Going Wild (Again): Feral Rabbits In Australia Evolve New Morphologies

Forbes

2 days ago

Is 'feralization' a process of recapitulating what domesticated animals once looked like and once were?
How does domestication change wild animals? When domesticated animals return to a wild state, is this 'feralization' a process of recapitulating what these animals once looked like and once were? Even Charles Darwin pondered the effects of domestication in his book, The variation of animals and plants under domestication, initially published in 1869 (ref). But first, let's understand a little better about feralization: what is it?
'Feralization is the process by which domestic animals become established in an environment without purposeful assistance from humans,' explained the study's lead author, evolutionary biologist Emma Sherratt, an Associate Professor at the University of Adelaide, where she specializes in macroevolution and morphometric methods. This study was part of Professor Sherratt's ARC Future Fellowship.
To do this study, Professor Sherratt collaborated with a team of international experts to assess the body sizes and skull shapes of domesticated, feral and wild rabbits. Their study revealed that when domesticated rabbit breeds return to the wild and feralize, they do not simply revert to their wild form – instead, they undergo distinct, novel anatomical changes.
'While you might expect that a feral animal would revert to body types seen in wild populations, we found that feral rabbits' body-size and skull-shape range is somewhere between wild and domestic rabbits, but also overlaps with them in large parts,' Professor Sherratt briefly explained.
Australia's feral rabbits are descendants of rabbits that newly arriving European colonists brought with them to supply meat and fur. The European rabbit, Oryctolagus cuniculus, or coney, is originally native to the Iberian Peninsula and southwestern France, but currently has an almost global presence. They live in grasslands and are herbivorous, mainly eating grasses and leaves, though they consume all sorts of things, including a variety of berries and even food crops, making them a persistent and formidable agricultural pest.
They dig burrows to live in and produce many litters of blind and helpless offspring, known as kits or kittens, every year. The European rabbit is the only rabbit species that has been widely domesticated for meat, fur, wool, or as a pet, so all domesticated rabbits belong to the same species. Paradoxically, this rabbit species is endangered in its native range, despite being an invasive pest just about everywhere else.
The goal of Professor Sherratt and collaborators' study was to measure and characterize the morphological differences of the European rabbit skull in wild, feral and domestic animals sampled globally, and contrast those measurements with other rabbit species. To do this, they sampled 912 rabbit specimens held by natural history museums or collected by invasive species control programs. They included wild individuals collected in their contemporary native range in Spain, Portugal and southwestern France, along with independent feral populations and domestic rabbits collected from 20 different worldwide locations (countries, territories, islands).
Professor Sherratt and collaborators used well-established scientific methods to quantify shape and size variation in the skull, and to assess size-related (allometric) shape variations that this species acquired through several hundred years of domestication and feralization.
Why focus specifically on these animals' skull shapes and sizes? What do these dimensions tell you?
'[W]e focus on skull shape because it tells us how animals interact with their environment, from feeding, sensing and even how they move,' Professor Sherratt replied.
Professor Sherratt and collaborators examined whether domestic rabbits have predictable skull proportions – relatively shorter face length and smaller braincase size, which are hypothesized to be part of 'domestication syndrome' – and whether feralization has resulted in a reversion to the original wild form. Finally, they compared their measurements to an existing dataset of 24 rabbit species that included representatives of all 11 modern rabbit genera to provide an evolutionary baseline of morphological changes with which to compare wild, feral and domesticated rabbits.
Not surprisingly, Professor Sherratt and collaborators discovered that the 121 domesticated study rabbits showed much more variation in skull shape and size than do wild and feral rabbits, with substantial shape differences (figure 1A,B), which is attributed in part to their greater diversity in body size (figure 1C).
Why is there so much variation in feral rabbits' skulls? To answer this, Professor Sherratt and collaborators investigated several hypotheses regarding the feralization process.
'Exposure to different environments and predators in introduced ranges may drive rabbit populations to evolve different traits that help them survive in novel environments, as has been shown in other species,' proposed Professor Sherratt.
'Alternatively, rabbits may be able to express more trait plasticity in environments with fewer evolutionary pressures,' Professor Sherratt continued. 'In particular, relaxed functional demands in habitats that are free of large predators, such as Australia and New Zealand, might drive body size variation, which we know drives cranial shape variation in introduced rabbits.'
Does the process of feralization follow a precise, predictable pathway?
'Because the range is so variable and sometimes like neither wild nor domestic, feralization in rabbits is not morphologically predictable if extrapolated from the wild or the domestic stock,' Professor Sherratt replied.
What surprised you most about this study's findings?
'That feral rabbits can get so big!" replied Professor Sherratt in email. 'Almost double the mass of one from southern Spain.'
Why don't rabbits show as much morphological diversity as dogs or cats? For example, a recent study (ref) found that dogs and cats have both been selected to have short faces, so why isn't this seen in rabbits?
'We think this is because the long face of rabbits is a biomechanical necessity for this species,' explained Professor Sherratt in email. 'Important for herbivores.'
Why is this research so important?
'Understanding how animals change when they become feral and invade new habitats helps us to predict what effect other invasive animals will have on our environment, and how we may mitigate their success.'
What's next?
'Our next paper will look at the environmental factors that have influenced the diversity of skull shapes in Australia,' Professor Sherratt replied in email. '[For example], we have found that temperatures and precipitation have a lot of influence on the traits we see.'
Source:
Emma Sherratt, Christine Böhmer, Cécile Callou, Thomas J. Nelson, Rishab Pillai, Irina Ruf, Thomas J. Sanger, Julia Schaar, Kévin Le Verger, Brian Kraatz and Madeleine Geiger (2025). From wild to domestic and in between: how domestication and feralization changed the morphology of rabbits, Proceedings of the Royal Society B: Biological Sciences 292:20251150 | doi:10.1098/rspb.2025.1150
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