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 UniversityAssociate Professor VeraWeisbecker, an ARC Future Fellowwho supervised the study, says everyone knows rodents all look similar, but the researchers expected far more variety in the details of their skull shape thanwhat they found. Dr Ariel Marcy, fromThe University of Queensland, says rodents first enteredAustralia 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 frommuseums using 3D surface scanners, and analysed their shape using a statistical procedure called geometric morphometrics. What the researchers foundwas the opposite of what they expected: there was lowvariation 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 dowith the very successful specialisation of rodent jaws, allowing their skulls to be a true multi-purpose tool. ProfessorWeisbecker 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.
Illustration: Australia’s smallest rodent, the molinipi (Pseudomys delicatulus), considers one of Australia’s largest rodents, the otter-like rakali (Hydromys chrysogaster). They share a skull shape gradient that goes back further than either species’ arrival to their shared continent. Illustration by Alison K. Carlisle (aka Papadore Illustrations).
DISCOVERY AND FUNDAMENTAL RESEARCH
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