Instituto De Ciencias Basicas

Akodon oenos Braun, Mares, and Ojeda, 2000 was described on a large sample of individuals collected from two localities near Mendoza city, Argentina. This sample was obtained in the 1980's by Julio R. Contreras and María I. Rossi and labeled, but never published, as "Akodon minoprioi new species." The description provided by Braun and collaborators was limited to craniodental and color pelage traits compared with those of five individuals of the sympatric form A. molinae . Akodon oenos was proposed as new and presumptively allied to the A. varius species group of Akodon. In February 2009 we collected an individual of Akodon in Llancanelo Natural Reserve, southern Mendoza, that morphologically fits the original description of A. oenos. Further study of some individuals of the type series of A. oenos reinforces this taxonomic hypothesis for the Llancanelo specimen. However, comparisons with other Akodon species overlooked by Braun and collaborators, reveals striking similarities with the widespread and phenotypically variable species A. spegazzinii Thomas, 1897. The evidence at hand, including morphological, karyological, and genetical traits, allows us to propose a new taxonomic scenario. A. oenos is considered here a junior synonym of A. spegazzinii and therefore belongs to the A. boliviensis species group of Akodon, extending the known geographic distribution for this species at least to southern Mendoza piedmont in the ecotone between the Monte and Patagonia eco-regions. More generally, this situation highlights the necessity when working with complex genera (as many sigmodontines are) to perform extensive comparisons and to use several sets of evidence in order to reduce the probability of generating biologically redundant names and more taxonomic confusion.

Water balance has been one of the main research focuses in the field of ecophysiology of arid-zone mammals. In animals living in South American deserts as well as in other arid lands, water balance is a great challenge (Diaz and Ojeda, '99; because of the high temperatures and high waterdeficit rates characteristic of the environment. As a strategy to face limited exogenous water or excessive loss, numerous species present very low water loss rates through evapotranspiration, urination, and digestion (Schmidt-Nielsen, '64, '79; MacMillen and Lee, '67; Degen, '97;.

Endozoochorous dispersal by Lepus europaeus (Lagomorpha, Leporidae) in the Monte-Patagonia ecotone, Argentina. Endozoochorous dispersal involves the dispersal of seeds through feces after being ingested by animals. This work assesses the role of the European hare, Lepus europaeus, as a legitimate seed dispersal in an environment of the Monte-Patagonia ecotone in the province of Mendoza. Sampling was conducted between March and April 2010. In 43 of the 200 feces analyzed, a total of 129 seeds was found which corresponded to 8 different plant taxa. Nearly 60% of them belonged to the family Poaceae, whereas the only exotic plant species found was Polygonum aviculare. However, the possibility of this leporid dispersing some other exotic monocots cannot be ruled out because some of them could not be determined. All seeds of P. aviculare and of species of the family Amaranthaceae were damaged, whereas the seeds of Prosopis sp. were undamaged. Our results indicate that the European hare is...

Las tierras áridas y los roedores han sido, y lo continúan siendo, el escenario y protagonistas de numerosas investigaciones en el campo de la biología evolutiva. Ya sea desde qué comen y cómo se reproducen, a cómo hacen para enfrentar la escasez de agua y altas temperaturas del medio en que viven. Diario Los Andes -Edición Impresa: domingo, 12 de diciembre de 2010  Por Ricardo A. Ojeda (1) -y Gabriela B. Diaz (2) -(1) Grupo de investigaciones de la Biodiversidad. Iadiza, Conicet, CCT Mendoza. -(2) Instituto de Ciencias Básicas. UNCuyo. Malargüe.

onvergent evolution among desert rodents has received a great deal of attention in recent years, with research centering on the question of how phylogenetically unrelated species evolving on different continents have developed similar morphological, behavioral, ecological, or physiological characteristics in response to similar selective pressures posed by the desert environment (Mares 1975, 1993a, 1993b, Schluter and Ricklefs 1993). The he at and aridity of deserts pose severe challenges for both plants and animals. Deserts gene rally support reduced levels of plant biomass compared with more mesic habitats (Hadley and Szarek 1981, Rosenzweig

