Mariela Nieves

Phylogenetic relationships among some Ateles species: the use of chromosomic and molecular characters

As with most platyrrhines, the systematics of Ateles is under discussion. In order to help clarify its systematic, we employed chromosomic and molecular characters to analyze the phylogenetic relationship among some species of the genus Ateles. Chromosomic studies were conducted on 14 atelid specimens: eight Ateles from A. paniscus, A. chamek, A. belzebuth and A. geoffroyi, and six Alouatta caraya. Ateles paniscus showed 2N=32, whereas A. chamek, A. belzebuth and A. geoffroyi presented 2N=34, XX/XY (with a submetacentric X and a variable Y) corroborated by male meiosis. Nucleotide sequence variation at the mitochondrial cytochrome c oxidase subunit II gene (COII) was analyzed in ten New World monkey specimens. Parsimony trees showed consistent phylogenetic relationships using both chromosomic forms and mitochondrial COII gene sequences as characters. Particularly, chromosomic phylogenies showed A. hybridus as a divergent taxon from the remaining group, whereas A. chamek, A. belzebuth and A. marginatus form an unresolved clade with A. geoffroyi as sister group.

Analysis of the heterochromatin of Cebus (Primates, Platyrrhini) by micro-FISH and banding pattern comparisons

The karyotype of the neotropical primate genus Cebus (Platyrrhini: Cebidae), considered the most ancestral one, shows the greatest amount of heterochromatin described among Platyrrhini genera. Banding techniques and restriction enzyme digestion have previously revealed great variability of quantity and composition of heterochromatin in this genus. In this context, we use fluorescence in situ hybridization (FISH) to analyse this genomic region and discuss its possible role in the diversification of Cebus. We used a heterochromatin probe for chromosome 11 of Cebus libidinosus (11qHe+ CLI probe), obtained by chromosome microdissection. Twenty-six specimens belonging to the families Atelidae, Cebidae, Callitrichidae and Pithecidae (Platyrrhini) were studied. Fourteen out of 26 specimens were Cebus (Cebidae) individuals of C. libidinosus, C. xanthosternos, C. apella, C. nigritus, C. albifrons, C. kaapori and C. olivaceus. In Cebus specimens, we found 6 to 22 positive signals located in interstitial and telomeric positions along the different species. No hybridization signal was observed among the remaining Ceboidea species, thus reinforcing the idea of a Cebus-specific heterochromatin composed of a complex system of repetitive sequences.

Multiple sex chromosome systems in howler monkeys (Platyrrhini, Alouatta).

Abstract In light of the multiple sex chromosome systems observed in howler monkeys (Alouatta Lacépède, 1799) a combined cladistic analysis using chromosomal and molecular characters was applied to discuss the possible origin of these systems. Mesoamerican and South American howlers were karyologically compared. FISH analysis using the chromosome painting probes for the #3 and #15 human chromosomes was applied to corroborate the homeology of the sexual systems. We found that the HSA3/15 syntenic association, present in the sex chromosome systems of South American Howlers, is not present in those of Mesoamerican ones. The autosomes involved in the translocation that formed the sexual systems in the Mesoamerican and South American species are different, thus suggesting an independent origin. Parsimony analysis resolved the phylogenetic relationships among howler species, demonstrating utility of the combined approach. A hypothesis for the origin of the multiple sex chromosome systems for the genus is proposed.

