Live bearing promotes family life among reptiles
The researchers from Lund University in Sweden and University of Tasmania in Australia have studied more than a thousand different species of lizards and snakes. Approximately 20 per cent give birth to live offspring. Around six per cent of all the species they have studied spend their lives in families or large social groups with individuals from several generations.
”Our most important result is that almost all species that live a life in groups bear live offspring instead of attending eggs. For snakes and lizards live bearing is almost a necessity in order to develop a complex family life”, says Tobias Uller, evolutionary ecologist at the Department of Biology at Lund University.
The researchers have compared the social life of the reptiles with their means of propagation and other factors of significance to the evolution of social systems. The affinity between different species is well known and because of this the researchers have been able to establish that social life and live bearing have evolved side by side.
”It shows how evolution of one character, live bearing for example, can open up new paths for the evolution. A classical problem within evolutionary biology is how family life has originated”, Tobias Uller says.
The new results show that the transition from laying eggs to bearing live offspring has made it possible for the natural selection to gradually modify social interactions and increase the tolerance between individuals. Young reptiles have stayed in the area where they are born and the evolution eventually has led to the development of stable social groups, sometimes with dozens of closely related individuals living together.
Almost all birds and mammals care for their offspring. Because of this there has been a lack of knowledge in the first evolutionary steps towards parental care and a social life in groups. The new study is unique in the respect that it tries to answer what is needed for the process to start.
Tobias Uller points out that the evolution of family life has taken other paths as well. Birds caring for their eggs before they are hatched is one possible path.
”Some lizards and snakes also care for their eggs, bu tour study shows that this has not been a feasible way to pursue for family life among reptiles. Instead live bearing has been the highway to family life for snakes and lizards”, he says.
The results are published online in an article in Nature Communications.