The aim of this paper was to analyze the renal performance of the insectivorous desert mouse opossum, Thylamys pusilla, a marsupial that inhabits temperate drylands of the Neotropics. We measured the urine concentrating ability of Ž. this marsupial in the field and under three different experimental conditions in the laboratory. 1 Ad libitum treatment: Ž. animals were fed ad lib. on apples, sausages and cat food; 2 restriction treatment: foods high in nitrogen were supplied Ž. ad lib., while only apple, a food with high water to nitrogen load, was restricted, and 3 fasting: 2 days of food deprivation. Osmolarity values recorded in the field were similar to those obtained under the restriction treatment. The Ž. maximum urinary concentration found 9015 mOsmrl is the highest reported for a marsupial and more in keeping with similarly sized desert rodents. Similar urine concentrations in T. pusilla and desert rodents suggest that xeric environments, rather than phylogeny, play a major role in water conservation. The kidney of T. pusilla possesses a long Ž. papilla and shows high renal indices MrC: 9.37; RMT: 11.76. Our results question the idea that urine concentration is not high in desert-dwelling insectivores. Although their dietary water intake is potentially high, this may not always be sufficient to eliminate the nitrogenous waste resulting from insectivory. Thus, T. pusilla uses its ability to conserve water to overcome periods of food shortage and high nitrogen load.

1. To determine whether variation in kidney morphology is associated with environmental aridity in South American hystricognaths, we used conventional and phylogenetic analysis (independent contrasts) to correlate mass-independent renal variables (kidney size; relative medullar thickness, RMT; medulla/cortex ratio, MC; inner medulla/ cortex ratio, MIC; relative medullar area, RMA) with environmental variables such as precipitation, temperature and a measure of primary productivity (NDVI). 2. Body mass and most renal indexes showed significant phylogenetic signal (the tendency of closely related species to resemble each other), as well as latitude, one index of minimum daily temperature (T min) and NDVI, indicating that correcting for phylogenetic effects is necessary, hence results from independent contrasts are more reliable for these traits. 3. All renal indexes except RMA and MIC were significantly correlated with body mass. After correcting for size effects, inclusion of precipitation or NDVI improved significantly the regression model for kidney size and MIC regardless of the analyses employed, whereas T min was also a significant predictor of both indices according to independent contrasts. Precipitation was the best predictor of kidney size, with animals from dryer environments having larger kidneys. RMT was not correlated with any of the environmental indexes employed here. 4. Our results suggest that hystricognaths from environments with lower rainfall have evolved larger kidneys, probably to cope with aridity. Additional renal indices (RMT, MC and RMA) were not correlated with any environmental variable, and their relative importance as predictors of urine concentration ability for this group of rodents remains unclear.

Octodontid rodents have a long evolutionary history in arid landscapes of South America. The red vizcacha rat, Tympanoctomys barrerae, is a monotypic, micro-endemic species that inhabits salt pan-sand dune habitats in west-central Argentina. Its natural history is almost unknown. We present an analysis of the ecology, morphology, behavior, and physiology of the red vizcacha rat and assess the overall degree of convergence of this species with rodents that inhabit similar habitats in different deserts. Our results show that Tympanoctomys barrerae is highly adapted to salt flat basin habitats. Its diet of halophytic vegetation with a high salt content, and physiological and anatomical traits related to salt consumption, are similar to those found in some members of the families Heteromyidae (Dipodomys microps) of North America, and Muridae (Psammomys obesus and Rhombomys opimus) of Africa and Asia. Similarities include feeding behavior, diet composition, kidney morphology, and urine concentration, among other traits. Tympanoctomys barrerae is more similar to these desert rodents than it is to confamilials that do not feed on halophytes.

Two large groups of rodents inhabit South America: the hystricognaths and the murids. It has been postulated that while the former show a high degree of specialization to desert habitats, the murids are not well adapted to xeric conditions. We studied the renal structure and function of selected desertdwelling murid and octodontid (hystricognath) rodents from Argentina to evaluate levels of adaptation to aridity. Our results show that the murids Salinomys, Andalgalomys, Calomys and Eligmodontia have the highest renal indices and urine concentration among Argentine desert rodents. The octodontid Tympanoctomys barrerae shows higher renal indices and urine osmolarity than those of its close relatives Octomys mimax and Octodontomys gliroides. We compare the renal traits of the Argentine desert murids with those of other world-desert rodents such as North American heteromyid rodents. The results show that these Argentine murid rodents posses renal adaptations to conditions which are as impressive as those of both octodontids and the classic desert-adapted heteromyids.