In large swaths of Australia, invasive predators such as feral cats have caused the decline of 43 native vertebrate species, and the extinction of about 22. Yet we’re still unclear about when and from where these invaders arrived. Now, researchers analyzing the DNA of hundreds of feral cats reveal that they likely descended from those that came over from Europe in the 19th century on boats. There may have also been a second wave from Asia. The findings were published in BMC Evolutionary Biology this week.
Unlike stray cats (or former house cats) that rely on us or our garbage, feral cats are free-living and independent of humans, and they reproduce in self-perpetuating populations. Following domestication, cats (Felis silvestris catus) have been moved around by people across continents. Especially beginning around 1800, cats were actively transported aboard sailboats of explorers, sealers, whalers, pearlers, and colonists as either pets or rodent-control.
It makes sense that cats were brought over to Australia by European settlers in the late 18th century to the 19th century. Though alternatively, they may have arrived before European settlement: from shipwrecks in Western Australia back in the 1600s or with Malaysian sea cucumber harvesters (called trepangers) in northern Australia around 1650.
A team led by Katrin Koch of the Senckenberg Biodiversity and Climate Research Centre analyzed DNA in fur, blood, and tissue samples from 269 feral and stray cats spanning six mainland Australia and seven island locations – including nearby Christmas Island and Cocos (Keeling) Island. Then they compared these with samples from Southeast Asia and Europe.
They found that the likeliest source of feral cats in Australia were the cats that arrived from Europe in the 19th century. Remnants of the historically introduced cat genomes can still be found on isolated islands: Australian mainland samples were distinct from those collected on Dirk Hartog, Flinders, Tasman, and Cocos (Keeling) islands. While the islands surrounding Australia may represent founding populations, the influx of domestic cats (including fancy breeds) into the feral cat population is still happening on the Australian mainland. Furthermore, in addition to the mostly European origin of Australia’s feral cats, the team also found a possible later, secondary introduction from Asia.
Earlier this summer, the Australian government announced that two million feral cats will be killed to save the country’s threatened wildlife.