University of Michigan
Department of Ecology and Evolutionary Biology

Forest carbon uptake recovers from modest tree losses

A paper titled “Disturbance and the resilience of coupled carbon and nitrogen cycling in a north temperate forest,” was published Oct. 29, 2011 in the Journal of Geophysical Research – Biogeosciences by Luke Nave, postdoctoral fellow, and colleagues. A recent editor’s highlight from the journal is excerpted here:  

By manipulating an experimental forest at the University of Michigan Biological Station, Nave and colleagues determined how forests' carbon and nitrogen cycles respond to subtle disruptions. In 2008, the authors and their team culled 39 percent of the forest's tree population using stem girdling—the process of removing a ring of the tree's bark and starving it of its nutrient and water supplies. The aim was to accelerate the loss of short-lived tree species, driving the forest into a more complex state, commonly found in older forests, rather than the homogeneous conditions that result from clear-cutting or a forest-clearing fire.

Initially, the authors found that the forest's carbon uptake declined and soil nitrogen availability and leaching increased, reminiscent of severe disturbances. However, most forest ecosystems are inherently limited by the availability of nitrogen, and the newly liberated stores were drawn up by the remaining longer-lived trees, producing new leaf area and mitigating the decrease in carbon uptake. The authors suggest that, as the forest structure continues to change in the wake of subtle disturbances, the forest's carbon uptake will continue to increase.

"Because we implemented the experimental treatment several years ago, we are gaining this knowledge a decade or two before most similar forests throughout the region undergo similar successional transition, making this study quite useful for forecasts of regional carbon cycling and interactions with the climate,” said Nave.

Co-researchers and co-authors include: Jim Le Moine, UMBS; Professor Knute Nadelhoffer, UMBS director; Chris Vogel, UMBS; and colleagues from Ohio State University, Columbus; Columbia University, New York City; Cornell University, Ithaca, New York; Virginia Polytechnic Institute and State University, Blacksburg, Virginia.

Journal of Geophysical Research – Biogeosciences, Editors' Highlight

U-M News Service Future forests video, Sept. 2008 (project initiation)

Like humans, the paper wasp has a special talent for learning faces

Though paper wasps have brains less than a millionth the size of humans', they have evolved specialized face-learning abilities analogous to the system used by humans, according to a University of Michigan evolutionary biologist and one of her graduate students.

"Wasps and humans have independently evolved similar and very specialized face-learning mechanisms, despite the fact that everything about the way we see and the way our brains are structured is different," said graduate student Michael Sheehan, who worked with evolutionary biologist Elizabeth Tibbetts, a professor of ecology and evolutionary biology, on the face-recognition study. "That's surprising and sort of bizarre."

The study marks the first time that any insect has demonstrated such a high level of specialized visual learning, said Sheehan, lead author of a paper published online in the journal Science on Thursday, Dec. 1.

"The evolutionary flexibility of specialized face learning is striking and suggests that specialized cognition may be a widespread adaptation to facilitate complex behavioral tasks such as individual recognition," they wrote.

The paper is receiving wide coverage in the media including in Discover Magazine, Nature.com, New Scientist, msnbc.com, and ABC online.

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Ancient whale skulls and directional hearing: a twisted tale

Skewed skulls may have helped early whales discriminate the direction of sounds in water and are not solely, as previously thought, a later adaptation related to echolocation. U-M researchers, including Professor Philip Gingerich, report the finding in a paper published online in the Proceedings of the National Academy of Sciences August 22, 2011.

Asymmetric skulls are a well-known characteristic of the modern whale group known as odontocetes (toothed whales). These whales also have highly modified nasal structures with which they produce high-frequency sounds for echolocation – a sort of biological sonar used to navigate and find food. The other modern whale group, mysticetes (baleen whales), has symmetrical skulls and does not echolocate.

These observations led scientists to believe that archaeocetes – the extinct, ancient whales that gave rise to all modern whales – had symmetrical skulls, and that asymmetry later developed in toothed whales in concert with echolocation. But this new analysis of archaeocete skulls shows that asymmetry evolved much earlier, as part of a suite of traits linked to directional hearing in water.

"This means that the initial asymmetry in whales is not related to echolocation," said U-M postdoctoral fellow Julia Fahlke, who is working with Gingerich, an internationally recognized authority on whale evolution, at the U-M Museum of Paleontology.

Fahlke didn't have to go far to explore the idea that maybe archaeocete skulls really were asymmetrical; the U-M Museum of Paleontology houses one of the world's largest and most complete archaeocete fossil collections. Fahlke began examining archaeocete skulls, and to her astonishment, "they all showed the same kind of asymmetry---a leftward bend when you look at them from the top down," she said.

