Subscribe free to our newsletters via your
. Earth Science News .




FLORA AND FAUNA
Bridge species drive tropical engine of biodiversity
by Greg Borzo for UC News
Chicago IL (SPX) Jun 12, 2013


The University of Chicago's David Jablonski is presenting new evidence that most evolutionary lineages started in the tropics and expanded outward in a process driven by what he and his colleagues call "bridge species." Credit: NASA Visible Earth.

Although scientists have known since the middle of the 19th century that the tropics are teeming with species while the poles harbor relatively few, the origin of the most dramatic and pervasive biodiversity on Earth has never been clear.

New research sheds light on how that pattern came about. Furthermore, it confirms that the tropics have been and continue to be the Earth's engine of biodiversity.

By examining marine bivalves (two-shelled mollusks including scallops, cockles and oysters), a model system for large-scale ecological and evolutionary analysis, the study shows that most evolutionary lineages started in the tropics and expanded outward.

"This 'out of the tropics' dynamic is the major process that shapes the latitudinal pattern of biodiversity that we see today on land and sea," said lead author David Jablonski, the William R. Kenan Jr. Professor in Geophysical Sciences at the University of Chicago.

His team focuses on marine bivalves because they combine a wealth of important biological patterns with a large but manageable number of living species (about 8,000) and a rich fossil record.

The new research will be published this week in the online Early Edition of the Proceedings of the National Academy of Sciences presents evidence that the "out of the tropics" process is driven mainly by bridge species, a new term referring to evolutionary lineages that straddle the boundary between the tropics and cooler neighboring regions.

"We thought the 'out of the tropics' process would be driven by the formation of new species at the edge of the tropics, but that doesn't seem to be true," Jablonski said.

"Whether bridge species really are the conduit, 'out of the tropics' for all those lineages still needs to be confirmed. We'll tackle that next, by examining molecular data on species within these lineages, inside and outside the tropics, to see how they're related."

As with the PNAS study, this follow-up research would require examining data on both fossils and living organisms. "Alas, it's still rare for paleontologists to integrate the fossil record with data on present-day organisms, but for large-scale biodiversity studies like this, it's a very powerful approach, often an essential one," Jablonski said.

"Biodiversity is a product of origination, extinction and immigration, and when the fossil record is adequate, as it is with bivalves, it provides the most robust window into the dynamics that produced present-day patterns."

Surprising findings
The new research corroborates the "out of the tropics" model that Jablonski and others introduced in a 2006 publication. In fact, the new research documents this dynamic over the past 12 million years-even during the Ice Ages, when the temperature differences between the equator and the poles became more severe.

That runs counter to the broadly accepted principle of "niche conservatism," which suggests that related species tend to retain the ecological limits of their ancestors, Jablonski said. "Most species we studied do adhere to that principle, but the ones that do not are crucial to the deployment of biodiversity on Earth."

There are many such bridge species but each evolutionary lineage generally has only one or two. Therefore, bridge species are widespread in an evolutionary sense but rare in terms of overall biodiversity, according to the research. And the fossil record shows that most of today's bridge species started as tropical species.

"Somehow they left their tropical cradle, adapting to the colder temperatures and more variable climates of the temperate zones," said Jablonski. "It's impressive that they apparently expanded their ability to tolerate these harsher conditions."

Another surprise is that the most widespread species of bivalves are not the ones with the broadest temperature tolerances. Rather, they are often the ones with limited temperature tolerances that have specialized on temperatures that are the most widespread.

"This is important because broad geographic range is one of the most reliable estimates of the extinction-resistance of a species," Jablonski said. "What surprised us is that the most widespread temperatures-and therefore many of the most widespread bivalve species-occur in the tropics."

Homo sapiens is even more impressive than the bridge species in this study, he added. Humans have not only immigrated out of the tropics but throughout the Earth.

Only a handful of marine species range all the way from equator to poles, Jablonski has found, but humans are as widespread as any species known today. "As a species we're pretty extinction-resistant, but even widespread tropical species may be at risk today," said Jablonski.

As research on both living and fossil species has shown, broad geographic ranges buffer species from extinction when pressures are local, such as from hurricanes, pollution or overexploitation. But when-for marine species-those pressures alter global ocean temperatures, circulation patterns or chemistry, a broad geographic range is less likely to help, Jablonski said.

"That's what happened at the end-Cretaceous mass extinction 65 million years ago, and that could be looming today."

"Out of the Tropics, but how? Fossils, bridge species, and thermal ranges in the dynamics of the marine latitudinal diversity gradient" will be published in the online Early Edition of Proceedings of the National Academy of Sciences the week of June 10, 2013, with a profile of lead author David Jablonski in the same issue. Other co-authors from UChicago are Christina L. Belanger (now at South Dakota School of Mines and Technology), Sarah K. Berke (now at Siena College), Shan Huang, Andrew Z. Krug (now at Flint Hill School), and Adam Tomasovych (now at Slovak Academy of Sciences). Kaustuv Roy, University of California, San Diego; and James W. Valentine, University of California, Berkeley, are also co-authors.

.


Related Links
University of Chicago
Darwin Today At TerraDaily.com






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle








FLORA AND FAUNA
Philippines to destroy 5 tonnes of ivory tusks
Manila (AFP) June 11, 2013
The Philippines said Tuesday it would destroy five tonnes of confiscated elephant tusks as part of a global campaign to raise awareness against the illegal trade of so-called "blood ivories". The seized tusks represent a portion of the 13.1 tonnes of Tanzanian elephant tusks seized in 2005 and 2009 that are kept in a government vault, said Protected Areas and Wildlife Bureau head Theresa Mun ... read more


FLORA AND FAUNA
Sandbags and raw nerves as flood peak hits Germany

More radioactive leaks reported at Fukushima plant

Japan disaster cash spent on counting turtles: report

Agreement over Statue of Liberty security screening

FLORA AND FAUNA
Sony eyes long game despite console launch triumph

Two New Russian Radars to Start Work Next Year

Sony wins opening skirmish in new-gen console war

Study: Moving business software to cloud promises big energy savings

FLORA AND FAUNA
AU urges Egypt and Ethiopia to hold talks on Nile row

Unfrozen mystery: H2O reveals a new secret

Chagos Islanders lose UK marine park challenge

Egypt eyes Nile deal with Ethiopia

FLORA AND FAUNA
Ancient trapped water explains Earth's first ice age

US senators urge Obama to block Alaska mine

Is a Sleeping Climate Giant Stirring in the Arctic

NASA's IceBridge Mission Contributes to New Map of Antarctica

FLORA AND FAUNA
How does inbreeding avoidance evolve in plants

How do you feed nine billion people

China approves imports of GM soybean from Brazil

Biotech crops vs. pests: Successes and failures from the first billion acres

FLORA AND FAUNA
Merkel urges greater flood protection as tours region

Germany begins to count cost as floods surge north

Merkel visits flooded region as Hungary waters recede

Earthquake acoustics can indicate if a massive tsunami is imminent

FLORA AND FAUNA
First pictures of Algeria's Bouteflika since mini-stroke

Gunfire at paramilitary barracks in Niger capital: residents

'Scorched earth' tactics in Sudan's Blue Nile: Amnesty

Rwandan general to command Mali UN force

FLORA AND FAUNA
Weapons testing data determines brain makes new neurons into adulthood

World's 'oldest woman' dies in China: family

Geneticist speculates humans could have big eyes, foreheads in future

How similar are the gestures of apes and human infants? More than you might suspect




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement