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Cane (Giant) Toad - Rhinella marinus
Cane (Giant) Toad - Rhinella marinus

[Image: Bufo%20marinus.jpg]

Scientific classification 
Kingdom: Animalia 
Phylum: Chordata 
Class: Amphibia 
Order: Anura 
Family: Bufonidae 
Genus: Rhinella
Species: Rhinella marinus

Physical Characteristics
Size - The Cane Toad is the largest species in its family. 
Adult Cane Toads are usually heavy-built and weigh an average of up to 1.8kg. (4 lbs.). Their size may vary from 15-23 cm.(4-9 in.) and their skin is warty. The female is usually bigger and has softer skin than the males. Most juvenile Cane Toads when they first appear are about 10-15mm.(1 inch) long. 

Color - Cane Toads will often blend in with its surrounding to hide itself from predators. Their back and sides may vary from olive-brown or reddish-brown, gray and yellow while their bellies are semi-yellow or semi-white with darker mottling. 

Anatomy - They have a round flat body, a prominent corneal crests, and light middorsal stripes. Their front feet are unwebbed while their back feet have leathery tough webbing. Cane Toads have short legs, a ridged bony head that extends forward from their eyes to their nose. Behind their ears are the parotid glands, which may cause their head to look swollen. These glands are used for defense against predators. The parotid gland produces milky toxic secretion or poison that is dangerous to all species. Some effects caused by its poison are burning of the eyes and hands, and skin irritation. 

Cane toads (Bufo marinus) are native to Central America and South America. In 1935 it was introduced to Australia from Hawaii. They also have been introduced to Florida, Caribbean Island, Venezuela, Puerto Rico and Philippines. The introduction of Cane Toads to many parts of the world was mainly to help control the population of insects that were threatening commercial sugar cane. 

The Cane Toads original habitat before its dispersal by humans was subtropical forests near fresh water. However, they can now be found in many places such as man made ponds, gardens, drain pipes, debris, under cement piles, and junk beneath houses. Cane Toads will usually stay on dry land; and reproduce in any shallow water near its surrounding. 

Cane Toads sit upright and move in short rapid hops. They are inactive during the day and are usually active at night. During the winter and dry seasons Cane Toads will often hide in hard to reach moist places such as beneath logs, rocks debris and hollow depressions. When a predator attacks a Cane Toad, their skin releases a milky white poison. The mating call of the male Cane Toad is a long loud purring trill, like a high-pitched telephone dial tone, or the sound of a distant motorboat. Juvenile Cane Toads, which are called toadlets or metamorphs are active both day and night. The younger toads are said to be less toxic than the adult. During feeding, these toads are known to be very quick, energetic, and persistent in capturing prey. 

Cane Toads normally prey on insects and will eat any animal that they can ingest. Cane Toads eat almost anything such as small lizards, frogs, birds, fish, mice, bees, worms, dung beetles, scarab beetles and even younger Cane Toads. They are also known to steal food from dogs and cats if their food dishes that are left outside. 

Cane Toads breed between the months of April and September in the Northern Hemisphere. They can be heard as they call their mates beginning in late March. Every year each female Cane Toad produce two clutches of about 8,000 to 35,000 eggs. The eggs are externally fertilize by the male's sperm. These eggs can be found floating on the surface of water in a jelly-like string or also wrapped around vegetation and other debris in the water. Age and size of the female will determine how many eggs the toad will produce. Within 24 to 72 hours (1-3 days) the eggs will hatch and form a school of tiny shiny black tadpoles. The rate of the tadpole's growth depends on the temperature of its habitat and the food availability. It has been estimated that only 0.5 percent of the Cane Toads survive to maturity. It takes a year to reach the maturity and they are about 75 mm. long. Cane Toads are estimated to live 10-40 years. 

Source -
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  • Claudiu Constantin Nicolaescu
Cane toad the size of a 'small dog' found in NT

March 27, 2007 03:22pm

A CANE toad the size of a small dog has been nabbed in the middle of a "breeding frenzy" at a Darwin suburb.