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In bubble-rafting snails, the eggs came first

It's "Waterworld" snail style: ocean-dwelling snails that spend most of their lives floating upside down, attached to rafts of mucus bubbles. Scientists have known about the snails' peculiar lifestyle since the 1600s, but they've wondered how the rafting habit evolved. What, exactly, were the step-by-step adaptations along the way?

Graduate student Celia Churchill and coauthors believe they've found the answer to that intriguing question. In a cover story published in the Oct. 11 issue of Current Biology, they show that bubble rafting evolved by way of modified egg masses.

The bubble-rafting snails, members of the family Janthinidae, secrete mucus from their "foot," a broad, muscular organ at the base of the snail's body. But instead of using slime to get around or to communicate chemically, as other types of snails do, they trap air inside quick-setting mucus to make bubbles that glom together and form rafts on which the snails spend the rest of their lives.

"We had a pretty good idea that that janthinids evolved from snails that live on the sea floor," Churchill said. The question was, which specific group of snails gave rise to the janthinids, and how did the janthinid lineage make the transition from bottom dwellers to surface surfers?

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Hidden soil fungus, now revealed, is in a class all its own

A type of fungus that's been lurking underground for millions of years, previously known to science only through its DNA, has been cultured, photographed, named and assigned a place on the tree of life.

Researchers say it represents an entirely new class of fungi: the Archaeorhizomycetes. Like the discovery of a weird type of aquatic fungus that made headlines a few months ago, this finding offers a glimpse at the rich diversity of microorganisms that share our world but remain hidden from view.

The fungal phenomenon, brought to light by Professor Timothy James and fellow researchers at the Swedish University of Agricultural Sciences, the Imperial College London and Royal Botanic Gardens and the University of Aberdeen, is described in the Aug. 12 issue of the journal Science.

Although unseen until recently, the fungus was known to be extremely common in soil. Its presence was detected in studies of environmental DNA – genetic material from a living organism that is detected in bulk environmental samples, such as samples of the soil or water in which the organism lives.

"You couldn't really sample the soil without finding evidence of it," said James, a U-M assistant professor of ecology and evolutionary biology and an assistant curator at the university's Herbarium. "So people really wanted to know what it looks like."

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Mass extinction victim survives! Snail long thought extinct, isn't

Think "mass extinction" and you probably envision dinosaurs dropping dead in the long-ago past or exotic tropical creatures being wiped out when their rainforest habitats are decimated. But a major mass extinction took place right here in North America in the first half of the 20th century, when 47 species of mollusk disappeared after the watershed in which they lived was dammed.

Now, a population of one of those species—a freshwater limpet last seen more than 60 years ago and presumed extinct—has been found in a tributary of the heavily dammed Coosa River in Alabama's Mobile River Basin. Researchers from the University of Michigan, including Professor Diarmaid Ó Foighil, among others,  reported the rediscovery May 31, 2011 in the online, open-access journal PLoS One.

The story of Rhodacmea filosa's disappearance and reappearance is both a conservation success story and a cautionary tale for other parts of the world where rivers are being dammed, said Ó Foighil, professor of ecology and evolutionary biology and a curator at the U-M Museum of Zoology. It's also an example of how museum specimens collected generations ago can inform scientists of today.

Working with Ó Foighil from the U-M Museum of Zoology were John Burch, professor emeritus; Jingchun Li, graduate student; and Taehwan Lee; collection coordinator.

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Probe human diseases in yeast? Possibly, protein study suggests

The molecular-level workings of proteins are surprisingly similar across a wide range of organisms, from humans to fungi and plants, research by Professor Jianzhi "George" Zhang and colleagues suggests.

This finding raises the possibility of using much simpler organisms, such as yeast, to study the mechanisms underlying human disease. The study was published online in the Proceedings of the National Academy of Sciences the week of May 9, 2011.

Most previous studies revealed only changes in protein sequence. What about changes in protein function? Those are more difficult to measure and compare, said Zhang, because of the wide variety of roles proteins perform. However, he and his coauthors came up with the idea of using interactions between pairs of proteins, known as protein-protein interactions or PPI, as an index of protein function that could be used to make comparisons among species and measure the rate of protein function evolution.

"Compared to sequence evolution, there's about a one thousand-fold difference," Zhang said. "That means that on average, it requires about one thousand amino acid changes in a protein to have one change in a protein-protein interaction."

"The corresponding proteins participate in very different physiological processes, yet, if the molecular functions of the proteins are conserved, you could still use plants or yeast to understand the molecular mechanisms involved in human disease, to see what molecular cellular processes are affected when these proteins malfunction," Zhang said.

Zhang's coauthors on the paper are graduate student Wenfeng Qian; former graduate student Xionglei He; former undergraduate student Edwin Chan; and visiting scholar Huailiang Xu of Sichuan Agricultural University in Sichuan, China. The research was supported by the National Institutes of Health.

