Solutions for chytrid

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Solutions for chytrid

Postby Evan » Tue Apr 24, 2007 10:11 pm

I have been thinking for quite a while about the possible solutions for which we can implement to reverse the effects of chytrid on frogs populations around the world.

The most obvious, and longterm, solution to the problem is for the species to build a resistance (presumably through natural selection), and then the population can rebuild with only resistant frogs.

The best influence that humans can make is to try and create conditions for the frogs to allow evolution to occur. I believe this is what the ARC is trying to do with the captive breeding program, by creating as large a gene pool as possible, and hoping that natural selection can choose those individuals with more resistance to the disease.

However, I thought of another idea, but I'm not sure of the feasability, and was wondering what others thought.

The use of a biological control for large pest species has been a method of control which has been used many times throughout Australian history. Some with huge success (Cactoblastis moth), and some a huge failure (Cane Toad).

What is the feasability of introducing a pathogen of the amphibian chytrid fungus to reduce its abundance in the waterways? I first thought of a mycophage (virus that infects a virus), but upon researching the idea, I came across a papers (abstract here, I haven't read in entirity) which talk about using a nematode to reduce the abundance of pest fungi (it was some sort of soil fungi). It resulted in a 97% reduction of the fungi compared to the control.

I was taught that nearly every living species which is large enough (and fungi are apparantly large enough) will have one or more nematodes which infect it. Should we be spending money and effort trying to find this nematode (in South Africa or wherever Chytrid is native) to bring more balance to the Australian scene. How difficult would it be to isolate the nematode from its environment to study it? Does anyone know of other biological control agents which are used to reduce pest, or better pathogenic, fungi species.

Surely if we decrease the concentration/abundance of chytrid in the environment, it would infect frogs at a lower rate and give them greater time evolve mechanisms of defence.

Thanks,

Evan

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Postby angel_saza » Tue Apr 24, 2007 11:15 pm

Introducing any sort of organisms to a location where it is not native is always risky. If it affects chytrid wouldn't it be likely to affect some 'native' fungi? I guess that's the trouble living on an island. Although, it does protect us from things getting here naturally, ie no human help at all!

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Postby Evan » Tue Apr 24, 2007 11:18 pm

Yes, I understand that would be the biggest hurdle after identifying it in the first place.

If it were to adveresly affect any of the native chytrids, then I wouldn't approve of it. However, if it is highly specialised, as the Cactoblastis moth is, then there would be a chance of success.

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Postby angel_saza » Tue Apr 24, 2007 11:22 pm

So much research needs to go into this topic.. so much reasearch, so much money, so little time :(

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Postby GrantW » Wed Apr 25, 2007 9:07 am

Yeah there is always a chance of it affecting native species, maybe not at first, but it may mutate later and affect them. That is also my main concern with the CSIRO trying ways to reduce cane toads fertility, can't remember the full sotry exactly, but I thought if it mutated and started to affect native species it would be catastrophic. In reality there may not be much we can do but wait and hope, many populations of endangered frogs are now fairly resistant to the disease, and in some areas they are increasing. It is likely that we have already lost everything we are going to lose, Chytrid has been in Australia for a long time now, and all the species that went extinct went out in a matter of a few years after first infection, everything that was affected by it is still around just at extremely lower numbers, so I guess all we can hope is that these low numbers are resistant to the disease and they start to increase their numbers again.

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Postby Evan » Wed May 30, 2007 4:34 pm


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Postby rionatindal » Sun Jun 24, 2007 12:28 am

One thought, most of chytid fatalties are often at the end of tadpole stage, if you read some of the paperwork at herp lab.. most tadpoles carry it as they dont have sufficent kertain and when they metamoprh, the kertain develops and then the fungi attacks this, blocking and breaking down the osmosis system.. so how is that good and vaild idea/concept can assist - bathing them with anit fungal baterica while in tadpole or ? what - pour the waterways with it ? too risky

but the idea of bathing adults before they breed may be good but the fungi occur in most of our waterways already....when temperatures are low...for them to florish...

Some frogs have it as adult and may be affected by it but the large majority are in tadpole stage..

One lady doing PHD on the fungi is going to a herpt conference in WA next week is going to talk about the fungi and how it is reduced by the increased saline solutes in water for some ponds......for certain species and how it affects tadpoles in the metapmorphis stage, so only 1-2 out of 5 survive it past the chytid stage, but it doesn't cover a lot of isolated species of frogs where the major extinctions have occured where there are fewer human impact. (global warming ?)

the idea is good and vaild but it is a tip of the iceberg ! I agree with Tnarg (grant I think) that some frogs already are walking dead....

