Back Greater genetic diversity found among the great apes than among humans

Greater genetic diversity found among the great apes than among humans

A scientific study by an international team of researchers, codirected by Tomàs Marquès Bonet, researcher at the Institute of Evolutionary Biology, has for the first time sequenced the genomes of a large number of individuals of the six species of great apes from Africa and south-east Asia.
02.07.2013

 

simisA scientific study by an international team of researchers has for the first time sequenced the genomes of a large number of individuals of the six species of great apes from Africa and south-east Asia.

The work, directed by  Tomàs Marquès Bonet, researcher at the Institute of Evolutionary Biology (Pompeu Fabra University-CSIC) in Barcelona, and  Evan Eichler, of Washington University (Seattle, USA), focused on including the greatest genetic diversity of wild specimens as possible, due to the rapid decrease in the great ape population worldwide.

The great apes -chimpanzees, gorillas and orangutans- comprise the closest group of living species to humans. We share a common ancestor who lived some 14-16 million years ago, but we share a far more recent predecessor with chimpanzees, just six million years ago.

The study, published today in the digital version of the prestigious journal Nature, provides the most comprehensive and detailed analysis to date of the genetic diversity of the great apes, species which are today threatened with extinction, and allows learning about the genetic diversity of the great apes in order to put the history of our genome in its context. Researchers from the UAB also took part in the work.

The study was carried out with wild and captive specimens to compare genomes

The recent breakthroughs in genome sequencing technologies have enabled researchers to make great progress in the knowledge of the human genome and genetic diversity by sequencing the individuals of our species. However, less attention has been paid to our closest relatives: the great apes. This is due, to a great extent, to the difficulty of obtaining DNA samples of these endangered species.

Although there is a large number of them in captivity, these specimens are a poor reflection of the natural diversity. Now, in this scientific paper, the researchers have worked with the genetic material taken from wild specimens, a task which was performed in collaboration with conservation groups, and the sequencing of most of the genomes was carried out at the laboratories of the National Centre for Genomic Analysis (CNAG), based in Barcelona.

The researchers found that human genomes show a greatly reduced variety compared to the genome of most of the great apes. Few species of apes display such low levels. "This reduction in genetic diversity is normally the result of a process known as "population bottleneck", characterized by a drastic decrease in the number of individuals in the population", comments  Javier Prado-Martínez, doctoral student at the Institute of Evolutionary Biology and co-first author of the study.

"What is surprising is the intensity of this bottleneck in human beings compared to most great apes", he adds. The genomes of a pair of orangutans, for example, differ in more than in more than 2 of every 1,000 base pairs, compared to 1 in every 1,000 base pairs between two humans. Some of the great ape species, eastern gorillas¡, western chimpanzees and bonobos, also have a very low variability as a result of these bottlenecks in the past".

The researchers concentrated, above all, on comparing the evolutionary history of our closest relatives, chimpanzees, which are spread throughout Africa, and are classified into four large groups, or sub-species. One open question among evolutionary biologists has been how these four populations relate among each other. By sequencing several individuals of each group, the researchers managed to solve the phylogenic relations between these sub-species and, by exploring the genome of the four groups, they have seen that the evolution of all of them has been rather complex.

What also became clear to the researchers was the complexity of the evolutionary history of chimpanzees in comparison with humans. The patterns of genetic diversity were consistent with a vast genetic flux or migration between ancestral populations with sudden expansions in population size, followed by accidents.

"Humans", conversely, "have a relatively simple evolutionary history", say the authors. "It is clear that in the last few million years chimpanzee populations fluctuated enormously in size and complexity." The basis of these population collapses is clear but it coincides, in part, with a period of time in which the human population began to prosper.

The paper stresses a message of reflection: "We must do more to protect these species and preserve their natural environment", says  Prado-Martínez. "Almost all of the great ape populations are critically endangered and at the mercy of our species more than ever." He is confident that all of the information obtained will help with conservation efforts since "knowing more about the genomes of these species will help field biologists to better identify the origin of the great apes, victims of illegal hunting and trade, and better management of breeding programmes in captivity", he concludes.

Reference work: Javier Prado-Martinez, Tomàs Marquès Bonet et al. "  Great ape genetic diversity and population history".  Nature. 3/7/2013. doi:10.1038/nature12228.

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