Dubbed the 'monster toad' by its catchers, the 861g male is the largest to be caught anywhere in the Northern Territory, according to environmental group Frogwatch. 

The warty pest was picked up by local volunteers during a community toad bust at Lee Point last night. 

Measuring 20.5cm in length, the colossal male was one of 39 toads caught in the middle of "a breeding frenzy", said FrogWatch co-ordinator Graeme Sawyer. 

"The biggest toads are usually females but this one was a rampant male," he said. 

"He is huge. I would hate to meet his big sister." 

The second largest toad to be caught in Darwin was a female measuring about 15cm. 

"This monster is another five centimetres long and one third heavier," Mr Sawyer said.

He said it was about the size of a small dog. 

First released in Queensland, cane toads have multiplied and spread across Australia, poisoning millions of native animals, including crocodiles in World Heritage-listed Kakadu. 


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  • Claudiu Constantin Nicolaescu
Invasion Is Backbreaking Work For Australia's Cane Toads

Science Daily — For the first time researchers have turned their attention onto the health effects of invasion on our old friend the cane toad, revealing that they are suffering from severe spinal arthritis brought on by the onslaught.

While conducting research into toad invasion front, scientists from the University of Sydney and from the Department of Primary Industries found that the larger 'invasion front' toads were displaying a high incidence of spinal abnormalities.

'Bigger, longer legs increase their ability to seek out new territory but also puts pressure on the body with every hop,' said Professor Shine from the University's School of Biological Sciences. 'And with much of their energy going towards movement, less is put into their immune system, which may predispose the toads towards infection with the soil bacteria that precipitate arthritis.'

'We found that around 10 per cent of toads had arthritis in their spine,' said Professor Shine. 'Ironically, factors that have contributed to the toads' rapid spread across the continent have also rendered it susceptible to arthritis,' he said.

The researchers also observed that the process of invasion appears to have selected for larger toad body sizes on the invasion front.

'Whilst the larger body size provides advantages to the coloniser, as they can move faster, eat a wider range of prey and are less vulnerable to predators, it also increase their susceptibility to arthritis,' he said.

'The major spinal deformations of these animals testify to the great stress that invading species place upon themselves, as well as upon the ecosystem they are overrunning. An important aspect of this research is that it highlights the importance of incorporating wildlife health perspectives in any analysis of the process of biological invasion,' said Professor Shine.

Their findings are published online in the Proceeding of the National Academy of Sciences, in a paper entitled 'Invades under stress: spinal arthritis ion invasive cane toads'.

Note: This story has been adapted from material provided by University of Sydney
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  • Claudiu Constantin Nicolaescu
Researcher seeks toad sightings on state borders

Posted Wed Dec 19, 2007 0:46am AEDT 
Updated Wed Dec 19, 2007 2:06am AEDT 

A researcher is calling for land managers near the intersection of the Northern Territory, South Australian and Queensland borders, to report cane toad sightings.

Professor Michael Tyler from the University of Adelaide has started a cane toad awareness and mapping project with remote cattle stations, 700 kilometres north of Adelaide.

He says the threat of the introduced pest has been greatly under-estimated across inland Australia, and the Lake Eyre Basin.

"We don't know how well distributed it is within the Lake Eyre Basin," he said.

"Through the Lake Eyre Basin Committee I have got a small grant and some help and what we are going to do is see if we can find out how far it is has dispersed - because, to be quite honest, it is not known."

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Cane toads have now spread beyond the borders of Queensland.
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  • Claudiu Constantin Nicolaescu
Cane toads threaten rare crocodile population

Posted Mon Feb 4, 2008 10:51am AEDT 
Updated 9 hours 9 minutes ago 

North Australian environmentalists say time is running out to save a rare miniature crocodile from extinction.

Ten dead freshwater crocodiles have been discovered in a remote billabong on Auvergne Station near the Northern Territory and Western Australia border.

