DIET DECISIONS: RESOLVING THE OMNIVORE'S PARADOX

This section is 3min long, with soundtrack (see also "SILENT CLIPS" for extracts)
	Chapter size: 29 MB (.mpg) or 5.3 MB (.mov).
	Topics and Behaviours covered: digging, eating; omnivority, long delay learning, social transmision of information, poisonned partner effect (see commentary below)

Chapter commentary:
(numbers in bold refer to behaviours also shown in the silent clips)

A new day brings new challenges: the rats are faced with foods that they have never encountered before. A buffet quite different from the homogenised pellets that they have been raised on. Some foods are immediately tempting. Others a little puzzling. (1,2)

Rats are omnivores, and their willingness to test a wide range of foods has contributed to their success: new foods are the key to new situations and environments. But this leads to a problem: not everything that looks like food is edible and some are potentially lethal.

Rats show typically a conflict of motivation: keen to test new foodstuffs, but caution. This is the “omnivores” paradox, a dilemma that rats share with humans. Wild rats have evolved a range of solutions to the omnivores paradox - would lab rats still use them?

Being social is one such solution: by checking what other rats do, members of the colony can learn from each other. This Hooded rat has already discovered the rewards of blackberries. Very soon her breath and coat are impregnated with this new smell. Other rats are sensitive to this and follow this hooded pioneer. This white rat learns quickly that it may be worth trying even though he has yet to learn to find out that ripe blackberries are best.(3).

But how can it tell that a particular food might be bad? Like humans, rats have evolved the capacity to make a connection between the taste and smell of what they eat and how they feel later - sometimes hours later. The ability to learn despite this time delay was a surprise when it was discovered: how do you know what has hurt you if the pain occurs several hours later? Yet research has shown that natural selection has shaped their brains so that these important connections are made when food is concerned. This is an important part of the omnivore’s armoury, an ability that has also been found in humans.

And being social helps once again, as rats can learn from the experience of other individuals; a phenomenon called the “poisoned partner effect”: if a rat, smelling of a particular foodstuff is looking unwell, other individuals will avoid that food in the future.

(Eating is not the only problem. Avoiding being eaten is another danger that small creatures face, see next section)