A Break in the Evolutionary Branch—Brachiating Gibbon Species Reveal Rapid Evolution
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If you've never heard of a gibbon, you've likely overlooked them at your local zoo. The unique arboreal apes are furry tree huggers that aren't very active in captivity, but occupy a unique place in evolutionary history and in the hearts of ecologists worldwide. And now, after sequencing and analyzing the genome of the northern white-cheeked gibbon species (Nomascus leucogenys), researchers believe they may have found an answer as to how the small apes were able to set themselves apart under such a short evolutionary time.
"Gibbons are small arboreal apes that display an accelerated rate of evolutionary chromosomal rearrangement, and occupy a key node in the primate phylogeny between Old World monkeys and the great apes" lead researcher of the study published in the newest issue of the journal Nature, Lucia Carbone says.
Gibbons are unique creatures that fall under the family of Hominoidea alongside the great apes and humans, however, their origins come from the family of the Old World monkeys. Though possessing hominoid characteristics, much like ourselves, the several species of gibbons are strictly arboreal apes. They have distinct physiological traits, such exaggerated limb proportions with long arms designed for brachiation or movement by swinging between adjacent branches, however, their genetic makeup is even far more distinct.
With diploid chromosome numbers ranging from 38 to 52, which delineate species from one another as they cannot interbreed, the large-scale chromosomal rearrangements and vastly different karyotypes of gibbon species are remarkably fast changes since the genus arose 4-6 million years ago. In order to investigate the plasticity of the gibbon genome, and to better understand the evolutionary relationships between the current species, a team of 92 international researchers looked into the propensity for a gibbon-specific retrotransposon (LAVA), needed for chromosome segregation, to alter transcription by providing a premature termination site. The discovery of the pliable genome, that can still function under multiple genetic mutations, revealed a viable reason for the radiation of many gibbon species ~5 million years ago, when changes in the landscape of southeast Asia required the gibbons to adapt to rapid compression and expansion of their niché habitats.
"Our sequencing, assembling and analysis of the gibbon genome has provided numerous insights into the accelerated evolution of the gibbon karyotype and identified genetic signatures related to gibbon biology" Carbone says. "These results advance our knowledge of the unique traits of the small apes and highlight the complex evolutionary history of these species."
While the mechanism for their genome plasticity was discovered in the study, the question remains of how so many chromosomal rearrangements could have become fixed in several different species over such a relatively short period of evolutionary time. Though the researchers will continue to investigate the working hypotheses they developed out of the results of this primary study, they are hopeful that the analyses of the genomes of such close ancestors may one day reveal a bit more information on our own origins on this Earth.
"Moreover, our analyses of the rearranged gibbon genome help to provide insight into the mechanisms of chromosome evolution, as well as, uncovering a new source of genome plasticity."
