Comparative gene assignment in Ateles paniscus chamek (Platyrrhini, Primates) and man: association of three separate human syntenic groups and evolutionary considerations

Regional assignment of eight markers to chromosome 2 of Ateles paniscus chamek (APC) confirmed a syntenic association similar to human (HSA) 12q + 14q + 15q. Three HSA 12q markers (RAP1B, PAH and ALDH2) were allocated to a shortest region of overlap (SRO) in APC 2p and found to be syntenic to other HSA 12q markers (PEPB and TCF1). Five HSA 14q markers (CTLA, PAX9, NSP, FOS and CHGA) were allocated to APC 2q and found to be syntenic to other HSA 14q markers (NP, TGM1, and CALM1) and to four HSA 15q markers (THBS1, B2M, HEXA and MPI) but dissociated from markers close to HSA 14qter (CKB) and HSA 15qter (FES-IDH2). Karyotypic comparisons showed an evident homoeology between APC 2p and HSA 12q while APC 2q was similar to an HSA 14qter::HSA 15qter fusion product. Comparative gene mapping data show that the HSA 14q + HSA 15q syntenic association is an ancestral mammalian gene cluster that has been maintained in several primate taxa. Conversely, in Ateles, it has been further associated with HSA 12q while, in Hominoids and Cebus, it has been independently dissociated into two separate syntenic groups, similar to HSA 14q and HSA 15q. Received: 24 October 1997; in revised form: 10 December 1997 / Accepted: 20 December 1997     

Multi-directional chromosome painting maps homologies between species belonging to three genera of New World monkeys and humans

We mapped chromosomal homologies in two species of Chiropotes (Pitheciini, Saki Monkeys) and one species of Aotus (Aotinae, Owl Monkey) by multi-directional chromosome painting. Human chromosome probes were hybridized to Chiropotes utahicki, C. israelita and Aotus nancymae metaphases. Wooly Monkey chromosome paints were also hybridized to Owl Monkey metaphases. We established Owl Monkey chromosome paint probes by flow sorting and reciprocally hybridized them to human chromosomes. The karyotypes of the Bearded Saki Monkeys studied here are close to the hypothesized ancestral platyrrhine karytoype, while that of the Owl Monkey appears to be highly derived. The A. nancymae karyotype is highly shuffled and only three human syntenic groups were found conserved coexisting with 17 derived human homologous associations. A minimum of 14 fissions and 13 fusions would be required to derive the A. nancymae karyotype from that of the ancestral New World primate karyotype. An inversion between homologs to segments of human 10 and 16 suggests a link between Callicebus and Chiropotes, while the syntenic association of 10/11 found in Aotus and Callicebus suggests a link between these two genera. Future molecular cytogenetic work will be needed to determine whether these rearrangements represent synapomorphic chromosomal traits.     

Colonization process of the Brazilian common vesper mouse, Calomys expulsus (Cricetidae, Sigmodontinae): a biogeographic hypothesis

Riverine barriers have been associated to genetic diversification and speciation of several taxa. The Rio S?o Francisco is one of the largest rivers in South America, representing the third largest river basin in Brazil and operating as a geographic barrier to gene flow of different taxa. To evaluate the influence of the Rio S?o Francisco in the speciation of small rodents, we investigated the genetic structure of Calomys expulsus with phylogenetic and network analyses of cytochrome b DNA. Our results suggested that C. expulsus can be divided into 3 subpopulations, 2 on the left and another one on the right bank of this river. The time of divergence of these subpopulations, using a Bayesian framework, suggested colonization from the south to the north/northeast. Spatial analysis using a clustering method and the Monmonier's algorithm suggested that the Rio S?o Francisco is a biogeographic barrier to gene flow and indicated that this river may play a role in the incipient speciation process of these subpopulations.     

Cytochrome b polymorphisms and population structure of two species of Alouatta (Primates)

We carried out a phylogenetic and population study in Alouatta caraya and Alouatta belzebul based on cytochrome b DNA sequence data. Maximum Parsimony and Median-Joining analyses grouped A. caraya from different localities showing a population structure in accordance with geographic distribution. The relation between A. caraya haplotypes could be explained with respect to the species range in the Cerrado, one of the most ancient morphoclimatic domains of South America, and the Chaco. Conversely, A. belzebul from the Amazonas and Atlantic forests grouped in a paraphyletic arrangement without an evident geographic pattern. Recent geologic events resulting in the separation of A. belzebul might explain why these geographically distant groups shared similar haplotypes and why ancestral polymorphisms might have been maintained in this species. Time of divergence estimates indicated that the splitting of the Alouatta lineage leading to A. caraya occurred some 4.58 MYA while the lineage leading to A. belzebul emerged 4.14 MYA.     

Phylogeographic analyses of Callicebus lugens (Platyrrhini, Primates)

A phylogeographic study of Callicebus lugens was carried out based on cytochrome b DNA sequence data. Here, we report, for the first time, the distribution of C. lugens south of the Rio Negro, in Barcelos municipality (Amazonas State, Brazil), indicating that this river is not the southern boundary of the distribution of this species as previously proposed. Specimens from the north and south banks showed the same diploid number (2n = 16), while phylogenetic reconstructions based on maximum parsimony, distance, and maximum likelihood analyses grouped all specimens in a strongly supported clade comprising 2 separate lineages, in coincidence with their geographic distribution along riverbanks. Median-joining analysis showed a similar separation, with 22 transitions between the 2 groups, whereas time of divergence estimates indicated that the splitting of the C. lugens lineages occurred some 2.2 million years before present. Conservation strategies should take into consideration that this species might be sympatric with Callicebus torquatus at the south bank of Rio Negro.     

