Sharing that crowded holiday flight with countless hitchhiking dust mites

Predicted structure of the group 1 allergen protein from an American house dust mite. Arrow points to the location of a novel mutation discovered by the University of Michigan-led team.
Credit: Rubaba Hamid

As if holiday travel isn't stressful enough. Now University of Michigan researchers say we're likely sharing that already overcrowded airline cabin with countless tiny creatures including house dust mites.

"What people might not realize when they board a plane is that they can share the flight with a myriad of microscopic passengers-- including house dust mites--that take advantage of humanity's technological progress for their own benefit," said U-M biologist Pavel Klimov.

"House dust mites can easily travel on an airline passenger's clothes, skin, food and baggage," said Klimov, an assistant research scientist in the U-M Department of Ecology and Evolutionary Biology. "Like humans, they use air travel to visit new places, where they establish new populations, expand their ranges and interact with other organisms through various means."

Air travel likely explains some of the findings of a new genetic study conducted by Klimov and U-M visiting scholar Rubaba Hamid that looked at the connections between house dust mite populations in the United States and South Asia.

They found genetic mutations shared by mites in the U.S. and Pakistan that demonstrate the eight-legged creatures' propensity for intercontinental dispersal, according to a research paper scheduled for online publication Dec. 10 in the journal PLOS ONE.

"What we found suggests that mite populations are indeed linked through migration across continents, though geographic differences still can be detected," Hamid said. "Every time a mite successfully migrates to a new place, it brings its own genetic signature that can be detected in the resident population a long time after the migration event."

The study focused on two medically important mite species, the American and European house dust mite. Both species have global distributions, though the former is more abundant in the U.S.

Ancestors of the two species probably separated from each other nearly 81 million years ago--long before the origin of humans--when they inhabited bird nests. Today, house dust mites are blamed for causing allergic reactions in more than 65 million people worldwide and thrive in the mattresses, sofas and carpets of even the cleanest homes.

Hamid, Klimov and their colleagues examined genetic variation in the group 1 allergen gene from samples of the two mite species collected in the U.S. and Pakistan. The group 1 allergen gene encodes for the most important allergy-causing protein in house dust mites.

An inactive form of this protein is used in clinics worldwide as part of the standard skin-prick test for allergies. Though the test can be inaccurate if it does not include local genetic variants of the allergy-causing protein, geographical variation in group 1 allergen proteins has not been extensively studied in the U.S., Klimov said.

"We need to have a better idea about the diversity of allergenic proteins around the world, and particularly in the United States," he said.

In genetic sequences from American house dust mites (Dermatophagoides farinae), the 
researchers observed mutations at 14 positions along the length of the group 1 allergen gene.

All but one of the mutations are "silent," meaning they occur at the DNA level without changing the amino acid structure of the protein. Only mutations at the protein level have medical significance because they can change allergenic properties.

"The most unexpected result was the finding that a previously unknown mutation occurred at the active site of the protein at position 197," Klimov said. "This was a rare mutation, found in only a single population of house dust mite in South Asia.

"Our analysis indicates that this mutation might alter the enzyme activity of the protein. But allergenic properties, immune response and cross-reactivity of the protein are unknown at this time," he said. "Follow-up experiments to elucidate these issues are underway in our lab."

Source: University of Michigan

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Parasites and the evolution of primate culture

Chimpanzees (stock image). A new study examines the ‘costs’ of innovation, and learning from others. Credit: © shiruikage / Fotolia

Learning from others and innovation have undoubtedly helped advance civilization. But these behaviours can carry costs as well as benefits. And a new study by an international team of evolutionary biologists sheds light on how one particular cost -- increased exposure to parasites -- may affect cultural evolution in non-human primates.

The results, published Dec. 3, 2014 in the journal Proceedings of the Royal Society B, suggest that species with members that learn from others suffer from a wider variety of socially transmitted parasites, while innovative, exploratory species suffer from a wider variety of parasites transmitted through the environment, such as in the soil or water.

"We tend to focus on innovation and learning from others as a good thing, but their costs have received relatively little attention," says McGill University biologist Simon Reader, co-author of the study. "Here, we uncover evidence that socially transmitted pathogen burdens rise with learning from others -- perhaps because close interaction is needed for such learning -- and environmentally transmitted pathogen burdens rise with exploratory behaviour such as innovation and extractive foraging."

Chimpanzees, for example, live in groups and have a wide range of such behaviours, such as digging for food underground or eating new kinds of insects.. Previously, studies have not been able to determine whether costly parasites force primates to engage in more exploratory behaviour -- by diversifying food sources, for example -- or whether exploratory behaviour leads to their having more parasites, Reader notes. "Our results support the idea that exploratory and social behaviours expose primates to specific kinds of parasites."

"The findings also lead to questions about how people and other primates have developed solutions to minimize these parasite costs -- such as eating medicinal plants -- and may help us better understand how the processes underlying human culture arose," Reader says.
The research team, led by Collin McCabe of Harvard University and Charles Nunn of Duke University, based their analyses on databases obtained by surveying thousands of articles on primate behaviour and parasites.

Funding for the research was provided by the National Science Foundation, the Natural Sciences and Engineering Research Council of Canada, and the Netherlands Organisation for Scientific Research.

Source: McGill University

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