How did the spread of feral cats begin?

Australian feral cats can reach two metres from head to tail and can fell a wallaby. They have a reputation for decimating the continent’s smaller native fauna, but is it truly deserved, or is another introduced predator the real culprit?

To find out, ecologists have tried to establish when cats first set paw on the continent. Did they jump off Portuguese shipwrecks 400 years ago? Island hop with Malaysian fishermen around the same time? Or hitch a ride with European colonisers in the 19^th century?

As suspected, they slunk off the first European settlers’ ships, and quickly spread across the continent, according to two genetic analyses published in December. One analysis by Katrin Koch of the Senckenberg Biodiversity and Climate Research Centre in Frankfurt and her colleagues appeared in BMC Evolutionary Biology, and the other by Peter Spencer of Murdoch University in Perth and his colleagues was published in the Journal of Heredity.

The timing of the cat’s arrival is important. After European settlement, Australia suffered a massive loss of biodiversity. If cats had been in Australia long before the First Fleet arrived, that would suggest another species Europeans introduced, such as the fox, was the real native fauna killer.

The new findings lay the blame at the paws of the feral cat. And the cats’ rapid movement across Australia – faster than Europeans could reach parts of the continent – tells us why feral cats are so hard to control today, says ecologist Chris Johnson of the University of Tasmania. “If you knock a population down, anywhere in Australia, more cats move in sooner or later. Probably sooner.”

The Koch team narrowed down the cats’ origin by analysing the genome of 266 feral cats from the Australian mainland and six of its islands, and comparing them to European and Southeast Asian cat populations.

They traced the cats’ lineages by examining slow-mutating genes in the cell’s mitochondria. These genetic clues pointed squarely at a European origin for mainland Australian feral cats. Cats on islands close to Asia – for example, Christmas Island, which lies closer to Indonesia than the Australian mainland – shared more of their genetic heritage with cats from Southeast Asia.

To get a handle on when the mainland feral cats arrived from Europe, the team also analysed the cats’ “short tandem repeats”, genetic sequences that are prone to mutation. These showed that most mainland cats stemmed from a few small populations, likely introduced a few hundred years ago, meshing with historic records of rat-catchers on the ships of the first Europeans.

The Spencer team used similar techniques to trace the cats’ rapid spread across Australia from east to west. This again pointed to early European colonisers who made land in the East, whereas Asian fisherman came from the “Top End”.

So bad news, cat lovers – feral felines are villains after all.