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"Whale Lice" Genes Offer Clues to Whale Evolution

Nicholas Bakalar
for National Geographic News
September 28, 2005
 
Right whales always swim with passengers aboard: small benign parasites called cyamids. The creatures, which 19th-century whalers nicknamed "whale lice," have coexisted with the whales for millennia.

Now scientists at the University of Utah say they can use data about the evolution of these tiny crustaceans to reveal useful facts about the history of right whales.

For example, the differences between certain genes in whale lice groups suggest that the right whale separated into three distinct species five to six million years ago.

"Cyamid populations on opposite sides of the Equator appear to have been fully (or almost fully) isolated for several million years," the study authors write.

"This finding strongly supports the view that the North Atlantic, North Pacific, and southern right whales also have been isolated for several million years and therefore should be considered distinct species."

The researchers report their findings in the October issue of the journal Molecular Ecology.

Finding a Niche

Whale lice don't live freely in the water—they spend their entire lives on whales. The lice move from mother to calf and among whales in close contact with each other.

The three types of right whale each carry three distinct species of cyamid that live in separate ecological niches on the whale's body.

Cyamus ovalis occupies the whale's callosities, the distinctive patches of raised and roughened skin on the whale's head.

Another louse species, C. gracilis, lives in the pits and grooves between the callosities, while C. erraticus takes refuge in the smooth skin of the genital and mammary openings.

The animals are small, measuring roughly one-fifth to three-fifths of an inch (one to two centimeters) long. About 7,500 of these hitchhikers live on a single whale, making their colonies large enough to be visible as white patches on a whale's head and body.

"Ticking" DNA

Just like animals on remote islands, whale lice species would evolve independently on whales that are geographically isolated, the researchers say.

The right whale was once a single species, but changes in land formations and ocean currents over millions of years eventually isolated groups of the whale species in three distinct regions: the North Atlantic, North Pacific, and southern oceans.

Right whales have been hunted extensively for the past 1,000 years. The name was coined by whalers, who considered the species the "right" whale to hunt because its blubber makes dead whales float, aiding recovery of the carcass.

About 300 right whales live in the northwestern Atlantic Ocean. But the population is not particularly robust, and the animal is considered endangered.

A small population of a different species of right whale lives in the northern Pacific, but this group has been poorly studied, and exact numbers are unknown.

Southern ocean right whales are doing better: More than 8,000 exist, and their numbers are increasing at about 7 percent a year, according to the International Whaling Commission.

Studying the whales' genetic history could help conservationists better understand how to protect the animal from further population decline. But whale evolution is a difficult path to trace.

Stephen R. Palumbi, a professor of biological sciences at Stanford University in California, said whale DNA is "ticking at a slow rate, and this obscures information about population size changes over time."

In other words, genetic changes in the whale lice happen faster and are therefore easier to trace than those in whales.

This, Palumbi said, "may be a way to infer past whale population changes."

Saving Right Whales

The University of Utah researchers found that the three whale lice species living on right whales in each region were different genetically from their counterparts.

The scientists also found high genetic variation between the parasites. Determining the rate of genetic change allowed the scientists to determine how long ago the right whale split into three species.

In addition, Jon Seger, a co-author of the study and professor of biology at the University of Utah, says high genetic variation is good news for whale conservation. It may mean that northern right whales fairly recently had populations just as large as their southern counterparts.

"The finding suggests that the northern right whales are suffering only from recent population reduction, not from a long history of small population size and reduced genetic variation," Seger said.

If the whale population had been small and struggling for a long period of time, genetic variation—both for the whales and their parasites—would start to disappear. In this case, inbreeding would lead to genetic diseases that would make it difficult for the whale population to bounce back.

But Palumbi, the Stanford biologist, says that the findings may not mean much for the future of whale conservation.

"The right whales are in desperate trouble, and the lice neither tell us that more strongly than we knew before, nor tell us new things to do about it."

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