Molecular phylogenetics of howler monkeys (Alouatta, Platyrrhini). A comparison with karyotypic data

Dentin hardness differences across various mammalian taxa

Differences in dentin microstructure have been used as a tool for dietary reconstruction; however, the extent that diet is associated with this aspect of dental morphology has yet to be empirically tested. We conducted microhardness tests of mammalian dentin sections, hypothesizing that species with adaptations to particularly hard diets would have softer dentin, owing to a higher proportion of soft intertubular dentin. Species adapted to abrasive diets, in contrast, should have harder dentin, resulting from a higher proportion of hypermineralized peritubular dentin. We examined molar dentin hardness in ten mammalian taxa with durophagous diets, abrasive diets, and a comparative "control" group of mechanical generalists. Samples included six primate taxa and four non-primate species representing various dietary regimes. Our results reveal significant variation among taxa in overall hardness, but the data do not distinguish between hard and abrasive diets. Several taxa with generalized (i.e., mechanically diverse) diets resemble each other in exhibiting large variance in hardness measurements and comparably soft dentin. The high variation in these species appears to be either a functional signal supporting the niche variation hypothesis or indicate the absence of sustained unidirectional selective pressure. A possible phylogenetic signal of dentin hardness in the data also holds promise for future systematic investigations.

Phylogenetic relationships, population demography, and species delimitation of the Alouatta belzebul species complex (Atelidae: Alouattinae)

Howler monkeys (genus Alouatta) exhibit the most extensive distribution among platyrrhines, comprising Mesoamerican and South American species groups, with the South American group including the Brazilian endemic A. belzebul species complex encompassing A. belzebul, A. discolor, and A. ululata. We herein analyzed their phylogenetic relationship, nucleotide and haplotype diversity, and population demography based on the mitochondrial gene cytochrome b. The phylogenetic and median-joining network analyses distinguished A. discolor, distributed in the west bank of the Xingu River, from A. belzebul on the east bank. This river is a zoogeographic barrier for these species. We did not find evidence of phylogenetic structure between the A. belzebul populations of opposite banks of the Tocantins River, likely related to the changes in the position of this river to the northeast in the late Pleistocene. The A. belzebul along this river showed great morphologic and haplotype diversity, and A. belzebul from the Amazon have kept a larger population size than A. discolor. We herein describe the karyotype of A. discolor, which was similar to those described for A. ululata and A. belzebul. Our results showed two well-defined and supported clades for A. discolor and A. belzebul. However, a new assessment of A. ululata across a large distribution of sampling is required due to the lack of a clear phylogenetic structure.

Phylogenetic relationships among Capuchin (Cebidae, Platyrrhini) lineages: An old event of sympatry explains the current distribution of Cebus and Sapajus

Capuchin monkeys are currently represented by four species of Cebus and eight of Sapajus. This group is taxonomically complex and several questions still need to be clarified. In the current study, using mtDNA markers and a larger sample representation than in previous studies, we seek to understand the phylogenetic relationships among the capuchin lineages and their historical biogeography. All 12 species of capuchins were analyzed for the mitochondrial Control Region and Cytochrome b to test two biogeographical hypotheses: "Reinvasion of the Amazon (ROA)" and "Sympatric Evolution (SEV)". The phylogenetic relationships among distinct lineages within genera is consistent with an evolutionary diversification pattern probably resulting from an explosive process of diversification and dispersal between 2.0 Ma and 3.0 Ma. Also, the analyses show that the ancestral capuchins were distributed in a wide area encompassing the Amazon and Atlantic Forest. Our results support the SEV hypothesis, showing that the current syntopic distribution of Cebus and Sapajus can be explained by a sympatric speciation event in the Amazon. We also indicate that the recently proposed species taxonomy of Cebus is not supported, and that S. cay and S. macrocephalus are a junior synonym of S. apella.

