Confirmation and location of the hybrid zone between wild populations of Macaca tonkeana and Macaca hecki in central Sulawesi, Indonesia

Studying the Tonkean macaques of Strasbourg, a tale full of sound and fury

In this paper, I chronicle the Strasbourg population of Tonkean macaques (Macaca tonkeana) over a period of half a century. In 1972, Tonkean macaques were imported from Sulawesi, Indonesia, to eastern France, leading to the establishment of two social groups in the Strasbourg region several years later. Our research team studied the social behavior and cognitive abilities of these Tonkean macaques for four decades. The species is characterized by a high degree of social tolerance. This has proven to be very informative in comparative studies of macaque social behavior, opening a new perspective on the evolution of primate societies. Over the years, the population has grown, and more social groups have been formed. However, the fact that some of the Tonkean macaques were healthy carriers of the herpes B virus led to disagreements over their management and eventually to the elimination of the positive individuals. Many individuals from the Strasbourg population are now kept in sanctuaries, and the number of captive breeding groups is limited. We still have much to learn about Tonkean macaques and there is a need for studies carried out in their native habitat in Sulawesi.

Comparative genomics reveals the hybrid origin of a macaque group

Although species can arise through hybridization, compelling evidence for hybrid speciation has been reported only rarely in animals. Here, we present phylogenomic analyses on genomes from 12 macaque species and show that the fascicularis group originated from an ancient hybridization between the sinica and silenus groups ~3.45 to 3.56 million years ago. The X chromosomes and low-recombination regions exhibited equal contributions from each parental lineage, suggesting that they were less affected by subsequent backcrossing and hence could have played an important role in maintaining hybrid integrity. We identified many reproduction-associated genes that could have contributed to the development of the mixed sexual phenotypes characteristic of the fascicularis group. The phylogeny within the silenus group was also resolved, and functional experimentation confirmed that all extant Western silenus species are susceptible to HIV-1 infection. Our study provides novel insights into macaque evolution and reveals a hybrid speciation event that has occurred only very rarely in primates.

Speciation over the edge: gene flow among non-human primate species across a formidable biogeographic barrier

Many genera of terrestrial vertebrates diversified exclusively on one or the other side of Wallace's Line, which lies between Borneo and Sulawesi islands in Southeast Asia, and demarcates one of the sharpest biogeographic transition zones in the world. Macaque monkeys are unusual among vertebrate genera in that they are distributed on both sides of Wallace's Line, raising the question of whether dispersal across this barrier was an evolutionary one-off or a more protracted exchange-and if the latter, what were the genomic consequences. To explore the nature of speciation over the edge of this biogeographic divide, we used genomic data to test for evidence of gene flow between macaque species across Wallace's Line after macaques colonized Sulawesi. We recovered evidence of post-colonization gene flow, most prominently on the X chromosome. These results are consistent with the proposal that gene flow is a pervasive component of speciation-even when barriers to gene flow seem almost insurmountable.

Full-length Numt analysis provides evidence for hybridization between the Asian colobine genera Trachypithecus and Semnopithecus

The phylogenetic position of the genus Semnopithecusis unresolved because of topological incongruence when inferred using different molecular markers. Although some studies proposed hybridization between the genera Semnopithecus and Trachypithecus to explain the discordance, no conclusive evidence for hybridization has been identified. To address this issue, we used DNA walking and long-range PCR to describe a nuclear mitochondrial DNA (Numt) segment present in Trachypithecus pileatus which extends over more than 15 kb, and represents approximately 92% of the entire mitochondrial genome. We assessed the presence of this Numt in 16 other colobine species, including four species of the genus Trachypithecus, six species of the genus Semnopithecus, and representative species of six other genera belonging to the subfamily Colobinae. We failed to detect a Numt sequence in any of the other colobine species except for T. shortridgei, which is closely related to T. pileatus. The sister relationship of this Numt within the genus Semnopithecus suggests that it was derived from the mt genome of the genus Semnopithecus and invaded the nuclear genome of T. pileatus by unidirectional introgression hybridization. These results offer the most conclusive evidence for the existence of hybridization between Semnopithecus and Trachypithecus.

