David Curnow

Hello and welcome to Where Are We At With? The podcast that brings you up to date with the promises of the future made in the past. I'm your host, David Curnow And in this episode we're finding out where we are at with the battle against cane toads in Australia. One of the highest profile cases of biocontrol failure in the world. Introduced to fight a pest, only to become a far greater pest itself. Seemingly unstoppable as it hops inexorably across a continent, and along the way developing into a stronger and faster version of the original. My guest today is a man who can be considered close to scientific royalty in Australia, if not globally. Professor Rick Shine is currently a Professor of Biology at Macquarie University in Sydney and also Emeritus Professor at the University of Sydney. He has two PhDs, achievement medals from senior scientific bodies in Australia, New Zealand and the US, China and Belgium.

Honestly, it would take the whole podcast just to read out all his awards over a career of more than half a century. But I will mention the Prime Minister's Prize for Science, three Australian Museum Eureka Awards. He's the only person to have those awards in three different fields. He was the first non-American to become president of the Society for the Study of Amphibians and Reptiles, the world's largest scientific herpetological society. Did get the point? Rick Shine is a big deal.

He's even managed to correct Charles Darwin on a few minor matters when it comes to evolution. and did I mention he's literally written the book on cane toads? Cane Toad Wars, well worth a read, as are his other entertaining and quite interesting books. Today we're going to find out how cane toads can be like a bottle of scotch, why fine young cannibals are not just a band from Birmingham, and how Peter Pan could help and maybe even win the fight against toads.

So... Where are we at with cane toads?

David Curnow (02:14)

Well, as we mentioned, our guest today is Professor Rick Shine from Macquarie University in Sydney at the moment. He's been in other places. And I suppose we'd call you King of Toads, Professor Shine.

Rick Shine (02:27)

⁓ I mean, I spent the first half of my career being the king of snakes, but I got dragged into the world of cane toads and maybe I'm a prince at best.

David Curnow (02:36)

We'll move on to snakes in a moment ⁓ and certainly into your current work with toads. Let's take a back a bit because while most Australians know about cane toads and particularly those in the tropical parts of the country know them firsthand, where are they from? What's their background?

Rick Shine (02:55)

Well, cane toads are just these very large frogs, one of the biggest frogs in the world, and they're found in quite a large area of the northeastern part of South America. You know, think Brazil, French Guiana, places like that, rainforests, basically. But very early on in the 1800s, people that were trying to grow sugar cane in the Caribbean decided that these toads might make great little pest control officers.

They might eat all the beetles and so forth that were a problem for the sugarcane. And so they brought the toads across to the Caribbean. They ended up in Puerto Rico where they were supposed to have done a great job in helping sugarcane yields, although the data in retrospect look pretty flimsy. From there, an enthusiastic American brought 150 toads to Hawaii in 1932. And in 1935, the Queensland government sent an agricultural scientist across to Hawaii to catch 101 toads and bring them back to northern Queensland ⁓ with the idea of releasing them and using them for pest control in the sugarcane plantations there.

David Curnow (04:05)

Now I understand that in Australia where they were brought this 101 toads Dalmatians as they were ⁓ breeding them in captivity was actually something that hadn't been achieved before and considered one of the hurdles. Am I right in that?

Rick Shine (04:20)

Yeah, that the sort of the guy, the American that had brought the toads from Puerto Rico to Hawaii was seen as the big guru, Cyril Pemberton. And they had failed to breed the toads in captivity in Hawaii and it ended up just releasing them and the toads had bred for themselves. So it was regarded as being pretty tough to do. But in fact, when young Reg Montgomery came back from Hawaii to Queensland and established his toads in the Pleasure Palace that had been specially built for them.

The toads bred almost immediately and the Australians were very proud of themselves for having overcome this supposed technical obstacle.

David Curnow (04:56)

It is hard to think of at the moment, just how excited people were, not just about the breeding program, but the very fact that the toads were here. I suppose in hindsight, when you look back in the fact that cactoblastis had been introduced, what, nine, eight years earlier, and had been a raging success in controlling another pest, you can see why people were a bit excited about the idea of not using incredibly harsh chemicals, but instead using a bio-control mechanism.

Rick Shine (05:27)

Yeah, look, I think you've got to give the people at the time credit for the notion that they were after an ecologically responsible control mechanism that would be better than these nasty poisons that were really the only alternative. It is kind of ironic because Reg Montgomery, the guy that was sent to Hawaii to get the toads, had actually worked on the Cactoblastis project and had seen the of the careful way in which they had evaluated potential downsides to bringing in Cactoblastis, and had decided, you know, eventually that it was okay before they did it. They kind of skipped all of that with the cane toads. Reg understood they could be a problem. He knew they were toxic, but there was so much enthusiasm from the politicians and the cane growers that I think it swept all before them.

David Curnow (06:14)

And I suppose even that success of the Cactoblastis having gone through all that ⁓ rigmarole effectively proved, look, it's okay. We didn't need to be worried after all. Everything's fine. Don't worry about it.

Rick Shine (06:26)

Yeah, look, absolutely, think, you know, scientists have a tendency to perhaps overestimate their ability to muck around with nature without recognising some of the unforeseen consequences. And it's the classic example of a decision that probably seemed terribly clever at the time and appears to be nothing but stupidity in retrospect.

David Curnow (06:49)

Let's talk a little bit about the toads themselves. You said they were native to South America. They produce toxin, but they themselves are also toxic. that right?

