Department NewsA female Anopheles stephensi mosquito taking a blood meal by Kedar Bhide
Warming climate boosts malaria in Kenya
In the highlands of East Africa, malaria transmission has skyrocketed over recent decades. New research suggests rising temperatures are at least partly to blame.
A mathematical model of malaria transmission developed by Professor Mercedes Pascual, Howard Hughes Medical Institute investigator and her colleagues, showed that warming could explain a significant part of the increase in malaria cases. While previous studies have considered scenarios for the future of the disease, the new study, published online November 10, 2010, in the British scientific journal, Proceedings of the Royal Society B, is one of the first to examine the effect of past warming on malaria transmission.
"When you go up in altitude, temperature decreases," Pascual says. "We know that climate may be playing a limiting role (in the spread of malaria)."
Pascual's models are changing the way scientists think about how climate variability influences the dynamics of infectious diseases. One of the long-term goals of her research is to build computational tools that will help scientists identify when epidemics will occur, thereby enabling them to alert public health agencies. Those agencies, in turn, would be in a better position to implement prevention measures and meet the increased demand for lifesaving medicine and supplies when an epidemic occurs.
Pascual's co-authors, and their affiliations at the time, are Dr. David Alonso, Community and Conservation Ecology Group, University of Groningen, CEES, Haren, The Netherlands and Dr. Menno J. Bouma, London School of Hygiene and Tropical Medicine, London, UK.
Contact among age groups key to understanding whooping cough spread and control
Strategies for preventing the spread of whooping cough—on the rise in the United States and several other countries in recent years—should take into account how often people in different age groups interact, research at the University of Michigan suggests.
The findings of epidemiologists Pej Rohani, Aaron King, and Xue Zhong appeared in the Nov. 12, 2010 issue of the journal Science.
Thanks to widespread childhood vaccination, whooping cough (pertussis) once seemed to be under control. But the illness, which in infants causes violent, gasping coughing spells, has made a comeback in some developed countries since the 1980s, becoming a major public health concern. In addition, there's been a shift in who's getting sick, with fewer cases seen in preschool children and more in teenagers, but the reasons for the changing patterns have been unclear.
A variety of explanations have been proposed—genetic changes in the bacterium that causes the disease or the "wearing off" of immunity in people who were vaccinated years ago, for example.
But by combining two independent sets of data from previous studies, Professor Rohani, Professor King and former U-M EEB postdoctoral fellow Xue Zhong, found that age-specific contact patterns alone can explain the observed shifts in prevalence and age-specific incidence.
The study makes two robust conclusions, said King. "The first point is that we see strong evidence for the efficacy of vaccination directed at children when compliance is high. The second is that better knowledge of actual contact patterns among age groups is crucial for the design of more effective and economical vaccination strategies."
Salamander hybrid zones in the southern Appalachian Mountains
"Hybrid zones are excellent systems to study evolutionary processes, such as speciation and the maintenance of species boundaries," said Matthew Chatfield, a recent Ph.D. graduate. "Some are also amenable to ecological studies, as they are influenced by such factors as elevation, rainfall, and temperature."
In the Great Smoky Mountains of North Carolina and Tennessee, a hybrid zone occurs among three species of fully terrestrial, woodland salamanders – Plethodon jordani, P. metcalfi, and P. teyahalee. Chatfield, Professor Priscilla Tucker, and colleagues used four different genetic and morphological markers and mapped the structure of this atypical, three-way hybrid zone. Their results indicated that one of the genetic markers (from the mitochondrial genome) showed a different pattern than the other markers. "Because this is a well studied system and there is considerable environmental information available from the southern Appalachians, we were able to take this finding one step further," Chatfield said.
One approach that they used was a geographic information system (GIS)-based method called ecological niche modeling. Using this method, they mapped the salamanders' preferred habitat types onto the geographic region encompassing the hybrid zone. They concluded that, while not being maintained by climate, the hybrid zone nonetheless settled into an area of suitable overlapping habitat types.
They explored other explanations for the different patterns observed in the genetic and morphological markers, such as sex-biased dispersal and asymmetrical reproductive isolation. One explanation that is consistent with all these lines of evidence is that the range of one species, P. jordani, is expanding into the ranges of the other two species, Chatfield said. "If true, then the pattern we observe in the mitochondrial DNA is a relict – that is, a genetic footprint – of the historic range of P. jordani. This project is unique because we were able to apply multiple approaches, from both an ecological and evolutionary perspective, in analyzing this hybrid zone, as well take advantage of the rich literature on the complex and fascinating salamanders of the southern Appalachians."