Reduced representation genome sequencing suggests low diversity on the sex chromosomes of tonkean macaque monkeys

In species with separate sexes, social systems can differ in the relative variances of male versus female reproductive success. Papionin monkeys (macaques, mangabeys, mandrills, drills, baboons, and geladas) exhibit hallmarks of a high variance in male reproductive success, including a female-biased adult sex ratio and prominent sexual dimorphism. To explore the potential genomic consequences of such sex differences, we used a reduced representation genome sequencing approach to quantifying polymorphism at sites on autosomes and sex chromosomes of the tonkean macaque (Macaca tonkeana), a species endemic to the Indonesian island of Sulawesi. The ratio of nucleotide diversity of the X chromosome to that of the autosomes was less than the value (0.75) expected with a 1:1 sex ratio and no sex differences in the variance in reproductive success. However, the significance of this difference was dependent on which outgroup was used to standardize diversity levels. Using a new model that includes the effects of varying population size, sex differences in mutation rate between the autosomes and X chromosome, and GC-biased gene conversion (gBGC) or selection on GC content, we found that the maximum-likelihood estimate of the ratio of effective population size of the X chromosome to that of the autosomes was 0.68, which did not differ significantly from 0.75. We also found evidence for 1) a higher level of purifying selection on genic than nongenic regions, 2) gBGC or natural selection favoring increased GC content, 3) a dynamic demography characterized by population growth and contraction, 4) a higher mutation rate in males than females, and 5) a very low polymorphism level on the Y chromosome. These findings shed light on the population genomic consequences of sex differences in the variance in reproductive success, which appear to be modest in the tonkean macaque; they also suggest the occurrence of hitchhiking on the Y chromosome.

Morphological variation of genetically confirmed Alouatta Pigra × A. palliata hybrids from a natural hybrid zone in Tabasco, Mexico

While hybridization has been reported for a large number of primate taxa, there is a general lack of data on hybrid morphology for wild individuals with known genetic ancestry. A confirmed hybrid zone for the closely related Neotropical primates Alouatta palliata and A. pigra has provided a unique opportunity to study primate hybrid morphological variation. Here we used molecular evidence based on mitochondrial, Y-chromosome, and autosomal data to assess hybrid ancestry. We conducted univariate and multivariate statistical comparisons of morphometric data collected from individuals both outside and within the hybrid zone in Tabasco, Mexico. Our results show that of all the hybrids detected (N = 128), only 12% of them were approximately genetically intermediate, and none of them were first generation hybrids. Univariate pairwise comparisons among parental individuals, multigenerational backcrossed hybrids, and intermediate hybrids showed that overall, multigenerational backcrossed hybrids resemble the parental species with which they share most of their alleles. Conversely, intermediates were highly variable. Similarly, principal component analysis depicts an overlap between the parental species and their backcrosses when considering overall morphological differences. Finally, discriminant function analysis of the morphological variables was overall unreliable for classifying individuals into their assigned genotypic classes. Taken together, our results suggest that primate natural hybridization studies should incorporate molecular methods for determining ancestry, because morphology may not always be a reliable indicator of hybrid status. Hybrid zones could comprise a large number of multigenerational backcrossed hybrids that are indistinguishable from the parental species. The implications for studying hybridization in the primate fossil record are discussed.

Morphological and molecular evidence reveals recent hybridization between gorilla taxa

