
Physaloptera sp. larvae in anurans from Mexico
| Host | Locality | Prevalence % (n) | Reference |
| Bufonidae | |||
| Anaxyrus kelloggi (=Bufo kelloggi) | Sonora | 3 (29) | Goldberg and Bursey, 2002 |
| Incilius mazatlanensis (=Bufo mazatlanensis) | Sonora | 35 (20) | Goldberg and Bursey, 2002 |
| Rhinella marina (=Bufo marinus) | Emiliano Zapata, Jalisco | 30.6 (49) | Galicia-Guerrero et al., 2000 |
| Lago de Catemaco, Veracruz | 9 (64) | Goldberg et al., 2002 | |
| Presa Cerro de Oro, Oaxaca | 8.3 (24) | Espinoza-Jimenez et al., 2007 | |
| Hylidae | |||
| Agalychnis dacnicolor (=Pachymedusa dacnicolor) | Sonora | 25(24) | Goldberg and Bursey, 2002 |
| Dendropsophus microcephalus (=Hyla microcephala) | Laguna el Zacatal, Veracruz | 4 (26) | Goldberg et al., 2002 |
| Pseudacris regilla (=Hyla regilla) | San Ignacio, Baja California Sur | 33 (3) | Goldberg et al., 2001 |
| Smilisca baudinii | Oxtankah, Chetumal; Juan Sarabia and Nuevo Paraiso, Quintana Roo | 25 (20) | Terán-Juarez, 2011 |
| Sinaloa | 5(19) | Goldberg and Bursey, 2002 | |
| Trachycephalus typhorius (=Trachycephalus venulosus) | Oxtankah, Chetumal; Juan Sarabia and Nuevo Paraiso, Quintana Roo | 45 (22) | Terán-Juarez, 2011 |
| Ranidae | |||
| Lithobates forreri (=Rana forreri) | Sonora | 15 (39) | Goldberg and Bursey, 2002 |
| Lithobates cf. forreri (=Rana forreri) | San Pedro las Playas, Guerrero | 2.5 (40) | Cabrera-Guzmán et al., 2007 |
| Lithobates magnaocularis (=Rana magnaocularis) | Sonora and Sinaloa | 8 (26) | Goldberg and Bursey, 2002 |
| Lithobates montezumae (=Rana montezumae) | Pedregal de San Ángel Ecological Reserve, México, D. F. | 50 (2) | Present study |
| Lithobates tarahumarae (=Rana tarahumarae) | Yécora, Sonora | 10 (42) | Bursey and Goldberg, 2001 |
The aim of the present work is to report for the first time the presence of Physaloptera sp. in L. montezumae.
On April 11, 2011, 2 specimens of L. montezumae were collected at the botanical garden of the Instituto de Biología, Universidad Nacional Autonóma de México in Mexico D. F., which is surrounded by the Pedregal de San Ángel Ecological Reserve. The frogs were ventrally dissected and all internal organs were examined for helminths using a dissecting microscope. Nematodes were isolated, rinsed in saline solution (0.65%), and fixed in 70% hot ethanol. Subsequently, they were cleared in ethanolglycerin (1:1) and examined via light microscopy. Some specimens were studied by scanning electron microscopy (SEM). These specimens were dehydrated in ethanol series, dried using the critical point technique, coated with gold, and examined with a Hitachi SU1510 scanning electron microscope. Measurements are presented as the range with means in parentheses and expressed in micrometers (μm), unless otherwise stated. Prevalence and intensity of infection were calculated based on Bush et al. (1997). The studied specimens have been deposited in the Colección Nacional de Helmintos, Instituto de Biología, UNAM (CNHE # 8399).
A total of 131 third-stage nematode larvae were found in the stomach of Lithobates montezumae (prevalence and intensity of infection: 1 of 2 host infected (50%), 131 specimens). Nematodes were identified as Physaloptera sp. Rudolphi, 1819 (Physalopteridae) by the presence of a cephalic collar and mouth with large and triangular lips, each provided with teeth (Yamaguti, 1961).
Description based on 10 specimens (Figs. 1, 2). Body length 2.04-2.5 (2.33) mm, maximum width at level of anterior intestine 90-120 (110); cuticle forming a collar around the anterior end, subsequently turning slightly grooved to tail. Apical end with 2 large and triangular lateral lips; each lip with 2 lateral papillae, an externolateral tooth, and 3 small internolateral teeths. Esophagus 0.86-1.09 (1) mm of total length; divided in short anterior muscular portion, and long posterior glandular portion: 130-180 (160) long, 21-26 (22) wide and 730-930 (840) long, 40-60 (54) wide, respectively. Nerve ring 90-130 (110) from the anterior end. Excretory pore close to anterior part of the glandular esophagus, 200-240 (210) from the anterior extremity. Tail conical, 82-100 (93) long.
Physaloptera sp. from the stomach of L. montezumae from Mexico D. F. SEM micrograph of anterior end, lateral view, showing the cephalic collar (a) and 2 triangular lips (b). SEM micrograph of anterior end, apical view, showing 2 lateral papillae (c) and 1 externolateral tooth on each lip (d).
From examination of table I, and considering the role of amphibians in food chains as prey of snakes and mammals, it is clear that anurans are commonly used as paratenic hosts of nematodes of the genus Physaloptera. Common carnivores in the Pedregal de San Ángel Ecological Reserve include mammals Urocyon cinereoargenteus nigrirostris (Canidae), Mephitis macroura macroura, Spilogale putorius angustifrons (Mephitidae), Bassariscus astutus astutus (Procyonidae), and Mustela frenata frenata (Mustelidae) (Hortelano-Moncada et al., 2009), and snakes Thamnophis cyrtopis cyrtopis, T. eques eques, T. scaliger, T. scalaris, Diadophis punctatus, and Rhadinaea laureata (Colubridae) (Méndez-de la Cruz et al., 2009), all of which are the potential definitive hosts of Physaloptera spp.
The conducting of more studies on the helminth fauna of these vertebrates can provide additional information on food webs in the reserve through the linkage of larval and adult stages of parasitic forms using identification tools such as DNA barcodes. This study adds L. montezumae as new host of third-stage larvae of Physaloptera sp. It is also the first record of anuran helminths in the Pedregal de San Ángel Ecological Reserve in Mexico D. F., and the first record of the genus in this locality.
The authors thank Cinthya Mendoza-Almeralla and Gabriela Parra-Olea, at the Laboratorio de Herpetología, IBUNAM, for donation of specimens of L. montezumane for examination. We also thank Luis García-Prieto, at the CNHE, IBUNAM for his help in providing access to the CNHE records, and Berenit Mendoza-Garfias at the Laboratory of Electron Microscopy and Photography, IBUNAM for processing the specimens for SEM. MGVA and ARRM thank Conacyt for support in the form of scholarships. This study was partially funded by PAPIITUNAM proj. IN203911-3 to VLR.