FROGS learn the scent of danger before they hatch, which may give tadpoles a head start in evading predators.
Animals learn that a smell or sound is a warning if it accompanies something dangerous. Maud Ferrari at the University of Saskatchewan in Saskatoon, Canada, and her team tested whether wood frog eggs could be primed to detect a predator鈥檚 scent.
The team bathed the eggs in water that had previously contained fire-bellied newts. Half the eggs were also given a whiff of danger, in the form of an infusion of crushed-up tadpoles, whose death is marked by chemical signals. After the eggs hatched, the researchers gave the tadpoles a second burst of newt odour. Tadpoles whose experience of newt had been accompanied by the odour of dead tadpoles froze in place 鈥� a classic defence against predators. Those that had not had this training continued swimming as normal (Proceedings of the Royal Society B, vol 275, p 2603).
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In a second study, Ferrari鈥檚 team showed that without encountering the 鈥渟mell of danger鈥� while frogspawn, frogs deem the newt odour as safe and are unable to associate it with danger thereafter (Biology Letters, ). The studies are the first to show that animals can learn the smell of a predator as embryos. The team has preliminary evidence that fish can do it too 鈥� suggesting the ability may be widespread.