Molecular studies have demonstrated a deep lineage split between the two gorilla species, as well as divisions within these taxa; estimates place this divergence in the mid-Pleistocene, with gene flow continuing until approximately 80,000 years ago. Here, we present analyses of skeletal data indicating the presence of substantial recent gene flow among gorillas at all taxonomic levels: between populations, subspecies, and species. Complementary analyses of DNA sequence variation suggest that low-level migration occurred primarily in a westerly-to-easterly direction. In western gorillas, the locations of hybrid phenotypes map closely to expectations based on population refugia and riverine barrier hypotheses, supporting the presence of significant vicariance-driven structuring and occasional admixture within this taxon. In eastern lowland gorillas, the high frequency of hybrid phenotypes is surprising, suggesting that this region represents a zone of introgression between eastern gorillas and migrants from the west, and underscoring the conservation priority of this critically endangered group. These results highlight the complex nature of evolutionary divergence in this genus, indicate that historical gene flow has played a major role in structuring gorilla diversity, and demonstrate that our understanding of the evolutionary processes responsible for shaping biodiversity can benefit immensely from consideration of morphological and molecular data in conjunction.

Divergence population genetic analysis of hybridization between rhesus and cynomolgus macaques

The geographic ranges of rhesus (Macaca mulatta) and cynomolgus (M. fascicularis) macaques adjoin in Indochina where they appear to hybridize. We used published and newly generated DNA sequences from 19 loci spanning approximately 20 kb to test whether introgression has occurred between these macaque species. We studied introgression at the level of nuclear DNA and distinguished between incomplete lineage sorting of ancestral polymorphisms or interspecific gene flow. We implemented a divergence population genetics approach by fitting our data to an isolation model implemented in the software IMa. The model that posits no gene flow from the rhesus into the cynomolgus macaque was rejected (P = 1.99 x 10(-8)). Gene flow in this direction was estimated as 2Nm approximately 1.2, while gene flow in the reverse direction was nonsignificantly different from zero (P = 0.16). The divergence time between species was estimated as approximately 1.3 million years. Balancing selection, a special case of incomplete sorting, was taken into consideration, as well as potential crossbreeding in captivity. Parameter estimates varied between analyses of subsets of data, although we still rejected isolation models. Geographic sampling of the data, where samples of cynomolgus macaques derived from Indochina were excluded, revealed a lost signature of gene flow, indicating that interspecific gene flow is restricted to mainland Indochina. Our results, in conjunction with those by others, justify future detailed analyses into the genetics of reproductive barriers and reticulate evolution in these two genome-enabled primates. Future studies of the natural hybridization between rhesus and cynomolgus macaques would expand the repertoire of systems available for speciation studies in primates.

Assessing natural introgression in 2 biomedical model species, the rhesus macaque (Macaca mulatta) and the long-tailed macaque (Macaca fascicularis)

Rhesus macaque (Macaca mulatta) and long-tailed macaque (Macaca fascicularis) are the 2 most commonly used primate model species in biomedical sciences. Although morphological studies have revealed a weak hybridization at the interspecific contact zone, in the north of Indochina, a molecular study has suggested an ancient introgression from rhesus to long-tailed macaque into the Indo-Chinese peninsula. However, the gene flow between these 2 taxa has never been quantified using genetic data and theoretical models. In this study, we have examined genetic variation within and between the parapatric Chinese rhesus macaque and Indo-Chinese long-tailed macaque populations, using 13 autosomal, 5 sex-linked microsatellite loci and mitochondrial DNA sequence data. From these data, we assessed genetic structure and estimated gene flow using a Bayesian clustering approach and the "Isolation with Migration" model. Our results reveal a weak interspecific genetic differentiation at both autosomal and sex-linked loci, suggesting large population sizes and/or gene flow between populations. According to the Bayesian clustering, Chinese rhesus macaque is a highly homogeneous gene pool that contributes strongly to the current Indo-Chinese long-tailed macaque genetic makeup, whether or not current admixture is assumed. Coalescent simulations, which integrated the characteristics of the loci, pointed out 1) a higher effective population size in rhesus macaque, 2) no mitochondrial gene flow, and 3) unilateral and male-mediated nuclear gene flow of approximately 10 migrants per generation from rhesus to long-tailed macaque. These patterns of genetic structure and gene flow suggest extensive ancient introgression from Chinese rhesus macaque into the Indo-Chinese long-tailed macaque population.