Phylogeography of the Mantled Howler Monkey (Alouatta palliata; Atelidae, Primates) across Its Geographical Range by Means of Mitochondrial Genetic Analyses and New Insights about the Phylogeny of Alouatta

We analyzed 156 specimens of diverse howler monkey taxa (Alouatta; Atelidae, Primates) for different mitochondrial genes (5,567 base pairs), with special emphasis on A. palliata and related taxa. Our results showed no relevant differences among individuals of different putative taxa, A. p. palliata, A. p. aequatorialis, A. coibensis coibensis, and A. c. trabeata. We found no spatial differences in genetic structure of A. p. palliata throughout Costa Rica, Nicaragua, and Honduras. A. p. mexicana (genetic distance: 1.6-2.1%) was the most differentiated taxon within A. palliata. Therefore, we postulate the existence of only 2 clearly defined subspecies within A. palliata (A. p. palliata and A. p. mexicana). A. palliata and A. pigra (traditionally considered a subspecies of A. palliata) are 2 clearly differentiated species as was demonstrated by Cortés-Ortiz and colleagues in 2003, with a temporal split between the 2 species around 3.6-3.7 million years ago (MYA). Our results with the Median Joining Network procedure showed that the ancestors of the cis-Andean Alouatta gave rise to the ancestors of the trans-Andean Alouatta around 6.0-6.9 MYA. As Cortés-Ortiz et al. showed, A. sara and A. macconnelli are differentiable species from A. seniculus, although the first 2 taxa were traditionally considered subspecies of A. seniculus. Our findings agree with the possibility that the ancestor of A. sara gave rise to the ancestor of A. pigra in northern South America. In turn, the ancestor of A. pigra originated the ancestor of A. palliata. Two of our results strongly support the hypothesis that the South American A. palliata (the putative A. p. aequatorialis) was the original population of this species; it has high genetic diversity and no evidence of population expansion. The Central America A. palliata is the derived population. It has low genetic diversity and there is clear evidence of population expansion. However, A. palliata and A. pigra probably migrated into Central America by 2 different routes: the Isthmus of Panama (A. palliata) and Caribbean island arch (A. pigra). Finally, the red howler monkeys from the island of Trinidad in the Caribbean Sea were not A. macconnelli (= A. s. stramineus) as Groves maintained in his influential 2001 publication on primate taxonomy. This taxon is more related to A. s. seniculus, although it formed a monophyletic clade. Future molecular and karyotypic studies will show if the Trinidad red howler monkeys should be considered as an extension of the Venezuelan taxon, A. arctoidea, as a subspecies of A. seniculus(A. s. seniculus), or, in the case of extensive chromosomal rearrangements, even a new species.

Cranial shape variation in adult howler monkeys (Alouatta seniculus)

Howler monkeys (genus Alouatta) display a distinctive cranial architecture characterized by airorhynchy (or retroflexion of the facial skeleton on the cranial base), a small braincase, and a posteriorly oriented foramen magnum. This configuration has been associated with distinct factors including a high folivory diet, locomotion, and the presence of a specialized vocal tract characterized by large hyoid bone. However, the morphological relationships between the facial and neurocranial blocks in Alouatta have been scarcely investigated. In this study we quantitatively analyzed the cranial shape variation in Alouatta seniculus, to evaluate possible influences and constraints in face and braincase associated with airorhynchy. We also considered the structural role of the pteric area within the cranial functional matrix. We applied landmark-based analysis and multivariate statistics to 31 adult crania, computing shape analyses based on 3D coordinates registration as well as the analysis of the Euclidean distance matrix to investigate patterns of intraspecific morphological variability. Our results suggest that allometry is the main source of variation involved in shaping cranial morphology in howlers, influencing the degree of facial proportions and braincase flattening, and generating the main sexual differences. Larger individuals are characterized by a higher degree of airorhynchy, neurocranial flattening, and expansion of the zygomatic arch. Allometric variations influence the skull as a whole, without distinct patterns for face and braincase, which behave as an integrated morphological unit. A preliminary survey on the pteric pattern suggests that the morphology of this area may be the result of variations in the vertical growth rates between face and braincase. Future studies should be dedicated to the ontogenetic series and focus on airorhynchy in terms of differential growth among distinct cranial districts.

