Whooping cough immunity long-lasting, study shows
Immunity to whooping cough lasts at least 30 years on average, much longer than previously thought, an analysis by Professor Pejman Rohani and his former postdoctoral fellow, Helen Wearing, shows. The study was published in the open-access journal PLoS Pathogens in October 2009.

Once thought to be under control, thanks to widespread childhood vaccination, whooping cough (pertussis) has been on the rise since the 1980s in the United States and several other countries. This increase has fueled concerns about the effectiveness of current vaccination practices and raised the question of whether whooping cough can ever be eradicated.

One leading idea for the recent surprising increase in cases is that the immunity conferred by vaccination or previous exposure wears off after some time. Because these are tough questions to address clinically, the researchers took a different approach, using mathematical models to explore various scenarios and comparing the predictions generated by those models to data on whooping cough incidence.

The analysis revealed that, on average, whooping cough immunity lasts at least 30 years and perhaps as long as 70 years after natural infection. "This is surprising because clinical epidemiologists currently believe the duration of pertussis immunity is somewhere between four and 20 years," said Rohani, who also has an appointment in the Center for the Study of Complex Systems.

If correct, the results represent encouraging news, Rohani said. "They suggest that loss of immunity may be playing a less significant role than is currently thought. And at least in these historical data, vaccination seems to interrupt transmission substantially."

U-M News Service press release

Standing out in a crowd is better than blending in, at least if you're a paper wasp in a colony where fights between nest-mates determine social status.

That's the conclusion of a study by EEB graduate student Michael Sheehan and Professor Elizabeth Tibbetts. The evolutionary biologists published their findings online in October, 2009, in the journal Evolution.

"It's good to be different, to wear a nametag advertising your identity," said Sheehan.

Read more about their previous research that brought them to this point in the U-M News Service press release linked below. In the latest work, Sheehan and Tibbetts wanted to see if individual wasps benefit not only by being able to recognize others, but by being recognizable themselves.

To investigate the pros and cons of being a standout, the researchers altered the wasps' facial patterns and set up groups of four unrelated wasp queens, in which three wasps looked alike and one looked distinctively different from the others. The experimenters then videotaped encounters among the wasps and played the tapes back, recording and scoring all acts of aggression. They found that distinctively-marked wasps were less likely to be the targets of aggression than were look-alike wasps.

"Given that receiving aggression is costly, in terms of injury or energy expenditure, these results indicate that being distinctive is beneficial," Sheehan said.

U-M News Service press release

Space: the final frontier of pathogen evolution
Scientists have been wondering why certain pathogens are so much more lethal than others for at least a century. Standard theory suggests that the amount of damage a pathogen inflicts on its host strikes a balance between the benefits of a higher pathogen load (more pathogen particles to be transmitted to new hosts) and drawbacks (often associated with more negative health consequences to the host, perhaps killing it before the pathogen particles can be transmitted). Termed the transmission-virulence tradeoff, this theory has become the default explanation for variation in pathogen virulence.

But there is growing evidence that the location of each host relative to other hosts can have at least as strong an influence on pathogen potency as a transmission-virulence tradeoff. Taking it one step further, graduate student Susanna Messinger and Professor Annette Ostling, community ecologists, have identified three specific aspects of host and pathogen ecology that can influence the spatial distribution of the host and thus ultimately determine whether a disease becomes more or less deadly. Their study was published in the October 2009 issue of the journal American Naturalist.

Pathogens have the potential to cause tens of millions of human deaths in a time span as short as a single year, making understanding their biology of foremost importance. The study by Messinger and Ostling is a push in the right direction. Their results suggest that researchers should more closely examine the role that spatial dynamics may play in emerging infectious disease. The ability to quantitatively predict the evolutionary trajectory of a pathogen’s transmission rate in a spatial context can contribute to our ability to design appropriate intervention strategies for newly emerging infectious diseases.