Rick Shine (07:01)

Well, the toads as a group, this family bufod it occurs over most of the planet where there's sort of suitable areas, know, South America, North America, Europe, Asia, Africa, they've all got toads. Australia just was so far away, so separated from everywhere else that toads never got here until Reg brought those 101 toads in 1935. What the toads, a lot of their success appears to really depend upon the fact that they have come up in evolutionary terms with this really distinctive powerful poison. And so they make it and these glands in the shoulders, the parotid glands, they can send it around to glands in the rest of the skin. The female sends the poison to the eggs in her ovaries before she lays them to protect them. But it's a really distinctive chemical, very unlike any of the defensive poisons that native frogs in Australia use, for example. And that was the key to the catastrophe that befell the native predators when cane toads eventually started to spread through Australia.

David Curnow (08:03)

How do they produce it? we know much about the scientific basis of the production of it? I know a lot of creatures say consume and then metabolize certain ingredients that create the toxin. Do we know how the toads do it?

Rick Shine (08:15)

Yeah, look, there are undoubtedly very learned people probably wearing white coats and sitting in front of ⁓ beakers full of coloured fluid that would give you a really good answer to that. I don't know. They synthesize it from their food, but they really put it all together in a very distinctive way. ⁓ Many other animals will actually take poison in their food and redirect it to somewhere else in their body to use for defense. And in fact, there's some snakes in Japan that take

David Curnow (08:20)

Hehehehe

Rick Shine (08:43)

toxin from toads and put it in their neck glands and if you approach one of these snakes with evil intent it contort itself around and sort of push its neck towards you because if you get a mouthful of that poison from the neck it's exactly the same as getting it from a cane toad.

David Curnow (08:59)

A bit like an echidna, curling itself up and any time something gets near it gives itself a little bit of a nudge towards you and makes its point, so to speak, fairly sharply.

Rick Shine (09:09)

Absolutely. Look, the cane toads are all about trying to convince other animals that they're a really bad dietary choice. And so they sit out in the open, they don't hide the way that most frogs do. They're out there, they don't run away from you unless they're really quite frightened. They're much more intent on showing you who they are and if you've evolved with them, you're well aware of the fact that a big warty amphibian with large shoulder glands is a really bad choice for male unless you've had a few million years of evolution to change your physiology in a way that enables you to handle that poison.

David Curnow (09:49)

And that I know is a key point in some of the work you've done. We'll get onto that a little bit later. The toads themselves, they eat a number of things, don't they? It's the sort of thing where they are effectively a creature that will eat just about whatever comes in front of them that's smaller than them really, isn't it?

Rick Shine (10:06)

Yeah, they really are mostly fixated on small dark objects that move in front of them. They love to eat beetles and ants and things like that. ⁓ Every once in a while they'll eat something bigger, an occasional earthworm or even an unlucky blind snake perhaps. But, you know, most of the time they eat quite small invertebrates. Every once in a while you get a... a toad that's got a baby bird in its stomach or something like this, but it really is the exception to the rule.

David Curnow (10:40)

Yeah, they're not out there hunting them. It's more just a case of what happens to have popped up in front of them.

Rick Shine (10:46)

Well, they've got this amazing ecological flexibility, so they're really good at locating food sources. So around the houses, for example, there plenty of cockroaches in the suburbs of Brisbane, and I'm sure the local Brissy toads get a hell of a lot of cockroaches. ⁓ One of the sites where we worked in Hawaii, where there were actually very few sort of insects roaming around in Hawaii, but there were some tree-dwelling cockroaches, and the toads were climbing up into the trees and shrubs to eat these cockroaches.

You you look at a cane toad, it really doesn't look like a mountain climber, but they were remarkably adept and athletic at climbing up into the bushes to get at the bugs.

David Curnow (11:25)

I thought that was one of the things that hindered them from getting the cane beetles themselves was the fact that they didn't climb but there we find they've even climbed. They do eat cane beetles and the larvae if they're in front of them though, don't they?

Rick Shine (11:37)

Look, indeed they do. ⁓ And the larvae probably not quite so much, but when the adult beetles come to the ground to lay their eggs, undoubtedly they do eat them and that's all good. But of course, the attempt to bring in toads for pest control against those beetles didn't allow for the fact that the sugarcane plantations already had some very effective beetle controllers like goannas and big lizards were roaming around and they ate vast numbers, not only of the adult beetles but also of the larvae. But because the toads were so poisonous and the goannas couldn't handle the poison, goannas that thought that a toad was just another frog died of a heart attack very quickly and so very rapidly the toads eradicated the native animals that were doing the job of controlling the beetles and they didn't do a terrific job themselves in replacing that role.

David Curnow (12:33)

It's a like saying that humans will eat a wholemeal bread sandwich, but gee whiz, if somebody puts a burger there, there's a good chance they'll snack on that and enjoy it.

Rick Shine (12:41)

Indeed.

David Curnow (12:43)

We're looking at where we are at with cane toads today. Professor Rick Shine from Macquarie University is with us. He has done quite a lot of research, particularly in recent years on the cane toad. We'll get onto your research in a moment. I do want to very quickly look at though, the fact that this was introduced with a fair bit of hype, particularly for cane growers. This was the solution in the same way that the cactoblastis solved the big cactus problem.

Here we had a solution to the cane beetle. All is solved, particularly North Queensland growers. Hallelujah. The release went ahead, mostly supportive people around abouts, one or two who voiced some fairly prescient ⁓ concerns. How long did it take before people started to question what was going on?

Rick Shine (13:33)

Yeah, there were all sorts of interesting politics involved here, I think. It became fairly clear to the people that were proselytizing on the virtues of the cane toad that it wasn't really having a big effect on sugar cane yields. I think that became apparent relatively early. And it also became apparent that the toads were likely to spread much further than anyone had thought.

