Posts Tagged ‘Evolution’

Cool Evolution Trick: Platinum Turns Baby Snails Into Slugs

08 Oct

Marisa cornuarietis snail

Evolution doesn’t have to operate at a snail’s pace, even for snails. In experiments designed to simulate the evolutionary transition that produced slugs, researchers exposed baby snails to the metal platinum, causing the animals to develop without external shells. The research illustrates how a big leap on the evolutionary path of animal body plans might have occurred. It also reopens a can of worms concerning the development and evolution of an entire class of shelled creatures.

sciencenewsScientists reared Marisa snails, best known for cleaning up algae and other debris in home aquariums, in petri dishes containing varying concentrations of platinum. At certain exposures, all of the roughly 80 percent of snails that survived were shell-less, Heinz Köhler of the University of Tübingen in Germany and his colleagues report in the September-October Evolution & Development. The researchers posit that the platinum is causing effects similar to the genetic mutation that turned off shell production in some snails, paving the way for their slug descendants.

“This shows that you can get really dramatic changes that could be similar to the genetic mutations that drive evolution, without worrying about doing everything in small incremental steps,” says comparative physiologist Roger Croll of Dalhousie University in Halifax, Nova Scotia. “This is a very concrete demonstration, a very clear demonstration of a large-scale change in body plan. All of a sudden you get shell-less animals.”

Evidence suggests that transitions from snails to slugs — or rather, from having a concrete outer shell to a greatly reduced internal one — have happened numerous times in evolution. Such losses or gains occurred repeatedly within the Mollusca, an enormous group that includes clams, oysters, squid, octopuses and of course the gastropods —snails and slugs. The internal flat bone of cuttlefish and squid, for example, is thought to be a pared-down version of an ancestral outer molluscan shell. And the shell game continued within the gastropods. Within the marine gastropods known as sea butterflies and sea hares, for example, there are both shelled and shell-less species.

Though the new study shows that shell loss in gastropods can happen in one fell swoop, it also suggests that another evolutionary transition might have required several steps to complete. Torsion is an anatomical hallmark of the gastropods that makes them look like their bottom halves were rotated 180 degrees relative to their top halves, putting their anuses over their heads. The term torsion also refers to the hypothetical evolutionary process that purportedly led to this awkward anatomy, says evolutionary biologist Louise Page of the University of Victoria in British Columbia.

The new research suggests that torsion might not have occurred in one grand swivel. In many gastropods the anus, gills and mantle cavity are rotated 180 degrees. But in some there is partial rotation. And in the snails that Köhler and his colleagues exposed to platinum there was partial rotation as well: The anus swiveled but the gills and mantle were left in their original positions. This suggests that the gastropod body plan could have arisen through physiological means other than torsion, such as asymmetrical growth, where one half of the body atrophied and the other blossomed.

“This paper helps people to think about the fact that these anatomical positions are not necessarily coupled together,” says Page. “It really demonstrates that development is modular, that you can have quite drastic modifications of the development of one component of the body plan but not others.”

See Also:

Image: Goethe University


Devastating volcanoes wiped out the Neanderthals [Mad Archaeology]

07 Oct
The ultimate fate of the Neanderthals remains a major mystery. We know they went extinct, but why did they die out when our ancestors thrived? New evidence suggests massive, deadly volcanoes killed off the Neanderthals while completely sparing our ancestors. More »

Mass Extinctions Change the Rules of Evolution

02 Sep

A reinterpretation of the fossil record suggests a new answer to one of evolution’s existential questions: whether global mass extinctions are just short-term diversions in life’s preordained course, or send life careening down wholly new paths.

Some scientists have suggested the former. Rates of species diversification — the speed at which groups adapt and fill open ecological niches — seemed to predict what’s flourished in the aftermath of past planetary cataclysms. But according to the calculations of Macquarie University paleobiologist John Alroy, that’s just not the case.

“Mass extinction fundamentally changes the dynamics. It changes the composition of the biosphere forever. You can’t simply predict the winners and losers from what groups have done before,” he said.

Alroy was once a student of paleontologist Jack Sepkoski, who in the 1980s formalized the notion that Earth has experienced five mass extinctions in the 550 million years since life became durable enough to leave a fossil record. Graphs of taxonomic abundance depict lines rising steadily as life diversifies, plunging precipitously during each extinction, and rising again as life proliferates anew.

As the fossil record is patchy and long-term evolutionary principles still debated, paleobiologists have historically disagreed about what these extinctions mean. Some held that, in the absence of extinctions, species would diversify endlessly. The Tree of Life could sprout new branches forever. Others argued that each taxonomic group had limits; once it reached a certain size, each branch would stop growing.