INTERSPECIES HYBRIDIZATION AND THE STRATIFICATION OF NUCLEAR GENETIC VARIATION OF RHESUS (MACACA MULATTA) AND LONG-TAILED MACAQUES (MACACA FASCICULARIS)

Genotypes for 13 short tandem repeats (STRs) were used to assess the genetic diversity within and differentiation among populations of rhesus macaques (Macaca mulatta) from mainland Asia and long-tailed macaques (M. fascicularis) from mainland and insular Southeast Asia. These animals were either recently captured in the wild or derived from wild-caught founders maintained in captivity for biomedical research.A large number of alleles is shared between the two macaque species but a significant genetic division between them persists. This distinction is more clear-cut among populations that are not, or are unlikely to have recently been, geographically contiguous. Our results suggest there has been significant interspecies nuclear gene flow between rhesus macaques and long-tailed macaques on the mainland. Comparisons of mainland and island populations of long-tailed macaques reflect marked genetic subdivisions due to barriers to migration. Geographic isolation has restricted gene flow, allowing island populations to become subdivided and genetically differentiated. Indonesian long-tailed macaques show evidence of long-term separation and genetic isolation from the mainland populations, while long-tailed macaques from the Philippines and Mauritius both display evidence of founder effects and subsequent isolation, with the impact from genetic drift being more profound in the latter.

Survey of Alouatta caraya, the black-and-gold howler monkey, and Alouatta guariba clamitans, the brown howler monkey, in a contact zone, State of Rio Grande do Sul, Brazil: evidence for hybridization

Sympatry and natural hybridization between howler monkey taxa (Alouatta spp.) has only recently being confirmed in the wild. Surveys in areas of potential contact between the distribution of two taxa have shown that sympatry is rare, although more common than previously known. Here we report the results of a survey conducted in a contact zone between the only two sexually dichromatic howler monkey taxa, Alouatta caraya and A. guariba clamitans, in São Francisco de Assis, State of Rio Grande do Sul, Brazil. Our survey, covering an area of about 400 ha at the Cerro dos Negros (29 degrees 33'50''-29 degrees 35'10''S, 54 degrees 58'40''-54 degrees 59'50''W; approximately 100-279 m a.s.l.), was successful in locating seven black-and-gold and one brown howler monkey social groups living syntopically. Black-and-gold group size ranged from 5 to 15 individuals, whereas the brown group was composed of 7 individuals. The pelage color of three adult males belonging to different black-and-gold groups and another adult male belonging to the brown howler group presented a mosaic of red or rufous and black. These adult males and an adult female living in another black-and-gold group are putative hybrids. Therefore, it appears that pre-zygotic reproductive isolation has not evolved, at least not completely, between these howler monkey species, corroborating previous reports for these and other Alouatta taxa. Future genetic studies need to confirm the occurrence of hybridization in this contact zone, and to determine the viability and fertility of hybrids and their possible offspring. In addition, there is no evidence supporting the existence of significant segregation in habitat and resource utilization by black-and-gold and brown howler monkeys.

Hybridization in large-bodied New World primates

Well-documented cases of natural hybridization among primates are not common. In New World primates, natural hybridization has been reported only for small-bodied species, but no genotypic data have ever been gathered that confirm these reports. Here we present genetic evidence of hybridization of two large-bodied species of neotropical primates that diverged approximately 3 MYA. We used species-diagnostic mitochondrial and microsatellite loci and the Y chromosome Sry gene to determine the hybrid status of 36 individuals collected from an area of sympatry in Tabasco, Mexico. Thirteen individuals were hybrids. We show that hybridization and subsequent backcrosses are directionally biased and that the only likely cross between parental species produces fertile hybrid females, but fails to produce viable or fertile males. This system can be used as a model to study gene interchange between primate species that have not achieved complete reproductive isolation.

