Amphibia , Anura , Leiuperidae , Pleurodema thaul ( Lesson , 1827 ) : Altitudinal distribution extension and new records from its northern range

The current study reports five new localities of the four-eyed frog Pleurodema thaul (Lesson, 1827) in the extreme north of its distribution (27° to 30° S) in the desertic and semidesertic ravines of Chile, including an increase in its altitudinal range up to 3125 m. Mediterranean bioclimate to a hyperoceanic temperate one (Luebert and Pliscoff 2006). Consequently, the species inhabits both isolated oasis in the northern desert (e.g. Carrera Pinto; Correa et al. 2007) and in temperate rainforests of southern Chile and Argentina, embracing an altitudinal range between 0 and 2727 m, which reflects its ecological plasticity (Cei 1962). The species has also invaded almost all of Robinson Crusoe Island (archipelago Juan Fernández, South Pacific, Chile) after being introduced in the 1970’s (Correa et al. 2008a), which ratifies its adaptive capacity. According to Duellman and Veloso (1977), the distribution of P. thaul in Chile is discontinuous north of La Serena (30° S), due to the aridity of this region. In fact, up to now only four localities north of this latitude had been described for the species, in an area covering approximately 320 km. Two of these localities are in the only rivers of the zone that flow all year long (Huasco river and Copiapó river; Figure 1; Correa et al. 2007); the other two are found in small isolated streams in ravines of the desert (Carrera Pinto) and semi-desert (Pajonales) area. The scarcity of natural aquatic habits due the reduction of precipitation towards the north can explain why only two species of amphibians, P. thaul and Rhinella atacamensis, have colonized Chile north of 30° S; the latter is the only species found between 25° and 27° S (Correa et al. 2008b). The small number of amphibian populations described in this zone is not only due to the arid conditions, but also to a lack of exploration, as may be deduced from the recent description of new localities of R. atacamensis in the same area (Correa et al. 2008b). Here we report five new localities of P. thaul in the extreme north of its distribution (27° to 30° S), including one which increases its altitudinal range to 3125 m (Río Figueroa; Table 1; Figure 2), which are a result of recent explorations in the zone (2006-2009). Two of these localities are in the drainage system of the Copiapó river (Las Juntas and Río Figueroa), while the other three 1 Universidad de Chile, Facultad de Ciencias, Departamento de Ciencias Ecológicas, Laboratorio de Genética y Evolución. Casilla Postal 653,