In all, its a vaild idea. Just have to pour buckets of funding into this and need to make sure it will not mutate and affect our fragile Australia and have to ensure it does not repeat the mistake - cane toad, bitou bush and so many little disasters that have changed our landscape forever already..

my 1 cent worth

Riona

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Postby GrantW » Sun Jun 24, 2007 10:31 am

Yes the vast majority of frogs that die from chytrid die when metamorphosing, if the tadpoles are being rasied in captivity this can be treated before the tadpole morphs, chytrid has a low tolerence for heat, so if the water in the tank the tadpole is being raised in is brought up to about 31C the tadpole has a higher chance of making it through metamorphosis. The is the reason why so many frogs are declining in rainforests and highlands, the water is not warm enough to kill the chytrid.

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Postby Evan » Sun Jun 24, 2007 12:43 pm

The water at high altitudes is also the temperature for maximal growth of Chytrid (21 degrees), so it is pretty perfect for it.

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Postby Aaron » Sun Aug 12, 2007 5:00 pm

http://www.smh.com.au/news/science/sex- ... 17604.html

An interesting article about chytrid in todays Sydney Morning Herald

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Postby GrantW » Sun Aug 12, 2007 5:02 pm

It would make sense, it spreads like crazy.

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Postby Aaron » Wed Oct 31, 2007 8:21 am

Another article on treating chytrid from http://news.bbc.co.uk/2/hi/science/nature/7067613.stm

Frog killer fungus 'breakthrough'

New Zealand scientists have found what appears to be a cure for the disease that is responsible for wiping out many of the world's frog populations.

Chloramphenicol, currently used as an eye ointment for humans, may be a lifesaver for the amphibians, they say.

The researchers found frogs bathed in the solution became resistant to the killer disease, chytridiomycosis.

The fungal disease has been blamed for the extinction of one-third of the 120 species lost since 1980.

Fearful that chytridiomycosis might wipe out New Zealand's critically endangered Archey's frog (Leiopelma archeyi), the researchers have been hunting for a compound that would kill off the disease's trigger, the fungus Batrachochytrium dendrobatidis.

They tested the chloramphenicol candidate on two species introduced to New Zealand from Australia: the brown tree frog (Litoria ewingii) and the southern bell frog (L. raniformis).

"We found that we could cure them completely of chytrids," said Phil Bishop from the University of Otago.

"And even when they were really sick in the control group, we managed to bring them back almost from the dead."

"You could put them on their back and they just wouldn't right themselves, they would just lie there. You could then treat them with chloramphenicol and they would come right," Dr Bishop explained.

But the Zoological Society of London (ZSL) expressed caution at the news. Wildlife epidemiologist Dr Trent Garner said there would be reluctance to take up chloramphenicol as a solution, certainly in Europe and North America, because of the chemical's link to harmful side-effects in humans.

Captive solution

The NZ researchers tried using chloramphenicol as both an ointment, applied to the frogs' backs, and as a solution.

They found that placing the animals in the solution delivered the best results. The team has admitted it was surprised by the outcome.

"You don't usually expect antibiotics to do anything to fungi at all. And it does. We don't understand why it does, but it does," said Russell Poulter.

The scientists are now making their research widely known ahead of formal publication in a science journal because of the pressing need for a safe and effective treatment for the chytrid disease.

The blow that chytrid has dealt to the frog population is already immense.

The disease has probably accounted for one-third of all the losses in amphibian species to date, says Professor Rick Speare, an expert in amphibian diseases who works with the University of Otago's frog research group.

These losses are huge - and this is in addition to other threats such as habitat destruction, climate change, pollution and hunting.

Since 1980, more than 120 amphibian species have disappeared; and according to the World Association of Zoos and Aquariums, in the near future many more species are in danger of vanishing.

Amphibians in deep trouble

"We are losing an awful lot of these creatures now and if we don't do something intelligent, then we're going to lose an awful lot more," said Professor Poulter.

But a hopeful finding is that the introduced frogs that have been infected with chytrids are now more resistant to further infections.

"We haven't quite understood how that could happen," said Dr Bishop. "It might be a natural thing; if a frog survives a chytrid infection then it is resistant when it gets attacked again."

The researchers believe that zoos now will have more options, either to be able to control an outbreak or to rescue infected frogs from the wild, knowing that they can be cured.

The next challenge the research team has set itself is to find a treatment that will work in the wild.

"I would really feel quite satisfied if we could say, 10 years from now, that you have to be careful walking around [Australia's] Kosiuszko National Park or you might tread on a corroboree frog because they're all over the place," said Professor Poulter. "I would take real satisfaction from that."

However, just how widely chloramphenicol might be adopted is open to debate. EU and US authorities are concerned the drug may cause aplastic anaemia in humans. "It is a banned substance; in particular, it is controlled where it comes into contact with food sources," commented Dr Garner from ZSL.

