Dining decisions: choosing a quality meal in a nice setting - even slime moulds do it

We all like a top quality meal in a nice setting, but new research by University of Sydney scientists, Dr Tanya Latty and Associate Professor Madeleine Beekman, has found that even simple slime moulds are able to make complex comparisons of food quality and risks in environment, deciding when the lure of a top quality meal overcomes a risky feeding environment.

Dining decisions: the single-celled slime mould, Physarum polycephalum, is able to make complex comparisons between two food options based on the quality difference of the food and riskiness of the feeding environment.

The research, published in the US journal Ecology, shows that the single-celled slime mould, Physarum polycephalum, is able to make complex comparisons between two food options based on the quality difference of the food and riskiness of the feeding environment.

Working in the Behaviour and Genetics of Social Insects Laboratory in the School of Biological Sciences at the University of Sydney, Dr Latty led the research on slime mould dining decisions.

"How individuals deal with multiple conflicting demands when they are choosing their food is an important aspect of foraging ecology in living things," explained Dr Latty.

"Yet the body of knowledge we have on foraging behaviour has pretty much ignored neurologically simple organisms, like the slime moulds," said Dr Latty.

"So we set out to see what level of comparison and decision making the slime moulds were capable of when we offered them two different food sources. Slime moulds don't have brains - they don't even have a nervous system. In fact, they are made up of just one big cell."

Exploring their environment by growing branches along a surface - in these experiments on agar, in their natural environment on leaf litter or fallen tree trunks - slime moulds are capable of migrating at a speed of up to five centimetres per hour.

To test dining decision making in the slime moulds, Dr Latty and Associate Professor Beekman offered each slime mould in the experiments two patches of food to choose from, with different qualities of food and different light exposure.

"Slime moulds don't like too much light - they turn and grow away from areas that are well lit. Light interferes with the slime mould's biology and also places them at risk of dehydration, so slime moulds are photophobic," explained Dr Latty.

"The slime moulds therefore viewed the food patches that were well lit as being 'risky' or not as appealing - they take mood lighting one step further than us and prefer to dine in the dark!"

"We wanted to see how complex their food decision making gets, so we presented different slime moulds with conflicting food options. So for example, some slime moulds were presented with a choice of two food patches where one was 'risky' by being well lit but offered good quality food, while the other was shaded but low quality food. Other slime moulds were offered the simpler choice of equally 'risky' food patches with differing food quality."

So what does good quality food mean for slime moulds? Dr Latty and Associate Professor Beekman made up four different concentrations of finely ground oatmeal and mixed it with agar for the slime moulds to grow across. A top quality meal was made up of 10% oatmeal, whereas the poorest quality meal was 1% oatmeal, with the other two options being 3% and 5% oatmeal.

"We tested the whole range of food quality difference combinations, to see at what point it became worth it for the slime moulds to risk themselves in the high light for better quality food," said Dr Latty.

"This method has been called 'behavioural titration', because it's a bit like the tipping point in a chemical reaction, where an organism will venture into risky territory because the food quality is just so much better in the risky environment.

"We found that when both food patches were shaded, 100% of our slime moulds made the decision to grow towards the better quality meal, even when the difference in quality was only small, such as the difference between the 1% and 3% oatmeal options. So that showed us they had no trouble discerning a better quality feed when offered the choice," said Dr Latty.

"Where it gets really interesting is that when they had to weigh up the light risk vs food quality value, the slime moulds chose to venture out into the light only when there was a big difference in food quality. When there wasn't much difference in the food quality, the slime moulds chose the lower quality, but safer food.

"It's amazing that a single celled organism like the slime mould Physarum polycephalum is able to weigh up such options and decide on the best food option. It shows they are capable of making really complicated foraging decisions," explained Dr Latty.

"We've shown that slime moulds are able to make very sophisticated trade-offs between danger and food. We humans are, of course, very capable of weighing up our options, but we can sometimes find the process hard - you wouldn't risk your life for $1, but you may consider weighing up the risks for $1 billion!

"The ability to weigh both risks and benefits is what makes the slime moulds behaviour 'smart'," said Dr Latty.

The results have implications for the field of foraging ecology, indicating that foraging theory should be applied to a much wider range of taxa, including those organisms without complex neural apparatus.

"Our work suggests that neurological complexity is not a prerequisite for complex foraging behaviour. So it turns out choosing a top quality meal in a nice setting is a no brainer - literally!"

Listen to a radio interview with Dr Tanya Latty on her research, broadcast on CBC's Quirks and Quarks in Canada at: www.cbc.ca/quirks/archives/09-10/qq-2010-03-06.html

Contact: Katynna Gill

Phone: 02 9351 6997

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