We've had a busy few weeks! We had an important paper published, and lots of people wanted to know about it. You can read about it in The Independent, The Times, and The Telegraph, and listen to our interview on BBC Radio 4 Inside Science.
Common frogs are commonly found in rural, urban & suburban gardens
This research hinged around a big citizen science dataset collected by the charity Froglife. Back in the early 1990s, when people were first noticing unusual looking dead frogs in the UK, many of those people got in touch with Froglife. A questionnaire was drawn up, so that the same information could be gathered from every person who rang in - details like how many frogs had died, what signs of disease there were, what other species were present in the pond, and garden management questions.
We looked at all the questionnaire data from 1992-2000 and divided the cases into ones which were consistent with Ranavirus infection, and ones which were not. We have a pretty reliable set of tried-and-tested criteria to make this distinction based only on the questionnaire data. We then looked for correlations in the data, trying to see if anything explained which ponds had Ranavirus, or why some had worse Ranavirus die-offs.
All sorts of things popped out of the data, some of which we understand better than others. The most interesting results were that the use of garden chemicals (herbicides and pesticides), and putting exotic fish like goldfish or koi in the pond, seem to lead to bigger die-offs. In a sense this is great news, because we now can do something about this problem simply through changing our own behaviour.
So, why would garden chemicals and exotic fish cause problems? There is good evidence that herbicides and pesticides suppress the immune systems of the frogs, so the frogs may simply be less able to cope with infections. These products are designed to kill, so we shouldn't be too surprised that they may be harmful to wildlife. Understanding the exotic fish result is a little harder - but there are two possible explanations. We know that goldfish and their relatives are susceptible to Ranavirus, and it might be that having more potential hosts for the pathogen simply means there is more pathogen around to infect the frogs (this is called an 'amplification effect'). The other possibility is that since fish predate small frogs, the frogs may be more stressed, and because of this their immune systems might not work so well.
Common frogs are commonly found in rural, urban & suburban gardens
This research hinged around a big citizen science dataset collected by the charity Froglife. Back in the early 1990s, when people were first noticing unusual looking dead frogs in the UK, many of those people got in touch with Froglife. A questionnaire was drawn up, so that the same information could be gathered from every person who rang in - details like how many frogs had died, what signs of disease there were, what other species were present in the pond, and garden management questions.
We looked at all the questionnaire data from 1992-2000 and divided the cases into ones which were consistent with Ranavirus infection, and ones which were not. We have a pretty reliable set of tried-and-tested criteria to make this distinction based only on the questionnaire data. We then looked for correlations in the data, trying to see if anything explained which ponds had Ranavirus, or why some had worse Ranavirus die-offs.
All sorts of things popped out of the data, some of which we understand better than others. The most interesting results were that the use of garden chemicals (herbicides and pesticides), and putting exotic fish like goldfish or koi in the pond, seem to lead to bigger die-offs. In a sense this is great news, because we now can do something about this problem simply through changing our own behaviour.
So, why would garden chemicals and exotic fish cause problems? There is good evidence that herbicides and pesticides suppress the immune systems of the frogs, so the frogs may simply be less able to cope with infections. These products are designed to kill, so we shouldn't be too surprised that they may be harmful to wildlife. Understanding the exotic fish result is a little harder - but there are two possible explanations. We know that goldfish and their relatives are susceptible to Ranavirus, and it might be that having more potential hosts for the pathogen simply means there is more pathogen around to infect the frogs (this is called an 'amplification effect'). The other possibility is that since fish predate small frogs, the frogs may be more stressed, and because of this their immune systems might not work so well.
Ornamental fish are commonly stocked in garden ponds - Photo by Roshan Nikam 'Japanese Garden at CSULB"
Although we won't understand the ins and out of these results for some years, garden owners can make some changes right away. The RHS has some good information on wildlife friendly ponds and once you have frogs around, you won't need pesticides anyway as the frogs will relish eating your slugs and snails! If you have pet goldfish, instead of releasing them into an outdoor pond, maybe you could get them a fancy apartment...