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Evolution repeated itself at the molecular level

Sometimes evolution appears to repeat itself, giving rise to traits that look similar but have evolved independently. By testing whether these "parallel" traits were achieved using the same or different genetic and molecular mechanisms, researchers can begin to understand whether evolution is predictable at the molecular level.

Arielle Cooley, EEB postdoctoral fellow, and her colleagues show that the parallel evolution of petal pigmentation, in two species of South American monkeyflowers (Mimulus), occurred using separate yet strikingly similar underlying mechanisms. In both cases, the genes required to make pigment have been recently "switched on" in the petals. In both cases, the "switch" is a single genomic region containing multiple, recently duplicated regulatory genes called R2R3 MYBs. Interestingly, they found that the two "switch" regions (one responsible for flower color in Mimulus luteus var. variegatus, the other for flower color in Mimulus cupreus) are themselves related through duplication. The authors conclude that in this case evolution has repeated itself with strong consistency at the molecular level.

Duplication has enabled that repetition to occur using two independent but functionally similar loci, highlighting the importance of genomic complexity to the evolutionary process.

The paper was the cover story in Current Biology’s April 26, 2011 issue.

Biodiversity improves water quality in streams through a division of labor

Biologically diverse streams are better at cleaning up pollutants than less rich waterways, and a University of Michigan ecologist says he has uncovered the long-sought mechanism that explains why this is so.

Professor Bradley Cardinale used 150 miniature model streams, which use recirculating water in flumes to mimic the variety of flow conditions found in natural streams. He grew between one and eight species of algae in each of the mini-streams, then measured each algae community's ability to soak up nitrate, a nitrogen compound that is a nutrient pollutant of global concern.

He found that nitrate uptake increased linearly with species richness. On average, the eight-species mix removed nitrate 4.5 times faster than a single species of algae grown alone. Cardinale reports his findings in the April 7 edition of the journal Nature.

"The primary implication of this paper is that naturally diverse habitats are pretty good at cleaning up the pollutants we dump into the environment, and loss of biodiversity through species extinctions could be compromising the ability of the planet to clean up after us," said Cardinale, an assistant professor at the U-M School of Natural Resources and Environment and the Department of Ecology and Evolutionary Biology.

"One of the obvious implications of this study is that if we want to enhance water quality in places like the Chesapeake Bay watershed or around the Great Lakes, then conserving natural biodiversity in our streams will have the added benefit of helping to clean up these larger bodies of water," Cardinale said.

The study was widely covered in the media including by Reuters, Science News magazine, Voice of America, and futurity.org.

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Mating mites trapped in amber reveal sex role reversal

In the mating game, some female mites are mightier than their mates, new research at the University of Michigan and the Russian Academy of Sciences suggests. The evidence comes, in part, from 40 million-year-old mating mites preserved in Baltic amber.

In a paper published March 1, 2011 in the Biological Journal of the Linnean Society, researchers Pavel Klimov and Ekaterina Sidorchuk describe an extinct mite species in which the traditional sex roles were reversed.

"In this species, it is the female who has partial or complete control of mating," said Klimov, an associate research scientist at the U-M Museum of Zoology. "This is in contrast to the present-day reproductive behavior of many mite species where almost all aspects of copulation are controlled by males."

In mites, as in other animals including humans, the battle of the sexes has been raging throughout evolutionary history. The story was extensively covered in the media including on MSNBC News and The Discovery Channel.

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Rising C02 may reroute evolution

Rising carbon dioxide levels associated with global warming may affect interactions between plants and the insects that eat them, altering the course of plant evolution, research by EEB graduate student Rachel Vannette and Professor Mark Hunter suggests.

The research focused on the effects of elevated carbon dioxide on common milkweed, Asclepias syriaca. Milkweed is one of many plants that produce toxic or bitter chemical compounds to protect themselves from being eaten by insects. These chemical defenses are the result of a long history of interactions between the plants and insects such as monarch caterpillars that feed on them.

Plant defenses -- and insect eating patterns -- also respond to environmental factors such as rising carbon dioxide. This suggests that elevated carbon dioxide could affect plant evolution by altering the "selection pressure" that plant-eating insects exert on plants.

Selection pressure, the driving force of evolution, induces changes in the genetic composition of a population. It works like this: if insects inflict too much damage on plants, the plants can't reproduce as successfully. This sets up a situation in which any plants that, by chance, have inherited insect-deterring traits are at an advantage. Because of that advantage, such traits are likely to spread through the population, urged on by "pressure" from the insects.

Vannette and Hunter investigated whether different genetic "families" of the common milkweed from a single population in Northern Michigan would respond differently to increasing carbon dioxide levels in the atmosphere and if so, how those responses might affect the plants' chances of being eaten by insects.

The findings were the cover story in the March issue of Global Change Biology.

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