Photomicrograph of skin of Northern Leopard Frog (Rana pipiens) revealing chytridiomycosis infection (spheres)

caused by Batrachochytrium

dendrobatidis. Photo by Joyce Longcore. Endangered Alytes muletensis, the Mallorcan midwife toad. Photo by Mat Fisher.

Bullfrogs make amphibians croak?
Amphibians are facing a current global extinction crisis of unprecedented magnitude. Chytridiomycosis is an emerging infectious fungal disease linked to the dramatic decline of numerous amphibian species worldwide.

Can we blame it on the bullfrogs? Using population genetics, Professor Timothy James and a team of fungal and amphibian biologists found that the sudden widespread appearance of the pathogen is due to the rapid dissemination of a virulent clonal lineage (identical cells that share a common ancestry) into new host populations, a phenomenon that has been described as “pathogen pollution.”

Their paper was published online in the May 2009 journal PLoS Pathogens. By acquiring fungal pathogen samples from single host individuals around the world, the researchers showed that declining and non-declining (apparently healthy) species and populations of amphibian are infected by the same clonal lineage. Bullfrogs, which are relatively resistant to the chytrid fungus, were found to be significantly more genetically diverse than other amphibian species, suggesting bullfrogs may be transmitting the disease. This is based on the theory that populations or species that are the source of the disease should be more genetically diverse than those that have only recently been infected. Furthermore, the widespread occurrence of the same lineage in healthy and declining populations suggests that the outcome of the disease is contingent on environmental factors and host resistance.

May 2009 PLoS Pathogens
Spring 2009 Natural Selections (article on James on Page 5)

Native Americans came from single group, DNA study shows
Researchers have pored over expanding genetic data for the past 20 years to investigate the origins of Native Americans. Did they migrate to the New World in one wave or in a series of waves? Did they originate from one founding population or from different founding populations?

An international team of scientists that included Professor Noah Rosenberg, senior author, studied a genetic variant that’s common among Native Americans throughout North and South America but absent from all human populations – except some inhabitants along the eastern edge of Siberia. The rare genetic variant has been found in nearly all Native American populations sampled to date.  

The team found convincing evidence that supports the single ancestral population theory. “What we’ve shown in this paper is that this variant has a single origin, which is evidence that all of the individuals who carry the variant have a single origin as well,” Rosenberg said. “Haplotypic background of a private allele at high frequency in the Americas” was published in the May 2009 journal Molecular Biology and Evolution.

Science Daily article, UPI article, Molecular Biology and Evolution, July 2009

Baby mammoth studies validate U-M researcher's techniques
Research featured in National Geographic cover story, TV program
Extensive studies of a 40,000-year-old baby mammoth carcass discovered in Siberia two years ago validate techniques developed by University of Michigan paleontologist Daniel Fisher for extracting information about prehistoric pachyderms' lives from their teeth and tusks.

Early results of the studies—which involved an international team of researchers and included CT scans, DNA analysis and surgical procedures in addition to tusk and tooth analyses—also are yielding insights into the young wooly mammoth's brief life and sudden death and clarifying aspects of mammoth ecology.

The discovery and subsequent studies of the baby mammoth, known as Lyuba, were the subject of a cover article in the May 2009 issue of National Geographic magazine. Fisher's work also was featured in “Waking the Baby Mammoth,” which premiered Sunday, April 26 on the National Geographic Channel.

Climate change driving Michigan mammals north
Some Michigan mammal species are rapidly expanding their ranges northward, apparently in response to climate change, a new study shows. In the process, these historically southern species are replacing their northern counterparts. The finding, by lead author Professor Philip Myers, appears in the June 2009 issue of the journal Global Change Biology.

"When you read about changes in flora and fauna related to climatic warming, most of what you read is either predictive—they're talking about things that are going to happen in the future—or it's restricted to single species living in extreme or remote environments, like polar bears in the Arctic," said Myers. "But this study documents things that are happening right now, here at home."

The story has been widely covered in the media including on NPR’s All Things Considered, WDIV-Channel 4 News, the Chicago Tribune and The Detroit Free Press. Read an interview with Myers in the Digital Journal.