You get a frog from a Brazilian rainforest and you put it on the North Queensland coast and you think, well, look, it's not going to go anywhere apart from these sort of, you know, wet eastern slopes of the dividing range. ⁓ But the toads started to spread out and they started to get into areas where people weren't growing cane and weren't keen. And there was also a huge amount of rivalry between Queensland and New South Wales. And New South Wales people, particularly beekeepers, were worried about the toads eating all of their bees. And so it was a bit of a public relations campaign in the newspapers. ⁓ And this is how the toad came to be called the cane toad. It was the Giant Toad when it was brought in. But the New South Wales people wanted to ensure that the Queenslanders were blamed for bringing in this big, damned ugly frog that was going to eat all their bees. And so they started to call it the Queensland cane toad. And it became the cane toad ever since. And if you go back to Brazil now, everyone calls them cane toads there as well.

David Curnow (14:56)

It's incredible what influence State of Origin can have even before it existed. They did eat cane beetles, but you're right. They were called the great tone or even sometimes the Marine Toad Very quickly, there was even been amphibian anger over the nomenclature about what to call it. Bufo originally, as you said, with toads ⁓ named initially by the father of Latin naming of scientific naming procedures, was a Carl Linneaus But it's changed its name over time.

Rick Shine (15:26)

Yeah, it's really very common for species to change their scientific names. Initially, Linnaeus and his mates didn't understand just what a massive diversity there was out there of species. And so, know, if you're sitting there in Sweden, there's a couple of things that are warty and you can call them toads and there are some amphibians with smooth skin and you can call them frogs and you lump them all in the same category. So the toads all around the world, most of them look pretty similar.

and they were all in the genus Bufo because nobody could work out how the hell to separate them, know, which ones were more closely related to which other ones. They were just all too similar. But when the geneticists got into the act and started to get data on gene sequences, of course, they were incredibly different. Some of these species have been separated from each other for 80 million years. And so they have evolved an enormous amount of genetic difference, even if they still look pretty much the same. And once we had the genetic data,

we could start splitting the venerable ol' genus Bufo into a whole bunch of smaller lineages. And so Bufo marinus became Rhinella marina.

David Curnow (16:35)

"A rose by any other name." Perhaps the look of it is still the biggest thing for a lot of people, I imagine, rather than what this name is.

Rick Shine (16:42)

Yeah, Australians love to talk about how ugly cane toads are. ⁓ You don't get that from people in other parts of the world. You know, if you're an English naturalist, you probably smile at the side of a European toad ambling down beside the creek. ⁓ I think there's been a really effective public relations campaign to tell us that cane toads are ugly and horrible. The more that I've worked on them, the more I see beauty in the humble cane toad.

David Curnow (17:12)

There is that element of we're told to hate it, this is bad, therefore it must be ugly. Whether it be the tales of warts from toads, again, Australians not used to them per se. Given the fact we tend to mistake cane toads for other native creatures fairly regularly, they're obviously not that dissimilar in some of the aspects.

Rick Shine (17:32)

Now the toads get quite a bit bigger than any of the Australian frogs. you know, if you can't identify an adult cane toad as a cane toad, you probably haven't been paying close attention. But the juveniles, you know, you're talking an animal that's one tenth of a gram. You know, it's a tiny little thing when it transformed from the tadpole stage to the metamorph stage. And, you know, it's just a little black dot moving around on the water's edge. It's incredibly difficult to tell the difference between a baby toad and a baby frog. And even when they're half grown, ⁓ it can be pretty tricky. you know, people have done various surveys in shopping centers with toads and frogs and asked the public which one's a toad, which one's a frog, and they get a heck of a lot of them wrong. And so a lot of native frogs get thumped on the head in mistake for toads.

David Curnow (18:24)

Yeah, the control mechanisms that were used once it was realized that A, they're not particularly successful at the one job we brought them for and B, no, they're out and they're continuing to get out. Were there any initial control measures attempted that we know of?

Rick Shine (18:44)

think you've got to put yourself back into the mindset in the late 1930s. Biodiversity and so forth was not really a catchphrase. And the kinds of animals that the toads have the greatest influence on, where they really are devastating, are things like quolls and goannas and venomous snakes. Now these are the kinds of animals that the farmers hate.

You know, the chicken farmers were losing their chickens to quolls. They didn't want to get bitten by snakes. The goannas were always a pain eating this and that. And so I suspect that plenty of people recognized that you were finding ⁓ dead animals. know, there's stories very early on of, you know, a dead taipan next to a dead toad and so forth. ⁓ But they didn't think it was a big deal. And it wasn't really for quite a long time until people started to... point out that the impact of toads on some of the native predators really was very substantial and something to worry about.

David Curnow (19:51)

And certainly probably not something that would have raised many eyebrows in urban parts of Australia, put it that way, given that we're losing, well, venomous snakes, thank goodness. ⁓ The creatures that perhaps we've never seen or heard of, the quolls, and all we know is they either eat your pet cat or your chooks. And the goannas, scary big things. What does it matter? It's not going to really concern people in the cities as much early on, it?

Rick Shine (20:19)

Yeah, look, I mean, I'm a lifelong ⁓ enthusiast for reptiles ⁓ and amphibians, but especially reptiles. And it's difficult to overstate just how much the worldview of Australians has changed. Even when I was a kid, which in Middle East quite a while ago, ⁓ snakes in particular were not part of the wildlife. National Parks rangers were killing snakes when they saw them to protect visitors to the park, you know, wildlife was koalas and lyrebirds and things like that, kangaroos. Reptiles were kind of weird, ugly things and we didn't really like them. And so it wasn't seen as an impact on wildlife because snakes were not part of wildlife. They were just one of the downsides of living in Australia. I think it was one of the Queensland councils wrote to the federal government calling for the CSIRO to ⁓ embark on a project to rid Australia of snakes.