Mediterranean bioclimate to a hyperoceanic temperate one (Luebert and Pliscoff 2006).Consequently, the species inhabits both isolated oasis in the northern desert (e.g.Carrera Pinto; Correa et al. 2007) and in temperate rainforests of southern Chile and Argentina, embracing an altitudinal range between 0 and 2727 m, which reflects its ecological plasticity (Cei 1962).The species has also invaded almost all of Robinson Crusoe Island (archipelago Juan Fernández, South Pacific, Chile) after being introduced in the 1970's (Correa et al. 2008a), which ratifies its adaptive capacity.
According to Duellman and Veloso (1977), the distribution of P. thaul in Chile is discontinuous north of La Serena (30° S), due to the aridity of this region.In fact, up to now only four localities north of this latitude had been described for the species, in an area covering approximately 320 km.Two of these localities are in the only rivers of the zone that flow all year long (Huasco river and Copiapó river; Figure 1; Correa et al. 2007); the other two are found in small isolated streams in ravines of the desert (Carrera Pinto) and semi-desert (Pajonales) area.The scarcity of natural aquatic habits due the reduction of precipitation towards the north can explain why only two species of amphibians, P. thaul and Rhinella atacamensis, have colonized Chile north of 30° S; the latter is the only species found between 25° and 27° S (Correa et al. 2008b).
The small number of amphibian populations described in this zone is not only due to the arid conditions, but also to a lack of exploration, as may be deduced from the recent description of new localities of R. atacamensis in the same area (Correa et al. 2008b).Here we report five new localities of P. thaul in the extreme north of its distribution (27° to 30° S), including one which increases its altitudinal range to 3125 m (Río Figueroa; Table 1; Figure 2), which are a result of recent explorations in the zone (2006)(2007)(2008)(2009).Two of these localities are in the drainage system of the Copiapó river (Las Juntas and Río Figueroa), while the other three are coastal ravines with little water.Frogs were collected from each of these localities for genetic and neuroethological studies and were deposited in the Herpetological Collection of the Departamento de Biología Celular y Genética of the Universidad de Chile (DBGUCH).
Río Figueroa is a mountain stream fed by underground springs, which in some places forms small ponds and swamps (Figure 3A).The area appears little disturbed by human activities and harbors an abundant population of the species.Las Juntas is a small town located close to the junction of the Manflas and Copiapó rivers, mostly dedicated to agriculture.The Copiapó river is channeled in this area, but there are a few places beside the canal where there is a slow flow of water where individuals of P. thaul and R. atacamensis may be found.Totoral is a very small town whose inhabitants are mainly farmers and artisans.Frogs can be found in a nearby ravine (Figure 3B), which only has an abundant flow of water from June to September.Totoral has the population of P. thaul with the smallest body size found so far (mean SVL = 29 mm, SVL range 25.3-31.3mm) (N.Velásquez and M. Penna, unpublished data).El Trapiche is a small creek where mainly farming activities are developed (Figure 3C).Finally, Cruce a Chungungo is a superficial runoff which forms small ponds in which both P. thaul and R. atacamensis live (Figure 3D).
The distributional limits of P. thaul appear to be determined by the same factors that determine the species richness of amphibians in Chile.The majority of the species are concentrated between 38° and 48° S; their richness and abundance diminishes both north and south of this area due to more extreme climatic conditions (Veloso and Navarro 1988;Vidal 2008).In the extreme south, temperate forests give way to Patagonian steppes and Magallenic tundra, where only two species can be found south of 50° S. One of these species, P. bufonina, is widely distributed in the Patagonia of Argentina and Chile and replaces P. thaul in Chile from approximately 46° S to the south (Cei 1962).By contrast, the Atacama Desert, whose southern limit is about 28° S, limits the presence of amphibians to the coast and interior of the country.Human pressure increases as water resources decrease towards the north of Chile, which is exacerbated by the intense mining and agricultural activities in this zone of the country.This has affected the integrity of the water drainage systems, affecting the habitat of amphibians directly or indirectly, as was recently shown for some R. atacamensis localities (Correa et al. 2008b).The current state of the Copiapó river exemplifies the negative effects of human activities.This river is channeled from Lautaro dam downriver (Figure 1), where its natural course is completely dry.Recent exploration around the city of Copiapó and towards the outlet of the river, where P. thaul used to be common, has not detected individuals of this species or of R. atacamensis (C.Correa, G. Lobos, personal observations).The situation upriver from the Lautaro dam is different; here the Copiapó river and its affluents still have significant water flow, albeit intermittent.However, there are currently intensive agricultural and mining activities which could affect the persistence of the recently discovered populations of P. thaul in Las Juntas and Río Figueroa.This last locality is of particular importance, not only because it increases the known altitude limit of P. thaul, but also because it shows that this species is capable of resisting the extreme climatic conditions of the high-altitude desert (Figure 3A).
In summary, P. thaul has been capable of persisting in the isolated and reduced water courses of water in the Chilean desert and semi-desert zone, in areas which are currently threatened by the growing human pressure on the water resources (e.g.Correa et al. 2008b).It is not currently known if these populations have genetic or ecological differences with respect to their more southern counterparts.We also know nothing about the population dynamics in these environments, whose integrity depends on scarce and irregular precipitation.The investigation of these aspects may be essential in order to implement conservation measures for these populations, which would also serve to protect other biotic components of these aquatic environments in Chile.

Table 1 .
Coordinates and elevations of the localities of Pleurodema thaul mentioned in the literature north of the Elqui river basin (30° S) and of the new localities described in this report.See the map of Figure1.