Tiny, freeloading clams find key to evolutionary success

What mechanisms control the generation and maintenance of biological diversity on the planet?

It’s a central question in evolutionary biology. For land-dwelling organisms such as insects and the flowers they pollinate, it’s clear that interactions between species are one of the main drivers of the evolutionary change that leads to biological diversity.

But the picture is much murkier for ocean dwellers, mainly because the scope of ecological interactions remains poorly characterized for most marine species. In one of the first efforts to examine how species interactions drive diversification of ocean-dwelling organisms, two U-M researchers and an Australian colleague looked at the lifestyle choices within an exceptionally diverse superfamily of tiny clams, the Galeommatoidea.

They found that the fingernail-size-and-smaller clams’ propensity to shack up with much larger, burrowing creatures such as sea urchins, shrimp and worms was a key adaptation that led to the evolutionary success of the superfamily, as measured by its “megadiverse” status among marine bivalves. There are about 500 described species of galeommatoidean clams and many more undescribed species.

By becoming the uninvited house guests of their burrowing hosts, these freeloading, thin-shelled clams acquire a safe haven from predators prowling soft-bottomed sediments, where there’s nowhere else to hide. Gaining this deep refuge opened up a vast habitat type — soft-bottom marine sediments composed of sand, silt and clay — that would otherwise have remained unavailable to these clams.

Galeommatoidean clams are found worldwide in all the major ocean basins, in both rocky and soft-bottom habitats. Some of the clams live a solitary existence, while others form so-called commensal relationships with larger invertebrate hosts. A commensal relationship is one in which one organism benefits and the other is not harmed.

“What was surprising was the overwhelming evidence that commensalism is associated with the soft-bottomed habitat. You seldom get such clear-cut data in an ecological study,” says Jingchun Li, a doctoral student in the Department of Ecology and Evolutionary Biology and first author of the PLoS ONE paper.

— Jim Erickson, News Service

Concussions, head impacts may accelerate brain aging

Concussions and even lesser head impacts may speed up the brain’s natural aging process by causing signaling pathways in the brain to break down more quickly than they would in someone who has never suffered a brain injury or concussion.

Researchers from the School of Kinesiology and the U-M Health System looked at college students with and without a history of concussion and found changes in gait, balance and in the brain’s electrical activity, specifically attention and impulse control, says Steven Broglio, assistant professor of kinesiology and director of the Neurotrauma Research Laboratory.

The declines were present in the brain injury group up to six years after injury, though the differences between the study groups were very subtle, and outwardly all of the participants looked and acted the same.

Broglio, who also is affiliated with Michigan NeuroSport, stressed that the studies lay out a hypothesis where concussions and head impacts accelerate the brain’s natural aging process.

The study, “Cognitive decline and aging: The role of concussive and subconcussive impacts,” appears in the July issue of journal Exercise and Sport Sciences Reviews.

“The last thing we want is for people to panic. Just because you’ve had a concussion does not mean your brain will age more quickly or you’ll get Alzheimer’s,” Broglio says. “We are only proposing how being hit in the head may lead to these other conditions, but we don’t know how it all goes together just yet.”

Broglio stresses that other factors, such as lifestyle choices, smoking, alcohol consumption, physical exercise, family history and whether or not you “exercise” your brain also impact the brain’s aging process. Concussion may only be one small factor.

Researchers from the departments of Physical Medicine and Rehabilitation, and Neurology, and the Michigan Alzheimer’s Disease Center also participated in the study.
— Laura Bailey, News Service

Entropy can lead to order, paving the route to nanostructures

Researchers trying to herd tiny particles into useful ordered formations have found an unlikely ally: entropy, a tendency generally described as “disorder.”

Computer simulations by U-M scientists and engineers show that the property can nudge particles to form organized structures. By analyzing the shapes of the particles beforehand, they can even predict what kinds of structures will form.

The findings, published in last week’s edition of Science, help lay the ground rules for making designer materials with wild capabilities such as shape-shifting skins to camouflage a vehicle or optimize its aerodynamics.