David Curnow (21:17)

Wow, it certainly has changed a bit. Let's move on to that because when we do want to know where we are with cane toads, one of the important steps for you was the creature that doesn't step, so to speak. How long have you been interested in snakes? When did you first realize that you loved reptiles ⁓ and wanted to get more involved?

Rick Shine (21:38)

My dear departed aunts tell me that as a very small child learning to walk in the backyard in the house in Brisbane that I was picking up small lizards and putting them in jam jars from which my aunts would release them when I wasn't looking. So look, I think I was born with that gene. ⁓ I've always found something elegant and fascinating about reptiles and amphibians and that... passion that curiosity has not dimmed in the slightest ⁓ as I hit my 75th year.

David Curnow (22:13)

You've been around the world, basically studying them and certainly the majority of your career was spent doing so alongside other reptilians and similar creatures. What were some of the places? What were some of the snakes? Do you have some favorite memories of those?

Rick Shine (22:29)

So many snakes, so little time. ⁓ I was very fortunate, Australian Research Council gave me ⁓ research fellowships ⁓ and I was able to travel quite widely. Snakes are hard to work on because you can't find enough of them. ⁓ English tourists think that Australia is full of them and you've got to wear knee-high boots everywhere you go, but the reality is you don't see snakes very often.

David Curnow (22:32)

Hahaha!

Rick Shine (22:55)

decided that the way to do research on the ecology and behaviour of snakes was to go to the few places where snakes were abundant. ⁓ The standout spot is actually in Canada, the ⁓ interior province of Winnipeg, ⁓ of Manitoba, rather just north of the city of Winnipeg, where the local garter snakes, they're harmless, sort of medium-sized snake. They occur in incredible numbers. They eat earthworms, which are very common there, it freezes so deep underground during winter that for eight months of the year a snake can't survive on the surface. They have to get down deep. And there's only a few caverns that are deep enough with underground streams that have dried up. And so the snakes from, you know, tens of kilometres around all go back to the same den and they come out in springtime for this brief four month orgy of mating and producing babies and then going back down again before snow starts. And so you can sit in a sunny den with 20,000 sex-crazed male garter snakes crawling all around you, completely ignoring you and asking questions about their sexual preferences and the tactics they're using to make a living as a garter snake. That's probably the most amazing sight.

David Curnow (24:06)

Let's talk cane toads because you, ⁓ it was through studying snakes and some of the snakes here in Australia that you effectively became more interested in the life and habitats of the toad. How did that happen?

Rick Shine (24:24)

Yeah, well for quite a long period, know, well over a decade, I had been doing very intensive research at a place called Frog Dam, about an hour's drive outside Darwin on the way to Kakadu. Fantastic habitat with incredible abundance of particularly water pythons, but also a bunch of other snakes. And with colleagues, we had been sort of trying to work out how year to year variation in monsoonal rains affect the availability of prey and the responses of the predators and you know, we were getting a sophisticated picture of the functioning of that system. And that's something that no one had been able to do almost anywhere in the tropics with almost anything, but sure as hell not with snakes and not within Australia. And that was all going very well. And then the snake was suddenly at threat because the cane toad invasion was going to arrive much more rapidly than we had ever expected. It wasn't supposed to get to that area near Darwin for another two or three decades. But in fact, the toads accelerated their march and they got there about 2005, right when my project was roaring along. And here I was sitting there with a whole bunch of government funded research on how a tropical system works. And here we had this high profile pest species about to invade and allegedly quite likely eradicate many of my study animals, this was a unique example to see what a biological invasion actually does and what we might be able to do about it. And so I expanded the work and increasingly shifted the emphasis from just the snakes to the interaction between the snakes and the toads and increasingly to the toads.

David Curnow (26:11)

Do we know why the cane toads accelerated? What was the reason behind them suddenly getting faster?

Rick Shine (26:18)

Yeah, that turned out to be one of the most fascinating questions in terms of sort of fundamental evolutionary mechanisms. Ever since Charles Darwin's day, the only mechanism people have believed to be responsible for sort of changing the appearance and the characteristic of animals was natural selection. Some individuals have characteristics that enable them to survive and reproduce better than others, and those successful traits therefore become more common in successive generations. Lovely story and it's absolutely true. But the toad showed us something quite different. We call it spatial sorting. If you imagine those initial toads there in the Queensland cane fields and they're looking west and they have the potential to spread this enormous distance, thousands of kilometres to the west across the Northern Territory and into Western Australia. And some of them start to spread out, some of them stay home. At the end of that first year or so, when time comes to breed, the only guys at the western edge of the invasion are the most dispersive toads. The guys with active personalities, long legs and good endurance and so on. So they breed with each other. And so we combine genes that make you a good disperser in the subset of the babies of those guys. And some of the baby toads get long legs from dad and good endurance from mum. So they're better at dispersing than either dad or mum.

And when it comes time to breed next generation, those guys are at the far western edge of the distribution and they're breeding with other toads that have also inherited unusually athletic capabilities. We call this the Olympic Village Effect because the athletes are breeding with each other. And so year by year, we get this cumulative effect where we get more and more dispersal able toads, toads that can move further and further in a day, a week, a year.

