Hares aren’t just crazy – they’re transformed into something new

When domesticated rabbits escape captivity and establish wild populations, they not only return to their ancestors, but do not produce unique anatomical features in wild or family rabbits. A comprehensive study of 912 rabbit skulls from around the world shows that wildness creates novel evolutionary pathways, while escaped domestic rabbits occupy the middle morphological space while also exploring a completely new body-planned territory.

The study was led by Emma Sherratt, associate professor at the University of Adelaide, and published traditional assumptions about how animals change when they return to their natural environment in the Proceedings of the Royal Society. Rabbits do not simply reverse the domestication effect, but rather demonstrate that human-influenced evolution can produce unpredictable anatomical innovations.

Form innovation

“Wild is the process of building domestic animals in the environment without the purposeful assistance of humans,” Sherratt explained. “While you might expect wild animals to recover to the type of body seen in wild populations, we found that hares’ body size and skull shape range between wild and domestic rabbits, but also overlap with them in most.”

The study analyzed specimens from 20 locations around the world, comparing wild rabbits from their native Iberian Peninsula with family breeds and wild populations established through human introduction. Using advanced geometric morphometric techniques, the researchers mapped skull shape changes throughout the rabbit population.

Domestic rabbits show the greatest morphological diversity, much larger shaped space than wild rabbits occupy. However, the wild population reveals the most interesting patterns, developing anatomical features that make them not only between wild and family forms, but also in previously undeveloped morphological fields.

Geographical models reveal environmental drivers

The degree of hare morphological changes is closely related to the distance from the natural range. European wild populations exhibit deviations from wild forms, while rabbits from Australia, New Zealand and remote islands exhibit the most compelling anatomical modifications.

Key findings include several notable patterns:

• The growth of Australian hares is significantly greater than that of European ancestors
• Skull proportions transfer to longer faces and relatively small brain cycles
• Island population does not follow Foster’s rule
• Latitude and body shape changes are weak

The largest specimens come from isolated sites, including Enderbi Island near New Zealand, Philip Island near Australia, and the populations of Argentina and parts of the United States. These increase in scale occurs in traditional biogeographic rules, suggesting that local environmental pressures drive the evolution of morphology.

Evolutionary influences outside rabbits

“The greater diversity seen in the skull shape of hare populations may be related to changes in evolutionary stress,” Sherratt noted. “In the scope of introduction, exposure to different environments and predators may drive rabbit populations to develop different traits, thereby helping them survive in new environments, as shown in other species.”

The study shows that hares follow the same fundamental evolutionary axes observed throughout the rabbit family (Leporidae), especially volume scaling, where body size drives proportional changes in skull characteristics. However, they pushed these patterns toward previously unexplored morphological space areas.

Domestic rabbits predict typical “domestic syndrome” predictions by developing longer faces rather than shorter rabbits, although they do show expected reductions in brain bin size. This pattern is consistent with the broader mammal isomorphic trend rather than domestication-specific changes.

Protection and management insights

These findings are of great significance for understanding invasive species and conservation biology. Rabbits represent ecological disasters in places like Australia, such as Australia, where they are on the verge of extinction despite the global abundance.

“Understanding how animals change in wild and invade new habitats can help us predict the environmental impact of other invasive animals and how we can mitigate their success,” Sherratt stressed.

The study suggests that relaxed predation stress in environments such as Australia and New Zealand may allow for greater morphological experiments, while new environmental challenges drive adaptive responses. This creates a complex landscape where wild populations can develop rapidly in multiple directions at the same time.

Future studies will investigate specific environmental factors that drive observed changes, especially in Australia, where hares become larger than their European ancestors. This work provides a framework to understand how human-mediated species introduction accelerates evolutionary processes and produces novel biological forms.

The morphological journey of rabbits from domestic captivity to wild success illustrates the ability to evolve as species encounter new environments and selective pressures, which leads to insight into how life adapts to our increasingly human-transformed world.

Related