From: Andy Soos, ENN
Published January 9, 2012 02:58 PM

Ancient Tortoise Lives On

The Galápagos tortoise or giant tortoise (Chelonoidis nigra) is the largest living species of tortoise, reaching weights of over 880 lb and lengths of over 5.9 feet. With life spans in the wild of over 100 years, it is one of the longest-lived vertebrates. The subspecies that lived on Floriana Island until 1850 had a modest fame as the one of the species that Darwin used in his studies. A new analysis, published January 9 in the journal Current Biology, suggests that the direct descendants of extinct Chelonoidis elephantopus live on the volcanic slopes of the northern shore of Isabela Island — 200 miles from their ancestral home of Floreana Island, where they disappeared after being hunted to extinction by whalers. "This is not just an academic exercise," said Gisella Caccone, senior research scientist in the Department of Ecology and Evolutionary Biology and senior author of the paper. "If we can find these individuals, we can restore them to their island of origin. This is important as these animals are keystone species playing a crucial role in maintaining the ecological integrity of the island communities."

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On his historic voyage to the Galapagos in 1835, Charles Darwin observed that the shells of tortoises living on different islands of the chain had different shapes — one of the observations that inspired his theory of natural selection. For instance, the shells of C. elephantopus on Floreana were saddle-shaped while tortoises on other islands had domed-shaped shells.

The exact number of subspecies of these tortoises that have existed in history is still under debate among scientists, but some recognize up to 15. Only ten subspecies now exist in the wild, one on Santiago, Santa Cruz, San Cristóbal, Pinzón and Española, and five on Isabela, although this number is controversial and may be fewer. An eleventh surviving subspecies, abingdoni from Pinta Island, is considered extinct in the wild and is represented by a single living specimen, "Lonesome George". The subspecies inhabiting Floreana island (C. n.  nigra) is thought to have been hunted to extinction by whalers and local workers.

A team of Yale researchers visiting Volcano Wolf on the northern tip of Isabela Island in 2008 took blood samples from more than 1600 tortoises and compared them to a genetic database of living and extinct tortoise species. An analysis detected the genetic signatures of C. elephantopus in 84 Volcano Wolf tortoises, meaning one of their parents was a purebred member of the missing species. In 30 cases breeding had taken place within the last 15 years. Since the lifespan of tortoises can exceed 100 years, there is a high probability that many purebreds are still alive.

"To our knowledge, this is the first report of the rediscovery of a species by way of tracking the genetic footprints left in the genomes of its hybrid offspring," said former Yale postdoctoral researcher Ryan Garrick, now assistant professor at the University of Mississipi and first author of the paper.

Intensive breeding of hybrids might allow scientists to resuscitate the C. elephantopus species even if sufficient numbers of purebred tortoises can not be found, Garrick said.

For further information: On his historic voyage to the Galapagos in 1835, Charles Darwin observed that the shells of tortoises living on different islands of the chain had different shapes — one of the observations that inspired his theory of natural selection. For instance, the shells of C. elephantopus on Floreana were saddle-shaped while tortoises on other islands had domed-shaped shells.

The exact number of subspecies of these tortoises that have existed in history is still under debate among scientists, but some recognize up to 15. Only ten subspecies now exist in the wild, one on Santiago, Santa Cruz, San Cristóbal, Pinzón and Española, and five on Isabela, although this number is controversial and may be fewer. An eleventh surviving subspecies, abingdoni from Pinta Island, is considered extinct in the wild and is represented by a single living specimen, "Lonesome George". The subspecies inhabiting Floreana island (C. n.  nigra) is thought to have been hunted to extinction by whalers and local workers.

A team of Yale researchers visiting Volcano Wolf on the northern tip of Isabela Island in 2008 took blood samples from more than 1600 tortoises and compared them to a genetic database of living and extinct tortoise species. An analysis detected the genetic signatures of C. elephantopus in 84 Volcano Wolf tortoises, meaning one of their parents was a purebred member of the missing species. In 30 cases breeding had taken place within the last 15 years. Since the lifespan of tortoises can exceed 100 years, there is a high probability that many purebreds are still alive.

"To our knowledge, this is the first report of the rediscovery of a species by way of tracking the genetic footprints left in the genomes of its hybrid offspring," said former Yale postdoctoral researcher Ryan Garrick, now assistant professor at the University of Mississipi and first author of the paper.

Intensive breeding of hybrids might allow scientists to resuscitate the C. elephantopus species even if sufficient numbers of purebred tortoises can not be found, Garrick said.

For further information: http://www.physorg.com/news/2012-01-genetic-analysis-tortoise-species-thought.html

Photo:  Yale University

Photo:  Yale University

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