And that builds on itself. And so originally the toads were spreading through Queensland at about 10 kilometres a year, which is not bad for a stumpy little frog. But by the time they got to the Northern Territory, they were probably up to about 30 kilometres a year. By the time they got through Darwin, they were up to about 50 kilometres a year. And to do that, it means that a toad has got to basically run in a straight line to the west almost every night when the ground is damp enough for it to be able to do so without dying.

It's a remarkable acceleration. No other amphibian in the world is a long distance runner the way that Australian Cane Toads are.

David Curnow (28:49)

Once again, Australia very proud of its athletes that it's producing, perhaps again, not the one we wanted to be the best. ⁓ So in a sense, they've accelerated. Is this evidence of evolution or is it just, it happens to be that the western edges are always going to be the faster, stronger creatures?

Rick Shine (29:09)

Look, it's entirely plausible that a lot of these differences you see among animals from different areas are simply due to the conditions they grow up in. You know, maybe it's something about the water in the billabongs of the territory that gives you an athletic baby toad and so forth. But we actually took adult toads from Queensland and the Northern Territory in Western Australia and we bred them at our facility near Darwin and we raised their babies and we tested them and the babies inherited the same characteristics as their parents.

Now we'd raised the babies in exactly the same conditions, so it can't have been the rearing conditions that made the guys at the invasion front such extraordinarily good dispersers. It had to be genetically based. And since then we've actually done quite a lot of work on the genetics. We've sequenced the genome of the toad and my collaborator Leanne Rollins from New South Wales Uni and her students have looked in great detail at the sorts of genetic changes that have enabled toads to colonise what looks at first sight to be an incredibly inhospitable landscape.

David Curnow (30:11)

You don't tend to think of parts of inland Australia, Northern Territory as tow friendly in the sense of lots of aquatic spots and ⁓ moisture laden areas and yet obviously they're making it work. How far have they got to this point?

Rick Shine (30:28)

Yeah, look, it is remarkable where they've got, know, I mean, if the toads had been released in the Northern Territory in 1935, they'd all be dead very quickly because there was no water. But we have put in dams and artificial water sources all over the place. And that's what's enabled the toads to keep going. So the toads have almost reached Broome on the west coast. They'll get there within a year or two. And remarkably, they've extended south in the tropics, way down into the fringes of the desert.

So I just came back two weeks ago ⁓ from a trip down near Daly Waters, which is harsh, arid conditions. It was 45 degrees every day. And the toads thrive there around the artificial dams on the properties. ⁓ It's an incredible life for a rainforest frog from Brazil.

David Curnow (31:17)

The fact that we effectively are creating the conditions to enable them to get further and I understand they've even reached Sydney but possibly with a little help from us again.

Rick Shine (31:28)

Yeah, so toads tend to be most abundant where people disturb the habitat. You don't see a lot of toads way out there in the beautiful scrub in the rainforest and so on. And that's true even in the native range. Toads love disturbance. Disturbance often means there's a subsidy of resources, people add water and that provides lots of bugs for food and so on.

And so the preference of toads for disturbed habitats means that they quite frequently end up hitching a ride ⁓ without the knowledge of the owners of the vehicles that they're in. And so often in landscaping materials or building materials or even in the back of a caravan from the grey nomads, the toads get transported long distances. know, people report you know, finding a cane toad inside their hiking boot when they get back to New Zealand after a trip to Queensland. And we estimate that well over 100 cane toads a year end up in Sydney, just brought down accidentally in trucks and containers. Most of them die a lonely death, but every once in a while enough toads are translocated in one shipment or they find each other and we get breeding. And toads have certainly managed to breed in the suburbs of Sydney and we managed to eradicate them, but that was a difficult challenge.

David Curnow (32:48)

Yeah, incredible to think that they can then continue, as you said, adaptable and survive in places that they shouldn't be surviving, but doing so nonetheless. You started off with looking at how they're affecting the biodiversity up in the area in the Northern Territory and some of the snakes that were being affected there as well as the other habitats. You've also moved into various control methods, you said, sequencing the genomes and looking at the way that the offspring and their traits. What are some of the techniques that you've attempted when it comes to either control or assisting native wildlife to cope?

Rick Shine (33:29)

Yeah, so I guess really the real thrust of the research program was based on the idea that if we're to do something about a problem like cane toads, getting out there and hitting them on the head is just not going to solve it. A female cane toad has 20,000 eggs in a clutch. Getting rid of 90 % of the adult toads has no effect in the long term because the few that are left rapidly replace the ones that you got rid of.

I think you need to understand the enemy before you can try to control it or do anything about it. And we got a couple of key insights from the fundamental research. ⁓ The first was about how native species deal with the arrival of toads. ⁓ The pattern is that the large predators like quolls and goannas and some of the big snakes, freshwater crocodiles, blue tongue skinks, they're the ones that die in huge numbers they're the ones whose populations are decimated. The smaller species related to those guys tend to do okay. They persist despite the presence of toads. And the key to that, we found out from the laboratory experiments, was that if you eat a big cane toad, it's got so much poison in it that you die of a heart attack almost immediately. But if you eat a small cane toad, it's got much less poison. It'll make you sick, but you're very unlikely to die.

And you rapidly learn that cane toads are a really bad idea to eat. And so you learn to avoid eating cane toads. It's a very general process. It's called conditioned taste aversion. Anyone that's ever ⁓ had food poisoning knows how miserable it is to be throwing up all night. And you remember the smell and the taste of that food. And it turns your stomach even long afterwards. When I was a teenager, somebody gave me a bottle of scotch on a camping trip. And I drank it all and I was desperately ill the next day. And, you know, 50 odd years later, I still don't like the smell of Scotch whisky ⁓ It is a remarkably long running aversion and that saves the predators. ⁓ If you meet a small cane toad first, you learn not to eat cane toads. If you eat a big cane toad, if you meet a big cane toad first and eat it, then you die. Now that suggested a novel approach to

David Curnow (35:48)

So hey.