Chatfield and Tucker published "Patterns of differential introgression in a salamander hybrid zone: inferences from genetic data and ecological niche modelling," in the October 2010 journal Molecular Ecology. Chatfield is a postdoctoral fellow at Tulane University, New Orleans.
Paper wasps punish peers for misrepresenting their might
Falsely advertising one's fighting ability might seem like a good strategy for a wimp who wants to come off as a toughie, but in paper wasp societies, such deception is discouraged through punishment, experiments at the University of Michigan suggest. The research by Professor Elizabeth Tibbetts and graduate student, Amanda Izzo, was published online Aug. 19, 2010 in the journal Current Biology.
Rather than wasting energy by constantly fighting with rivals, many animals use signals that say, in effect, "Don't mess with me; I can whip you." But what's to prevent a weakling from gaining the upper hand by falsely signaling strength?
One explanation for why that doesn't often happen is that phony signalers are punished for their misdeeds. For cheaters to be punished, though, the deception must be detected. Tibbetts and Izzo used the paper wasp Polistes dominulus, a widespread species that nests on the eaves of houses throughout the U.S. and Europe, to explore.
Shade-coffee farms support native bees that maintain genetic diversity in tropical forests
Shade-grown coffee farms support native bees that help maintain the health of some of the world's most biodiverse tropical regions, according to a study by Professor Chris Dick and alumna Shalene Jha.
The study suggests that by pollinating native trees on shade-coffee farms and adjacent patches of forest, the bees help preserve the genetic diversity of remnant native-tree populations. The study was published online in July 2010 in the Proceedings of the National Academy of Sciences.
"A concern in tropical agriculture areas is that increasingly fragmented landscapes isolate native plant populations, eventually leading to lower genetic diversity," said Dick. "But this study shows that specialized native bees help enhance the fecundity and the genetic diversity of remnant native trees, which could serve as reservoirs for future forest regeneration."
In the latest study, U-M's Dick and UC-Berkeley's Shalene Jha investigated the role of native bees that pollinate native trees in and around shade-grown coffee farms in the highlands of southern Chiapas, Mexico. In their study area, tropical forest now represents less than 10 percent of the land cover.
The enhanced genetic diversity of the shade-farm trees could provide a reservoir for future forest regeneration, as the coffee farms typically fall out of production in less than a century. Given that potential, along with the shade farm's previously identified roles in connecting habitat patches and sheltering native wildlife, it is important to encourage this traditional style of agriculture, Jha and Dick said.
Have we met? Research finds 'missing social knowledge'
The face looks familiar but . . . just as humans don't always know their neighbors, new research at U-M shows even the most social of animals don't always recognize individuals they regularly encounter, the first known evidence of "missing social knowledge" in non-human primates.
Professor Thore Bergman details his findings in the journal Proceedings of the Royal Society B. Bergman looked at individual recognition in male geladas (Theropithecus gelada, close relatives of baboons) that live in fluid, multilevel groups that can number more than 1,200 individuals -- 10 times larger than baboon groups.
By observing how geladas responded to playbacks of different calls, Bergman found recognition only among geladas with the very highest levels of overlap. This finding "suggests that geladas are either unable or unmotivated to keep track of the individual identities of other males in their multi-level society – even males with whom they have a high degree of social overlap,'' Bergman writes. He compared these findings with published accounts of social knowledge in chacma baboons (Papio ursinus). Responses indicate that male geladas, unlike baboons, do not use vocalizations to recognize all of the individuals they regularly encounter.
For years, scientists have pursued the social intelligence hypothesis, the idea that solving social problems has driven the evolution of intelligence, not only in humans but also in other big-brained species. The missing social knowledge of geladas actually supports this hypothesis.
"This finding is potentially significant because if sociality drives cognitive evolution, then we would expect to see evidence that sociality is cognitively challenging," he said.
Form or function? Evolution takes different paths
Biologists have long known that both the appearance of organisms and their inner workings are shaped by evolution. But do the same genetic mechanisms underlie changes in form and function? A study by U-M evolutionary biologist Jianzhi Zhang and colleague Ben-Yang Liao, a recent U-M EEB alumnus, suggests not.