Reanalysis of the biogeographical hypothesis of range expansion between robust and gracile capuchin monkeys

The data used by Lynch Alfaro et al. (2012a, Journal of Biogeography, 39 , 272–288) and the biogeographical hypothesis postulated by these authors to explain the current distribution of capuchin monkeys were reanalysed including additional cytochrome b data from Sapajus xanthosternos and Sapajus flavius. Our reconstructed phylogeny placed S. xanthosternos in a monophyletic clade representing the most basal lineage of this genus. All analyses indicated polyphyletic arrangements for several capuchin species, suggesting that incomplete lineage sorting has occurred during their evolution. These results also suggest that available molecular data lack adequate variation for accurately resolving species relationships. These results suggest that the divergence of capuchin monkey genera may have occurred in the Atlantic Forest. However, a more conclusive scenario and better resolution of the species tree requires correct identification of species, data from several unlinked nuclear loci from a higher number of individuals per species, and careful analysis of ancient DNA data from museum specimens.     

Molecular phylogeny of the genus Oryzomys (Rodentia: Sigmodontinae) based on cytochrome b DNA sequences

The genus Oryzomys comprises 40 species arranged in several species groups. To test the monophyly of three Oryzomys species groups ("capito," nitidus, and subflavus), we analyzed, by distance, parsimony, and maximum-likelihood (ML), 801 bp of the mitochondrial gene cytochrome b. Our results did not sustain the monophyly of Oryzomys nor of the nitidus and subflavus species groups. Within the "capito" species group, O. perenensis appeared as a valid species, as a sister branch of the clade formed by O. megacephalus and O. laticeps. Within the nitidius species group, only the association between O. nitidus and O. lamia was well supported.The subflavus species group split into two clades: one with O. subflavus karyomorphotypes and another grouping O. angouya with species of different genera in the parsimony, distance, and ML trees.     

Reproductive isolation due to the genetic incompatibilities between Thrichomys pachyurus and two subspecies of Thrichomys apereoides (Rodentia, Echimyidae).

We tested intrinsic reproductive isolation between 3 taxa of the South American caviomorph rodent Thrichomys (Rodentia, Echimyidae): T. pachyurus, T. apereoides subsp. apereoides and T. apereoides subsp. laurentius. They were mated in captivity and produced viable progeny. Some F1 hybrid females were fertile, whereas all F1 males were sterile. Histological examination revealed meiotic arrest at the primary spermatocyte stage. No sperm was detected in testes or epididymes. Electron microscopic analysis of surface spread synaptonemal complexes revealed a complete failure of chromosome pairing in F1 hybrids of T. pachyurus with T. apereoides subsp. laurentius and T. apereoides subsp. apereoides. In the male hybrids between T. apereoides subsp. apereoides and T. apereoides subsp. laurentius, meiosis did not proceed beyond diplotene, although all of the chromosomes, including heteromorphic ones, paired in an orderly fashion. Backcross males with homomorphic karyotypes showed segregation in meiosis progression. This indicates that male hybrid sterility is due to genetic, but not chromosomal, incompatibility of the parental taxa.     

A new karyotype of Oligoryzomys (Sigmodontinae, Rodentia) from central Brazil

A new karyotype of the genus Oligoryzomys was described for specimens collected in Brazilian Cerrado in Tocantins and Goiás States. Conventional staining, G-, C-banding, and Ag-NOR staining techniques were used for describe this karyotype with 2n=70, AN=74 or 76. The chromosome complement, with the highest diploid number known among Oligoryzomys species, differs from all others previously reported. This small sized Oligoryzomys species can be differentiated from other Brazilian Oligoryzomys not only by chromosomal complement, but also in some morphological attributes. The new species is apparently restricted in distribution and endemic of Brazilian Cerrado, occurring only in Rio Tocantins basin.     

A new species of sigmodontine rodent from the Atlantic forest of eastern Brazil

We describe a new sigmodontine species on the basis of three specimens obtained from a high-altitude locality in the Atlantic forest of eastern Brazil. This new form, a small-bodied pentalophodont with tail longer than head and body, long soft fur, and a brownish ochraceous dorsum, is diagnosed by the presence of an open slit in the suture between the frontal bones in prepared skulls, and by a reduced diploid number of 20 coupled with a relatively high fundamental number of 34. Although the low diploid number suggests a derived sigmodontine, analyses of morphological characters and DNA sequence data (720 bp of the cytochrome-b gene) point to its placement within the recently described genusJuliomys González, 2000, a taxon regarded as belonging to an old and independent sigmodontine lineage. This finding reinforces current hypotheses of the Atlantic forest domain as an important center of diversification for a primitive sigmodontine stock. It also suggests that at least some surviving lineages, often considered rather ancient and unspeciose relicts, were subject to relatively more recent speciation events.