Morphological and genetic diversity in Callithrix hybrids in an anthropogenic area in southeastern Brazil (Primates: Cebidae: Callitrichinae)

Two species of Callithrix, C. jacchus (Linnaeus, 1758) and C. penicillata (É. Geoffroy, 1812), are considered invasive in Rio de Janeiro. This study determined the genetic and morphological diversity and verified the species involved in the hybridization of 10 individuals from the municipalities of Silva Jardim (N = 9) and Rio das Ostras (N = 1). We compared the external morphology and skull of C. jacchus (N = 15) and C. penicillata (N = 14) specimens deposited in the collection of the National Museum of Rio de Janeiro (MN- UFRJ). Phylogenetic (maximum likelihood and Bayesian inference) and phylogeographical analyses (network analysis) were performed based on cytochrome b sequences. These analyses included hybrids from the metropolitan region of Rio de Janeiro (N = 3), C. penicillata (N = 2), C. jacchus (N = 2), C. geoffroyi (N = 2), C. kuhlii (N = 2), C. aurita (N = 1), and as outgroups, Mico emiliae (N = 1) and Saguinus mystax (N = 1). The pelage and skull characters of most hybrids were more closely related to C. jacchus. Skull morphometric analysis revealed an intermediate state for the hybrids. Phylogenetic analyses revealed a high similarity between the hybrids and C. penicillata. Six haplotypes of hybrids were identified. Network analysis including them and C. penicillata recovered the topology generated by phylogenetic analysis. The results corroborate that C. jacchus and C. penicillata participate in the hybridization process. There was no geographic structure between hybrids from the coastal lowlands and from the metropolitan region of Rio de Janeiro.

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

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.

Macroevolutionary dynamics and historical biogeography of primate diversification inferred from a species supermatrix

Phylogenetic relationships, divergence times, and patterns of biogeographic descent among primate species are both complex and contentious. Here, we generate a robust molecular phylogeny for 70 primate genera and 367 primate species based on a concatenation of 69 nuclear gene segments and ten mitochondrial gene sequences, most of which were extracted from GenBank. Relaxed clock analyses of divergence times with 14 fossil-calibrated nodes suggest that living Primates last shared a common ancestor 71-63 Ma, and that divergences within both Strepsirrhini and Haplorhini are entirely post-Cretaceous. These results are consistent with the hypothesis that the Cretaceous-Paleogene mass extinction of non-avian dinosaurs played an important role in the diversification of placental mammals. Previous queries into primate historical biogeography have suggested Africa, Asia, Europe, or North America as the ancestral area of crown primates, but were based on methods that were coopted from phylogeny reconstruction. By contrast, we analyzed our molecular phylogeny with two methods that were developed explicitly for ancestral area reconstruction, and find support for the hypothesis that the most recent common ancestor of living Primates resided in Asia. Analyses of primate macroevolutionary dynamics provide support for a diversification rate increase in the late Miocene, possibly in response to elevated global mean temperatures, and are consistent with the fossil record. By contrast, diversification analyses failed to detect evidence for rate-shift changes near the Eocene-Oligocene boundary even though the fossil record provides clear evidence for a major turnover event ("Grande Coupure") at this time. Our results highlight the power and limitations of inferring diversification dynamics from molecular phylogenies, as well as the sensitivity of diversification analyses to different species concepts.

Coalescent analysis of mtDNA indicates Pleistocene divergence among three species of howler monkey (Alouatta spp.) and population subdivision within the Atlantic Coastal Forest species, A. guariba

We have used coalescent analysis of mtDNA cytochrome b (cyt b) sequences to estimate times of divergence of three species of Alouatta--A. caraya, A. belzebul, and A. guariba--which are in close geographic proximity. A. caraya is inferred to have diverged from the A. guariba/A. belzebul clade approximately 3.83 million years ago (MYA), with the later pair diverging approximately 1.55 MYA. These dates are much more recent than previous dates based on molecular-clock methods. In addition, analyses of new sequences from the Atlantic Coastal Forest species A. guariba indicate the presence of two distinct haplogroups corresponding to northern and southern populations with both haplogroups occurring in sympatry within Sao Paulo state. The time of divergence of these two haplogroups is estimated to be 1.2 MYA and so follows quite closely after the divergence of A. guariba and A. belzebul. These more recent dates point to the importance of Pleistocene environmental events as important factors in the diversification of A. belzebul and A. guariba. We discuss the diversification of the three Alouatta species in the context of recent models of climatic change and with regard to recent molecular phylogeographic analyses of other animal groups distributed in Brazil.

