The lice and the whale

Natural History, Dec, 2005 by Graciela Flores

Whale lice--diminutive crustaceans that feed on dead skin--spend their lives attached to right whales (Eubalaena spp.). The benign parasites, also called cyamids, grow in thick masses, forming distinctive white patches on the whales' dark skin; marine biologists often use those living scars to identify individual whales. Zofia A. Kaliszewska, an evolutionary biologist at the University of Utah in Salt Lake City, and her colleagues have found that cyamids can also help track genetic changes and migration patterns in right whales.

Kaliszewska and her colleagues compared sequences of the mitochondrial gene COI in what they thought were three species of whale lice. It turned out that there were actually nine separate species. Three species of lice infected the three species of right whale, each of which lives in a different ocean: the North Atlantic, the North Pacific, and the Southern. The evolutionary divergence of the lice proves that the whales themselves diverged from a single species about 6 million years ago.

The study also shows that North Atlantic and North Pacific right whales, which are both highly endangered, might once have been as abundant as the more successful right whales in the Southern Ocean. Thus, the investigators suggest, the dramatic reduction in the whale populations in the past few centuries more likely results from intense whaling than from an original lack of genetic diversity. If so, there is reason to hope the two endangered species can recover. (Molecular Ecology 14:3439-56, 2005)