Lovelorn frogs take revenge

2004-09-16 12:16

Paris - Spanish zoologists have discovered that male frogs that are losers in love get their revenge by spreading their sperm over eggs that have been left by a pair of romancing amphibians.

The sneaky manoeuvre is dubbed "clutch piracy" by the researchers, who say it sheds intriguing light on the principle of mate selection among frogs and helps explain the creatures' wide genetic diversity.

Until now, the species in question - the common frog (Rana temporaria) - was believed to have a rather humdrum sex life.

The female chose a mate, who would then grasp her and, as she shed a spherical batch of eggs, shed his sperm over the clutch.

After a frantic froggy coupling, the couple would then separate, leaving the eggs to develop into tadpoles and then into frogs.

But observations made from the undergrowth surrounding a Pyrenean pond by University of Vigo frog-watcher David Vieities and colleagues show that, once the blissful pair are out of sight, a pirate often moves in, shedding his own sperm over the egg clutch.

"Clutch piracy" was seen in 84% of the clutches they observed.

The findings are interesting because they weaken the Darwinian idea of mate selection - that the female chooses a single male with the best genetic selection and mates only with him in order to reproduce.

In this case, the big winner is the pirate frog, who gets the chance of fertilising some eggs even though he lost out in the mating competition.

But the female, too, is also a beneficiary, because her eggs get a better chance of being fertilised, the researchers say.

The study is published on Thursday in Nature, the British weekly scientific journal.

- AFP