Sepkoski’s calculations put him on the limits side of this argument. He also proposed that, by looking at the rate at which each group produced new species, one could predict the winners and losers of each mass extinction’s aftermath. Groups that diversified rapidly would flourish. Their destiny was already established.

“It’s a clockmaker vision of evolution. Each group has fixed dynamics, and if there’s an extinction, it just messes it up a bit,” said Alroy. “That’s what I’m challenging in this paper. There are limits, and that’s why we don’t have a trillion species. But those limits can change.”

Alroy crunched marine fossil data in the Paleobiology Database, which gathers specimen records from nearly 100,000 fossil collections around the world. He used a statistical adjustment method designed to reduce the skewing influences of paleontological circumstance — the greater chances of finding young fossils rather than old, the ease of studying some types of rock rather than others.

Historical species diversity among marine animals of Cambrian, Paleozoic and Modern origin.

The analysis, published September 2 in Science, produced what Alroy considers to be the most accurate reflection of extinction dynamics to date. And while his data supported the notion that each group’s diversity eventually hits a limit, he didn’t find Sepkoski’s correlation between pre-mass-extinction diversity rates and post-extinction success. Each mass extinction event seemed to change the rules. Past didn’t indicate future.

In an accompanying commentary, paleontologist Charles Marshall of the University of California, Berkeley noted that Alroy’s statistical methods still need review by the paleobiology community. The Paleobiological Database, for all its thoroughness, might also be incomplete in as-yet-unappreciated ways. “There will be no immediate consensus on the details of the pattern of diversity,” he wrote. But “the pieces are falling into place.”

Enough pieces have come together for Alroy to speculate on his findings’ implication for the future, given that Earth is now experiencing another mass extinction. Starting with extinctions of large land animals more than 50,000 years ago that continued as modern humans proliferated around the globe, and picking up pace in the Agricultural and Industrial ages, current extinction rates are far beyond levels capable of unraveling entire food webs in coming centuries. Ecologists estimate that between 50 and 90 percent of all species are doomed without profound changes in human resource use.

In the past, many evolutionary biologists thought life would eventually recover its present composition, said Alroy. In 100 million years or so, the same general creatures would again roam the Earth. “But that isn’t in the data,” he said.

Instead Alroy’s analysis suggests that the future is inherently unpredictable, that what comes next can’t be extrapolated from what is measured now, no more than a mid-Cretaceous observer could have guessed that a few tiny rodents would someday occupy every ecological niche then ruled by reptiles.

“The current mass extinction is not going to simply put things out of whack for a while, and then things will go back to where we started, or would have gone anyway,” said Alroy. Mass extinction “changes the rules of evolution.”

Images: 1) A fossil skull of Dunkleosteus, an apex predator fish that lived between 380 million and 360 million years ago, and had what is believed to be history’s most powerful bite./Michael LaBarbera, courtesy of The Field Museum. 2) Graph of species diversity among marine animals of Cambrian, Paleozoic and Modern origin./Science.

See Also:

Citations: “The Shifting Balance of Diversity Among Major Marine Animal Groups.” By J. Alroy. Science, Vol. 329 No. 5996, September 3, 2010.

“Marine Biodiversity Dynamics over Deep Time.” By Charles R. Marshall. Science, Vol. 329 No. 5996, September 3, 2010.

Brandon Keim’s Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecological tipping points.


Valley of the Whales

08 Aug

Paleontologist Philip Gingerich looks for sea monsters in the Egyptian desert. He assembles fossils of ancient whales that died there when it was covered by an ocean. One such whale is the Basilosaurus, which had small hind legs.

“Complete specimens like that Basilosaurus are Rosetta stones,” Gingerich told me as we drove back to his field camp. “They tell us vastly more about how the animal lived than fragmentary remains.”

Wadi Hitan—literally “valley of whales”—has proved phenomenally rich in such Rosetta stones. Over the past 27 years Gingerich and his colleagues have located the remains of more than a thousand whales here, and countless more are left to be discovered.

Researchers hope that whale fossils can help them understand how a land mammal evolved into an aquatic form that became our modern whales. Link

(Image credit: Richard Barnes/National Geographic)


Humans’ treatment of other animals shaped our evolution [Evolution]

22 Jul
Humans are one of the few animals that adopts and cares for other animals. Our cross-species connections might be older and more important than we ever imagined, driving human evolution for millions of years and even helping us invent language. More »