The research was published online in the Proceedings of the National Academy of Sciences, April 2010.
In the study, Zhang and colleagues Liao and Meng-Pin Weng set out to systematically test a hypothesis proposed by molecular biologist Sean Carroll in 2005. Carroll posited that changes in morphology (such things as shape, color and structure of external and internal parts) occur through different genetic mechanisms than changes in physiology (inner workings). Carroll backed up his assertion with examples, but the idea, which challenged previous dogma, was controversial, Zhang said.
To test the hypothesis, Zhang's team turned to a database of knockout mice—lab mice that have been engineered to lack particular genes.
The finding that morphology and physiology are shaped by different evolutionary genetic processes can not only aid in future evolutionary studies, but can also be helpful in the study of human disease, Zhang said. "Our analysis of the knockout mouse data suggests that morphological defects are more likely due to problems with gene expression. This knowledge could help identify the disease-causing mutations more quickly, because it narrows the set of candidate genes and mutations that one needs to search from."
Zhang's coauthors, Liao and Weng, are at the National Health Research Institutes (NHRI) in Taiwan.
Flu doesn't die out, it hides out
Every autumn, as predictably as falling leaves, flu season descends upon us. Every spring, just as predictably, the season comes to a close. This cyclical pattern, common in temperate regions, is well known, but the driving forces behind it have been in question.
Do existing strains die off each spring, only to be replaced each fall by new founding strains from other parts of the world, or does a "hidden chain of sickness" persist over the summer, seeding the next season's epidemic?
A genetic analysis by U-M EEB postdoctoral fellow Trevor Bedford and colleagues at U-M, Howard Hughes Medical Institute and Florida State University reveals that in the United States, not all strains of influenza die off at the end of winter; some move southward to South America, and some migrate even farther.
The results have implications for public health efforts aimed at combating the disease. In addition, growing knowledge about patterns of flu migration eventually may make it possible to tailor vaccines to particular locations, Bedford said.
U-M colleagues include Professor Mercedes Pascual and Sarah Cobey, postdoctoral fellow. The paper was published online May 27, 2010 in the open-access journal PLoS Pathogens.
U-M News Service press release
Temperature controls on aquatic bacterial communities
Bacteria are important organisms in ecosystems, performing the critical tasks of decomposing organic matter, regenerating nutrients and forming the base of microbial food webs. The rates of these critical tasks can be modified by temperature, and understanding the bacterial response to temperature is necessary for understanding ecosystem function. For example, at higher temperatures, metabolic rates increase considerably and bacteria are able to break down organic substrates more rapidly. However, shifts in dominant community members can occur on ecologically relevant time scales (days), and may result in a community with different metabolic capabilies.
EEB alumnus Dr. Heather Adams and Professor George Kling published a paper in the online May issue of Environmental Microbiology on their research in lakes and streams in northern Alaska measuring the impact of temperature on bacterial activity and community composition.
Aquatic bacterial communities incubated at different temperatures had different rates of production, indicating that populations within the communities had different optimum temperatures. The researchers found that temperature controls on aquatic bacteria are more complex than previously thought due to the interactions of changing temperature and rapid shifts in community composition.
Responses to temperature are important to consider when examining the effects of climate change, because predicted increases in water temperatures in the region are suboptimal for the current bacterial communities, and could result in lower bacterial activity, rather than greater as is usually assumed.
Climate change, mountain building led to mammal diversity patterns
Travel from the tropics to the poles, and you'll notice that the diversity of mammals declines with distance from the equator. Move from lowland to mountains, and you'll see diversity increase as the landscape becomes more varied.
Ecologists have proposed various explanations for these well-known "biodiversity gradients," invoking ecological, evolutionary and historical processes. New findings by U-M researchers Catherine Badgley and John Finarelli, of Geological Sciences, suggest that the elevational patterns of diversity we see today have appeared, disappeared and reappeared over Earth's history and that these patterns arise from interactions between climate change and mountain building.
The results, published online April 28 in the journal Proceedings of the Royal Society B, also have implications for conservation efforts in the face of modern-day global warming. The print version will be published Sept. 7, 2010.
