Toad tadpoles and the ‘Laurel and Hardy’ effect

Research at the University of Kent has revealed a remarkable phenomenon among tadpoles of the Mallorcan midwife toad, one of Europe’s most threatened species. The researchers, from the University’s Durrell Institute for Conservation and Ecology, (DICE) have discovered that the toad tadpoles can change shape when they smell snakes swimming nearby. Tadpoles found in pools where there are no snakes tend to be short and fat, whereas tadpoles in pools which attract snakes are long and thin.

Dr Richard Griffiths from DICE calls this the ‘Laurel and Hardy’ effect, and laboratory tests have shown that ‘Hardy’ tadpoles can become ‘Laurel’ tadpoles within a couple of weeks if they are treated with snake chemical cues. The long, streamlined tadpoles also have thicker tail muscles that enable them to swim faster and escape from snakes.

The Mallorcan midwife toad is under threat from snakes originally introduced by the Romans for religious purposes. The toad population is currently restricted to a few mountain gorges in the northern part of the island although toads from the DICE breeding colony are now being successfully reintroduced to Mallorca as part of the conservation programme.

Once the ‘Laurel and Hardy’ effect had been identified by team member Robin Moore, the researchers were anxious to discover whether the captive-bred toads have lost any of their natural ability to respond to snakes through several generations of captive breeding. However, work by Dr Femmie Kraaijeveld-Smit, using microsatellite DNA analyses to test for any inbreeding effects, established that the captive bred toads seem to have retained nearly as much genetic variability as their wild counterparts and so are able to respond to snakes in exactly the same way.

This research has contributed significantly to the overall recovery programme for the Mallorcan midwife toad being developed by a consortium of European partners.