Rick Shine (35:51)

buffering the impact of toads and enabling native predators to coexist with them, we simply have to make sure that the first toad you meet is a small one. And we can do that. Well, we can do that by breeding up toads close to the front and releasing the babies just in advance of the front in an area that's going to be overrun within the next month or two anyway by tens of thousands of big toads. And if we do that, we give the predators a chance to learn that toads are a bad idea to eat.

David Curnow (35:59)

How do you do that?

Rick Shine (36:21)

And so that idea, when I first suggested it, was widely believed to be the stupidest idea that any human beings ever had. You know, this idiot from down south wants to release more cane toads in advance of the front. But we did the trials with quolls and we showed it worked. You know, the guys we trained survived, the guys we didn't train died immediately we released them. We did it with blue tongue skinks, we did it with crocodiles, we did it with goannas. And so now it's actually a key component of the government department in Western Australia who are in charge of conservation, it's a key component of their work, the toads. They are breeding, and in conjunction with us, they're breeding and releasing tens of thousands of baby toads in advance of the front, and it's working. We put out camera traps, and the areas where we haven't released baby toads, the goannas just completely disappear after the toads arrive. And the areas where we released the teacher toads, the goannas are still thriving.

David Curnow (37:20)

Seems counterintuitive doesn't it? The idea of well how are we going to make this better? Well we'll just release a lot more of them ⁓ ahead of the throng that's coming so that then when they do come they won't be as bad.

Rick Shine (37:33)

Yeah, you know, it's giving a bit of credit to the marsupials and the reptiles for probably being a bit smarter than we might have thought they were. It doesn't work for every species. My beloved venomous snakes seem to be the bottom of the class when it comes to learning taste aversion. But for a whole bunch of species like the quolls and the goannas and the crocodiles, it works incredibly well. We've also done the taste aversion work with crocodiles, freshwater crocodiles working with indigenous communities in the Kimberley as well as the Department of Biodiversity Conservation and Attractions and it worked there as a charm. As soon as we started deploying our baits, the mortality stopped and hasn't started again. Whereas in sites we didn't do it, there are dead crocodiles floating in the river.

David Curnow (38:18)

So that is technique which is showing great promise when it comes to the front lines effectively, the expansion of the toad where it is on the fringe. What about the places where it already is? I know that there's been some work on the other end of the life cycle, as you mentioned, the number of adult toads versus the number of babies that are produced, trying to turn them into Fine Young Cannibals

Rick Shine (38:40)

Yeah, look, look, absolutely. I'll just I'll throw in one other point, which is that the problem at the invasion front is that all the toads that arrive first are big because they move fastest. There's no baby toads. So after a couple of years, when those toads are breeding and producing babies, the predators that are still alive can have babies that will grow up around baby toads and they can learn for themselves. So hopefully it's a it's a one off education system that saves that entire area forever. But the other

David Curnow (39:09)

Okay,

so yeah, it's not a learned behavior of don't eat that ever again. It's a learned behavior if you can eat them as long as it's these ones.

Rick Shine (39:15)

Yeah,

yeah, as long as you grow up in a world with the small toads around, you'll have a chance to learn not to eat cane toads. If you grow up in a world with there's only big toads, you don't get that chance. But yeah, the other work and really the main thrust of our current work is looking at another characteristic that evolved very rapidly in the cane toads, like the rate of dispersal did. But this trait is cannibalism in the tadpoles of cane toads. ⁓ If you offer cane toad tadpoles in Australia,

some newly laid toad eggs, they squeal with glee and they race across and they consume them. They are incredibly, just amazingly enthusiastic, obsessive cannibals on the eggs of cane toads. They're not very interested in the eggs of frogs, but they really want to nail the eggs of other cane toads. Now you don't see that in the cane toads in French Guiana or the cane toads in Hawaii. They'll eat cane toad eggs, but they're not really all that interested. But it's really intense in Australia.

David Curnow (40:03)

Why's that?

Rick Shine (40:14)

The reason probably is that cane toads are much more abundant in Australian habitats than they are in their native range. Because they've lost a lot of their co-evolved enemies and so forth, there's no other toads to compete with because Australia had no toads before cane toads arrived. Cane toads reach amazing densities. So if you're a cane toad, your worst enemy is another cane toad. If you're a tadpole sitting in a pond and a female toad, not your mum, comes along and lays 20,000 eggs, you're going to be competing for a very small amount of food in that pond with 20,000 hungry mouths. And you're much better off getting rid of the opposition before those eggs hatch. And so that's what Australian cane toads do. Once we discovered that, we realized they must have a way of finding these eggs and it can't be vision because the water is far from clear in a lot of tropical billabongs. It had to be chemical. And we worked out that the chemical was the poison that the female toad puts into the eggs. It's the same as the poison that she has in her shoulder glands. So that if we simply squeeze the poison out of the shoulder glands of an adult toad and we use that as bait in the funnel trap, tens of thousands of canto tadpoles come roaring towards it and they go into the trap. The frogs of, the tadpoles of native frogs go the other direction. They're not interested at all. So it's incredibly selective. And a company called Watergum has rolled that technology out really across the toad's entire Australian range and millions of toad tadpoles are now being pulled out using that approach.

David Curnow (41:50)

That's incredible to think that you can actually selectively target tadpoles in a murky, billabong, waterway, dam, whatever it might be, and have them swim towards you rather than swim away.

