Frogs are in trouble, and some herpetologists fear a huge extinction event may be only months away, says Germaine Greer
Happiness is frog-shaped. I was clomping miserably round my tiny wood, anxiously scanning my ash trees, trying not to grieve for the broken branches that littered the ground, gazing glumly at a pond that seemed utterly dead, when my eye caught a sign of something different at the far end. I tramped across the violets to take a look and found the last thing I expected — frogspawn. As I shifted some of the debris on the pond bank, a young frog sprang away from me into the murky water. My misery dissolved and my tired heart leapt up. My frogs are still in with a chance. The cold snap might have killed the developing embryos; I won’t know for a week or two whether the spawn will hatch. I can only hope that the jelly provided good insulation and that the eggs simply stalled in their development until conditions improved.
Time was when every trip to the wood would turn up dozens of common frogs (Rana temporaria) of all sizes, in a surprising variety of colours; but those days are long gone. Frog and toad spawn used to appear in my ponds in February, but for years there has been none. I hoped it was because we had too many newts, but it was a faint hope. Frogs are in trouble all over our adorable planet, and some herpetologists fear that a huge extinction event may be only months away. However, frogs are cryptic creatures that will retreat into habitats where they can escape detection by even the most dedicated researchers; take the pressure off by restoring habitat and keeping humans and their marauding activities well away and a frog species long despaired of may turn up again. Having said that, of 6,800 amphibian species on Earth nearly a third are either already extinct or on the brink of extinction.
Why should it matter if a bunch of slippery jumping things goes extinct? For one thing, frogs are an infallible indicator of the health of an ecosystem; for another they are astonishingly wonderful. Even as metamorphs no bigger than your littlest fingernail, they are fully equipped with lightning reflexes, with amazingly prehensile tongues that can pluck their prey from the air, 360-degree vision, legs that propel them many times their own length, hearts that beat, lungs that more or less breathe and a digestive system that can handle almost anything. If the creature they have swallowed turns out to disagree with them they can cough up their stomach (turned inside out), brush off the offending foodstuff and push it back in again. They have hands and feet, not paws. Some regularly shed their skin and eat it.
Baby frogs are at the bottom of the food chain; only a small percentage will ever make it to adulthood. Even as adults they are prey to a vast range of creatures, from reptiles to birds — and other frogs. This too makes them important; if they go extinct their predators will eventually follow. In 1995 for the first time mass deaths of common frogs in Britain were found to have been caused by redleg, a ranavirus probably carried by American bullfrogs (R catesbeiana or, some say, Lithobates catesbeiana) imported for the pet trade. The sale of American bullfrogs is now banned.
I shall watch the spawn with more dedication because, having appeared so late, it may be that of the pool frog, Pelophylax lessonae. The species was only identified in 1973 and there was a good deal of disagreement as to whether or not it was truly native. It was eventually concluded that the pool frog had been for millennia an inhabitant of the Breckland in East Anglia, but by 1995 it was presumed extinct. When the last known native pool frog — absurdly dubbed “Lucky” — died in captivity in 1999, it seemed that there was nothing to be done. Then it was found that the British amphibian was genetically identical with the northern clade of pool frog found in Sweden and Norway. On August 12, 2005, after they had been carefully screened and given a clean bill of health, Swedish animals were introduced to a secret area in Norfolk, where they are now said to be established and breeding successfully. So runs the official version of the current status of the second of Britain’s native frog species.
There is another version. In 2002 James Cranfield, then herpetofauna reporter for the Essex Field Club, recorded the existence of colonies of pool frogs in Basildon and Witham. He assumed then that they were introductions, but it could be that the British pool frog had never died out at all, but simply abandoned the Breckland when the Scotch pines took over.
Further research into the genetics of the various populations of pool frog, these days to be found in Hampshire and Surrey as well as in Norfolk and Essex, would be needed to decide the issue.
Besides the Scandinavian pool frogs, we may have pool frogs from elsewhere in Europe, plus the marsh frog (P ridibundus) and its hybrid relative the edible frog (P kl esculentus), both considered to be introductions.
Frog taxonomy has always been a problem area however, and species are going extinct faster than herpetologists can sort out their phylogeny. As global warming continues we should perhaps expect that migrant European species will move into the space vacated by our two endemic species as they retreat further north.
My suspicion that what has colonised my pond might be the pool frog is strengthened because the last time we saw tadpoles there it was at the end of summer, and I couldn’t work out why they were still around. Pool frogs breed so much later than common frogs that they can even overwinter as tadpoles. I won’t know which frogs have spawned in the pond this year until the metamorphs have got big enough to be recognisable. The common frog has a pointed snout, the pool frog’s is rounder; the common frog has a dark brown patch behind its eyes, the pool frog a wobbly dorsal stripe — and spots rather than bars on its hind limbs. The male pool frog has a vocal sac each side of its mouth, and emits a louder call than the common frog can.
Not that it matters which species mine turn out to be, just as long as I have frogs.
The Daily Telegraph
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