Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Raft or bridge: How did iguanas reach tiny Pacific islands?

12.01.2010
Scientists have long puzzled over how iguanas, a group of lizards mostly found in the Americas, came to inhabit the isolated Pacific islands of Fiji and Tonga.

For years, the leading explanation has been that progenitors of the island species must have rafted there, riding across the Pacific on a mat of vegetation or floating debris. But new research in the January issue of The American Naturalist suggests a more grounded explanation.

Using the latest genetic, geological and fossil data, biologists Brice Noonan of the University of Mississippi and Jack Sites of Brigham Young University have found that iguanas may have simply walked to Fiji and Tonga when the islands were still a part of an ancient southern supercontinent.

The two islands, located about 2000 miles east of Australia, are home to several iguana species, and their presence there is "one of the most perplexing scenarios in island biogeography," Noonan says. The other islands in the region, and closest continental landmass, Australia, have no iguanid species at all. In fact the closest iguanids are found about 5,000 miles away in the Americas. So how did these species get to these remote islands?

Some scientists have hypothesized that they must have rafted there—a journey of around 5,000 miles from South America to the islands. There is some precedent for rafting iguanas. There are documented cases of iguanas reaching remote Caribbean islands and the Galapagos Islands on floating logs. But crossing the Pacific is another matter entirely. Noonan and Sites estimate the trip would take six months or more—a long time for an iguana to survive on a log or vegetation mat.

So Noonan and Sites tested the possibility that iguanas simply walked to the islands millions of years ago, before the islands broke off from Gondwana—the ancient supercontinent made up of present-day Africa, Australia, Antarctica and parts of Asia. If that's the case, the island species would need to be old—very old. Using "molecular clock" analysis of living iguana DNA, Noonan and Sites found that, sure enough, the island lineages have been around for more than 60 million years—easily old enough to have been in the area when the islands were still connected via land bridges to Asia or Australia.

Fossil evidence backs the finding. Fossils uncovered in Mongolia suggest that iguanid ancestors did once live in Asia. Though there's currently no fossil evidence of iguanas in Australia, that doesn't necessarily mean they were never there. "[T]he fossil record of this continent is surprisingly poor and cannot be taken as evidence of true absence," the authors write.

So if the iguanas simply migrated to Fiji and Tonga from Asia or possibly Australia, why are they not also found on the rest of the Pacific islands? Noonan and Sites say fossil evidence suggests that iguana species did once inhabit other islands, but went extinct right around the time humans colonized those island. That's an indication that iguanas were on the menu for the early islanders. But Fiji and Tonga have a much shorter history of human presence, which may have helped the iguanas living there to escape extinction.

The molecular clock analysis combined with the fossil evidence suggests a "connection via drifting Australasian continental fragments that may have introduced [iguanas] to Fiji and Tonga," Noonan says. "The 'raft' they used may have been the land."

The researchers say that their study can't completely rule out the rafting hypothesis, but it does make the land bridge scenario "far more plausible than previously thought."

Brice P. Noonan and Jack W. Sites Jr., "Tracing the Origins of Iguanid Lizards and Boine Snakes of the Pacific." The American Naturalist 175:1 (January 2010).

Since its inception in 1867, The American Naturalist has maintained its position as one of the world's most renowned, peer-reviewed publications in ecology, evolution, and population and integrative biology research. The journal is published by The University of Chicago Press for the American Society of Naturalists.

Kevin Stacey | EurekAlert!
Further information:
http://www.uchicago.edu

More articles from Life Sciences:

nachricht A novel socio-ecological approach helps identifying suitable wolf habitats
17.02.2017 | Universität Zürich

nachricht New, ultra-flexible probes form reliable, scar-free integration with the brain
16.02.2017 | University of Texas at Austin

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Switched-on DNA

20.02.2017 | Materials Sciences

Second cause of hidden hearing loss identified

20.02.2017 | Health and Medicine

Prospect for more effective treatment of nerve pain

20.02.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>