Archives of The Cold Blooded News

The Newsletter of the Colorado Herpetological Society

Volume 30, Number 10;   October, 2003

Lizards' Family Values

Close-knit families occur in some bird species and in many species of mammals, with humans as the prime example, of course. But many scientists believe that snug social behavior could, in theory, evolve in any kind of animal, as long as the conditions are right. And that may be the case for the Black Rock Skink, Egernia saxatilis, which inhabits rocky areas in southeastern Australia. Herpetologists had already noticed that this and related species of lizard live in groups, says Richard Shine, an evolutionary biologist specializing in reptile at the University of Sydney, Australia. But they didn't know who belonged to each group.

Shine and his student, Dave O'Connor, studied the animals living an a large granite outcrop in the Blue Mountains in New South Wales. They caught 115 lizards and gave each an individual "barcode" by clipping the tips of their toes in a unique pattern (a commonly used method for marking small animals). The animals were then released and followed for up to three years. A few lizards roamed the rocks as loners, but 72% spent their time in a stable social group, never more than half a meter away from other members of the same group. DNA profiling showed that the groups usually consisted of a father, a mother, and their children. Occasionally, a half-sibling or an adoptee had been welcomed as well.

Although he's accustomed to the wonders of the reptilian world, the fact that the nuclear family is the cornerstone in rock skink society came as a surprise to Shine. "It challenges one's ideas of the sophistication and subtlety of interpersonal relationships among reptiles," he says. He thinks that the advantage may lie in the protection that juvenile lizards get from their folks against unfriendly neighbors. "These are very aggressive lizards," he adds respectfully.

Michael Bruford, a population geneticist at Cardiff University in the U.K., thinks the new study is a valuable step forward in understanding how sociality evolves in animals. This is "clearly an exciting development," he says.