|
U.S.: "Whale Lice" Genes Reveal How One Whale Species Became Three |
| September 14, 2005 |
 | | Click image to enlarge. Dark, callus-like material called callosities on the head of this right whale are covered by white parasitic crustaceans called cyamids, nick-named 'whale lice.' Photo: Mariano Sironi, Institute of Whale Conservation, Buenos Aires |
Over the past five years, researchers at the University of Utah have studied "whale lice" – tiny, hitchhiking crustaceans that cling to whales and eat their sloughed skin. By analyzing the DNA of lice from right whales, they showed that millions of years ago a single right whale species diverged into three species, and that all three species may have been equally abundant before the advent of commercial whaling.
Right whales and their 'lice' – which are really cyamids, related to crabs and shrimp – share millions of years of common history. Because the lice reproduce frequently and spend their lives devoted to a single host, they offer a jackpot of genetic evidence to scientists interested in understanding important events in this common evolution.
Sea Change
Through careful genetic sleuthing, the researchers estimate the evolutionary 'point of departure' for right whales took place 5-6 million years ago, due in large part to the movement of the continents. It was around this time that the isthmus of Panama began to form, slowly dividing the great sea between the Americas into the modern Atlantic and Pacific Oceans. Around 5-6 million years ago, the sea between the two continents had become so shallow that whales could not traverse it.
The warm equatorial currents that formed around Panama further prevented the blubbery whales from migrating north or south across the equator: they are unable to efficiently shed heat in warm waters. Thus, one species of whale diverged into three: the North Atlantic, the North Pacific, and southern ocean right whales. At the same time, each of the three louse species infesting right whales also split into three species, tripling the number of cyamid species infesting right whales.
Whaling Legacy
In today's post-commercial whaling era, the endangered North Atlantic right whales are less abundant and less genetically diverse than their southern ocean counterparts. One might expect, then, that the sea lice of each species would show a corresponding difference in genetic diversity—but the study found they were almost identical.
Based on this finding, the authors believe the two populations were historically comparable in size. Whale louse populations correlate with population sizes of right whales: if North Atlantic right whales had had small pre-whaling populations, the diversity of their whale lice today would be less than that of the lice on the southern right whales.
"This suggests that the reduced genetic diversity of North Atlantic right whales happened recently, possibly due to whaling, not because the whale population was small even before whaling," noted John Seger, a University of Utah biology professor and the study's principal author.
The study was published in the October 2005 issue of the journal Molecular Ecology.
|
