versão On-line ISSN 1852-5768
Cuad. herpetol. vol.25 no.2 San Salvador de Jujuy Jul./set. 2011
First record of the American bullfrog Lithobates catesbeianus (Shaw, 1802) in Mendoza province, Argentina
Sanabria Eduardo1,2, Guillermo Debandi3,4, Lorena Quiroga1,2, Flavio Martínez4,5, Valeria Corbalán3,4
1 Departamento de Biología, Facultad de Ciencias Exactas Físicas y Naturales, Universidad Nacional de San
Juan. Av. Ignacio de la Roza 592 (O), San Juan, Argentina.
2 Laboratorio de Investigaciones Andrológicas de Mendoza, Instituto de Histología y Embriología de Mendoza,
Facultad de Ciencias Médicas, UN Cuyo, CCT Mendoza, CONICET, Mendoza, Argentina.
3 IADIZA-CCT Mendoza-CONICET. Av. Ruiz Leal s/n Parque Gral. San Martín, 5500, Mendoza, Argentina;
4 BIOTA (Asociación para la Conservación de la Diversidad Biológica Argentina);
5 Dirección de Recursos Naturales Renovables de la Provincia de Mendoza, Parque Gral. San Martín, 5500 Mendoza, Argentina.
Introduction of non-native species by humans is a growing biological concern. The reasons for such introductions are varied and include biological control, human consumption, and pet trade (Kraus, 2009). Impacts include extinction or extirpation of native species, biotic homogenization, disruption of food webs, changes in primary productivity of the ecosystem, changes in soil formation, and vectors of diseases (Kraus, 2009).
The American bullfrog, Lithobates catesbeianus (Shaw, 1802), is considered one of the most invasive species in the world (Lowe et al., 2004). This species can act as a vector for pathogens, especially Batrachochytrium dendrobatidis, the fungus that causes chytridiomycosis in amphibians. Chytridiomycosis is syndicated as one of the principal causes of global amphibian decline (Berger et al., 1998; Longcore et al., 1999; Ron and Merino, 2000; Daszak et al., 2003). Also, the ecological impacts of bullfrogs on native species and environments include competition with, or removal of, native prey and predators and cascading community and ecosystem changes (Kraus, 2009).
The native range of the American bullfrog extends from eastern Canada, through central and eastern United States, to northeastern Mexico (Frost, 2011). Ecologically, the American bullfrog is a highly adaptable species. This adaptability has led to its success in invading diverse environments ranging from deserts to the tropics (Adams and Pearl, 2007). This species has been widely introduced around the world, and feral populations have been reported in almost all countries of South America (Frost, 2011). Populations of L. catesbeianus have recently been reported from Argentina in the provinces of San Juan (Sanabria et al., 2005; Sanabria et al., 2011), Misiones (Pereyra et al., 2006), Buenos Aires (Barrasso et al., 2009), Córdoba (Akmentins et al., 2009; Nori et al., 2011), and Salta (Akmentins and Cardozo, 2010). Here we report a first record of Lithobates catesbeianus from Mendoza province, Argentina.
We discovered a well established population of L. catesbeianus in Mendoza province, San Carlos department, Capiz locality (33° 41' 11''S, 68° 59' 09'' W; elevation: 920 m) and other nearby localities at Tunuyán department (Fig. 1 and Table 1). This record extends the distribution range of this species 270 km S-SE from Calingasta, San Juan, and 400 km W-SW from Villa Dolores, Córdoba. The region is part of the Monte phytogeographic province, which is characterized by an arid climate with mean annual temperature of 17.7ºC (mean annual minimum and maximum: -1.4 and 38.0ºC, respectively) and mean annual rainfall of 331.2 mm, which occurs mainly in summer (San Carlos meteorological station; Capitanelli, 1999).
Figure 1. Geographic location of the new records of the American bullfrog (Lithobates catesbeianus) in Mendoza province, Argentina.
Table 1. Additional localities near Capiz for L.catesbeianus from Mendoza province
This area has been deeply modified for agriculture, and is irrigated by a channel system that connects rivers, streams, and natural spring waters throughout the entire area. Frequently, land holders collect water in artificial ponds to use during wáter shortages. We found L. catesbeianus using artificial ponds for reproduction, as well as irrigation channels for adult and tadpole dispersal between water bodies.
