Some lizards are no loners, research finds. They hook up with mates and raise tight broods.
- A genetic study of desert night lizards shows they live in family groups.
- The lizards most likely to have social groups give birth to young rather than lay eggs.
- The stereotype of a loner lizard may often be very wrong Lizards get a bad rap when it comes to their families: They lay their eggs and never look back.
But that's not the case for desert night lizards, which have been found investing time and energy in their young and forming families -- a strategy that was thought exclusive to mammals and birds.
"Birds, mammals and reptiles are so different in so many ways," said Alison Davis, a postdoctoral researcher at the University of California at Berkeley. Reptiles aren't even warm-blooded, she notes, yet here they are forming families just like their warmer cousins.
It's a seismic shift for the way we think of reptiles, and evidence of how a survival strategy -- like parental care and social groups -- evolves over and over, in very divergent groups. "It's basically the same rules of the game," Davis said.
The discovery of the desert night lizard family groups comes as a result of a five-year genetic study of more than 2,100 adults and juvenile lizards from the Mojave Desert of California. Davis, who conducted the research as a graduate student at the University of California at Santa Cruz, is the lead author of a paper describing the desert night lizard discovery in the latest issue of Proceedings of the Royal Society B: Biological Sciences.
Davis started the work on the desert night lizards after reading a decades-old scientific paper which, in passing, mentioned that these lizards collected in groups.
"So we went out and looked for these fabled groups," she said. And she found them under the spiny trunks of fallen Joshua trees. By carefully tracking the individuals for five years and checking how groups that huddle under logs in the winter were genetically related, she discovered the family structures.
"One of the coolest parts was doing the DNA analysis," said Davis. "It's like you are revealing the secret lives of lizards."
The existence of family groups in lizards seems to coincide with species of lizards that give birth to their offspring (called viviparity), as do the desert night lizards, rather than lay eggs, as do about 85 percent of lizards, Davis said.
Viviparity typically means fewer offspring and longer-lived individuals. And since she estimates some of the desert night lizards she has studied are up to 20 years old, this matches the pattern and contrasts with some egg-laying lizards that live just one year, she said.
"Viviparity has evolved about a hundred times in reptiles," said herpetologist Rick Shine of the University of Sydney in Australia. And it's not surprising that this less prolific, more troublesome way of reproducing usually results in reptiles that show more parental care and the evolution of social groups, like those found by Davis, he said.
For example, said Shine, in Australia there are reptiles that find and mate with the same individual monogamously for 20 years. And there are siblings that seem to recognize each other as such, he said.
"We have this very simplistic view of reptiles," said Shine.
And it is very often wrong. The ongoing discoveries of social structures among reptiles, such as the desert night lizards, is such a major theoretical shift for herpetologists that it has caused Shine to stop collecting lizards.
"If you go and pick up a lizard from the field you could be disrupting a sophisticated social order," Shine told Discovery News. "There may be somebody at home waiting for that individual."