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Why Cane Toad Testicles Are A Hop Topic Right Now

It turns out the testes of Queensland-based cane toads are 30 percent larger than their WA and NSW counterparts.

Chris Friesen from the University of Wollongong, and Professor Rick Shine from the University of Sydney, were researching cane toad reproduction and needed to mix sperm from a male to eggs from a female.

The easiest way? Remove the testes, which sit inside the animal.

In doing so they found an unexpected pattern -- the gonads of toads finding new habitats are generally a third smaller than those in the core of the species range.

So basically, in Queensland, where toads are very much established, they are much larger, while in WA and NSW where the toads are invading new territory, the testes are smaller.

A huge 20.5 cm toad caught in the Northern Territory in 2007. Photo: Getty

"Population densities are so much less at the front, so there is less sexual competition and less sperm competition," Friesen told 10daily.

He likened finding a mate in a place like Queensland to winning the lottery.

"Everyone wants to win the lotto so how do you increase your chances of winning? You get a bigger ticket," he told 10daily. "In this particular case, you have bigger testes."

Friesen also pointed to energy as a possible factor for the differing testicle size.

"There are trade-offs, especially on the western front, where the cane toads may have a bigger body size, longer legs, they might be more active and so it can't invest that energy into its testes," Friesen told 10 daily.

The next step is to figure out if smaller testes impact breeding.

Cane toads in northern Australia Photo: Getty

Cane toads have fairly large testicles in comparison to other animals, with each one being about the size of their kidneys.

READ MORE: NSW Cane Toad Discovery 'Extremely Alarming' Sign Of Southern Invasion

While there is no confirmation as to why, scientists believe it could be because females can produce up to 30,000 eggs in a clutch.

The cane toad was introduced into Queensland in 1935 in an attempt to control the native grey-backed cane beetle, since then the fast-breeding pests have taken over a large chunk of the state, leaving a trail of carnage as they march south over the border.

Just last week, the Australian Reptile Park was handed in its first cane toad.

'Toad-Runner' was found in Somersby on the the NSW Central Coast. Photo: Australian Reptile Park

'Toad-Runner', as it's now called, was found by a family on the NSW Central Coast.

It had been croaking, which researchers say meant he was looking for a female to breed with.

While we're being assured there is no danger, researchers are working to find a sustainable way to keep populations under control.

You can read the study, published on Wednesday in Biological Letters, here.