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Global Warming Fungus 'Wiping Out Frogs'
Wednesday, 25th October 2006, 07:08Category: Healthy Living
A type of fungus spread by global warming is wiping out frogs, according to scientists.
It infects amphibians' skin and is believed to cause disease by interfering with their ability to absorb water.
British and Spanish researchers have found compelling links between the changing temperature in Spain and the emergence of a chytrid fungus called BD (Batrachochytrium dendrobatidis) in the area.
They fear the fungus - which has already killed many frogs - could spread quickly across the rest of the continent as the earth gets hotter and more clouds gather causing it to grow.
The chytrid fungus is found throughout the world - possibly carried by invasive species such as bull frogs. It clings to the skins of amphibians causing a disease called chytridiomycosis.
The fungus attacks the parts of a frog's skin that have keratin in them. Since frogs use their skin in respiration this makes it difficult for the frog to breathe. The fungus also damages the nervous system affecting the frog's behaviour.
Dr Matthew Fisher, of the Department of Infectious Disease Epidemiology at Imperial College London, said: "You can't overstate how serious this pathogen is - it is the worst infectious disease ever recorded among vertebrates in terms of the number of species impacted and its propensity to drive them to extinction.
"When you look at the reality of the disease it's the hardest hitter there is and the amphibian tree of life is being very severely pruned by it."
Dr Fisher said the fungus was introduced into the UK in 2000 by North American bull frogs and although they have since been eradicated the fungus has not.
He said: "The problem is frogs are being transported around the world willy-nilly which is causing this potential for spreading disease.
"Over the past few years frog populations in the UK have generally been going down owing to viruses, pollution and urbanisation.
"Although our frogs are completely resistant to BD the common toad is not and they would be particularly susceptible to a sudden outbreak."
Dr Fisher said scientists cannot quantify the impact on the environment if there were no frogs but it certainly would not do better and "could possibly do worse."
He said: "Frogs are predators and farmers like them because they eat slugs and they also help to get rid of garden pests like midges and mosquitoes.
"Bird populations also depend on amphibians for their food - at least the ones that are not toxic. Herons for instance love frogs.
"So they play an important role in the whole balance of nature which would be upset without them - although to what extent we do not know yet."
The 26 year study between 1976 and 2002 showed the common midwife toad is now virtually extinct in the mountainous Penalara Natural Park where it was once thriving because of BD.
As amphibians are cold-blooded their body temperature is linked to the surrounding environment - meaning global warming could affect their bodies' ability to respond to disease.
The researchers whose findings are published in Proceedings of the Royal Society B also believe BD may be better able to thrive in warmer conditions with milder winters allowing it to survive and grow throughout the year.
They now want to assess whether changing climatic patterns are likely to impact on the rates of BD in frog populations across the rest of Europe.
Dr Fisher said: "This is a wake up call that we are losing biodiversity fast. Climate change appears to be changing patterns of disease and previously resistant species are becoming highly infected and even, in a number of cases, becoming extinct."
The new study follows on from the Global Amphibian Assessment survey published in Science earlier this year which revealed a third of the world's amphibian species are in danger of extinction - many of these as a consequence of infection by BD
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