Cytogenetic diversity of non-volant small mammals in the Serra dos Órgãos region, Rio de Janeiro state, Brazil

Abstract

The Atlantic Forest is one of South America's most biodiverse regions, hosting a significant portion of Brazil's small non-volant mammal diversity, including 267 rodent and 66 marsupial species.  The Serra dos Órgãos region in Rio de Janeiro state is a key area for studying this diversity, as it houses 32 rodent and 13 marsupial species.  Rodents, unlike marsupials, exhibit a high diversity of chromosomal forms, which serve as important taxonomic tools for identifying cryptic species.  Our study used cytogenetic analyses to enhance the taxonomic resolution and understanding of small mammal biodiversity in the Serra dos Órgãos, focusing on the high chromosomal variation in rodents, particularly those within the Sigmodontinae.  We collected and karyotyped specimens from 25 localities within the municipalities of Cachoeiras de Macacu, Guapimirim, Petrópolis, and Teresópolis in Rio de Janeiro.  These areas include montane and lowland regions of the Serra dos Órgãos, ranging from 100 to 2,100 meters in altitude.  Specimens were captured using live traps and handled following ethical guidelines, with karyotypic analysis performed on metaphase chromosomes obtained from bone marrow cell cultures.  We analyzed 220 specimens, representing 20 rodent and five marsupial species.  Significant intraspecific chromosomal variation was observed in seven rodent species, particularly within the sigmodontines.  Akodon cursor displayed variation in fundamental numbers, while Brucepattersonius nebulosus exhibited variation in both diploid and fundamental numbers. New karyotypes were identified for the echimyid Phyllomys spp..  Our findings underscore the importance of cytogenetic analyses in revealing cryptic species and enhancing taxonomic resolution among South American rodents.  The chromosomal variation observed highlights the need for integrating cytogenetic data to understand the evolutionary dynamics and biodiversity of the Atlantic Forest.