Natural hybridization in primates: one evolutionary mechanism

The role and importance of natural hybridization in the evolutionary histories of animal taxa is still debated. This results largely from a history of zoological investigations that assumed, rather than documented, a limited evolutionary role for this process. However, it is now becoming apparent that, just as for plants, the creative effects of reticulate evolution are widespread in animal taxa as well. This conclusion is supported by the documentation of numerous instances of the formation of new taxa and the genetic enrichment through introgressive hybridization. In the present review, we use primates as a paradigm for how natural hybridization can affect the evolution of species complexes and remains a footprint on genomes. Findings for a number of groups, including basal (e.g. lemurs) and derived (e.g. Old World apes) lineages, demonstrate that introgression and hybrid speciation have caused a reticulate pattern that is still detectable in the, often mosaic, genomes of primates. For example, results from genetic analyses of our own species demonstrate the process of past introgressive hybridization with the progenitors of our sister taxa (i.e. chimpanzees and gorillas) and most likely also our extinct, close relatives in the hominid lineage.

Identifying the morphological signatures of hybridization in primate and human evolution

Recent studies point to contact and possible admixture among contemporaneous hominin species during the Plio-Pleistocene. However, detection of hybridization in fossils-and especially fossil hominins-is contentious, and it is hindered in large part by our lack of understanding about how morphological hybridity is manifested in the primate skeleton. Here, we report on a study of known-pedigree, purebred yellow and olive baboons (n = 112) and their hybrids (n = 57), derived from the baboon colony of the Southwest Foundation for Biomedical Research. The hybrids were analyzed in two different groups: (1) F1 = olive x yellow first-generation hybrids; (2) B1 = olive x F1 backcross hybrids. Thirty-nine metric variables were tested for heterosis and dysgenesis. Nonmetric data were also collected from the crania. Results show that these primate hybrids are somewhat heterotic relative to their parental populations, are highly variable, and display novel phenotypes. These effects are most evident in the dentition and probably indicate the mixing of two separately coadapted genomes and the breakdown in the coordination of early development, despite the fact that these populations diverged fairly recently. Similar variation is also observed in museum samples drawn from natural hybrid zones. The results offer a strategy for detecting hybrid zones in the fossil record; implications for interpreting the hominin fossil record are discussed.

The effects of hybridization on growth allometry and craniofacial form in Sulawesi macaques

The present research investigates the effects of hybridization between Macaca maurus and M. tonkeana on adult male form and patterns of growth allometry. Comparisons of adult hybrid mean phenotypic values with the adult averages of the parental species indicate a condition of heterosis for cranial vault length and crown-rump length. Negative heterosis is indicated for body mass. Regression parameters describing growth allometry are generated for four craniofacial measurement variables and one body measurement using both least squares and reduced major axis regression. Comparisons of hybrid and parental regression slopes and intercepts using analysis of covariance and t-tests suggest that there is a hybrid pattern of growth allometry characterized by an increase in regression slope values coupled with lower intercept values compared to those of the parental species and the parental averages for most regression parameters. Multivariate analyses of the adult and ontogenetic morphometric data indicate significant differences across species taxa in form and shape during development and adulthood. Our finding of significant differences between hybrids and their parental taxa in growth allometry and craniofacial form and shape during development challenges the assumption often made regarding the reproductive and taxonomic significance of observed ontogenetic divergence between Neandertals and modern humans. We propose that anthropological primatology, with its goal of developing nonhuman primate models for investigating human evolution, can provide a biologically relevant means by which to empirically estimate the taxonomic significance of morphological and ontogenetic divergence observed in the hominid fossil record.

Diversification of Sulawesi macaque monkeys: decoupled evolution of mitochondrial and autosomal DNA

