How captivity affects the brain size of animals

By Jenna Hanson 17 February 2012
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Keeping animals in captivity reduce their brain size, and limits their chances of success in the wild.

CAPTIVE ANIMALS HAVE A better chance of survival after reintroduction into the wild, if they are only kept for short periods of time, and if they have enclosures that closely resemble their natural habitats, researchers say.

Previous studies have indicated that animals kept in captivity over many generations have smaller brains – and therefore less brain function – than their wild counterparts. It’s thought that they become adapted to a less-stimulating environment, leading to an irreversible decrease in brain size.

To add credence to this finding, a new Australian study has now found that stripe-faced dunnarts (Sminthopsis macroura) – mouse-sized marsupials – which are only bred in captivity for short periods of time, retain the same brain size as wild dunnarts.

Captivity leads to loss of wild behaviours

Dr Patrick Guay an ecologist and lead author of the study at Victoria University, says short-term brain reduction over a single generation is temporary, so it’s basically a case of “you use it or you lose it”.

“However, long-term reduction, [over generations], is irreversible because it’s the initial step towards domestication,” says Patrick, whose study is published in the journal Zoo Biology.  “[Animals] never regain the larger brain size of their ancestors, because it’s lost.”

This irreparable reduction in brain size, through breeding, is believed to be responsible for the loss of wild behaviours, such as skills for nesting, avoiding predators, finding food and rearing young. 

“If you don’t provide them with a similar environment to their wild habitat, the captive animals won’t have the same behaviour as those in the wild,” says Patrick. “This could explain why there is such a low success rate of reintroduction in some species.”

Good habitat essential to species reintroduction

Patrick believes that keeping the animals captive for fewer generations – between two and seven – and providing them with an enriched environment, that’s as close to their wild habitat as possible, will produce animals that have no marked brain size reduction.

The long-term captivity of animals “may explain why there is such a low success rate for the reintroduction of some species,” he says.

The dunnart study reinforces the importance that captive habitat plays in success of species reintroduction. “It gives hope to the idea that captive breeding can occur without decreasing the brain size of animals if it’s managed properly,” Patrick says.

Professor Chris Dickman, an ecologist at the University of Sydney agrees that the research could help improve the success of reintroducing small mammals like the dunnart, and conservation in general.

“Reintroductions are a key conservation tool for many species of mammals, including marsupials, but if the animals being reintroduced have been bred in captivity it is important to know that they have the street smarts to survive,” he says. “This research is important in showing that good husbandry can effectively maintain the brain size of dunnarts and avoid the brain shrinkage that can occur if captive conditions are poor [and] this should in turn improve the chances of dunnarts surviving once released.” 

The future for Tasmanian devil breeding

Patrick is continuing his research, working with zoos and the Save the Tasmanian Devil Program to discover whether captivity has decreased the brain size of Tasmanian devils. “It’s important to verify that the devils are not adapting to captivity,” says Patrick. “We hope the new research will show that there is no difference and that the captive breeding program will be successful.

Chris agrees that further research is needed to “see how medium sized, larger and more social species respond to captive conditions”, but he also thinks there may be another route for this research.

“[A] fascinating next step would be to compare how captive-bred and wild dunnarts perform when released back into the wild. This could be done by following animals that have been fitted with tiny radio-tags,” he suggests.