Agustina A. Ojeda

Discovery of desert-adapted Tympanoctomys barrerae in Central Patagonia, Argentina

No abstract available

Historia natural de un roedor raro del desierto argentino, Salinomys delicatus (Cricetidae: Sigmodontinae)

El raton delicado de los salares (Salinomys delicatus) es un pequeno roedor endemico de Argentina. Ha sido considerado como vulnerable a la extincion dada su distribucion restringida y en parches, tamano poblacional pequeno y especializacion en habitats salinos. A pesar de que el raton delicado tiene adaptaciones morfologicas y fisiologicas para la supervivencia en ambientes aridos y salitrosos, poco es lo que se conoce de su historia natural. El presente trabajo tiene como objetivo estudiar la historia natural de S. delicatus, reportar nuevas localidades de ocurrencia, caracterizar el uso de habitat, su dieta y el ensamble acompanante, y describir su biologia reproductiva y morfologia. Se registraron dos nuevos sitios de ocurrencia en ambientes de bosques en galeria y bajos salinos en la region noreste de la provincia de Mendoza (Argentina), siendo las primeras citas para esta provincia. S. delicatus presenta una dieta omnivora, como es frecuente en otros roedores de desierto, y consume en igual medida semillas, artropodos y plantas halofitas. El ensamble acompanante esta compuesto por no mas de tres especies de pequenos mamiferos que varian segun la localidad, siendo esta riqueza similar a otros sitios del Monte. La proporcion de sexos y el patron de dimorfismo sexual mostraron un marcado desvio hacia las hembras (H:M = 3.6:1.1 y H:M = 1.151 respectivamente). La morfologia externa y craneal presenta una importante variabilidad intra e interpoblacional, sugiriendo que el aislamiento juega un rol importante. Cuando se consideraron adultos y juveniles, conjuntamente dos de las seis medidas externas (longitud total y longitud de cabeza y cuerpo) y siete de las 22 medidas craneales resultaron significativamente mayores en hembras que en machos. Cuando se compararon solo los adultos, cuatro caracteristicas externas (longitud total, longitud de cabeza y cuerpo, largo de la cola y peso) y seis medidas craneales fueron significativamente mayores en hembras que en machos. Este trabajo refuerza la importancia del desarrollo de nuevos estudios mas detallados sobre la historia de vida de S. delicatus y permite reafirmar la importancia de conservacion de esta especie.

Habitat selection and coexistence in small mammals of the southern Andean foothills (Argentina)

Habitat partitioning is considered one of the main mechanisms of coexistence among small mammals. This is especially evident in arid environments where resources are particularly scarce. Habitat characteristics such as vegetation heterogeneity and complexity are expected to increase species coexistence, increasing the number of microhabitats that can be occupied by species with different requirements. The Andean foothills can be considered as an ecotone between the Monte and Altoandina phytogeographic provinces as they harbor species from both. Consequently more species are thought to coexist in this area. The objectives of this study were to assess the macro- and microhabitat selection of the small mammal assemblage inhabiting the Andean foothills during wet and dry season and to determine how animals segregate environmental resources to ensure their coexistence. We found that habitat selection occurs at both scales in the Andean foothills. Two species, Eligmodontia moreni and Phyllotis xanthophygus, were capable of distinguishing among macrohabitat types, whereas all species showed habitat selection at the microhabitat scale. We registered selection during both seasons, with some overlap of resource selection during the wet season and the greatest segregation of microhabitat resources during the dry season. Therefore, this work evidence that the assembly of small mammals is sensitive to habitat structure especially in dry seasons where resources are constraints due to arid conditions of Andean foothills.

Geographic variation in quantitative skull traits and systematic of southern populations of the leaf-eared mice of the Phyllotis xanthopygus complex (Cricetidae, Phyllotini) in southern South America

The leaf-eared mice of the genus Phyllotis (Cricetidae, Phyllotini) encompasses at least 20 species of medium-sized Neotropical rodents mostly distributed throughout the Andean region. Its limits and contents were reviewed by several authors, based both on morphological and molecular data. However, no integrative approaches were conducted based on large samples of individuals with a wide geographical coverage. The purposes of this paper are: (i) to evaluate species limits; and (ii) to test the congruence between molecular and quantitative morphological evidences within the Phyllotis xanthopygus complex in southern South America. Our results questioned the specific status of P. bonariensis, a geographically isolated form that was either considered as a valid species or as a synonym of P. xanthopygus. Quantitative morphological (size and shape of the skull) and molecular data linked P. bonariensis with populations from central Argentina traditionally referred as P. xanthopygus vaccarum. Individuals belonging to populations from southern Argentina and Chile (P. x. xanthopygus) were remarkably homogeneous in their skull morphology, showing a subtle to non-existent differentiation from those of north-central and west-central Argentina referred to P. x. vaccarum. We found some incongruence between groups inferred from morphological (this work) and mitochondrial DNA results of previous studies. This is the case of the north-central and west-central populations, where morphological traits do not show the strong differentiation detected by molecular characters. Our results highlight the need for integrative taxonomic studies, not only to delimitate taxonomic units but also for a better and more comprehensive understanding of population variability and differentiation.