Whale Riders Reveal Secrets of Their Giant Hosts

Whale lice are tiny crab-like creatures that live out their entire lives on the surface of right whales, sharing the same fate as their giant hosts.

Using this knowledge, a group of marine biologists from the University of Utah have track the evolution of the whales the lice live upon and have shown that they split into three species—the North Atlantic, North Pacific and Southern Ocean right whales—around 5 or 6 million years ago.

Whale lice aren't really lice. Rather, they are tiny crustaceans called cyamids that look like minature crabs that range from one-fifth to three-fifths of an inch in length. The whale lice live on raised coverings of rough skin called callosities and within the slits that cover the mammary glands and genitals of the whales. A single right whale can be home to about 7,500 whale lice [closeup photo above].

Before the right whales divided into separate species, they were home to three different species of whale lice. When the whales split, the three lice species also split three different ways so that now there are 9 different whale lice species. Each whale species now harbor three different lice species apiece.

By comparing the types of mutations found among the 9 lice species and by comparing the rate at which they occurred, the researchers were able to construct detailed family trees to show the relationship between the lice species. Doing so also allowed the researchers to construct family trees of the whales the lice lived upon.

The researchers believe the whale species split when a shifting of the many floating plates that forms the Earth's crust caused the Isthmus of Panama to form. The narrow strip of land cleaved what was once a single ocean in two: the Pacific and the Atlantic Oceans.

The right whales, once a single species, became isolated. One group was found in the North Atlantic, one in the North Pacific and one in the southern oceans of the world. The shifting of the Earth's crust also set warm waters flowing along the equator, creating a barrier that the right whales could not cross on account of their blubber being too thick.

Over time, each of the three whale groups—and the lice that lived on them—became distinct species.

The study is published in the October issue of journal Molecular Ecology.

--Ker Than

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Credit: Iain Kerr, Ocean Alliance/Whale Conservation Institute