Inside Iowa State: Iowa State University

February 28, 2003

Shark-infested science

Gavin Naylor studies the relationship between sharks and parasites in hopes of learning how viruses are spread. Photo by Bob Elbert.

by Bridget Bailey, News Service intern
Gavin Naylor isn't afraid to venture into shark-infested waters. In fact, he's been navigating the habitats of these generally fast-swimming, sharp-toothed fish for 18 years, and has returned home unscathed each time.

He has trekked to exotic locations in Australia, Sulawesi, Mexico and India to examine sharks that have been caught by native fishermen or ones sold to local markets.

Naylor, associate professor of zoology and genetics, readily admits it's not really sharks that he's interested in. His life's work has been all about evolution.

Naylor and a group of researchers from the University of Connecticut are collecting information about parasite diversity in sharks and rays, to find out if sharks and their parasites co-evolved.

Naylor said his research could provide the science world with information about how epidemics are spread.

"A lot of epidemics caused by viruses can be traced to host-switching events," Naylor said. "The virus will leave one host, jump to another and then spread like wild fire through the population. Many flu epidemics seem to start this way."

Naylor said if scientists can understand how easy it is for parasites to "switch hosts" (move from one host species to another) and if they can understand the conditions that favor host switching, it might shed some light on how parasitic host switching causes disease.

Sharks are the perfect fit for this approach because they possess excellent fossil records, and have a high rate of diversity with more than 380 different living species.

Naylor said that the scores of shark teeth allow biologists to trace sharks' evolutionary patterns. Biologists believe the huge variety of shark adaptations and variations may be linked with their parasites.

Through DNA sequencing methods, researchers determine if and how sharks are related to one another. That's the principle of an "evolutionary tree." "The best way to study evolution is to take a diverse group and reconstruct its evolutionary tree," Naylor said.

DNA samples are taken from living sharks to estimate their place on the evolutionary tree. Fossil teeth indicate when various types of sharks first appeared.

"Taken together, these data provide us with a reasonable estimate of both the sequence and the timing of events that gave rise to the diversity of living sharks," Naylor said.

This information tells researchers which groups of sharks are most closely related, which of their traits arose independently and which species need to be compared in order to understand changes in development.

"If you want to understand how birds acquired their wings, you wouldn't contrast their development against worms. You contrast them with the closest relative to birds that did not have wings," he added.

Naylor said the primary goal of the study is to discover new species of sharks and parasites -- only 10 percent of all parasitic life is known to man -- and compare the evolutionary patterns of the two.

"It will give us a sense of how specifically tied a pathogen is to its host," Naylor said. Basically, it will tell the research team how "faithful" parasites are to their host species of shark.