Identification, classification and evolution of owl monkeys (Aotus, Illiger 1811)

BACKGROUND

Owl monkeys, belonging to the genus Aotus, have been extensively used as animal models in biomedical research but few reports have focused on the taxonomy and phylogeography of this genus. Moreover, the morphological similarity of several Aotus species has led to frequent misidentifications, mainly at the boundaries of their distribution. In this study, sequence data from five mitochondrial regions and the nuclear, Y-linked, SRY gene were used for species identification and phylogenetic reconstructions using well characterized specimens of Aotus nancymaae, A. vociferans, A. lemurinus, A. griseimembra, A. trivirgatus, A. nigriceps, A. azarae boliviensis and A. infulatus.

RESULTS

The complete MT-CO1, MT-TS1, MT-TD, MT-CO2, MT-CYB regions were sequenced in 18 Aotus specimens. ML and Bayesian topologies of concatenated data and separate regions allowed for the proposition of a tentative Aotus phylogeny, indicating that Aotus diverged some 4.62 Million years before present (MYBP). Similar analyses with included GenBank specimens were useful for assessing species identification of deposited data.

CONCLUSIONS

Alternative phylogenetic reconstructions, when compared with karyotypic and biogeographic data, led to the proposition of evolutionary scenarios questioning the conventional diversification of this genus in monophyletic groups with grey and red necks. Moreover, genetic distance estimates and haplotypic differences were useful for species validations.

Phylogeny and phylogeography of squirrel monkeys (genus Saimiri) based on cytochrome b genetic analysis

Squirrel monkeys (genus Saimiri) are distributed over a wide area encompassing the Amazon Basin: French Guiana, Suriname, and Guyana, together with Western Panama and Western Costa Rica. The genus Saimiri includes a complex of species and subspecies displaying considerable morphological variation. Taxonomic and systematic studies have identified, in this genus, one to seven species comprising up to 16 subspecies. The phylogenetic relationships between these taxa are poorly understood. Molecular markers have yielded a consistent framework for the systematics of Central and South American Saimiri, identifying four distinct clades: S. oerstedii, S. sciureus, S. boliviensis, and S. ustus. Here, we reconsider the phylogenetic and biogeographic history of Saimiri on the basis of mitochondrial (mtDNA) sequence data, focusing mostly on individuals originating from the Amazon Basin. We studied 32 monkeys with well-defined geographic origins and inferred the phylogenetic relationships between them on the basis of full-length cytochrome b gene nucleotide sequences. The high level of gene diversity observed (0.966) is consistent with the high level of behavioral and morphological variation observed across the geographic range of the genus: 20 mtDNA haplotypes were identified with a maximum divergence of 4.81% between S. b. boliviensis and S. ustus. In addition to confirming the existence of the four clades previously identified on the basis of molecular characters, we suggest several new lineages, including S. s. macrodon, S. s. albigena, S. s. cassiquiarensis, and S. s. collinsi. We also propose new patterns of dispersion and diversification for the genus Saimiri, and discuss the contribution of certain rivers and forest refuges to its structuring.

Mitochondrial divergence between 2 populations of the hooded capuchin, Cebus (Sapajus) cay (Platyrrhini, Primates)

We analyzed the molecular divergence of 2 separate populations of Cebus apella paraguayanus, recently considered a junior synonym of Cebus cay, and estimated its time of separation from C. apella. Cytochrome b DNA from 23 C. cay from Brazil and 9 from Paraguay showed 24 haplotypes (20 and 4, respectively), accounting for 29 variable sites (19 transitions and 10 transversions), with 40.0%, 26.7%, and 33.0% replacements at first, second, and third codon positions, respectively. Genetic distance between haplotypes averaged 0.5%, with 1.1% between C. cay populations. Phylogenetic reconstructions and median joining separated C. cay from Brazil and Paraguay. Neighbor joining showed C. cay and C. apella as sister groups, although C. cay and C. apella collapsed in maximum parsimony and maximum likelihood topologies. Analysis of molecular variance showed the highest variance component between C. cay populations, and mismatch distribution indicated that this species suffered a recent demographic expansion. Divergence time estimates suggested that the 2 populations of C. cay split in the Pleistocene, a period of repeated glaciation events leading to drastic changes in the vegetation composition of different biomes.

