Lab talk: why sleepy lizards avoid their family

As Christmas often reminds us, family relationships form a fundamental part of our social network. For many animal societies, family comes first too. By helping their family, animals can increase the chances that some of their genes will survive to the next generation. But does family still matter to less social species? 

The sleepy lizard (Tiliqua rugosa) is commonly found across the southern half of Australia. These slow-moving, stumpy-tailed, blue-tongued specimens are remarkably monogamous – for eight weeks each spring they pair up with their partner, with some pairs reuniting for more than 20 consecutive years. But outside of these eight weeks, the lizards are loners. 

To see what they get up to – and who they meet – either side of the breeding season, we fitted them out with “lizard loggers”. These micro-GPS units, attached to their tail, record the number of steps taken and the lizards’ locations for around 12 days at a time. 

We’ve spied on their movements and found they come in contact with each other less often than if they wandered randomly. This suggests deliberate avoidance – and it appears that they avoid their relatives most of all. 

Perhaps not surprisingly, males and females that are related spend the least time together. Since most interactions between males and females are of a “romantic” nature, this is important to avoid inbreeding. 

Lizards have a well-developed sense of smell, and research in related species has shown that they can recognise familiar and related individuals. It’s possible that these lizards “sniff out” suitable (and unsuitable) mates. 

But sleepy lizards seem to sniff out and avoid related males, too. When two males meet, they will usually fight over territory, grappling and trying to flip each other over with their powerful jaws – which can lead to debilitating injuries. By keeping away from each other and avoiding this fighting, related male sleepy lizards may be showing an unusual form of “brotherly love”. 

So it seems that family does matter for less social species – just not in the way we are used to thinking about it.  

PAPER: A contact-based social network of lizards is defined by low genetic relatedness among strongly connected individuals, Animal Behaviour, 2014, vol 97, p35-43.