The dominant native plants of these streams and channels include Eupatorium sp., Scirpus sp., Juncus sp., Cortaderia rudiuscula, Typha dominguensis, and many floating-leaf emergent plant species like Nasturtium nasturtiumaquaticum and Hydrocotyle ranunculoides. It is also common to find the invasive species Tamarix gallica in river and stream banks, and planted trees of Salix spp. on the margins of main irrigation channels.
On 3 February 2011, we surveyed the area searching for amphibians in an artificial pool (2.25 ha) and its surrounding waterways. During six hours at night (from 7 pm to 1 am), we collected adult frogs and tadpoles of L. catesbeianus by hand and hand net. The captured frogs were euthanized by immersion in 40 % ethanol, fixed in 10% formalin, and preserved in 70% ethanol. Larvae were preserved in 10% formalin. All specimens of L. catesbeianus were deposited at the Herpetological Collection of the Instituto Argentino de Investigaciones de las Zonas Áridas (CH-IADIZA 343, 344- 1 to 344-22, 345).
We observed tadpoles of L. catesbeianus in the artificial waterways and pools. These environments provide a suitable habitat for the larvae to complete their development and for adults to thrive and reproduce. We captured 52 tadpoles of L. catesbeianus representing various stages of development (Fig. 2). Also, we captured one adult male and 22 juveniles. American bullfrog's males vocalized actively during our field surveys.
Figure 2. Tadpole stages found at the surveyed area. Stages classified according Gosner (1960).
Other amphibian species present in the area were adults of Rhinella arenarum and a juvenile of Leptodactylus latrans, which were released at the capture site. We did not find tadpoles of these two species in the surveyed water bodies. Akmentins et al. (2009) and Sanabria and Quiroga (2010) reported that L. catesbeianus eat amphibians, snakes, mammals, and invertebrates, and Barrasso et al. (2009) reported Leptadactylus latrans as part of its diet. In accordance to this, local people from Capiz pointed out that in the past the Rana criolla (L. latrans) were more abundant than today and that they have disappeared from several sites.
In a recent publication about the invasion of L. catesbeianus, Nori et al. (2011) reported 12 localities that can be assumed to contain feral populations from Argentina and modeled the potential invasion areas of L. catesbeianus in Argentina using data from the native range of this species. In the prediction map, Mendoza shows an area with a high probability of invasion by L. catesbeianus at 70 km NE from the locality reported here. Although the authors indicate that factors such as low precipitation or high altitudes could be limiting the species' ability to invade the west and south of Argentina, other factors like local environmental conditions where frog farms are located can be important for successful establishment of new populations. The new locality reported here is located in a highly vegetated and shaded area with many natural springs and irrigation channels, which represent suitable conditions for this species but are not captured by traditional modeling procedures. Clearly, predictive models are developed with environmental parameters under natural conditions, the new area is not detected by the model because is an artificial ecosystem. These ecosystems provide local conditions that allow the reproduction of bullfrog.
Akmentins and Cardozo (2010) mentioned that the lack of government regulation or control over frog-farming facilities is the most probable source of feral populations in Argentina. According to local people from Capiz, L. catesbeianus was first introduced at least 20 years ago when specimens were released from a frog farm located close to the sites reported here (33° 40' 37'' S, 68° 58' 49'' W). Also they expressed that teachers from a school of Capiz encouraged the students to breed bullfrogs in channels and streams near their homes. Thus, a combination of factors, including a lack of awareness by the people about the risks of species introduction, and relaxed governmental policy in controlling frog farms, are likely to be the origin of the introduction of L. catesbeianus in this region of Mendoza.
Studies of reproductive potential, trophic ecology and prevalence of chytrid fungus infection of this feral population of American bullfrog are needed to better understand the impacts of this invasive species on native biodiversity of Mendoza. Also, it is necessary to determine the actual distribution in the studied area. The finding of some individuals in the Tunuyán river, close to El Carrizal dam, makes it imperative to alert to environmental authorities and take the necessary actions to restrict the spread of this species in a more extensive irrigation system. We suggest a review and update of the legislation concerning exotic species trade in order to prevent the establishment of additional populations of L. catesbeianus in Argentina. Furthermore, application of control measures and integrated management of previously established populations of American bullfrog should involve local people, land owners, government decisionmakers, and academic institutions.
We would like to thank agricultural land managers for allowing access to their pond and irrigation channels, and J. Warner and N. Horák for helping us with the English version.
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