Population genetic studies of Alouatta caraya (Alouattinae, Primates): inferences on geographic distribution and ecology

Cytochrome b DNA sequence data (ca. 1,140 bp) of 44 Alouatta caraya, including 42 specimens from three localities of Brazil and two from Bolivia, were used for phylogenetic reconstructions and population studies. Seventeen haplotypes were identified, eight of which were present in more than one individual. Seven of these eight haplotypes were shared by individuals from a same locality and one by individuals from two localities. We found 26 variable sites along the entire gene, consisting of 18 transitions and eight transversions; most replacements occurring at the third codon position (65.39%) in contrast to first and second positions (26.92 and 7.69%, respectively). In the sample collected at Chapada dos Guimarães (Brazil), nucleotide and haplotype diversity estimates were pi=0.002325 and h=0.8772, respectively. Maximum parsimony analysis grouped all haplotypes in two clades, separating Bolivian haplotypes from Brazilian haplotypes, the grouping of which did not show a straightforward correspondence with geographic distribution. Median-joining and TCS network pointed to haplotypes 11 or 12 as the most likely ancestral ones. Mismatch distribution and the goodness-of-fit test (SSD estimate=0.0027; P=0.6999) indicated that the population from Chapada dos Guimarães experienced a demographic expansion, in agreement with the median-joining star-like pattern, although this finding could not be confirmed by Fu's F(s) test.

Genetic Variability in Four Alouatta Species Measured by Means of Nine DNA Microsatellite Markers: Genetic Structure and Recent Bottlenecks

We used microsatellite DNA to study the population genetics of 4 Alouatta species from Central and South America. Our main findings include the following: (1) A. seniculus had the highest level of microsatellite variability while A. caraya and A. palliata had the lowest mean number of alleles per locus and the lowest expected heterozygosity, respectively; (2) the samples of A. seniculus and A. palliata came from different regions and were not in Hardy-Weinberg equilibrium (HWE) which may indicate a Wahlund effect and differentiated gene pools -- in contrast, A. macconnelli and A. caraya were in HWE; (3) the microsatellite genetic heterogeneity of the 4 Alouatta species was similar to the karyotype divergence found among these Alouatta species; the species pair with the lowest level of heterogeneity (genetic differentiation) was A. seniculus/A. caraya, while the Central American species, A. palliata, was highly differentiated from the other 3 South American species; (4) we recommend the establishment of a conservation plan to help protect A. caraya because the Cornuet and Luikart procedure demonstrated a recent bottleneck for this species.

Mitochondrial sequence diversity of the southernmost extant New World monkey, Alouatta caraya

Variability in mitochondrial DNA sequences was analyzed in the howler monkey, Alouatta caraya, in order to delineate evolutionary relationships among populations in the most southerly distributed New World monkey. Based on new and previously published sequence data, fourteen cytochrome b haplotypes were observed among 33 howlers sampled in Argentina, Paraguay and Brazil, and grouped in two main haplogroups. In northeastern Argentina and southern Paraguay, new sequence data on 73 specimens sampled from six localities gave 34 control region haplotypes that also clustered in two main haplogroups. At this southern distribution, both mitochondrial markers revealed the presence of two sympatric and differentiated clades that we interpret to be the consequence of a secondary contact between previously allopatric populations. Given evidence for a demographic expansion at the beginning of the Holocene 15,500-7000 years ago (Fu's test, F(S)=-12.137; P<0.001), we suggest that atleast two populations of A. caraya have colonized the southernmost range since the Holocene employing forested corridors on the Paraná and Paraguay Rivers.

