Allozymic characterization and evolutionary relationships in the Brazilian Akodon cursor species group (Rodentia-Cricetidae)

Zoonotic pathogens in Atlantic Forest wild rodents in Brazil: Bartonella and Coxiella infections

Zoonotic pathogens comprise a significant and increasing fraction of all emerging and re-emerging infectious diseases that plague humans. Identifying host species is one of the keys to controlling emerging infectious diseases. From March 2007 until April 2012, we collected a total of 131 wild rodents in eight municipalities of Rio de Janeiro, Brazil. We investigated these rodents for infection with Coxiella burnetii, Bartonella spp. and Rickettsia spp. In total, 22.1% (29/131) of the rodents were infected by at least one pathogen; co-infection was detected in 1.5% (2/131) of rodents. Coxiella burnetii was detected in 4.6% (6/131) of the wild animals, 17.6% of the rodents harbored Bartonella spp. No cases of Rickettsia were identified. Bartonella doshiae and Bartonella vinsonii were the species found on the wild mammals. This report is the first to note C. burnetii, B. doshiae and B. vinsonii natural infections in Atlantic Forest wild rodents in Brazil. Our work highlights the potential risk of transmission to humans, since most of the infected specimens belong to generalist species that live near human dwellings.

Karyotype composition of some rodents and marsupials from Chapada Diamantina (Bahia, Brasil)

The Chapada Diamantina (CD) is located in Bahia State, between 11-14° S and 41-43° W, being part of the Serra do Espinhaço. The occurrence of different habitats and transition areas permits an interesting mammal fauna composition, with species from different biomes living in sympatry. Species of Didelphimorphia and Rodentia are important members of mammal communities in almost all different habitats, and morphological and cytogenetic characters are important for a correct identification of most of these species. In this work 258 specimens of small mammals from the orders Didelphimorphia (six genera and six species) and Rodentia (two families, five Sigmodontinae tribes, nine genera and 11 species) were collected during the whole field work (44 nights with traps). Chromosome preparations were obtained from 145 specimens from the species: Marmosops incanus, Gracilinanus microtarsus, Monodelphis domestica, Akodon aff. cursor, Necromys lasiurus, Cerradomys sp., Oligoryzomys fornesi, O. nigripes, O. rupestris, Calomys expulsus, Rhipidomys macrurus, Wiedomys pyrrhorhinus and Thrichomys inermis. Didelphis albiventris, Micoureus demerarae, Thylamys karymii and Nectomys sp. were identified by morphological characters. Most analyzed specimens do not show karyotype variation. However, numerical chromosomic variation was found in two individuals of Akodon aff. cursor (2n = 15) and in one individual of Cerradomys sp. (2n = 51). Structural variation in karyotype was observed in seven individuals of Cerradomys sp., showing one additional pair of metacentric chromosomes.

Multiple origins of XY female mice (genus Akodon): phylogenetic and chromosomal evidence

Despite the diversity in sex determination across organisms, theory predicts that the evolution of XY females is rare in mammals due to fitness consequences associated with infertility or the loss of YY zygotes. We investigated this hypothesis from a phylogenetic perspective by examining the inter- and intraspecific distribution of Y chromosomes in males and females (XY females) in South American field mice (Akodon). We found that XY females occurred at appreciable frequencies (10-66%) in at least eight Akodon species, raising the possibility that this system of sex determination has arisen multiple times independently. To determine the number of origins of XY females in Akodon, we constructed a molecular phylogeny of 16 species of Akodon based on mitochondrial DNA control region sequences. Both parsimony and maximum-likelihood reconstruction of ancestral states suggest that multiple steps (gains or losses of XY females) best explain the evolution of XY females, but do not clearly differentiate between single and multiple origins. We then directly compared functional and non-functional Y chromosomes in six species by Southern blot analysis. We found that male and female Y chromosome restriction fragment length polymorphism patterns were identical within species, but always differed between species, providing evidence that XY females arose at least six times within the Akodon lineage. To our knowledge, this pattern in Akodon is the first documentation of a novel sex-determining system arising multiple times within a tight clade of mammals. In addition, this system provides a clear test of the accuracy of phylogenetic methods to reconstruct ancestral states.