Post-mortem results showed they died from eating cane toads. 

Toadbuster volunteer Sandy Boulter says the rare pygmy crocodile on Bullo River Station further west may suffer a similar fate.

"It doesn't matter the size of the animal, the toxin of the cane toad will kill all of our Australian fauna. Birds, fish, reptiles. 

"Cane toads are mighty clever, vigorous little animals and ... they are only 20 kilometres from the pygmy crocodile population."

Toads moving on Kununurra

The Friends of the Kimberley Toadbusters group say almost forty cane toads have also been found on Newry Station, about fifty kilometres from the Northern Territory - Western Australia border.

The group says it's the first time large numbers of male toads have attempted to colonise this close to Kununurra.

Volunteer Sandy Boulter says the pest could reach Western Australia by the end of the year.

"One of (our) teams found three male toads in the culvert beside the Victoria Highway in Fish Creek.

"Five kilometres back they found 32 males and this is the closest that we have found the cane toads on the Victoria Highway corridor."

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Ten crocodiles on Auvergne Station are the latest victims of the cane toads march across Northern Australia. (Chris Mills)

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Toad Busters use a mini-helicopter, or gyrocopter, to access areas cut off by wet season floods.
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  • Claudiu Constantin Nicolaescu
Biological Weapons To Control Cane Toad Invasion In Australia

ScienceDaily (May 10, 2008) — New research on cane toads in Northern Australia has discovered a way to control the cane toad invasion using parasites and toad communication signals.

Professor Rick Shine from the University of Sydney has been studying the biology of cane toads, and will reveal his new research May 7 at the Academy of Science's peak annual event Science at the Shine Dome.

He says that controlling toads has been difficult as things that kill them will often kill frogs. Professor Shine and his team studied cane toads in Queensland that lagged behind the invasion front and found they were infected with a lungworm parasite which slows down adults and, in laboratory tests, kills around 30% of baby toads.

It was originally thought cane toads left their parasites behind when they came to Australia and that the lungworm parasite came from Australian frogs. This ruled out using the parasite for toad control due to potential frog impacts. However, DNA sequencing by Professor Shine's team has shown the parasite species came from the Amazon and is genetically different to those found in Australian frogs.

'The toads have brought with them a parasite that kills them and that doesn't attack Australian frogs, so this is a phenomenal opportunity for biological control' he said.

Professor Shine's team have also discovered pheromones used to communicate danger between toad tadpoles that have significant impacts on their size and survival. The 'alarm pheromones' are released into a pond when a tadpole is frightened or injured and warns other toad tadpoles to flee the area.

The signal stresses the toad tadpoles so much that in field trials around half of them died before they became adult toads, and those that become adults were half the size they should've been. The pheromones were also found to be different to those of Australian frogs and didn't affect them.

Using the lungworm parasite and the alarm pheromone together would be particularly powerful as the pheromone either kills or produces smaller 'toadlets', and the parasite is more effective at killing these smaller sized toads.

'...the combination of those two things start to suggest, I think, a pretty straightforward, pretty low risk, but probably pretty effective way to start controlling toads.'

Attractant pheromones have also been found by his team which can be used to lure toad tadpoles for catching and removal.

Professor Shine hopes to involve community groups in the use of these new control methods. He says that although there has been a huge effort to slow the toad front by communities in Western Australia and the Northern Territory, the toad front is progressing as fast as ever.

'We've got the toads moving across Australia faster and faster. They're widely seen as a major problem. In community surveys they're identified by many people as the worst invasive species we have.'

Previous methods for controlling cane toad numbers have included traps and fences but have mainly involved physically removing them from the environment, often by putting them in a plastic bag in the freezer.

'People have spent certainly well over $15 million on cane toads in Australia on research and control. Very little of that has actually been devoted to try to understand what toads are doing. Now that we've done that, it does seem that there are really encouraging avenues.

'By doing the detailed ecology and actually finding out about communication systems and where the parasite came from and things like this, we've got new ways to attack toads that haven't been thought of before'.

