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Earwig Mothers Spoil Their Healthiest Offspring

May 13, 2009

A recent study has shown that earwig mothers are able to detect odors from the unhealthiest “nymphs” of their brood and accordingly adjust their behavior to ensure that the fittest young receive more attention than their siblings.

Though frequent amongst many higher classes of animals, this study was the first of its kind to demonstrate such behavior in insects.

For earwig parents, it seems that the name of the game is favoritism.  When the mother detects chemical signals released from her hungry, unhealthy young, she begins investing less time and effort in feeding and tending to them.

Scientists associated with the project say they were actually looking for the opposite response, expecting that the mother would tend to dote on the weaker nymphs to nurture them into good health and ensure their survival.

But the in logic of evolution, the survival of good genes means everything, and the researchers now suspect that the mothers are instead looking “for signs of quality instead of need.”

“These insects have a clutch of 30-60 offspring, and there is lots of mortality, so there is no point in investing (resources) in offspring that are already in bad shape,” explained Flore Mas, lead researcher of the project at the Zoological Institute at the University of Basel, Switzerland.

Though communicating information through chemical signals has long been understood as a critical tool in colonies of social insects, the results of the study, published in Proceedings of the Royal Society B, are the first to demonstrate that this ability is also employed in the rearing of young.

The research team explained that “begging signals” are a common tool of youngsters in the animal kingdom and are commonly used to indicate to parents the need to be fed.

“So we expected to see the opposite of what we found here,” said Mas.

The experiment was conducted by exposing earwig mothers to the chemical odors from well-fed and under-fed youngsters and then comparing their reactions.

“We made a chemical extraction using the nymphs,” Mas explained.  “They were divided into two groups ““ one group was given lots of food and one very little food.”

Both groups of young were then killed and a hydrocarbon solvent was used to extract their chemical aromas.  Researchers then exposed the earwig mothers to the two solutions.

“They were presented with the chemical extracts, or to a control solvent, for 30 minutes, and were then allowed to forage in a dish of food for an hour before being returned to their nests,” explained Mas.

As earwigs feed their young by regurgitation, the researchers were able to dye their food with green food coloring and see the food in the digestive tracts of the transparent nymphs.  By weighing the dish before and after the mother’s food-collection trips, they were also able to determine how much effort she was investing in collecting food for the young.

In the 1960′s, the biochemist Gary Blomquist, began pioneering investigations into the role of hydrocarbons in insect communication and was able to identify how chemical signals were used is such phenomenon as gender recognition, dominance and fertility.

“It does not surprise me that an additional function, that of offspring quality affecting maternal care, has been determined for hydrocarbons,” Blomquist told a BBC reporter.

Professor Blomquist admitted, however, that when he began his work in the field of hydrocarbon research, he never could have imagined the vast variety of functions that these chemicals play in insect communication.

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