The primates of the Neotropics: genomes and chromosomes

The classification of neotropical primates has been controversial. Different arrangements have been proposed, depending on taxonomic criteria and on the traits selected for phylogenetic reconstructions. These include gross morphologic characters, karyotypic attributes and DNA sequence data of nuclear and mitochondrial genes and of repetitive genomic components. These approaches have substantially clarified the main intergeneric relationships although several intrageneric arrangements still remain to be elucidated. In this review, we compare karyologic and molecular data of this speciose group.

Fine structure and meiotic behaviour of the male multiple sex chromosomes in the genus Alouatta

The meiotic cytology and fine structure of the sex multiples in males from two species of the genus Alouatta are presented and compared with descriptions from other species of this genus. As shown in pachytene by synaptonemal complex analysis and in metaphase I by spreading, there is a quadrivalent in male meiosis in A. caraya, which is formed by an X(1)X(2)Y(1)Y(2) complex, while in A. palliata there is a trivalent formed by an X(1)X(2)Y(1) complex. Chromosome painting with human probes shows that A. caraya sex multiples share the same components as those of A. seniculus sara and A. seniculus arctoidea. However, as shown here for A. palliata and by others in A. fusca, there are differences among the multiples of some species. It is shown that in this genus there are several varieties of sex multiples that share some features, and that the origin of these multiples is most probably a primitive development in the genus Alouatta.

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.

Morphologic, karyotypic, and molecular evidence of a new form of Chiropotes (primates, pitheciinae)

Morphologic, karyotypic, and molecular analyses were carried out in 25 specimens of a distinct morph of Chiropotes (henceforth termed Chiropotes sp.) obtained from a number of localities in the Brazilian Amazon. Pelage coloration clearly distinguishes the collected specimens and all other known species of this genus. A distinct karyotype was described for Chiropotes sp. It differs from C. satanas chiropotes by two pericentric inversions, and from C. satanas utahicki by three, which suggests that these taxa are reproductively isolated. Morphometric analyses did not show significant differentiation between these Chiropotes taxa. Molecular analyses confirmed the monophyly of the subfamily Pitheciinae and genera Chiropotes, Cacajao, and Pithecia (the latter appearing as the most basal lineage of the pithecine clade). The genetic distances between C. s. utahicki and Chiropotes sp. from Rio Negro were greater than those between three recognized species of Pithecia, but smaller than those between Cacajao calvus and Cacajao melanocephalus. The most appropriate name for Chiropotes sp. from Rio Negro is C. israelita. This species, C. s. chiropotes, and C. s. utahicki are allopatric. Pelage coloration, karyotype, and molecular analysis strongly indicate that C. chiropotes, C. utahicki, and Chiropotes israelita deserve species status.

The phylogeny of howler monkeys (Alouatta, Platyrrhini): reconstruction by multicolor cross-species chromosome painting

We performed multidirectional chromosome painting in a comparative cytogenetic study of the three howler monkey species Alouatta fusca, A. caraya and A. seniculus macconnelli (Atelinae, Platyrrhini) in order to reconstruct phylogenetic relationships within this genus. Comparative genome maps between these species were established by multicolor fluorescence in-situ hybridization (FISH) employing human, Saguinus oedipus and Lagothrix lagothricha chromosome-specific probes. The three species included in this study and previously analyzed howler monkey species were subjected to a phylogenetic analysis on the basis of a data matrix comprised of 98 discrete molecular cytogenetic characters. The results revealed that howler monkeys represent the genus with the most extensive karyotype diversity within Platyrrhini so far analyzed with high levels of intraspecific chromosomal variability. Two different multiple sex chromosome systems were identified. The phylogenetic analysis indicated that Alouatta is a monophyletic clade which can be derived from a proposed ancestral Atelinae karyotype of 2n = 62 chromosomes by a chromosome fusion, a fission, a Y-autosomal translocation and a pericentric inversion. Following these suggestions, the genus Alouatta can be divided into two distinct species groups: the first includes A. caraya and A. belzebul, the second A. s. macconnelli, A. sara, A. s. arctoidea and A. fusca.