A Sixth Sense for Similarity

A lizard's multiple hues provide genetic cues.

By Jocelyn Selim|Friday, September 26, 2003

For the side-blotched lizard, a ubiquitous inhabitant of the American west, kinship is about more than family. While many other animals collaborate primarily with close relatives, these lizards somehow sense deeper genetic similarities when deciding whom to help, says Barry Sinervo, an ecologist at the University of California at Santa Cruz.

The lizards come in three color varieties, each of which denotes distinct mate-seeking behaviors. Oranges aggressively try to steal females; blues try to guard the females; and yellows try to sneak access. Only blue males form alliances: They band together so they can defend a much larger territory from sneaky yellows. When Sinervo analyzed DNA from a group of blue males to determine how they choose their allies, the results were unusual. Cooperating blue males sought alliances with others having the greatest overall genetic resemblance, regardless of their kinship. A blue side-blotched lizard would choose to assist an unrelated lizard with a nearly identical genome over a less similar brother or cousin.

How do they know? Because the side-blotched lizard's skin color—and hence genetic makeup—is closely associated with social strategy, the blue lizards might actually be picking up on subtle behavioral similarities, Sinervo speculates. “The complement of genes and associated behavioral traits that make a successful orange lizard is very different than that for a blue lizard, so there’s intense selection pressure for the genes that control these behavioral traits to be passed on together,” he says. If Sinervo is right, this is the first evidence of animals using nonlearned behavioral traits to identify genetic relationships. But that skill might actually be common. “I don’t see why this strategy should work much differently for mammals, humans included,” he says. In our world, scent or immune-system cues might substitute for the bright colors of the lizards.

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