He says the main impact of the toad invasion has been on large predators such as goannas, quolls, king brown snakes and death adders. 'We've had, for example, probably 90% mortality of the big goannas and the big lizards in our study site. Its dramatic, and that has all sorts of flow on effects. You take out 90% of the big predators and that really changes the system.'

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New research on cane toads in Northern Australia has discovered a way to control the cane toad invasion using parasites and toad communication signals. 
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  • Claudiu Constantin Nicolaescu
Inflatable toad shrugs off wimpy suitors

Posted Wed Jan 6, 2010 9:14pm AEDT 
Updated Wed Jan 6, 2010 9:22pm AEDT 

The female cane toad can pump herself up to mega-size to throw off smaller males striving to mate with her, Australian biologists said.

The unusual tactic suggests that female anurans, as frogs and toads are called, may have far more power to select their sex partner than thought, according to their study in in the British journal, Biology Letters.

Female cane toads (Bufo marinus) are typically choosier than males when it comes to reproduction.

They discriminate among potential mates by approaching the toad with the best call.

But as they head to a rendezvous with the hunk with the mightiest ribbit, they also have to run the gauntlet of excited rival males.

An unwanted suitor will seek to climb on the female's back, grasping her tightly in the armpit or groin, waiting until she starts laying her eggs in order to fertilise them.

This is where the pneumatic trick comes in, say the scientists, led by Benjamin Phillips of the University of Sydney.

By inflating sacs in her body, the female is able to loosen the grip and the luckless male slides off her body, defeated.

As a result, the female is able to choose the size of her mate, a factor that is important to the species, says the team. 

Fertilisation among cane toads is most successful when males and females are similar in size.

Mr Phillips and his two colleagues worked on the small-to-XXXL hunch after noting that the cane toad puffs itself up in the presence of a predator to make itself look scarier.

Female toads likewise inflate at copulation time, but until now this was presumed to be a reflex to being pushed, kicked and occasionally flipped over as panting males wrestled for amorous contact.

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Failed romance: By inflating sacs in her body, the female is able to loosen the suitor's grip 
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  • Claudiu Constantin Nicolaescu
Cane toad threat spreads beyond Australia to Caribbean 

By Matt Walker 
Editor, Earth News 
Page last updated at 07:43 GMT, Wednesday, 9 June 2010 08:43 UK

[Image: _48023892_0001772841.jpg]
Toxic invader

Cane toads, one of the world's most destructive invasive species, have started killing native wildlife outside of Australia.

Cane toads are poisonous, secreting a toxin that kills predators not adapted to eat them, and as a result the toads have caused a decline in native Australian reptiles and marsupials. 

Now scientists have discovered that the toads are also killing boa snakes in the West Indies, suggesting that other predators in the Caribbean and elsewhere may also be at risk. 

The cane toad is a large toad species, which secretes a powerful bufogenin toxin.

Its native range extends from northern South America through Central America and into the southern United States. 

In the early to mid 19th Century, the toad was intentionally introduced to islands in the Caribbean, including Jamacia in 1844, and then through the south Pacific. 

The toad was introduced to eat and control pests of sugar cane, including rats and beetles. 

However, the toad has had a destructive impact in many places where it has spread, outcompeting native species. 

More recently, the toad has devastated populations of amphibian predators, including large lizards, snakes and marsupials, in Australia.

[Image: _48023997_jamaicanboa.jpg] 
Jamacian boas are falling victim

The threat there continues to grow as the toads spread west across the country from Queensland into New South Wales and the Northern Territory. 

Cane toads are so prevalent in Australia that people in the Australian state of Queensland have even taken part in a mass capture of the poisonous amphibians, as part of a collective effort at pest control. 

Threat widens

Now scientists have documented the cane toad killing rare native fauna in the Carribean. 