Cytogenetics of Howler Monkeys

Cytogenetic studies of howler monkeys show diploid numbers ranging from 2N = 43 in Alouatta seniculus to 2N = 58 in A. pigra with several interspecific chromosomal rearrangements such as translocations and inversions. Other remarkable genetic features are the multiple sex chromosome systems and the presence of microchromosomes. Multiple sexual systems are originated by Y-autosome translocations, resulting in the formation of trivalents X1X2Y in males of A. belzebul and A. palliata and quadrivalents X1X2Y1Y2 in males of A. seniculus, A. pigra, A. macconnelli, and A. caraya. Fluorescence in situ hybridization (FISH) analyses in the South American species have revealed that segments with homeology to human chromosomes #3 and #15 (synteny 3/15) are involved in these sexual systems. Different authors agreed with the assumption that these diverse sex chromosome systems share the same autosomal pair and the rearrangement may have occurred once. Recent cytogenetic characterization of A. pigra and A. palliata has shown that the autosomes involved in the translocation that formed the sex chromosome systems in the Mesoamerican and South American species are different. Two independent events of Y-autosome translocations might have led to different sexual systems. Together with the multiple autosomal rearrangements found in the genus, the howler monkey’s sex chromosome systems constitute an illustrative example of the possible chromosomal evolutionary mechanisms in Platyrrhini.

Intra and Interspecific Variation in Cranial Morphology on the Southernmost Distributed Cebus (Platyrrhini, Primates) Species

Capuchin monkeys (Cebus) are one of the genera with the widest distribution among Neotropical primates (New World Monkeys, Platyrrhini), accompanied by an elevated genetic, phenotypic, behavioral, morphological, and ecological diversity, both at the interspecific and population levels. Despite being one of the most studied primate genera, this high diversity has led to a particularly complex and controversial taxonomy. In this contribution, we explored the patterns of skull size and shape variation among the southernmost distributed populations of Cebus using three-dimensional geometric morphometric techniques. Results showed a marked morphological differentiation (in size and shape) between previously recognized species (C. nigritus and southern C. libidinosus), and also among C. libidinosus populations, which were quantitatively related with the geographic distance between them. This pattern supports a differentiation between the northwestern Argentina and southern Bolivia and Paraguay forms. Other taxonomic implications are also discussed.

Association between Genomic Instability and Evolutionary Chromosomal Rearrangements in Neotropical Primates

Abstract During the last decades, the mammalian genome has been proposed to have regions prone to breakage and reorganization concentrated in certain chromosomal bands that seem to correspond to evolutionary breakpoints. These bands are likely to be involved in chromosome fragility or instability. In Primates, some biomarkers of genetic damage may be associated with various degrees of genomic instability. Here, we investigated the usefulness of Sister Chromatid Exchange as a biomarker of potential sites of frequent chromosome breakage and rearrangement in Alouatta caraya, Ateles chamek, Ateles paniscus, and Cebus cay. These Neotropical species have particular genomic and chromosomal features allowing the analysis of genomic instability for comparative purposes. We determined the frequency of spontaneous induction of Sister Chromatid Exchanges and assessed the relationship between these and structural rearrangements implicated in the evolution of the primates of interest. Overall, A. caraya and C. cay presented a low proportion of statistically significant unstable bands, suggesting fairly stable genomes and the existence of some kind of protection against endogenous damage. In contrast, Ateles showed a highly significant proportion of unstable bands; these were mainly found in the rearranged regions, which is consistent with the numerous genomic reorganizations that might have occurred during the evolution of this genus.

Accuracy Assessment of Datasets on the Geographic Distribution of Aotus spp. Using a New Georeferencing Reliability Index

Studies on species distribution models evaluate the reliability and discrimination capacity of the models, while the accuracy of the spatial component of the data is often disregarded. The objective of our work was to design and validate an index, the Georeferencing Reliability Index (GRI), to measure and compare quality of different databases containing presence data of Aotus species. The database of A. lemurinus showed the highest georeferencing accuracy (GRI = 0.608) and that of A. zonalis the lowest (GRI = 0.167). Results indicated that there is poor-quality spatial information data for Aotus spp. Therefore, the distribution areas of all species should be more accurately established to evaluate whether they are at conservation risk. In addition, the index can be used to select the most accurate spatial data for constructing a species distribution model. Finally, we strongly believe that the GRI may provide accurate, up-to-date information essential for wildlife management programs.