We employed a live trapping grid to analyse the effect of heterogeneity habitat on dispersion of Akodon azarae, Oxymycterus rutilans and Oryzomys delticola. The reproduction and survival of three species are associated with their residency in the grassland, avoided the use of woodland. A. azarae reproductive and non-reproductive individuals preferentially use the sites dominated by Ambrosia scabra (microhabitat 1). Their residency at those sites would present nutritional advantages due to higher availability of seeds. This species begins to use other microhabitats more frequently only after the population peak. O. delticola preferentially uses the sites dominated by Lonicera japonicaBaccharis spicata (microhabitat 3). As both species present similarities in their diets, the differential use of the grassland microhabitat would contributate to diminish competitive interactions between them. O. rutilans reproductive individuals do not show preference for either microhabitat. During autumn-winter, non-reproductive individuals are more frequently captured in microhabitat 1. The important diminution herbaceous cover among Cortaderia selloana bushes (microhabitat 2) and under the dominant shrubs of microhabitat 3, led as to think that predation could be an important factor regarding the habitat use pattern of A. azarae and O. rutilans during autumn and winter. The climbing ability of O. delticola would contribute to diminish the impact of predation it could suffer at microhabitat 3.Resume. -Les auteurs ont etudie ä Paide d'une grille de piegeage 1'effet d'un habitat heterogene sur la dispersion a'Akodon azarae, Oxymycterus rutilans et Oryzomys delticola. Les trois especes vivent dans la prairie et evitent la foret, ce qui assure leur reproduction et leur survie. A. azarae, qu'il soit ou non en reproduction, utilise de preference des sites ou domine Ambrosia scabra (microhabitat 1) oil il doit trouver des graines tres nourrissantes. Cette espece ne commence ä utiliser d'autres sites qu'apres le pic de population. O. delticola frequente de preference les sites ou dominent Lonicera japonica et Baccharis spicata (microhabitat 3). Les deux especes ayant des regimes alimentaires compa- Mammalia, t. 55, n° 3, 199L Brought to you by | University of Arizona Authenticated Download Date | 6/3/15 4:49 PM 340 MAMMALIA rabies, la frequentation par chacune de microhabitats differents dans la prairie peut contribuer ä diminuer la competition entre elles. O. rutilans en periode de reproduction ne montre pas de preference pour Tun ou Pautre microhabitat. En automne et hiver, les individus non reproducteurs sont plus frequemment captures dans le microhabitat 1. Une importante reduction du couvert herbace entre les buissons de Cortaderia selloana (microhabitat 2) et sous les plantes dominantes du microhabitat 3, conduit ä penser que la predation peut etre un facteur important d'utilisation de Phabitat a 1 A. azarae et de . rutilans en automne et en hiver. L'aptitude au grimper que presente O. delticola doit contribuer ä diminuer Pimpact...

We employed a live-trapping grid encompassing several discrete vegetation patches to analyze spatial differences in the demographic structure of an Oxymycterus rufus (Fischer, 1814) population living on the delta of the Paraná River, Argentina. Abundance, residence and reproduction of both females and males have been associated with microhabitats where food (measured through the availability of arthropods) was more abundant, and were not associated with the plant cover of those microhabitats. Our results emphasize the importance of food availability in the spatial distribution of resident and reproductive individuals, and hence in the survival and breeding success of their populations in the Paraná delta area.

No abstract

The karyotype of specimens identified as Calomys lepidus, trapped at 3600 m above sea level in the Puna region, northwestern Argentina, was studied. All specimens analysed showed a 2n = 44 (NF(a) = 68) asymmetrical karyotype with 13 pairs of metacentric/submetacentric autosomes and 7 pairs of telocentric chromosomes. The X was a medium-sized submetacentric and the Y a small submetacentric chromosome. This karyotype was quite different from that previously described for C. lepidus from Peru (2n = 36, NF(a) = 68). However, both karyotypes may be easily interrelated by means of four centric fusions, and the chromosome complement of Punian C. lepidus fitted into a previously proposed chromosomal phylogeny of the genus. In addition, the spermatozoa of specimens corresponded to a morphological pattern previously described for other species of Calomys.

SUMMARY Fibroblasts from a patient with ICF syndrome were grown in the presence of excess of nucleotides, in media with different amounts of folic acid, and with caffeine in an attempt to induce the chromosomal anomalies observed in lymphocytes. We induced despiralisation and breakages in the centromeric heterochromatin of chromosomes 1 and 16 but not associations and multibranching. We suggest that the absence of the major chromosomal anomalies in fibroblasts from patients with ICF might be the result of both a longer G2 in these cells and differential patterns of interphase heterochromatin associations in the two tissues.The ICF syndrome is characterised by immunodeficiency, centromeric heterochromatin instability of chromosomes 1, 9, and 16, and facial anomalies.1