Dr Byron Wilson at the University of West Indies in Jamaica and colleagues there and in the US have found numerous examples of cane toads poisoning Jamaican boas (Epicrates subflavus), a large predatory snake that is endemic to the island of Jamaica. 

The boa, also known as the yellow snake, is Jamaica's top native terrestrial predator. 

Already rare, the snake is threatened by habitat destruction and introduced dogs and pigs.

"To our knowledge, this is the first report of cane toads causing mortality in naturally occurring predators outside of Australia," say the authors in the journal Biological Invasions. 

"Although cane toads have been present on Jamaica for more than 160 years, it is clear from our observatiosn that Jamaican boas have not yet learnt to avoid this toxic prey species." 

The researchers now fear that the toads could pose a threat to the snake across its island range. 

They also worry that other species in Jamaica and on other Caribbean islands are at risk from bufotoxin poisoning. 
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  • Claudiu Constantin Nicolaescu
Toad personalities key to territorial takeover

Monday, 25 August 2014 Christopher Doyle

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Grumpy toad: a mix of bold and shy personalities has given cane toads a foothold in Australia, say researchers (David Gray/Reuters)

Cane toads with the personality to boldly go where no cane toad has gone before pave the way for more timid toads to rapidly take over new territories, say Australian researchers.

First introduced into Queensland in the 1930s, cane toads are now found as far south as Sydney and as far west as Kununurra. Despite originating from the rainforests of South America, the toads have managed to conquer some of the hottest and driest parts of the Australian continent.

To understand why cane toads continue to venture into new and potentially hostile environments, the scientists put cane toads from a recently established population in the Northern Territory through a mix of behavioural tests.

They found that some toads were bold and daring, while others were shy and cautious, they report in the journal PLoS One .

It is this mix of bold and shy personalities that has given the cane toads a foothold in Australia, says study co-author Professor Rick Shine of the University of Sydney.

"It is a pretty amazing situation that most frogs are stay-at-home creatures and don't really move too far from where they live, yet here we have got cane toads romping across the landscape," Shine says.

"But if cane toads were all timid then presumably they would still be sitting in Queensland."

Personality test

To examine how personality traits varied within a cane toad population, the researchers set up feeding stations in the field using artificial lights to attract both insects as food and wild cane toads.

At some of the feeding stations the researchers placed a single cane toad in a mesh enclosure while the other feeding stations were left empty, allowing the wild toads to choose between an empty foraging site or one with another toad present.

A total of 95 cane toads approached the feeding stations within a two-hour period, with an almost even mix between those happy to eat on their own and those that preferred another toad to be present.

Shine says the presence of another toad in the area provided some of the toads with valuable social cues about the suitability of the area for foraging. But for those toads that fed alone, the social cues weren't needed.

To further test their personalities, the researchers placed each toad into a makeshift shelter in the laboratory and timed how long it took for the toad to leave the shelter and begin exploring its new environment.

They found the cane toads that happily ate on their own left their shelters much quicker than the more social cane toads, which tended to be more timid.

Bold v timid toads

"The bolder toads were happy to waltz out and walk around and the other guys stayed hiding," says Shine.

"It shows that some toads are prepared to leap out there into the unknown while some are scaredy-cats."

Shine believes it is the bold cane toads that venture forth and invade new areas. The shy toads follow on later, using social cues from the bolder toads to guide them. The result is a rapid swell in cane toad numbers in the first few years following the invasion into a new area.

"To boldly go where no toad has gone before is probably the sort of thing that a bolder individual is going to do better than a shy individual."

While there are advantages to being a bold toad, such as less competition for food, Shine says there is also the added risk of greater predation.

"Being the bold toad may well pay off or it may end up with you being dinner for the local rats," he says.

"So a population with a mix of personalities is probably going to do better than either one alone. You need a few extroverts as well as a few introverts."

