Batrachochytrium dendrobatidis in Argentina: first record in Leptodatylus gracilis and another record in Leptodactylus ocellatus.

GHIRARDI, R.; LESCANO, J. N.; LONGO, M. S.; ROBLEDO, G.; STECIOW, M. M.; PEROTTI, M. G.

HERPETOLOGICAL REVIEW

Society for the Study of Amphibians and Reptiles

Año: 2009 vol. 40 p. 175 - 176

0018-084X

In the last few decades, rapid declines and extinctions of populations have been reported in more than 400 amphibian species all over the world. A pathogen that has received attention relative to these losses is the chytridiomycete Batrachochytrium dendrobatidis (Bd). Ron (2005) identified potentially suitable regions for Bd establishment in the New World. In South America, Ron predicted suitable regions included the Brazilian Atlantic forest, the temperate forest in Chile and western Argentina (south to 30ºS), northeastern Argentina, Uruguay, and Paraguay. Thus far in Argentina, Bd has been reported in four anuran species at three geographic locations: 1) Barrionuevo and Mangione (2006) found Bd in Telmatobius pisanoi and T. atacamensis (Anura: Leptodactylidae) in mountainous areas of Northern Argentina; 2) Arellano et al. (2006) and Herrera et al. (2005) reported Bd in adult specimens of Leptodactylus ocellatus (Anura: Leptodactilidae) in Buenos Aires province; and 3) in North Patagonia, Fox et al. (2006) found Bd in Atelognathus patagonicus (Anura: Leptodactilidae). We present Bd detections in central Argentina: a new occurrence in the Striped Thin-toed Frog (Leptodactylus gracilis) and another occurrence in the Spotted Thin-toed Frog (Leptodactylus ocellatus). Dead specimens of the two leptodactilids were found during field surveys and were deposited in the collection of Centro de Zoologia Aplicada (Universidad Nacional de Córdoba, Argentina). A specimen of Leptodactylus ocellatus (CZA a-00011) was collected on May 2005 (31.3967ºS, 64.5936ºW) and a specimen of Leptodactylus gracilis (CZA a-00010) was collected on March 2006 (31.3855ºS, 64.6057ºW), on the banks of the Toro Muerto stream, in the locality of Villa Flor Serrana, in a mountainous area of Córdoba province, Central Argentina, at 800 m elevation. The stream had a mean depth of 70 cm and flowed intermittently over granitic rock. The physiognomy of the surrounding vegetation was that of serrano secondary forest and thorny shrublands, typical of the Chacoan region (Cabrera 1976). Annual rainfall is 950 mm and is mainly concentrated in spring and summer. Mean annual temperature is 18.9°C, ranging from peak values in summer that may exceed 38°C to winter frosts (Capitanelli 1979). The specimens were fixed in the field in 10% neutral formaldehyde solution and then were transferred to 70% ethanol. In the laboratory, abdominal and hind limb ventral skin patches (~5 x 10 mm) were excised from the anurans, stored in 70% ethanol and dehydrated to embed in paraffin. Then, tissues were sectioned at 5- μm thickness with a Reitcher microtome for histology, and stained with hematoxylin & eosin. With a stereomicroscope, we looked for spores and sporangia in the corneous epithelium of the tissue samples following Berger et al. (1999) and Pessier et al. (1999). We identified Bd in the two specimens analyzed. Zoosporangia at different developmental stages, empty or containing rounded basophilic zoospores, were identified in the stratum corneum. With those results, we increase the geographic distribution of Bd in Leptodactylus ocellatus, and report the first record of infection in L. gracilis. These two species are widespread in a broad region of Argentina, supporting the need to conduct further studies of Bd to investigate the status of these populations and the risk to sympatric species. The first case of Bd in Argentina was detected in 2002 in a dead specimen (Herrera et al. 2005), and until now eleven specimens (include our two) belonging to five different species have been found infected (Arellano et al. 2006, Barrionuevo and Mangione 2006, Fox et al. 2006, Herrera et al. 2005). Our finding expands the known distribution of Bd to the wilderness area of the Chacoan phytogeographic region of Argentina, Chaco Serrano district (Cabrera 1976) (Fig. 1). Although Ron’s (2005) prediction map of potentially suitable regions for Bd establishment infections detection, these prediction have been made on the bases of only 44 points over the New World, and none of these points was either from Argentina or neighboring countries, resulting in a low precision. Further information is needed about the prevalence and habitat requirements of Bd infecting anurans inhabiting Argentina for modeling an actualized and more precise Bd distribution map. An increase in the number of amphibian species monitored will help us to estimate the health of wild populations. The collection of environmental and biological data will provide us with valuable tools to predict new scenarios and implement adequate and specific conservation policies in order to manage disease outbreaks in Argentina.