Small family farms in tropics can feed the hungry and preserve biodiversity
Conventional wisdom among many ecologists is that industrial-scale agriculture is the best way to produce lots of food while preserving biodiversity in the world's remaining tropical forests. But two University of Michigan researchers reject that idea and argue that small, family-owned farms may provide a better way to meet both goals.
In many tropical zones around the world, small family farms can match or exceed the productivity of industrial-scale operations, according to Professors John Vandermeer and Ivette Perfecto. At the same time, smaller diversified farms are more likely to help preserve biodiversity in tropical regions undergoing massive amounts of deforestation. Their findings were published online Feb. 22, 2010 in the Proceedings of the National Academy of Sciences (PNAS).
"Most of the tropical forest that's left is fragmented, and what you have are patches of forest surrounded by agriculture," said Perfecto, a professor at the School of Natural Resources and Environment. "If you want to maintain biodiversity in those patches of forest, then the key is to allow organisms to migrate between the patches. "And small-scale family farms that adopt sustainable agricultural technologies are more likely to favor migration of species than a huge, monocultural plantation of soybeans or sugar cane or some other crop."
The PNAS article by Vandermeer and Perfecto, who is with the School of Natural Resources and Environment, is part of a special report in the journal about solutions to the world food crisis. Perfecto, Vandermeer and Angus Wright discuss the links between agriculture, conservation and food sovereignty in their book "Nature's Matrix," published last year by Earthscan.
Bats and whales share molecular mechanism
With high-pitched squeaks, clicks and chirps and ultra-sensitive hearing, toothed whales and some bats zero in on prey by emitting pulses of sound and interpreting the echoes that bounce back.
Over the course of evolution, the two groups acquired this remarkable ability independently, for use in very different environments, so you'd expect the means by which each accomplishes the feat to differ. Surprisingly, that's not the case, a new study by Professor Jianzhi Zhang and U-M visiting scholar Ying Li suggests.
"The seemingly different echolocation abilities that evolved independently in whales and bats have a similar underlying molecular mechanism," said Zhang. The finding overturns conventional thinking that the evolutionary phenomenon known as convergence is rare at the molecular level. The research was reported in the Jan. 26, 2010 issue of the journal Current Biology.
Co-authors are Zhen Liu and Peng Shi of the Chinese Academy of Sciences. The research was supported by the National Institutes of Health.
The paper was widely covered in the media, including BBC, CBS, Scientific American, Science Daily, and a spot on the U-M Gateway.
The past matters to plants
It's commonly known that plants interact with each other on an everyday basis: they shade each other out or take up nutrients from the soil before neighboring plants can get them. Now, researchers at the University of Michigan have learned that plants also respond to the past. The research appeared in the February 2010 issue of The American Naturalist.
Recent doctoral graduate Emily Farrer and Professors Deborah Goldberg and Aaron King modeled four years of population fluctuations in four species common to the Michigan dry sand prairie to determine how plants interacted with each other. They found that plants tended to compete, or negatively affect one another, over the summer, fall, and spring; but interestingly the researchers also found that the more crowded together plants were in one growing season, the more their growth was enhanced the following year.
"For example, if a species had a large, dense population a year ago, this would promote current population growth, even though the plants are currently competing," said Farrer, a graduate student in the U-M Department of Ecology and Evolutionary Biology.
These time-lagged interactions may be due to effects from plant litter, Farrer said. After plants die back over the winter, the dead plant material starts to decompose, releasing nutrients that encourage plant growth. The litter layer also holds in soil moisture, a boon to plants struggling to survive in the dry environment.
Study reveals how Arctic food webs affect mercury in polar bears
With growing concerns about the effects of global warming on polar bears, it's increasingly important to understand how other environmental threats, such as mercury pollution, are affecting these magnificent Arctic animals.
New research led by U-M professor and biogeochemist Joel Blum and Travis Horton, University of Canterbury, lays the groundwork for assessing current and future effects of mercury deposition and climate change on polar bears.
Details of how mercury moves through different food webs— particularly in the Arctic, where snow and ice contribute to mercury deposition—are not well understood. To tease out that information, Blum, Horton and co-workers studied polar bear hair samples from museum specimens collected in the late 19th and early 20th centuries, before mercury emissions from human-generated sources began to escalate.
The study showed that polar bears that get most of their nutrition from phytoplankton-based food webs have greater mercury concentrations than those that participate primarily in ice algae-based webs.