Invasive Cane Toads: Social Facilitation Depends upon an Individual’s Personality

Edna González-Bernal, Gregory P. Brown, Richard Shine
Published: July 17, 2014DOI: 10.1371/journal.pone.0102880

Individual variation in behavioural traits (including responses to social cues) may influence the success of invasive populations. We studied the relationship between sociality and personality in invasive cane toads (Rhinella marina) from a recently established population in tropical Australia. In our field experiments, we manipulated social cues (the presence of a feeding conspecific) near a food source. We captured and compared toads that only approached feeding sites where another toad was already present, with conspecifics that approached unoccupied feeding sites. Subsequent laboratory trials showed correlated personality differences (behavioural syndromes) between these two groups of toads. For example, toads that approached already-occupied rather than unoccupied feeding sites in the field, took longer to emerge from a shelter-site in standardized trials, suggesting these individuals are ‘shy’ (whereas toads that approached unoccupied feeding stations tended to be ‘bold’). Manipulating hunger levels did not abolish this difference. In feeding trials, a bold toad typically outcompeted a shy toad under conditions of low prey availability, but the outcome was reversed when multiple prey items were present. Thus, both personality types may be favored under different circumstances. This invasive population of toads contains individuals that exhibit a range of personalities, hinting at the existence of a wide range of social dynamics in taxa traditionally considered to be asocial. 
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Ceratodromeus Wrote:Interesting feeding behavior documented in the 2000 Herpetological review
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There is also this predation account on a neonate B.irregulars, documented from the same issue:

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Cane toad: Scientists crack genetic code

Date:  September 19, 2018
Source:  University of New South Wales

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Cane toad, Rhinella marina (stock image).
Credit: © Yakov / Fotolia

A group of scientists from UNSW Sydney, the University of Sydney, Deakin University, Portugal and Brazil have unlocked the DNA of the cane toad, a poisonous amphibian that is a threat to many native Australian species. The findings were published in academic journal GigaScience today.
"Despite its iconic status, there are major gaps in our understanding of cane toad genetics, and up until now, no one had put the genome together," says Peter White, project leader and Professor in Microbiology and Molecular Biology at UNSW.
A decade ago, researchers in WA had already tried to sequence the cane toad genome, but they encountered obstacles when it came to assembling it, and didn't complete the project.
For this project, the UNSW-University of Sydney team worked at the Ramaciotti Centre for Genomics at UNSW, which has played a role in decoding the genomes of other iconic Australian species, including the koala.
"Sequencing and assembling a genome is a complicated process. By using the cutting-edge sequencing technology and expertise available at UNSW, we sequenced 360-odd billion base pairs and assembled one of the best quality amphibian genomes to date," says Senior Lecturer Dr Rich Edwards, lead author of the study.
"We managed to decipher more than 90% of the cane toad genes using technology that can sequence very long pieces of DNA, which makes the task of putting together the genome jigsaw much easier."
Having a draft cane toad genome will help to close key knowledge gaps and accelerate cane toad research. More toads can now be sequenced at a fraction of the cost, and the genome is freely available -- anyone can access it now and conduct further research.
"Future analysis of the genome will provide insights into cane toad evolution and enrich our understanding of their interplay with the ecosystem at large -- it will help us understand how the toad spreads, how its toxin works, and provide new avenues to try to control its population," says cane toad expert and Emeritus Professor Rick Shine from the University of Sydney.
"Very few amphibian genomes have been sequenced to date, so this is also great news for amphibians. Having a reference genome could provide valuable insights into how invasive species evolve to adapt to new environments."
Having the genome will also help researchers to find new options for controlling the toad population.
"Current measures like physical removal haven't been successful, but new methods to teach native species not to eat the toad -- called taste aversion -- give new hope. However, we need more approaches to control this invasive species," Professor White says.
For one such alternative measure -- biocontrol, i.e. using a virus to help control the toad population -- the toad's genetic material is essential.
"To find a virus for biocontrol, we need access to the toad's DNA and RNA," explains Alice Russo, a PhD student at UNSW who specialises on finding potential viruses to control the toad.
"DNA contains ancient fragments of viruses -- the DNA of every animal can sometimes catalogue past infections."
Viruses have previously been successfully used to control the European rabbit population. The issue with cane toad viruses studied so far was that they could potentially infect native amphibians -- which is why this study aimed to find a cane toad-specific virus.
In a paper published this month in the Journal of Virology, the researchers describe how they sampled cane toads from different Australian locations, and, using a combination of DNA and RNA sequencing, found three new viruses.
"Up until we published this paper, only one family of viruses was known to affect the cane toad. This is the first paper that has found different viruses, which is very promising," Russo says.
"This paper has opened the door: we found a retrovirus, a picornavirus and a circovirus which are genetically similar to viruses infecting frogs, reptiles and fish. For two of them, we found a full genome -- both could potentially be used as biocontrol agents."
Knowing these new viral sequences will help inform future studies which will investigate their prevalence and potential as agents for biocontrol.
"There's a lot more work to be done. However, these two papers are the first -- but most important -- steps in finding an effective way to control the cane toad," Professor White concludes.
Cane toads are highly adaptable and have destructive impacts on native fauna in invaded regions, of which there are many; they are present in 138 countries. Since the toad was introduced in Queensland for control of the cane beetle in 1935, it has spread widely -- millions of toads now occupy more than 1.2 million square kilometres. It fatally poisons native species like the northern quoll, freshwater crocodiles, and several species of native lizards and snakes.

