Unhealthy diets make cockroaches fat

Cockroaches get fat and unhealthy if they have an unbalanced diet while they are young. The effects of unbalanced nutrition cannot be compensated for later in life and lead to less reproductive success and shorter life as adults.

While most people try desperately to get rid of cockroaches, Dr Patricia Moore, from the University of Exeter, has been studying the bugs for the past decade.

'It's important to have biodiversity in the lab as well as in the wild,' Moore says. 'Cockroaches are unusual lab animals, but they are very different from white mice and zebra fish and we can learn different things from their development and behaviour.'

As part of her long-term project, Moore looked at how female cockroaches change their mating behaviour. 'We already knew that what they eat as adults influences reproductive decisions,' Moore says. But what about the effects of diet early in life?

To find out, Moore and colleagues from Exeter picked young female cockroach nymphs and divided them into two dietary groups. Half were fed on a good-quality balanced diet of protein-rich fish food and high-carbohydrate oatmeal, while the rest was raised on fish food only. Both groups were allowed to eat as much as they wanted. The difference in diets 'was not quantity but variety,' explains Moore.

After the last moult, when the nymphs became adults, the team switched the diets of some animals. Half of the cockroaches raised with good quality diet lost their oatmeal, while half of the bugs fed on poor standards were promoted to a good-quality diet. Eighteen days after the switch, the diet control ended and some of the surviving cockroaches were dissected. The rest were allowed to live on and reproduce.

Cockroaches get fat with unhealthy diets

The results show that the type of diet has a strong effect on cockroach development and body mass. Overall life span did not change much between groups, but cockroaches fed on poor-quality diets as nymphs took longer to mature and spent less of their lives as adults. They were also fatter than nymphs raised with good-quality diets.

Moore suggests that the cockroaches fed on poor diets meals delayed their growth and stored excess fat as an insurance against further decreases in food quality. 'This was a surprising result,' says Moore, 'but it shows the importance of a balanced diet for healthy development.'

The effects of unbalanced meals continued throughout the cockroaches' lives, even for the few that were switched to good-quality food. Females that ate a poor-quality diet were less willing to mate and less likely to produce offspring. They were also more picky and spent more time considering possible mates, write the authors on the report published today in the Proceedings of the Royal Society B.

Perhaps if the cockroaches 'are not particularly healthy, they might be waiting for better conditions to mate,' Moore suggests. But regardless of the reasons behind their behavioural change, this paper shows that 'poor diets [during early life] have an effect on the way cockroaches respond to their environment and cannot be reset later on,' she adds.

Source: Planet Earth Online