Mammalia , Rodentia , Sigmodontinae , Akodon molinae Contreras , 1968 : New locality records and filling gaps

Akodon molinae Contreras, 1968 is a large (holotype: 42.5 g), diurnal species with long and hispid fur, the dorsum is dark grey and the belly is whitish. The tail is shorter (holotype: 78 mm) than head and body (holotype: 108 mm), black dorsally and white in its centrally proximal third. The skull is large and strong, the zygomatic plate is wide and its edge is slightly convex and directed obliquely backwards and down (type description, Contreras 1968). The mandible has a short and robust coronoid process and an anteromedian flexus/flexid on the first upper and lower molars respectively, like other species in the genus Akodon. Cranial and dental remains of A. molinae are shown in Figure 1. The holotype was collected in vivero del Ministerio de Asuntos Agrarios, Laguna Chasicó, Buenos Aires province, Argentina, in grasslands near water bodies (Contreras 1968). Near the Atlantic coast, it lives in shrub steppes and halophilic plant communities (Daciuk 1974). Its distribution in northern Patagonia was associated with the Monte Phytogeographical Province (Pardiñas et al. 2003).

Akodon molinae Contreras, 1968 is a large (holotype: 42.5 g), diurnal species with long and hispid fur, the dorsum is dark grey and the belly is whitish.The tail is shorter (holotype: 78 mm) than head and body (holotype: 108 mm), black dorsally and white in its centrally proximal third.The skull is large and strong, the zygomatic plate is wide and its edge is slightly convex and directed obliquely backwards and down (type description, Contreras 1968).The mandible has a short and robust coronoid process and an anteromedian flexus/flexid on the first upper and lower molars respectively, like other species in the genus Akodon.Cranial and dental remains of A. molinae are shown in Figure 1.
The holotype was collected in vivero del Ministerio de Asuntos Agrarios, Laguna Chasicó, Buenos Aires province, Argentina, in grasslands near water bodies (Contreras 1968).Near the Atlantic coast, it lives in shrub steppes and halophilic plant communities (Daciuk 1974).Its distribution in northern Patagonia was associated with the Monte Phytogeographical Province (Pardiñas et al. 2003).
However, the distribution of these southern populations is still fragmented and poorly explored.Some authors have raised doubts about the taxonomic status of A. molinae (for the discussion on taxonomic aspects, see Wittouck et al. 1995, Pardiñas et al. 2003, 2006).Braun et al. (2008) have suggested that the species A. molinae and A. dolores Thomas, 1916 are synonymous (with different chromosomal races, 2n= 42-44 for A. molinae and 2n= 34 for A. dolores) and A. dolores is the valid name for priority.In this work, we refer the studied specimens to the species A. molinae until this synonymy is broadly accepted.
In this paper, we present 23 new locality records for A. molinae in the provinces of Río Negro and Chubut and we discuss its distribution in northeastern Patagonia.The specimens were collected on two protected areas from the arid and semiarid extra-andean Patagonia in Argentina: Meseta de Somuncurá (Río Negro) and Área Natural Protegida Península Valdés (Chubut), and in some surrounding localities.Field work was conducted between 2004 and 2007.
Somuncurá is a 25,000 km 2 volcanic plain located in the middle of the North extra-andean Patagonian steppes, lying in the provinces of Río Negro and Chubut.The vegetation is associated with the altitudinal gradient (between 600 -1,600 m a.s.l.Beeskow et al. 1982).While the Monte Phytogeographical Province dominates the lower levels, the Patagonian Phytogeographical Province prevails above.These units gradually interchange species in an ecotone area (Ecotono Rionegrino, sensu León et al. 1998).Área Natural Protegida Península Valdés with its 4,000 km 2 is located in northeastern Chubut, within the Monte Phytogeographical Province and Península Valdés Ecotone (Ecotono de la Península de Valdés, sensu León et al. 1998).
The overall distribution of A. molinae in the study area is associated with the Monte Phytogeographical Province.However, 11 of the 23 localities reported here are located within the ecotone area between the Monte and the Patagonian Phytogeographical Provinces (sensu León et al. 1998): the Rionegrino Ecotone (1, 2, 7) and the Península Valdés Ecotone (16 to 23).
Previous records of this rodent species in the Área Natural Protegida Península Valdés were from coastal localities at Isla de los Pájaros (Daciuk 1974), Playa El Doradillo (Apfelbaum and Reig 1989), Riacho San José (Massoia et al. 1988 [here mentioned as A. varius neocenus]) and Puerto Lobos (Udrizar Sauthier and Pardiñas 2006).Nabte et al. (2008) referred this species for the Protected Area but they did not detail in which localities it was registered.These localities are presented in this paper (12, 14 and 15).In or near Somuncurá, the species was previously recorded in Sierra Pailemán (Trejo and Lambertucci 2007), Estancia Campana Mahuida and Sierra Grande (Andrade 2007) and El Rincón (Pardiñas et al. 2003).Considering known locality records, the distribution of the Argentinean endemic A. molinae could be delimited approximately from 31º S in the north (Córdoba province, Wittouck et al. 1995) to Laguna Blanca, 15 km south of Puerto Madryn, in the southeast (Chubut province, De Santis and Pagnoni 1989).Some of those localities are within or near the limits of the Espinal Phytogeographical Province (sensu Cabrera 1971).Even the type locality of A. molinae is within those limits (a summary of the distribution in central Argentina was performed by Pardiñas et al. 2004).
The 23 new records reported in this paper contribute to fill in the information gaps of the poorly known A. molinae and to broaden its distribution towards the west within northern Patagonia.This paper also reaffirms its distribution in association with the Monte Phytogeographical Province and extends it into ecotone areas with the Patagonian Phytogeographical Province (Ecotono Rionegrino and Ecotono de la Península Valdés), in agreement with Pardiñas et al. (2003) who proposed the ingression of A. molinae into the Rionegrino Ecotone.It is important to notice that if the synonymy of A. molinae and A. dolores is accepted, the distribution of this species will be widely extended.
Meseta de Somuncurá and Península Valdés were declared as a Protected Area by the Provincial Government of Río Negro and Chubut respectively.As for most of Patagonia, both areas have been grazed since the beginning of the twentieth century.There is evidence that grazing by domestic herbivores has modified the vegetation and accelerated soil degradation processes (e.g.Beeskow et al. 1987;Rostagno and del Valle 1988;Bisigato and Bertiller 1997).It would be necessary to evaluate the possible influence of ovine and goats livestock on the A. molinae populations, to protect the biodiversity of those reserves.

Figure 2 .
Figure 2. New locality records for Akodon molinae in the province of Río Negro and Chubut (Patagonia, Argentina).