Study of rat skulls reveals an unexpectedly simple recipe for adaptive success

An ARC-supported study, co-led by scientists from Flinders University and The University of Queensland, has revealed that the skulls of rodents resemble each other in any given size, meaning little adaptation seems to be necessary for a rodent to survive in a variety of habitats.

Flinders University Associate Professor Vera Weisbecker, an ARC Future Fellow who supervised the study, says everyone knows rodents all look similar, but the researchers expected far more variety in the details of their skull shape than what they found.

Dr Ariel Marcy, from The University of Queensland, says rodents first entered Australia around four million years ago, and quickly adapted to the diversity of habitats available on our continent. ‘Because well-adapted skulls are key to the survival of mammals, we expected to find a lot of locally adapted skull shapes.’

To understand the patterns of adaptation they expected to see, the team scanned hundreds of rodent skulls of 38 species from museums using 3D surface scanners, and analysed their shape using a statistical procedure called geometric morphometrics.

What the researchers found was the opposite of what they expected:

 there was low variation in the skull shape of rodents, which could be explained mostly by body size. The researchers think this astonishing conservatism of shape may have to do with the very successful specialisation of rodent jaws, allowing their skulls to be a true multi-purpose tool. Professor Weisbecker notes that the results make an important point in one of the biggest questions in evolutionary biology – why some groups of animals are more diverse than others.

	‘It seems intuitive that a group of animals that displays a wide variety of shapes should be more successful in evolution. But, Australian rodents demonstrate that shape diversity doesn’t always mean evolutionary success. So for Australian rodents, if the skull ain’t broke, don’t fix it!’ says Professor Weisbecker.