Rick Shine (42:05)

Yeah, look, it's getting close to science fiction. And of course, we're going to get even closer to science fiction in a couple of minutes when we keep talking. But the key here is that if you want to reduce the number of cane toads in an area, you've got to stop them breeding. You've got to stop thousands of baby toads emerging from the water. Excuse me. And the tadpole traps can do that. ⁓ know, culling adult toads will never do it, but culling tadpoles really will.

David Curnow (42:36)

Before we get to science fiction, we spoke about culling toads and of course, for people who live in areas with a cane toad infestation, and that can be all parts, many parts of Eastern Australia, particularly north of the cane fields in New South Wales, the idea of meeting out deaths to cane toads with a blunt instrument while harsh is still part of our living memory. Are there ways that are humane to control adult toads? Should we be even attempting it?

Rick Shine (43:04)

Oh yeah, look, it's clear that particularly at the edges of the invasion, know, like in north-eastern New South Wales, culling by volunteers, know, relatively untrained people can be incredibly effective. know, our estimates that about 50 % of the adult toads in an area can be taken out within a night or two because they do sit out there in the open and they're pretty easy to catch. it may well have an impact down there. It's not going to have much of an impact up there in the remote tropical areas where there's very few people and a hell of a lot of toads and the toads are moving across the landscape, but it has a role. ⁓ We looked a bit at how you could humanely kill the toad. ⁓ I quite like cane toads and it's not their fault they're here. People brought them here. ⁓ Their impact on the native wildlife comes because the native wildlife tries to kill them. So, you know, it's pretty harsh to blame the toad for the problem that's arisen. ⁓ We found out that a very old fashioned method works really well.

You pick up your toad, you put it in a plastic bag, you put it in the fridge for a few hours. That essentially puts it to sleep. I mean, it gets cold every night in most places and the toads just sort of drift down into a state that's a lot like sleep. And you move it from the refrigerator into the freezer. The toad just quietly drifts down and down and down until it becomes a toad sickle. We've measured brain activity and it's just not even a bleep. So the toad doesn't feel a thing.

Leave the bags in the freezer for a few days until you're sure that they're and truly frozen sift and bring them out and bury them somewhere. know, they're reasonably good fertilizer.

David Curnow (44:41)

I do have to say here with a personal note, having done that myself a number of times, ⁓ it is important to label the bag when I put one in the freezer and wrapped it in the white butcher's paper and wrapped it and put it in a plastic bag. And my wife removed it not that long afterwards, but long enough that it was quite sluggish until it sat on the bench for five minutes and warmed up. And the bag started to move quite rapidly.

Rick Shine (45:10)

I'd like to make a personal apology for the stress that I've inflicted on your marital relationship,

David Curnow (45:10)

I wasn't very popular.

I'd like to say it's all your fault, but no, and I can also say while I'm relating personal stories, we know that they're toxic. My toddler has indeed attempted to eat a rotting one, ⁓ which is concerning given that it is actually toxic. It's not like the whole, it'll improve their immune system. ⁓ It was rotting at the time and I had to brush maggots off its face. Apologies, anyone listening who has a delicate stomach, but.

even even the look of a cane toad rotting with maggots in it, it doesn't put off a two-year-old boy anyway he survived

Rick Shine (45:51)

I don't don't think science has found anything that will put off a two-year-old boy as yet, but we're still looking.

David Curnow (45:57)

I did notice the other day and I was in my local very large hardware store, thank you Hammer Barn, and they're actually selling sprays to squirt on the toads. What do we think of these and how do they compare to the freezing method?

Rick Shine (46:07)

Mmm.

People have run some trials. They claim that these are relatively humane. ⁓ I have seen them used a couple of times and I was not happy. ⁓ It seemed to me that those were undergoing substantial pain before they died. that may just be an unusual circumstance. I'm not qualified to talk directly, but I think the pop them into the fridge and then the freezer is the most humane way to do it as long as you're happy to actually handle a cane toad.

David Curnow (46:44)

And that obviously is the rub for some people, isn't it? The physical touching of the toad in some fashion, even if you've got gloves on or a bag of some sort. still, I think most people agree that you don't want any creature to suffer. ⁓ And particularly in this case where, unlike, say, a fox, which is out there killing creatures because that's what it does, the toad isn't even doing that. ⁓ It's just protecting itself from consumption.

Let's talk then about moving forward and science fiction. What are we looking at?

Rick Shine (47:15)

(chuckles) Okay, well this, the idea that has driven our research over the last few years came to me when I was reflecting on the tadpole trapping and it's a lot of work. You you've got to put the traps out, you've got to get the bait, you've got to put it in, you've got to replace the bait, you've got to pull the tadpoles out, you've got to keep doing this regularly. And it occurred to me that actually the perfect targeted cane toad control officer was a cane toad tadpole.

They actually have very little poison themselves, so predators can eat them without any ill effect. The poison is in the eggs and it's in the adult toads, but it's not in the older tadpoles. So they're not causing any problems. And as long as they're sitting in the pond, then if any female toad comes along and lays her eggs there, the tadpoles will eat them. So that's great. The difficulty comes that after a few weeks, very helpful tadpoles will metamorphose into baby cane toads and then start to make the problem worse again.

And it occurred to me that if we could stop the toads from transforming from the tadpole stage into the baby toad stage, we would have these eternal tadpoles. I call them Peter Pans after the fairy tale character that never grow up. And the idea is you can modify a toad tadpole so that it loses the ability to transform into an adult toad. And that sounds pretty weird, but the reality is that geneticists have now developed methods particularly CRISPR-Cas9 where you inject the egg of say a toad with a chemical that targets the gene that makes the hormone that is needed to transform from a tadpole to a baby toad and you simply knock it out. So this is not a GMO, this is not a genetically modified organism, it's not transgenic, you haven't moved genetic material from one animal to another, you haven't created anything new.

