DNA Analysis Leads to Cryptics and Tick-tricks

Sandy Marie Bonny
18 December 2012

Above: Deer tick, Ixodes scapularis, on a fingernail (Stuart Meek)

Did You Know? Increasing numbers of cryptic species are being discovered through DNA analysis, re-opening biological “cold cases” that had been stalled by the assumption that visually or “phenotypically” identical organisms must belong to the same species.“TICKS Dead or Alive!” That's the wanted poster on the laboratory door of Neil Chilton, an Australian-born parasitologist who works at the University of Saskatchewan. Ticks turned in by the public are carefully observed and classified, and then… into the grinder they go! Of course, Neil and his students aren't ruthlessly tracking down and punishing criminal ticks. In fact, they are using DNA analysis to identify “cryptic species.” These are genetically disinct organisms that, when studied under a microscope, look similar or even identical.

Most ticks have a hard exoskeleton. So, to extract the ticks' DNA, Neil’s graduate students pulverize their specimens with small drill bits. The resulting “tick juice” is then chemically digested, freeing DNA molecules for amplification (DNA “photocopying”) and typing (identification). These techniques—the same ones used by crime scene investigators—have allowed Neil’s lab to shed new light on how animal parasites interact with their hosts.

During the summer, Neil and his students head out on the prairie to collect specimens. They catch ticks by waving white flannel flags across leaves, flowers, and branches. Mentoring students is a part of Neil's job that he really enjoys. As a student at Flinders University in South Australia, he once collected ticks from Australian lizards. This was his first introduction to parasitology, and he was immediately hooked. There were so many unsolved mysteries!

Did You Know? In the animal kingdom, over 50% of species exist as parasites in or on a host animal at some stage in their development.In the 1990s, as a post-graduate researcher at the South Australian Museum, Neil studied a parasitic worm called Hypodontus macropi. It lives in the large intestines of many, but not all, species of kangaroos and wallabies. At the time, Neil couldn't explain why some marsupials remain free of the worm, even when they share territory with other species that have the parasite. But nearly twenty years later, DNA evidence is pointing to an answer. What had previously been considered a single worm is turning out to be at least ten different species, each of which prefers different hosts. So it’s not surprising that the parasite Neil thought he was studying isn’t more widespread, and why some kangaroos and wallabies are free of it.

At the University of Saskatchewan, Neil and his students use DNA typing to identify various species of ticks that live in western Canada. They use the same technology to explore tick evolution, diversity, and migration, as well as for identifying microorganisms that live inside ticks. This interest in single-celled organisms in significant because pathogenic bacteria, not the ticks themselves, actually cause tick-borne infections like Lyme disease. Neil has also discovered beneficial bacteria living in ticks, bacteria that restrict the growth or transmission of pathogens. These discoveries may help control infectious diseases spread by ticks.

Did You Know? Like mites and spiders, ticks are arachnids, not insects. However, newly-hatched larvae have only six legs. Ticks grow another two legs as they mature through the nymph and adult phases.Although they both rely on DNA analysis, there are some important differences between a university biology lab and a crime lab. Unlike crime scene investigators, who would would be faced with an unknown suspect, research biologists are never disappointed when they discover unmatched DNA codes. It means they have discovered a new species, and these new discoveries are being typed (identified) on a daily basis.

The sheer abundance of new data means that biologists need to have a strong background in statistics, math, and bioinformatics. If Neil had one suggestion for high school students, it would be to take all the senior math and science classes they can. “One discipline is important to understand another,” Neil says, because “each discipline provides another set of tools for a researcher to approach problems with.” The most important tool? A creative and inquisitive mind.

Learn More!

Chilton Parasitology Laboratory (University of Saskatchewan)

http://www.usask.ca/biology/chilton/ Mites and Ticks (Animal Planet)

http://animals.howstuffworks.com/arachnids/mite-and-tick-info.htm Lyme Disease in Canada (Canadian Lyme Disease Foundation)

http://www.canlyme.com/ The Dark Side of DNA (American Scientist)

http://www.americanscientist.org/bookshelf/pub/the-dark-side-of-dna DNA Forensics (Human Genome Project)

http://www.ornl.gov/sci/techresources/Human_Genome/elsi/forensics.shtml

Sandy Marie Bonny

I am a geobiologist with a doctorate in Earth and Atmospheric Sciences from the University of Alberta. I work as a sessional lecturer, science writer, and creative writer - and yes, the science is almost always stranger than my fiction!


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