The forest refuge hypothesis (FRH) has long been a paradigm for explaining the extreme biological diversity of tropical forests. According to this hypothesis, forest retraction and fragmentation during glacial periods would have promoted reproductive isolation and consequently speciation in forest patches (ecological refuges) surrounded by open habitats. The recent use of paleoclimatic models of species and habitat distributions revitalized the FRH, not by considering refuges as the main drivers of allopatric speciation, but instead by suggesting that high contemporary diversity is associated with historically stable forest areas. However, the role of the emerged continental shelf on the Atlantic Forest biodiversity hotspot of eastern South America during glacial periods has been ignored in the literature. Here, we combined results of species distribution models with coalescent simulations based on DNA sequences to explore the congruence between scenarios of forest dynamics through time and the genetic structure of mammal species cooccurring in the central region of the Atlantic Forest. Contrary to the FRH predictions, we found more fragmentation of suitable habitats during the last interglacial (LIG) and the present than in the last glacial maximum (LGM), probably due to topography. We also detected expansion of suitable climatic conditions onto the emerged continental shelf during the LGM, which would have allowed forests and forest-adapted species to expand. The interplay of sea level and land distribution must have been crucial in the biogeographic history of the Atlantic Forest, and forest refuges played only a minor role, if any, in this biodiversity hotspot during glacial periods.T he extreme biological diversity of tropical forests has inspired and puzzled naturalists and scientists for centuries, and the forest refuge hypothesis (FRH) has long been one of the major paradigms to explain it. According to the FRH, forest retraction and fragmentation during glacial periods would have promoted isolation and consequently allopatric speciation in forest patches, or ecological refuges, surrounded by open habitats in the Amazon (1). Although originally based on climate fluctuations in the Pleistocene, the FRH was subsequently invoked for climate changes irrespective of the time period (2). The FRH was also applied to South America's Atlantic Forest (3), one of the topfive biodiversity hotspots on Earth (4). The FRH gained broad acceptance during the 1980s when empirical paleoecological data from neotropical rainforests were still lacking. Nevertheless, heavy criticism came upon the FRH because some paleobotanical data showed that forests had persisted throughout glacial cycles (5). As paleoclimatic models of species and habitats became widely used, recent studies revitalized the FRH, not by considering refuges as the main drivers of allopatric speciation, but instead by suggesting that high contemporary diversity and endemism are associated with historically stable Atlantic Forest areas (6).This hypothesis is ba...

The karyotypes of 85 specimens of Oligoryzomys nigripes (Rodentia, Sigmodontinae) collected in the Cerrado and Atlantic Forest of seven states of Brazil were analyzed. Eighty four specimens presented a karyotype with 2n = 62 and one individual had 2n = 61 due to a monosomy of the X chromosome. High levels of intra-and inter-population karyotypic variability, due to sex chromosomes heteromorphisms and pericentric inversions in four autosomes (pairs 2, 3, 4 and 8), led to a variation of the autosomal arm numbers (fundamental number, FN) from 78 to 82. Synaptonemal complex analyses revealed normal meiosis in males heterozygous for pericentric inversions. We found 39 different cytotypes, 27 of which are herein described for the first time. A literature survey revealed 46 described karyotypes for O. nigripes. We tested the hypothesis that chromosomal variants frequencies are dependent on geographical distribution and we propose a model for the karyotypical evolution of Oligoryzomys nigripes with 2n = 62/FN = 78-82.

We report the results of a terrestrial small mammal survey at one National Park in the northeastern Brazil, in the state of Pernambuco. The Catimbau National Park is located within the Caatinga domain with the characteristic thorn scrub vegetation. Our sampling encompasses several different vegetation/habitat types within the park area. All specimens collected were prepared as vouchers to be deposited in the Museu de Zoologia da Universidade de São Paulo. Karyotypes were obtained for all representative purported species collected. We report here the results of this first survey – two species of marsupials and seven of rodents - and added new occurrence localities for several small mammal species of this region, provide karyotypic information and register an undescribed species of arboreal rat of the genus Rhipidomys. This survey illustrates the need for extensive and planned sampling of the Caatinga domain.

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