U-M News Service press release

Insights into mammalian genome mutations
A phylogenetic study that appeared online the week of April 6, 2009 in the Proceedings of the National Academy of Sciences indicates that Piwi-interacting RNAs (piRNAs) evolve through rapid recombination and expansion in mammals.  piRNAs are the largest class of small RNA molecules expressed in mammalian germline cells.

Raquel Assis, a graduate student in evolutionary genetics, and Professor Alexey Kondrashov, who is affiliated with EEB and the Life Sciences Institute, compared 140 rat and mouse piRNA cluster regions to orthologous regions (genes in different species that are similar to each other because they originated from a common ancestor) in human, cow, and dog genomes. Their findings suggest that over 40 percent of rodent piRNA clusters appeared since rodent and primate lineages split. This is a faster expansion than any known for mammalian protein-coding genes. The pattern was even stronger for clusters in non-protein coding parts of the genome. The researchers didn’t find any piRNA cluster losses.

The researchers explain that rapid piRNA cluster expansion, coupled with the lack of cluster losses, could be driven by positive selection, perhaps caused by the need to silence the growing number of mammalian transposons. piRNAs are believed to silence mammal transposons. Transposons are sequences of DNA that can move to different positions within the genome of a single cell, causing mutations in the process. Transposons can cause diseases such as hemophilia and a predisposition to cancer.

GenomeWeb Daily News
Photo: from flickr, coxy's photostream

A venomous tale: Vipers shape lizards' tail-shedding abilities
Professor Johannes Foufopoulos and his colleagues have answered a question that has puzzled biologists for more than a century: What is the main factor that determines a lizard's ability to shed its tail when predators attack?

The answer, in a word: venom.

The ease with which lizards shed their tails varies from species to species and from place to place. For more than a century, biologists have suspected that this variation is controlled mainly by predator pressure: As the number of local lizard-eaters rises, so does the need for this effective defense mechanism.

Their conclusion? The predator-pressure hypothesis, while generally true, comes with an unexpected twist: Not all predators are created equal.

"The only predators that truly matter are vipers," said U-M vertebrate ecologist Foufopoulos, co-author of a study published online in late March 2009 in the journal Evolution.

U-M News Service press release
Photo by Elizabeth Menexiadou

Yeast biology yields insights into human knowledge expansion
How does human knowledge expand over time? Intriguing as the question is, it's not easy to investigate, due to the difficulty of measuring knowledge and its spread. But by analyzing three decades of discoveries about baker's yeast (Saccharomyces cerevisiae) – an organism that has been extensively studied for insights into the workings of genes and proteins – Professor Jianzhi Zhang and his former graduate student Xionglei He, have revealed some interesting patterns in the proliferation of scientific understanding. Their findings, published online March 20, 2009, in the open-access journal PLoS Computational Biology, suggest ways of making scientific endeavors more productive.

Some of their surprising findings suggest that large group collaborations are less efficient than small teams; researchers tend to focus on determining properties of previously-discovered genes rather than probing newly-discovered genes; and that “important” genes (those that later are found to be essential for yeast growth) get more attention as study subjects before less influential genes. The analysis also debunked a popular belief among yeast researchers: that the rate of discovery increased even more dramatically after the yeast genome was deciphered in 1996.

U-M News Service press release

Early whales gave birth on land, fossil find reveals

Two newly described fossil whales – a pregnant female and a male of the same species – reveal how primitive whales gave birth and provide new insights into how whales made the transition from land to sea.

The 47.5 million-year-old fossils, discovered in Pakistan in 2000 and 2004 and studied at the University of Michigan, are described in a paper published Feb. 4, 2009, in the online journal PLoS.

U-M paleontologist Philip Gingerich, who led the team that made the discoveries, was at first perplexed by the assortment of adult female and fetal bones found together. "When I first saw the small teeth in the field, I thought we were dealing with a small adult whale, but then we continued to expose the specimen and found ribs that seemed to too large to go with those teeth," he said. "By the end of the day, I realized we had found a female whale with a fetus."

U-M News Service press release including a video