All you've done is exactly what normal mutations do, happen in every clutch of cane toads that's ever been laid. There's always a few sad little tadpoles that don't metamorphose. You're just making it happen at an industrial scale. Excuse me. And so if we can do that, then suddenly we have this band of long-lived tadpoles that are never going to become a problem themselves, but are going to mop up any of the eggs that are laid in the pond.

David Curnow (49:26)

right now.

Rick Shine (49:41)

There's an obvious difficulty in that these guys can't breed and you can't stick a needle with that chemical into every egg. But what you can do is you can add the chemical, the hormone that they lack, and that will make them metamorphose. And then if you give them that hormone as they grow up, they will grow into nice healthy toads because they have that hormone that they need. And then when they breed, they will produce their 20,000 non-metamorphosing tadpoles.

And so you have a source of vast numbers of non-menomorphosing tadpoles. And because this is not a GMO, we've been able to get permission from wildlife authorities in New South Wales, Western Australia, and the Northern Territory to release these guys. And we're just in the process of starting those field trials. Under carefully controlled conditions, we've done a year's worth now of lab trials where we've exposed the Peter Pan tadpoles to fish and water birds and turtles and everything else we can think of and they're no problem at all. They're just exactly like a normal cane toad tadpole. They just don't poison anybody. They don't cause any difficulty.

David Curnow (50:51)

A little pill of protein that native creatures can eat.

Rick Shine (50:53)

Yeah, yeah, exactly. Yeah.

You get the feeling that toads don't taste very good. So most of the fish spit them out as soon as they grab them. ⁓ But they certainly don't cause any illness or anything like that. So we think we really do have a, it's a high tech solution, sure. But it's at heart very simple. We're using cane toads to control themselves. Because the Peter Pan tadpoles get bigger than normal toad tadpoles, they eat a hell of a lot more toad eggs.

They're not very interested in frog eggs. They mostly just need algae and things like that. And that doesn't really seem to disrupt any of the food chains. So particularly in an area that's already full of cane toads, all we're doing is we're replacing normal tadpoles with these tadpoles that can't develop past the tadpole stage. And it looks at the moment from our field trials as if it works like a charm. We get close to zero survival of any eggs that are laid into those ponds with no ill effects on any of native fauna. So look, this is an exciting time. We need to scale the work up. We need to carefully monitor for any other effects. The cane toad is the classic poster boy for scientists making stupid mistakes trying to play God with nature. And I don't want to repeat the mistakes of 1935. So we're moving slowly and carefully. We're looking at any possible ill effects. But at the moment, it's looking pretty damn good.

David Curnow (52:20)

incredible to think that the toad itself could be the control vector that we need. ⁓ Is there a chance of ridding the country of cane toads or is it just a case of we have to learn to live with them and reduce them as much as we can?

Rick Shine (52:35)

I think we could have a really big impact on toad populations in areas where there are very few water bodies and the toads can't move very easily from one to the other. So particularly down in that semi-arid area on the fringe of the desert in the Northern Territory, know, Longreach in Queensland, that sort of place, there's really very few farm dams and if we took them out of play, there'd be no baby toads coming into that system as soon as the adult toads have died of old age or misadventure, which probably happens relatively quickly, then there'd be no toads over vast areas. To push that back into the well-watered areas is going to be harder and we're going to need some more complex strategies, but there's all sorts of possibilities. If the Peter Pan tadpoles work as well as they seem to be, then we have a lot of directions to go to make it work also up in other parts of Australia.

David Curnow (53:28)

It's incredibly exciting to think that that might be a method, even if it's just one of many, and I know there's lots of people looking at different ones. Do we have a timeframe that this study needs to go for?

Rick Shine (53:41)

It's moving incredibly quickly. I I thought it would take us years to develop the Peter Pan tadpoles, you know, and it took weeks. And so we're racing along. I would hope within a year or two, we would really be in a position of having the evidence to be able to sit and talk with stakeholders, with landowners, indigenous communities, know, concerned environmentalists, whatever, to say, look, this is a weapon in the toolkit and how do you guys feel about deploying it?

You know, if you're living on a small island off Queensland and there's only two ponds where toads can breed, I reckon we could get rid of toads from your island very, very fast if the Peter Pans work half as well as they look as if they will. So look, I think it's a matter of a few years rather than long term. It dovetails beautifully with some of the other ideas that are emerging about the toad containment zone, trying to stop the toads moving south of Broome into the Pilbara because we need methods to reduce the densities of toads along the edges of those zones and so forth. So it all seems to be coming together in a very exciting way.

David Curnow (54:47)

really is exciting for those of us who live with toads and those who feared their arrival and sensed that it was ⁓ pretty much unstoppable. Who knows? Perhaps it is. There you go. That's where we're at with cane toads. Wonderful to think of and wonderful that the work of people such as Rick Shine and those working with him can contribute to it. Rick, I really appreciate your time today. Thank you so much.

Rick Shine (55:09)

Been a great pleasure talking to you, David.

David Curnow (55:16)

Thanks for listening to Where We Are At With Cane Toads. The transcript for the show is on our website, www.wawawpod.com along with links to things like Professor Shine's book, Cane Toad Wars, as well as the group he created while at the University of Sydney, Team Bufo Don't forget on our website, you can also send us suggestions for future topics, if there are subjects you're dying to know, where are we at with? Until next time, thanks for joining me. Goodbye.