Story Source: University of New South Wales. "Cane toad: Scientists crack genetic code." ScienceDaily. (accessed September 21, 2018).

Journal Reference:
  1. Richard J Edwards, Daniel Enosi Tuipulotu, Timothy G Amos, Denis O'Meally, Mark F Richardson, Tonia L Russell, Marcelo Vallinoto, Miguel Carneiro, Nuno Ferrand, Marc R Wilkins, Fernando Sequeira, Lee A Rollins, Edward C Holmes, Richard Shine, Peter A White. Draft genome assembly of the invasive cane toad, Rhinella marina. GigaScience, 2018; 7 (9) DOI: 10.1093/gigascience/giy095

The cane toad (Rhinella marina formerly Bufo marinus) is a species native to Central and South America that has spread across many regions of the globe. Cane toads are known for their rapid adaptation and deleterious impacts on native fauna in invaded regions. However, despite an iconic status, there are major gaps in our understanding of cane toad genetics. The availability of a genome would help to close these gaps and accelerate cane toad research.
We report a draft genome assembly for R. marina, the first of its kind for the Bufonidae family. We used a combination of long-read Pacific Biosciences RS II and short-read Illumina HiSeq X sequencing to generate 359.5 Gb of raw sequence data. The final hybrid assembly of 31,392 scaffolds was 2.55 Gb in length with a scaffold N50 of 168 kb. BUSCO analysis revealed that the assembly included full length or partial fragments of 90.6% of tetrapod universal single-copy orthologs (n = 3950), illustrating that the gene-containing regions have been well assembled. Annotation predicted 25,846 protein coding genes with similarity to known proteins in Swiss-Prot. Repeat sequences were estimated to account for 63.9% of the assembly.
The R. marina draft genome assembly will be an invaluable resource that can be used to further probe the biology of this invasive species. Future analysis of the genome will provide insights into cane toad evolution and enrich our understanding of their interplay with the ecosystem at large.
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  • Claudiu Constantin Nicolaescu
New research finds cane toads use poison as a last resort

by University of Sydney

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Cane toads can be distinguished from frogs because they sit upright. Credit: Greg Brown.

