UI Geologist Helps Yale-led Biologists Find Tortoise Disaster ‘Smoking Gun’
Thursday, October 2 2003
Oct. 2, 2003^MOSCOW, Idaho – A Yale University-led team reports DNA of Galápagos Island tortoises records a cataclysm that almost once exterminated the largest remaining population.^University of Idaho geologist Dennis Geist found the smoking gun of sorts, a volcano, that was responsible for the tortoise disaster 100,000 years ago.^Yale biologist Luciano B. Beheregaray, Geist, James P. Gibbs of the State University of New York at Syracuse and three other Yale scientists reported their findings in the Oct. 3 issue of Science Magazine.^“I call it a Pompei of tortoises,” quipped Geist, professor and chairman of the UI Geological Sciences Department. Rather than finding the statue-like casts of the animals, the geologist identified the ash and pumice explosively ejected by the volcano that nearly wiped out the lumbering giants.^His fascination with Galápagos volcanoes led Geist to a 22-year focus on the remote island chain off Ecuador. More than 10 UI undergraduate and graduate students have worked with him in the Galápagos. The islands helped make Charles Darwin famous and evolution a household word.^“The geologic record at Alcedo is extraordinary because it shows it had had a very large, explosive eruption,” Geist said.^The Alcedo eruption was violent and unique among Galápagos volcanoes, which normally have relatively gentle eruptions of lava. Geist independently had used potassium-argon dating to estimate the eruption at 100,000 years ago, give or take about 30,000 years.^The collaboration between biologists and the UI geologist occurred when Beheregaray and his colleagues took DNA samples of tortoises on the Galápagos volcano Alcedo.^Alcedo is home to the largest surviving population of giant tortoises, an estimated 3,000 to 5,000 animals.^The tortoises there live high on the mountain and so were less vulnerable to the hunting parties that gathered their lower-elevation relatives to provision sailing ships.^The Alcedo tortoises’ DNA showed the least genetic variability among the five distinct populations living on the five Isabela Island volcanoes, despite having the largest number of individuals.^Using sophisticated DNA analysis techniques, the Yale team estimated the genetic bottleneck, or narrowing of diversity, happened about 88,000 years ago.^Geist said the biologists contacted him to correlate their genetic record with the geologic record he’d studied.^The genetic study may have implications for the future of some of the other Galápagos tortoises, Geist said, since hunting and habitat loss decimated many populations.^Beheregaray’s team of biologists says the genetic record shows the tortoise population crash was nearly total. The biologists estimate 91 percent of all tortoises now living on Alcedo descend from the same female, the lucky one who must have survived the cataclysm.^Contacts: Dennis Geist, UI professor and chairman Department of Geological Sciences, dgeist@uidaho.edu, (208)885-6491, or Bill Loftus, UI science writer, bloftus@uidaho.edu, (208) 885-7694^Editor’s note: A photo of Dennis Geist in the Galápagos is available by contacting Bill Loftus.^-30-^BL–10/2/2003–GEO
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