In macaque monkeys, females are philopatric and males are obligate dispersers. This social system is expected to differently affect evolution of genetic elements depending on their mode of inheritance. Because of this, the geographic structure of molecular variation may differ considerably in mitochondrial DNA (mtDNA) and in autosomal DNA (aDNA) in the same individuals, even though these genomes are partially co-inherited. On the Indonesian island of Sulawesi, macaque monkeys underwent an explosive diversification as a result of range fragmentation. Today, barriers to dispersal have receded and fertile hybrid individuals can be found at contact zones between parapatric species. In this study, we examine the impact of range fragmentation on Sulawesi macaque mtDNA and aDNA by comparing evolution, phylogeography, and population subdivision of each genome. Our results suggest that mtDNA is paraphyletic in some species, and that mtDNA phylogeography is largely consistent with a pattern of isolation by distance. Autosomal DNA, however, is suggestive of fragmentation, in that interspecific differentiation across most contact zones is significant but intraspecific differentiation between contact zones is not. Furthermore, in mtDNA, most molecular variation is partitioned between populations within species but in aDNA most variation is partitioned within populations. That mtDNA has a different geographic structure than aDNA (and morphology) in these primates is a probable consequence of (1) a high level of ancestral polymorphism in mtDNA, (2) differences between patterns of ancestral dispersal of matrilines and contemporary dispersal of males, and (3) the fact that female philopatry impedes gene flow of macaque mtDNA.

Monkeys and toads define areas of endemism on Sulawesi

Ecological or geological phenomena can impose limits on geographic diversification that cause biogeographical patterns of distantly related but sympatrically occurring taxa to be similar. Concordant patterns of diversity facilitate conservation management because strategic designation of protected areas can capture complementary rather than redundant components of variation. Here we demonstrate that on the biodiverse Indonesian island of Sulawesi, seemingly idiosyncratic distributions of diversity in endemic monkeys (Macaca species) and toads (Bufo celebensis) are actually virtually identical on a fine geographic scale. It appears that range fragmentation has generated seven multi-taxon areas of genetic endemism, each of which should be targeted for conservation. Joint consideration of molecular phylogeography, morphology, and demography helps resolve apparent contradictions in paraphyletic macaque mitochondrial DNA and in undifferentiated toad morphology, and facilitates an understanding of biogeography and conservation genetics of Sulawesi fauna.

Genetic assessment of a white-collared x red-fronted lemur hybrid zone at Andringitra, Madagascar

We examined a purported lemur (Eulemur fulvus rufusxE. albocollaris) hybrid zone at Andringitra, Madagascar, using sequences from five genes (one mitochondrial gene (d-loop) and four nuclear introns (hemopexin, malic enzyme, ceruloplasmin, and microsatellite 26 flanking region)), from 60 individuals (E. albocollaris (n = 16), E.f. rufus (n = 14), E. collaris (n = 9), and purported hybrids from Andringitra (n = 21)). Diagnostic (d-loop and microsatellite 26) and private sites (all other genes) were found in all gene regions for E. albocollaris and E.f. rufus. Also, private sites were found for the purported hybrid population in two gene regions (d-loop and ceruloplasmin). When the putative hybrids were examined for diagnostic and private markers, 18 of 21 were found to contain markers from both E. albocollaris and E.f. rufus populations. The remaining three individuals were found to contain only markers for E. albocollaris. These results indicate that the population at Andringitra is a hybrid population between E. albocollaris and E.f. rufus.

Morphological variation within a macaque hybrid zone

A hybrid zone exists between Macaca tonkeana and Macaca hecki (Primates: Cercopithecidae), centered along the Tawaeli-Toboli road in the narrow isthmus that connects North and Central Sulawesi, Indonesia. The current study demonstrates morphological substructure from north to south across the hybrid zone. Macaques to the northwest of the Tawaeli-Toboli road more closely resemble M. hecki, and macaques to the southeast of the road resemble M. tonkeana. While morphology shifted for both males and females over a distance of 1,500-2,000 m, adult males were significantly more M. tonkeana-like across the morphological gradient. This suggests that in the study area, males of M. tonkeana-like morphology are dispersing into hybrid groups at the expense of M. hecki-like males. A permutation analysis of diagnostic character states indicated that associations existed among several morphological traits. This could be due to the operation of one or several nonexclusive evolutionary processes, including recent secondary contact, pleiotropic effects, physical linkage of loci, natural selection against hybrids, the influx of parental types, or assortative mating. Continued environmental perturbation associated with the Tawaeli-Toboli road is likely to be a significant factor in the future of the M. tonkeana/M. hecki hybrid interaction.

