Daniela Rodríguez

Differential use of vertical space by small mammals in the Monte Desert, Argentina

Abstract Space use in deserts usually has been considered only along the horizontal dimension; however, vertical structure could be an important variable for habitat segregation among small mammal species. Our study assessed the use of vertical space by small mammals of the Monte Desert by live-trapping animals at different heights. We recorded 1,336 captures of 4 rodent and 1 marsupial species in 27,600 trap nights. All 5 species were captured on the ground and in tree layers, but only the gray leaf-eared mouse (Graomys griseoflavus) and the desert mouse opossum (Thylamys pallidior) used vertical space appreciably. G. griseoflavus used the arboreal space independently of habitat, plant species, or branch diameter, whereas T. pallidior showed a more selective behavior, being present at greater heights and on large-diameter branches of Prosopis trees. All rodent species used lower more than higher parts of arboreal strata. They used vertical space more or only during the dry season when resource availability is low. Our study suggests that vertical structure offers greater opportunities to acquire resources when these are scarce and plays a role in the coexistence of small desert mammals.

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.

Distribution of Telomeric Sequences (TTAGGG)n in Rearranged Chromosomes of Phyllotine Rodents (Cricetidae, Sigmodontinae)

Phyllotines are sigmodontine rodents endemic to South America with broad genetic variability, Robertsonian polymorphisms being the most frequent. Moreover, this taxon includes a species with multiple sex chromosomes, which is infrequent in mammals. However, molecular cytogenetic techniques have never been applied to phyllotines to elucidate their karyotypic evolution. We studied the chromosomes of 4 phyllotine species using FISH with a pantelomeric probe (TTAGGG)n. Graomys griseoflavus, Eligmodontia puerulus, and E. morgani are polymorphic for Robertsonian translocations, whereas Salinomys delicatus possesses XX/ XY1Y2 sex chromosomes. Telomeric signals were detected at both ends of all chromosomes of the studied species. In S. delicatus interstitial telomeric sequences (ITS) were observed in the 3 major chromosome pairs, which are equidistant from one of the telomeres in these chromosomes. These results suggest that ITS are important in the reshuffling of the highly derived karyotype of S. delicatus. Considering the phylogeny of phyllotines, the Robertsonian rearrangements of G. griseoflavus, E. puerulus, and E. morgani possibly represent chromosome fusions which have occurred independently. The pericentromeric regions of the biarmed chromosomes of these species do not contain telomeric sequences characteristic for strict fusions of recent origin, suggesting a common pattern of telomeric repeat loss during chromosomal evolution of these rodents.