Study says some lizards form social groups, families

By Victoria Pardini

A U. California-Berkeley scientist has found that lizards, which normally lead solitary lives, can form social groups too, according to a study released online in the Proceedings of the Royal Society B: Biological Sciences Oct. 6.

According to the researchers, some desert night lizards formed nuclear families, complete with two parents and a number of offspring. The close-knit family structure of the lizards differs from other species because most lizards do not interact with others unless fighting for resources or mating.

The sociality is primarily explained by the fact that desert night lizards give birth to live offspring rather than laying eggs, said Alison Davis, a UC Berkeley postdoctoral student and lead author of the study.

“The standard sort of lizard archetype is that the lizard hatches from an egg, it grows up very quickly, it mates and then it dies,” Davis said.

Desert night lizards, by contrast, form a connection between mother and offspring in giving birth. Because live births occur less frequently per year, lizards who give birth to live offspring have a longer lifespan than those who lay eggs.

“They’ve demonstrated convincingly, perhaps for the first time, that there’s been a completely independent demonstration of social behavior in another group of animals,” said Ted Papenfuss, a research scientist at UC Berkeley’s Museum of Vertebrate Zoology.

Davis began research for the study as a graduate student at UC Santa Cruz in August 2003. Over the course of the next five years, Davis and her team looked under Joshua trees in the Mojave Desert, observing a total of 2,120 lizards and classifying them by age group.

The researchers also collected samples from the lizards’ tails to conduct paternity testing using their DNA. Juvenile lizards were found still living with parent lizards up to three years after birth, according to the study.

“What is particularly exciting is that the same sorts of patterns are observed in social mammals and birds,” said Ammon Corl, who co-authored the study when he was a former graduate student at UC Santa Cruz, in an e-mail.

Because desert night lizards offer relatively little parental care after childbirth, it is not yet clear why offspring are staying with the parents for as long as they are, Davis said. She said researchers are currently attempting to discover the reasons lizard offspring choose to stay and continue to share resources rather than seeking another area.

Davis said the best way to understand if the offspring are genuinely attached to their parents is to transplant juveniles to another set of parents.

Barry Sinervo, Davis’ adviser in the study and a professor of ecology and evolutionary biology at UC Santa Cruz, said that while these “social” lizards are being found, they are slowly going extinct because of climate change.

“You’d hate to have all of this biology disappear before you can show it to your kids,” Sinervo said.

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