"There are other antifungals that are being piloted and some are looking promising. Treating infection in amphibians is possible, but determining if there are any side-effects takes time. Also, how you apply an antifungal at the individual, the population and the species level is a whole set of questions which needs to be addressed."

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Postby GrantW » Wed Oct 31, 2007 2:31 pm

Wow this is cool, but I feel it has come a few years too late. Most of the frogs left are now fairly resistant to the disease, and we've already lost about 8 species (just in Australia), however this could be a lifesaver for corroborees and new zealands natives.

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Postby Evan » Wed Oct 31, 2007 2:35 pm

I don't belive that those that are left are resistant. It is only because of habitat that certain populations of many species are still surviving, and it could be that many are still declining, but less dramatically than species that went extinct initially.

I don't think this is a great option for population recovery, but it allows the biding of time whilst other alternatives are discovered.

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Postby GrantW » Wed Oct 31, 2007 2:37 pm

A lot are, Mix. fleayi is now found with chytrid fungus all the time in south east queensland but they do not die from it, same reason why other frogs seem to be coming back (eg. Mix iteratus in the Watagans), chytrid is everywhere, yet frogs survive with it.

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Postby Evan » Wed Oct 31, 2007 2:39 pm

Some are, but many aren't.

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Postby GrantW » Wed Oct 31, 2007 2:43 pm

I'd say from the species that are left (the survived the initial major declines from about 1980-2000) are now fairly resistant to it (either that or the disease has lost its strength), some like Pseud. corroboree are still in the decline from it, but from my personal observations and what some other people have told me, most species these days are managing fine with it.

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Postby Evan » Wed Oct 31, 2007 2:50 pm

The Corroboree Frogs, bell frogs, Baw Baw Frog, the Western Australian species which are in bad shape, Lit. burrowsae, Lit. booroolongensis have never shown any sign of resistance, and are only surviving because of: habitat which selects against chytrid, chytrid-free areas and biology of the frog which means the decline is slow.

It is an exciting time, because many species are showing a come-back. But there are lots of species which are still in trouble and need help.

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Postby GrantW » Wed Oct 31, 2007 2:59 pm

Yes I agree, defaintely there are those which have not aquried resistance.

But I think booroolongensis have got some resistance, they are still survivng in the central and southern tablelands despite chytrid being there (if they had no resistance wouldn't you expected those populations to have dissappeared when the northern tablelands ones crashed), also burrowsae, there haven't been reported declines within this species yet (although chytrid is a new event to Tasmania so the effects may take some time to be noted). From what I am aware the speices in decline in Western Australia (mostly geocrinia) are largely endangered due to habitat loss, species such as Lit. mooreii (which due to its relation to aurea) which you would expect to decline have not despite chytrid being there.

But then on the other note there are many which have obviously got some restance to it (best example I can think of is Taud. eungellensis), but chytrid is still a problem in part of Australia, I'm just saying that too many species of frogs, its not such a big problem as it used to be.

Cheers,
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Postby Aaron » Wed Oct 31, 2007 3:05 pm

I think this chloramphenicol treatment is really good in a captive situation to treat infected frogs. But I am suspicious of how applicable it would be in the wild. You would need to innoculate lots of frogs/tadpoles which would require a lot of antibiotics. Chloramphenicol is actually not used that much now medically, whilst it is broad spectrum it can have side effects like aplastic anaemia in some people. And there is a risk of antibiotic resistance and creation of "super bugs" once you start spraying antibiotics around the environment.

But in a captive situation its really good news, combined with proper sterilisation techniques threatened species can be maintained in captivity and treated if they come into contact with chytrid.

Aaron

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Postby Evan » Wed Oct 31, 2007 3:13 pm

We can't tell whether booroolongensis has resitance, but I suspect it is due to some environmental aspect which allows them to survive (similar to salt levels in bell frog habitat). If they were resistant, they would begin recolonising their old habitat, like many of the Mixos are.

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Postby GrantW » Wed Oct 31, 2007 3:16 pm

Hmm they were basically entirely wiped out from the northern tablelands which you make it quite difficult to recolonise that region. I suspect it has a lot to do with genetic variations within different populations of species of frogs. Where the booroolongs in the north didn't have the resistance in their genes the ones in the south did, I think the same thing applies for Mix. balbus they are booming in the north but have almost completely vanished from the south.

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Postby Evan » Wed Oct 31, 2007 3:21 pm

I mean even just recolonising areas surrounding where they are found. Are they common in the central and southern tablelands or just restricted to a few disjunct populations?

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Postby GrantW » Wed Oct 31, 2007 3:27 pm

They aren't common, the only occur in a few different rivers, and even in the ones there occur in they aren't a common species. Chytrid has effected them to a degree in that area, but not nearly as bad in the north, I think it'll still be a few more years for them to start regaining lost ground.


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