Cane toads are exhausted by releasing their deadly toxin and will go to great lengths not to release it. They far prefer to run or freeze when a predator approaches.
The cost to the cane toad for releasing the poison is substantial, including reduced growth and activity. The toad takes several months to replenish its toxin after using it to repel a predator, which could explain why it uses it frugally.
This is good news for Australian wildlife, said Dr. Gregory Brown, the lead author on the paper published today in Proceedings of the Royal Society B.
"Although cane toads possess outrageously potent toxin, they aren't out there using it to maliciously slaughter everything they encounter," said Dr. Brown, an honorary associate in the School of Life and Environmental Sciences. "Instead, they will go to great lengths to avoid using it because manufacturing more is so costly. These animals are reluctant warriors."
The study, co-authored by acclaimed evolutionary biologist Emeritus Professor Rick Shine and Associate Professor Kim Bell-Anderson, has three major findings:
  • Cane toads produce potent toxin to protect themselves against predators but they are miserly with it.
  • The costs of producing toxin are more than just time and energy. There are flow-on costs, such as reduced growth and activity, that can be more substantial.
  • Although the researchers measured the cost of deploying toxin specifically in cane toads, the concept is likely to apply to many toxic and venomous animals.

Credit: University of Sydney

The cane toad is an invasive species in Australia and a fatal source of poison for many native fauna and pets. Toads mostly eat insects, including honey bees, ants, termites and beetles, but they have been known to eat small native frogs, snakes and mammals. They have few predators in Australia.
"The cane toads possess toxin that is outlandishly lethal to many Australian predators, such as goannas and quolls," Dr. Brown said. "The toxin is less lethal to the toads' natural predators in South America because they have been engaged in an arms race with toads for millions of years and have had time to evolve resistance to their toxin. But many Australian predators are naive, and so sensitive to the toxin that even ingesting a tiny bit will quickly kill them."

Cane toads: fight or flight?

Cane toads prefer to run away from a predator, or freeze and rely on their camouflage, rather than release their toxins, Dr. Brown said. They also try puffing up to look bigger or jumping towards the predator to spook them.
"These tactics are often successful, the toad escapes and the predator is stymied but still alive," Dr. Brown said. "It's only as a very last line of defence, usually when the predator has them in its mouth and chewing on them, that toads use their 'nuclear option'. But you can imagine that a lot more predators would end up dead, if toads slathered themselves in toxin as a first, rather than a last, line of defence."

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The cane toad is not "malicious." Credit: Greg Brown.

Cane toad invasion

Dr. Brown said the research probably doesn't have a practical application in slowing the spread of cane toads but it does have implications for understanding the factors that affect their rate of spread.
"Predator density could have a big influence on the rate of spread," Dr. Brown said. "If toads continually encounter threats and have to repeatedly deploy and replace their toxin, they won't have the energy or inclination to disperse very far. Another implication is that the fastest invading toads, may be individuals less disposed to use their toxin. It's possible the best dispersers are braver, bolder individuals who rarely release toxin."

Journal Reference:
Ryann A. Blennerhassett et al. The cost of chemical defence: the impact of toxin depletion on growth and behaviour of cane toads ( Rhinella marina ), Proceedings of the Royal Society B: Biological Sciences (2019). DOI: 10.1098/rspb.2019.0867

Many animals capable of deploying chemical defences are reluctant to use them, suggesting that synthesis of toxins imposes a substantial cost. Typically, such costs have been quantified by measuring the elevation in metabolic rate induced by toxin depletion (i.e. during replenishment of toxin stores). More generally, we might expect that toxin depletion will induce shifts in a broad suite of fitness-relevant traits. In cane toads (Rhinella marina), toxic compounds that protect against predators and pathogens are stored in large parotoid (shoulder) glands. We used correlational and experimental approaches in field and laboratory settings to investigate impacts of toxin depletion on growth rate and behaviour in cane toads. In free-ranging toads, larger toxin stores were associated with smaller gonads and livers, suggesting energetic trade-offs between toxin production and both reproduction and energy metabolism. Experimental removal of toxin (by manually squeezing parotoid glands) reduced rates of growth in body mass in both captive and free-ranging toads. Radio tracking demonstrated that de-toxined toads dispersed more slowly than did control toads. Given that toxin stores in cane toads take several months to fully replenish, deploying toxin to repel a predator may impose a substantial cost, explaining why toads use toxin only as a final line of defence.
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