Hybridization and population genetics of two macaque species in Sulawesi, Indonesia

This study investigates hybridization and population genetics of two species of macaque monkey in Sulawesi, Indonesia, using molecular markers from mitochondrial, autosomal, and Y-chromosome DNA. Hybridization is the interbreeding of individuals from different parental taxa that are distinguishable by one or more heritable characteristics. Because hybridization can affect population structure of the parental taxa, it is an important consideration for conservation management. On the Indonesian island of Sulawesi an explosive diversification of macaques has occurred; seven of 19 species in the genus Macaca live on this island. The contact zone of the subjects of this study, M. maura and M. tonkeana, is located at the base of the southwestern peninsula of Sulawesi. Land conversion in Sulawesi is occurring at an alarming pace; currently two species of Sulawesi macaque, one of which is M. maura, are classified as endangered species. Results of this study indicate that hybridization among M. maura and M. tonkeana has led to different distributions of molecular variation in mitochondrial DNA and nuclear DNA in the contact zone; mitochondrial DNA shows a sharp transition from M. maura to M. tonkeana haplotypes, but nuclear DNA from the parental taxa is homogenized in a narrow hybrid zone. Similarly, within M. maura divergent mitochondrial DNA haplotypes are geographically structured but population subdivision in the nuclear genome is low or absent. In M. tonkeana, mitochondrial DNA haplotypes are geographically structured and a high level of nuclear DNA population subdivision is present in this species. These results are largely consistent with a macaque behavioral paradigm of female philopatry and obligate male dispersal, suggest that introgression between M. maura and M. tonkeana is restricted to the hybrid zone, and delineate one conservation management unit in M. maura and at least two in M. tonkeana.

Nonhuman primate hybridization and the taxonomic status of Neanderthals

The present study examines the taxonomic status of Middle Paleolithic Neanderthals by comparing their observed minimum genetic divergence from Upper Paleolithic modern humans in Europe with that observed between macaque species from Sulawesi that are known to hybridize and fully intergrade in the wild. The genetic divergence, and differentiation between Neanderthals and Upper Paleolithic modern humans, as indicated by pairwise minimum genetic distances and F(ST) values calculated from the estimated minimum genetic relationship (R) matrix derived from craniometric data, are significantly greater than those observed both between hybridizing and noninterbreeding Sulawesi macaque species, suggesting that mate recognition and the possibility of gene flow between Neanderthals and Upper Paleolithic modern humans might have been greatly reduced. These results support a species-level taxonomic distinction for the Neanderthals as suggested by proponents of the replacement model. Furthermore, assumptions regarding the monophyletic origin of modern humans from outside Europe are likely valid.

Islet cell antibodies in Sulawesi macaques

Older monkeys of the Sulawesian species Macaca nigra spontaneously develop a lesion in the pancreatic islets of Langerhans in which there is deposition of amyloid and gradual degeneration of all cells, which can lead eventually to development of diabetes mellitus. Islet cell antibodies (ICA), formed in response to the release of cellular antigens, can be used to detect the islet lesion and to monitor the progression of each monkey toward diabetes. Numerous M. nigra and one M. tonkeana in captivity have been tested, but it is unknown whether the islet lesion occurs in monkeys in their natural habitat of Sulawesi. Blood samples collected from M. maurus, M. tonkeana, and hybrid M. maurus/tonkeana were assayed for ICA. When all monkeys were considered together, 33% had ICA positive against beta cells and 14% had ICA positive against alpha and/or D cells. Appearance of ICA in blood of males was virtually the same as in females. These results are similar to those found in M. nigra examined in captivity. Since all Sulawesian species share a common genetic heritage, these results would support the appearance of this lesion in their natural habitat. Cause(s) for formation of the lesion and eventual development of diabetes are unknown. There may be genetic factors or genetic predisposition to environmental factors. If environmental factors are responsible, then they must be present not only in the wild, but either carried with the monkeys or universally available, since M. nigra born in captivity also develop the lesion and diabetes after physical maturity at ca. 7+ years.