Karyotypes of Brazilian non-volant small mammals (Didelphidae and Rodentia): An online tool for accessing the chromosomal diversity

A new species of Akodon Meyen, 1833 (Rodentia: Cricetidae: Sigmodontinae) endemic from the Brazilian Cerrado

Akodon is the second most diverse genus of sigmodontine rodents, comprising 40 extant species. Widely distributed through different environments of South America, the genus ranges from forested to open-vegetation areas, from semiarid to mesic regions, and from Andean altitudes to the lowlands of eastern Brazil. In Brazil, most species are from the Atlantic Forest, inhabiting lowland and montane habitats, with a few taxa also present in areas transitional with the Cerrado and Pantanal. Based on an integrative approach of genetics (cytogenetic and molecular data) and morphology (qualitative and quantitative external and craniodental data), we present in this contribution the hypothesis of a new species of Akodon based on specimens collected in the southwestern limit of the Cerrado domain, in the seasonally dry forests of the Serra da Bodoquena, Mato Grosso do Sul, Brazil. The new species was recovered as a distinct lineage sister to Akodon philipmyersi, a poorly known species from the Northern Campos grasslands of Misiones Province, Argentina, and can be distinguished from its congeners by its karyotype (2n = 40, FN = 40), morphology (morphometric, pelage, and skull characters), as well as by its degree of genetic divergence (above 7.5% in Cytb sequences). This new species is endemic to the Cerrado, one of the world’s biodiversity hotspots, and to Serra da Bodoquena, one of the top priority areas for conservation in Brazil. Moreover, the new species increases the number of lineages of Akodon in Brazil, emphasizing the richness and endemism currently found in the Cerrado domain, and the importance of the open formations to the diversification of Neotropical taxa.

Introducing the Bird Chromosome Database: An Overview of Cytogenetic Studies in Birds

Bird chromosomes, which have been investigated scientifically for more than a century, present a number of unique features. In general, bird karyotypes have a high diploid number (2n) of typically around 80 chromosomes that are divided into macro- and microchromosomes. In recent decades, FISH studies using whole chromosome painting probes have shown that the macrochromosomes evolved through both inter- and intrachromosomal rearrangements. However, chromosome painting data are available for only a few bird species, which hinders a more systematic approach to the understanding of the evolutionary history of the enigmatic bird karyotype. Thus, we decided to create an innovative database through compilation of the cytogenetic data available for birds, including chromosome numbers and the results of chromosome painting with chicken (Gallus gallus) probes. The data were obtained through an extensive literature review, which focused on cytogenetic studies published up to 2019. In the first version of the "Bird Chromosome Database (BCD)" (https://sites.unipampa.edu.br/birdchromosomedatabase) we have compiled data on the chromosome numbers of 1,067 bird species and chromosome painting data on 96 species. We found considerable variation in the diploid numbers, which ranged from 40 to 142, although most (around 50%) of the species studied up to now have between 78 and 82 chromosomes. Despite its importance for cytogenetic research, chromosome painting has been applied to less than 1% of all bird species. The BCD will enable researchers to identify the main knowledge gaps in bird cytogenetics, including the most under-sampled groups, and make inferences on chromosomal homologies in phylogenetic studies.