Physicist and chemical engineering professor Sharon Glotzer proposes that such materials could be designed by working backward from the desired properties to generate a blueprint. That design can then be realized with nanoparticles — particles a thousand times smaller than the width of a human hair that can combine in ways that would be impossible through ordinary chemistry alone.

One of the major challenges is persuading the nanoparticles to create the intended structures, but recent studies by Glotzer’s group and others showed that some simple particle shapes do so spontaneously as the particles are crowded together. The team wondered if other particle shapes could do the same.

“We studied 145 different shapes, and that gave us more data than anyone has ever had on these types of potential crystal-formers,” Glotzer says. “With so much information, we could begin to see just how many structures are possible from particle shape alone, and look for trends.”

The simulation results showed that nearly 70 percent of the shapes tested produced crystal-like structures under entropy alone. But the shocker was how complicated some of these structures were, with up to 52 particles involved in the pattern that repeated throughout the crystal.

— Nicole Casal Moore, News Service

Michigan courts use HIV disclosure laws to punish poor, marginalized

Michigan’s felony HIV disclosure law is a tool to control and punish marginalized and poor individuals in criminal court cases, a new U-M study shows.

In many states, a person with HIV can be charged with a crime if he/she engages in sexual activity without telling the other person. Many of those convicted under Michigan’s law are African-American men with female partners and people suffering from mental illness or substance abuse problems, the research showed.

Trevor Hoppe, a doctoral student in sociology and women’s studies, recently presented his findings — Punishing HIV: How Michigan Trial Courts Frame Criminal HIV Disclosure Cases —at the International AIDS Conference in Washington, D.C.

Framing HIV as a deadly disease is a strategy used by prosecutors seeking to convict a defendant of failing to disclose the health status. Although HIV has been transformed into a chronic, manageable illness since the introduction of effective therapies in 1995, prosecutors and judges in Michigan routinely compare the failure to disclose to murder in criminal non-disclosure cases and treat HIV as though it were still a death sentence.

This is noteworthy because transmission is not alleged in the vast majority of cases Hoppe studied, and many of the cases involve sexual activity that poses little to no risk of transmission.

“As we enter into the fourth decade of HIV, it is time we reconsider how these unjust laws are enforced in a time when the Obama Administration is calling for an AIDS-free generation,” Hoppe says. “You cannot call for universal testing when getting an HIV-positive test result can present substantial legal risks.”

At least 24 states presently have a criminal law making it a misdemeanor or felony for HIV-positive people to have sex without first disclosing their status. In Michigan, conviction is a four-year felony.

— Jared Wadley, News Service

‘Sexting’ may be just a normal part of dating for Internet generation

For young adults today who were weaned on iPods and the Internet, the practice of “sexting,” or sending sexually explicit photos or messages through phones, may be just another normal, healthy component of modern dating.

U-M researchers looked at the sexting behavior of 3,447 men and women ages 18-24 and found that while sexting is very common, sexting isn’t associated with sexually risky behaviors or with psychological problems.

The findings contradict the public perception of sexting, which is often portrayed in the media and elsewhere as unsavory, deviant or even criminal behavior, says Jose Bauermeister, an assistant professor at the School of Public Health and co-principal investigator of the study.

However, most of those negative stories involve sexting among pre-teens and teenagers, and the U-M study group was considerably older, says study co-author Debbie Gordon-Messer.

“For younger age groups, legality is an issue,” Gordon-Messer says. “They are also in a very different place in their sexual development.”

This is the first known study to connect sexting with a behavioral outcome, Bauermeister says. Previous studies on sexting focus on demographic; in other words, who is doing the sexting, not how sexting impacts the health of the participants.

In the larger picture, the sexting research is a very important piece of understanding how technology impacts sexuality and health, Bauermeister says.

The study “Sexting Among Young Adults” will appear in an upcoming edition of the Journal of Adolescent Health.

— Laura Bailey, News Service

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