Could feral animals in Australia become distinct species?

By Bill Bateman, Associate Professor, Curtin University

January 24, 2023

It’s possible – and we’re seeing some early signs.

You might think that evolution is glacially slow. At the species level, this is true. But evolution happens every time organisms produce offspring. The daily mixing of genes – combined with mutations – throws up new generations on which “selection pressure” will act.

This pressure is popularly known as survival of the fittest, where fittest means “best fit” individuals. Tiger snakes with a mutation for a larger head can eat larger prey. Evolution is the zoomed-out version, where species change – or evolve into new ones, better adapted to the environment in which they find themselves.

Evolution takes place over millennia. But with the right conditions, it can also work surprisingly quickly. The isolation of Australia has produced us different animals. But until recently in a geological sense it did not have camels, cats, toads and dogs. Now it does. Millions of wild animals, birds and amphibians now call Australia home. And their new home begins to change them in turn.

Can evolution run fast?

We have long thought that evolution is slow. But given the right conditions, the pressure can change much faster. A recent study found that evolution is acting up to four times faster than previous estimates. On average, the species in the study had an 18.5% increase per generation in their ability to survive and reproduce. This remarkably rapid change suggests that many species (not all) are well able to adapt to rapid environmental changes.

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Australia’s feral animal species all arrived through human efforts. Dogs first came through contact between First Nations peoples and traders from what is now Indonesia. Cats came next, accompanying European colonists in the 1700s (and perhaps earlier). Camels in the 1840s. Cane toads came in the 1930s. That means nothing from deer, horses, goats, pigs, water buffalo, mynah, foxes and rabbits.

Once here, dogs, camels and cats quickly gave up domestication, giving way to dingoes, wild camels and wild cats. With each generation, these animals have become better adapted to their new environment. They are now developing in Australia.

Dog or dingo?

The status of the dingo has been hotly contested and we even argue about what to call them. Because it can interbreed with domestic dogs, it is not a separate species. Recent research suggests that there is an intermediary between wolves and domestic dogs. Dingoes have been implicated in the extinction of the thylacine on the mainland.

The dingo’s closest relative is the New Guinea singing dog, which howls like a wolf with overtones of whale song, the dingo may have already evolved from its ancestors. There is certainly evidence of unique selection pressures, but nowhere near enough to be considered a separate species. Similarly, dingoes tend to have wider heads than domestic dogs and more flexible joints. They do not shout, but scream.

fraser island dingo
The last pure dingo population lives on Fraser Island. Dingoes elsewhere have some degree of interbreeding with domestic dogs. Image credits: Shutterstock

An Australian camel?

It is a similar story for camels. Australia’s one-humped dromedaries were imported from Afghanistan and Pakistan because of their ability to live in arid environments. It is no surprise that they thrived. Hundreds of thousands are now roaming in the Red Center. We may now have the largest wild population of dromedaries in the world. Given their numbers, in time, we may have a unique Australian camel.

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Although we have a huge population of camels, they have a low genetic diversity because they came from a small original population. Low diversity usually means that a species is less able to adapt to changes in the environment.

Cats keep getting bigger

Domestication is easy on cats, with the difference between a domestic cat and a feral just a few missed meals.

Cats are one of the most invasive species worldwide. In Australia they have done the worst damage, killing everything from native mice to wallabies with abandon and pushing many to extinction.

Ferals are getting bigger, with reports of 7 kilogram cats now common, well out of their domestic range of 4-5 kg. Tales of panther-like cats may well be giant wild cats. Some were estimated at 12-15 kg. Take the estimated 1.5 meter feral killed in 2005 – double the nose-to-tail length of a domestic cat.

What’s going on? One reason is that feral cats are not desexed, meaning toms can grow as big as a small dingo. But it also seems that selection pressures favor bigger cats. We do not know whether it is due to genetic changes or the rich diet of endangered animals. Usually gigantism – where species grow larger than usual sizes – is associated with islands. Think of the giant Komodo dragon, or the extinct dodo – actually a giant pigeon.

feral cat kill wallaby
Cats can even kill wallabies, as this picture shows. Image credit: Northern Territory Department of Environment and Natural Resources, CC BY

Cane Toads: Phase shifter with longer legs

In 1935, the infamous cane toad was introduced to eat the beetles that plague sugar plantations. As we know, the toads soon discovered that there was much more to eat. Protected by poisonous glands on their backs, they spread across the tropical north to the Kimberley and the east coast, reaching Sydney.

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Toads at the forefront of the invasion have developed longer legs, making faster travel possible. Remarkably, in some sharp canyons in the Kimberley, some have switched from nocturnal to diurnal.

Adaptation is underway – but will we actually see new species?

Also consider Darwin’s famous Galápagos finches. On these isolated islands, the finches calved in separate species. Seed-eaters evolved thicker beaks, while the vampire finch evolved to drink blood from larger birds.

So could it happen here? Yes – if the conditions are right. Let’s speculate that natural selection pushes more and more feral cats to get bigger and bigger.

Finally, these giant cats will see all the domestic cats that escape from farms or houses, not as companions – but as cats. If the gene flow of smaller cats was cut off, the gene pool would be limited – and we would be on track for a new species. Maybe one day we will have a unique Australian cat alongside our unique Australian dog.

This article is released from The Conversation under a Creative Commons license. Read the original article.



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