"If you want to understand the potential effects of changing ecosystems on polar bears, you need to be aware of the existence of these two food webs, which may possibly be affected by sea ice," Blum said. "This work provides background information that will be important in our in-depth understanding of mercury bioaccumulation in polar bears." The study appears in the December issue of the journal Polar Research.
Killer catfish? Venomous species surprisingly common, study finds
Name all the venomous animals you can think of and you probably come up with snakes, spiders, bees, wasps and perhaps poisonous frogs. But catfish?
A new study by graduate student Jeremy Wright finds that at least 1,250 and possibly more than 1,600 species of catfish may be venomous—far more than previously believed. The research is described in a paper published online in December 2009 in the open access journal BMC Evolutionary Biology.
Scientists have focused a great deal of attention of venom produced by snakes and spiders, but venomous fish had been largely neglected, said Wright, who used histological and toxicological techniques, as well as previous studies of evolutionary relationships among catfish species, to catalog the presence of venom glands and investigate their biological effects.
"I'm currently working to isolate particular toxins and determine their chemical structures and the genes responsible for their production," Wright said. "It's a very poorly-studied area, with little in the way of scientific literature to draw on, and my studies are just getting off the ground. So at this point it remains to be seen whether they'll have any therapeutic value, though it's worth pointing out that toxins from the venoms of other organisms — snakes, cone snails and scorpions, for example — have all been put to pharmaceutical and therapeutic use."
Wright's paper was widely covered in the media, including a mention in the "Findings" section of Harper Magazine (February 2010), U.S. News and World Report, and USA Today.
U-M study reveals surprising lack of genetic diversity in the most widely used human embryonic stem cell lines
The most widely used human embryonic stem cell lines lack genetic diversity, a finding that raises social justice questions that must be addressed to ensure that all sectors of society benefit from stem cell advances, according to a University of Michigan research team, which included Professor Noah Rosenberg, a population geneticist.
In the first published study of its kind, the U-M team analyzed 47 embryonic stem cell lines, including most of the lines commonly used by stem cell researchers. The scientists determined the genetic ancestry of each line and found that most were derived from donors of northern and western European ancestry. The paper was published Dec. 16, 2009 in the New England Journal of Medicine. Several of the lines are of Middle Eastern or southern European ancestry. Two of the lines are of East Asian origin. None of the lines were derived from individuals of recent African ancestry, from Pacific Islanders, or from populations indigenous to the Americas.
A fundamental principle of medical research is that new therapies are tested on patients that mirror the diversity in society, because certain groups may respond to medications and treatments differently. By evaluating new therapies in diverse patients, researchers are more likely to detect the different effects these therapies might have.
This interdisciplinary research involved the U-M Center for Stem Cell Biology and the Life Sciences Institute.
Shining light on luminous fish
Professor Paul Dunlap and his colleagues in Japan published a paper in the September 2009 journal Marine Biology that provides the first detailed description of the inception of formation and early morphogenesis of the light organ in a bacterially luminous fish.
Although over 400 species of marine fish bearing bacterial light organs are known and nascent light organs have been observed in larval specimens of a few species, little information has been available on the developmental timing of light organ morphogenesis, the origin of tissues and cells that form the light organ, and the temporal and developmental relationships between light organ morphogenesis and bacterial colonization. This information is central, however, to understanding the developmental and microbiological events surrounding initiation of light organ symbiosis, a critical stage in the life history of these luminescent fish. One of their findings is that initiation of light organ morphogenesis precedes colonization by the symbiotic bacteria, which demonstrates that light organ formation is not triggered by the symbiotic bacteria.
The cardinalfish, Siphamia versicolor, is a nocturnally active coral reef fish living in Okinawa, Japan. It forms a bioluminescent symbiosis with the marine luminous bacterium Photobacterium mandapamensis, harboring the bacteria in a ventral, disc-shaped light organ and using the bacterial light for attracting and seeing prey and possibly also for avoiding predators. The researchers succeeded in raising larvae of S. versicolor obtained from brooding males, to examine early stages of the development of its light organ. Until now, not much was known about the early development of this or other luminous fish because collecting and raising larvae of marine fish is difficult. The ability to raise larvae of S. versicolor opens up research on the bacterial specificity of this symbiosis, the mechanism by which the fish acquires its bacteria, and identification of the bacterial genes necessary for symbiosis.
Marine Biology, September 2009
