KU News Release

Oct. 7, 2009
Contact: Brendan M. Lynch, University Relations, (785) 864-8855

Researchers show climate change triggers dwarfism in soil-dwelling creatures

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LAWRENCE — Investigators at the University of Kansas have discovered that ancient soil-inhabiting creatures decreased in body size by nearly half in response to boosted carbon dioxide levels and higher temperatures.

The KU researchers’ findings were published this week’s early online edition of the Proceedings of the National Academy of Sciences.

Jon Smith, assistant scientist with the Kansas Geological Survey, based at KU, and Stephen Hasiotis, KU associate professor of geology, have demonstrated that soil-inhabiting creatures contracted in size by 30 percent to 46 percent during the Paleocene–Eocene Thermal Maximum. The PETM was a short interval 55 million years ago marked by a spike in the atmosphere’s C02 levels and global temperatures, conditions being repeated on Earth now.

The study is the first to establish that soil biota — or above- and below-ground soil organisms — experienced a loss in size similar to mammals, which were reduced in size by as much as 50 percent during the PETM. The work was supported by collaborative grants totaling nearly $400,000 from the National Science Foundation to Hasiotis and colleague Mary Kraus at the University of Colorado.

The researchers set up three hypotheses to test for the PETM.

“In our initial hypothesis, we thought that there would be no response to climate change, that the animals would be protected because they’re underground,” said Hasiotis. “We also proposed that there would be minimal and protracted change or some sort of a delayed response. Instead, we find that they did experience the same kind of change as vertebrates living during the same period.”

The soil-dwelling organisms examined by Smith and Hasiotis are ancient relatives of modern ants, cicadas, dung beetles, earthworms and crayfish. To establish their findings, the KU researchers examined trace fossils, or the burrows, nests, tracks, trails and borings of organisms preserved within the Willwood Formation, a thick sequence of mudstones and sandstones in Wyoming’s Bighorn Basin. They found that diameters of burrows and other traces were smaller during the PETM, suggesting that soil-inhabiting organisms that had created the traces were correspondingly lesser in size.

The KU scientists say that their results foreshadow biological outcomes that may result because of the planet’s current jump in C02 concentration and temperatures. They suggest that museum collections of insects compiled over the last few hundred years should be studied to determine if body sizes of modern insects are indeed getting smaller.

“The PETM is seen as a good analog for modern climate change because it’s occurring at roughly the same speed and magnitude,” said Smith. “The take-home lesson is that there can be cascading effects that ripple through an ecosystem when you change just one aspect. Modern climate change can have many effects that aren’t going to be as immediately visible as sea-level change. We could be changing soil conditions over vast portions of the world and affecting the soil organisms themselves — that will impact our own agriculture.”

The KU researchers attribute dwarfism in soil-dwelling creatures to faster rates of development in individuals, along with decreasing life spans. According to the scientists, conditions brought about by increased C02 and higher temperatures — such as altered precipitation, nutrition and soil drainage — drove evolution in the size of subterranean biology.

“The soil biota evolved for certain soil temperatures and conditions — and for this geologically brief period of time, those conditions were changed,” Hasiotis said. “They probably were adapting to those warmer conditions by having a smaller body size.”

In the Bighorn Basin, a typical day in the field for the researchers involved digging shoulder-width trenches that were a meter or so deep and several meters tall, then searching the soil for specific geometric shapes indicating ancient nests, cocoons and burrows.

“For each individual trace fossil, we’d measure the diameter,” said Smith. “We’d compare like trace fossils from rocks that occurred before the PETM event, within the event, and after the event. Then we’d look for changes in those diameters through time. We were surprised to find that they were in fact smaller through the PETM.”

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