BBC - Earth - The monkeys that sailed across the Atlantic to South America
Today there are about species of New World monkeys (also called tree by using software that reconstructs evolutionary relationships. Divergence Time Estimates Between New World Monkeys-Old World Anthropoids for group relationship of NWM and Old World Anthropoids. More importantly, it provides for the first time a direct link between the ancestors of today's New World monkeys and the ancient monkeys of.
Fossils of Earliest Old World Monkeys Unearthed
Larger New World species include the acrobatic spider monkeys and the noisy howlers. Other New World monkeys include uakarissakisand titis. Old World monkeys include many that are often seen in zoos, especially the beautifully coloured African guenons e.
The graceful langurs include the hanuman, or sacred monkey, also of southern Asia. Among the more unusual monkeys are the large and strikingly coloured African drills and mandrillsthe proboscis monkey of Borneo, and the rare and bizarre snub-nosed monkeys of China and Vietnam.
The Old World monkeys are divided into two subfamilies: The cercopithecines have cheek pouches, in which they store food; these include baboons, macaques, guenons, and their relatives. The colobines lack cheek pouches but have complicated three- or four-chambered stomachs, where bacterial fermentation of cellulose and hemicellulose occurs and thereby enriches the nutrient content of their diet, which consists partially of leaves and seeds. Colobines include colobus monkeys, langurs, and their relatives.
- Old World monkeys versus New World monkeys
- 1. Introduction
The moustached monkey Cercopithecus cephus is a species of guenon. In particular, the squirrel monkeys genus Saimiri of the New World and the talapoin genus Miopithecus of West-Central Africa are remarkably convergent; both are small about 1 kg [2.
No New World monkey lives on the savanna or has a multichambered cellulose-fermenting stomach, and no Old World monkey is nocturnal like the durukuli. The closest analogue to the complex society of the spider monkey is found not in an Old World monkey but in the chimpanzee. For protein-coding genes, we selected first and second codon positions only. This was done because analyses using third codon positions, although theoretically more appropriate because of weaker selective pressures Russo, Takezaki, and Neipresented huge branch lengths and large associated errors.
This preliminary result indicates a high degree of saturation that severely affected the statistical significance of the estimates results not shown and, thus, we excluded these sites from the analysis.
Fossils of Earliest Old World Monkeys Unearthed
Because the phylogenetic relationships between species were known, the topology in figure 1 was assumed a priori, and the analyses concerned solely branch length i. Felsenstein and the multigene Bayesian approach Thorne and Kishino In the first approach, individual genes and concatenated sequences were submitted to the following analysis: All ML trees were submitted to rate constancy tests before the clock was assumed.
Log-likelihoods of clock-constrained and unconstrained trees were compared with the LRT. For sequences in which the clock was not rejected, individual divergence times were averaged following the procedure of Nei, Xu, and Glazko to yield global estimates for DNA and amino acid sequences. Thorne was used to perform the multigene Bayesian analysis to estimate divergence times Thorne and Kishino The method also permits entering time constraints, and four were input based on the fossil record.
The first was the minimum age for the Homo-Pan divergence that was set at 6 MYA minimum age of Sahelanthropus tchadensis— Brunet et al. Fleagle ; the third was the minimum age for the cercopithecoid-hominoid divergence at 21 MYA and, finally, the minimum age for the Platyrrhini-Catarrhini divergence at 27 MYA the age of the oldest Platyrrhini, Branisella boliviana: Markov chain Monte Carlo analyses were performed to approximate posterior distributions of node times.
The analyses were run forcycles before the first sample of Markov chain was taken. Another cycles were run, and the second sample was taken.
The monkeys that sailed across the Atlantic to South America
This procedure was repeated until 10, samples were obtained every cycles. The entire analysis was conducted twice to check for consistency of the posterior approximations.
