Frog spawn knows how death smells

Embryo frogs can associate smells with predators

source: New Scientist vol 2000 no 2685 December 6 2008 p16

Researchers at Saskachewan University, Canada, led by Maud Ferrari, have shown that embryo wood frogs can associate smells with predators. The researchers exposed frogspawn to the smell of newts, by bathing it in water that the newts had previously occupied. Half the spawn was also exposed to crushed tadpoles in an infusion. After the eggs had hatched into tadpoles, those tadpoles which had smelled crushed tadpole with newt, reacted to a new exposure to newt smells by freezing - a way of defending themselves against predators. Those reptiles which had only smelled newt, without crushed tadpole, when they were eggs, did not freeze. The team later discovered that tadpoles need to associate the smell of newt with danger before they hatch, and cannot later learn this association