The time estimates also varied little when comparisons were made of individual nucleotide We were expecting that the clock would be rejected for COII, because a faster evolutionary rate has been reported in the branches leading to hominoids and platyrrhines for this gene Adkins and Honeycutt The molecular clock could not be assumed for the concatenated sequences of amino acids and nucleotides because hominoid proteins evolved significantly slower than those of other primates. Even not behaving clocklike, if the clock is assumed for the concatenated sequences, a time estimate of This estimate falls to Remarkably, these concatenated estimates are very close to individual nondeviant estimates and corroborates the suggestion that molecular clock estimates are minimally affected by a few deviant sequences Nei and Kumar As expected, the multigene credibility interval was considerably narrower than individual Bayesian estimations made by the same method see also Thorne and Kishino Nevertheless, for amino acid sequences, the multigene Bayesian approach presented a much older estimate for the Platyrrhini-Catarrhini split, mean of This Bayesian estimate exceeds the remaining divergence time estimates by at least 5 myr.
One explanation for this difference in means and the larger associated error could be the use of the JTT matrix to correct amino acid sequences in the Bayesian analysis.
In our results, we have several estimates that converge for a split around 35 MYA for Platyrrhini and Catarrhini, namely individual and concatenated nucleotide sequences; individual and concatenated amino acid sequences—both calculated by LRT—and the multigene Bayesian nucleotide analysis. In addition, this result is also consistent with those of a recent paper including mitochondrial and nuclear gene sequences analyzed with distance approaches Glazko and Nei Hence, we feel that the use of an inappropriate amino acid transition matrix might be causing the difference between nucleotide and amino acid sequences in the multigene Bayesian approach.
For the sake of comparison, we have also shown the divergence times of the other anthropoids used in this study table 2. Concatenated sequences rendered time estimates for this split at around 5 MYA, whereas the Bayesian approach dates the origin of hominids at 7.
Our estimates for the origin of the lineages leading to Hylobates 15—19 MYA and Pongo 13—16 MYA also present small errors by both methods and are in agreement with previous molecular studies Hasegawa, Kishino, and Yano ; Stauffer et al.
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These estimates are also corroborated by a recent fossil finding, Lufengpithecus chiangmuanensis, recovered from Middle Miocene deposits of Thailand Chaimanee et al. Finally, the Papio-Macaca 10—12 MYA divergence was relatively old compared to the fossil diversity of cercopithecines, showing that the major lineages of the Cercopithecoidea were already diversified by the late Miocene Fleagle Discussion The origin of Platyrrhini has been one of most intriguing questions in primatology Ciochon and Chiarelli ; Martin ; Fleagle Although internally consistent at around 35 MYA, our divergence time estimates are at odds with those obtained by Arnason and coworkerswho used virtually the same mitochondrial data set, yet they estimated the Platyrrhini-Catarrhini divergence at around 70 MYA.
A possible explanation for this discrepancy is that they used a calibration point outside primates, implying a global clock assumption for mammals that is not expected to hold Gissi et al.
This twofold difference in the divergence time for NWM and OWA illustrates the importance of a reliable calibration point in molecular clock studies. It has been advocated that mitochondrial genes should not be used for divergence time studies for reasons such as rate heterogeneity between lineages e.
However, we feel that rate heterogeneity can be overcome if adequate calibration points and molecular clock tests are applied, even without the necessity of sophisticated statistical tools. Most nuclear estimates show much older divergence times for this split Takahata and Satta ; Kumar and Hedgesbut a single recent study provided a nuclear estimate that falls very close to our estimate ca. Nei and Glazko ; see also Glazko and Nei Interestingly, in their study, Nei and Glazko explicitly tried to select orthologous sequences to estimate time, probably avoiding most problems associated with paralogy.
The fact that our several mitochondrial estimates were consistent and very close to this nuclear estimate suggests that we might have reached a divergence time very close to the actual date of Platyrrhini and Catarrhini split.
Several vicariant and dispersal hypotheses have been suggested to explain how and when the Platyrrhini ancestor arrived on the South American continent.