Exploring mothers' nature

An insect whose unusual maternal behavior puzzles scientists has attracted the attention of acclaimed wildlife filmmaker Sir David Attenborough and brought his videographer to a College of Agriculture and Natural Resources laboratory this summer.

Kevin Flay, from the British Broadcasting Corp., came to campus to film lace bugs in the Townsend Hall lab of Douglas W. Tallamy, professor and chairperson of the College's Department of Entomology and Wildlife Ecology. The video may become part of Attenborough's next nature film, tentatively titled Life in the Undergrowth, which will feature a wealth of information about terrestrial arthropods with a focus on insects.

Tallamy has conducted extensive research on the lace bug, an insect that exhibits a rare behavior in the maternal care of its eggs. The mother lays a clutch of eggs and then guards them from predators, which is unusual among insects because it requires a great deal of time and certain defensive skills.

"It is an expensive behavior because when the mother is guarding those eggs, she is unable to make more eggs," Tallamy says. As a result, most female lace bugs that guard their young lay just one clutch, or sometimes two, in their lifetime.

To compensate, Tallamy says, the lace bug has developed a reproductive alternative called "egg dumping." Before she lays eggs, a female often will seek out another female that already is guarding eggs and leave her own clutch there.

"It is like taking the kids to the babysitter and never coming back to pick them up," Tallamy says.

At one point, scientists thought the practice was purely parasitic, he says, because it was believed that while it clearly benefited the dumper, there were no benefits to the mother-guard. Now, however, scientists believe there is no harm to the recipient and that there actually might be some benefits to her.

Tallamy says the mother-guard already is physiologically committed to guarding her own eggs, with hormonal changes making it impossible for her to produce more eggs for a certain period of time. In addition, there is evidence that the new eggs from a dumper's clutch provide a buffer that physically protects the guard's own eggs from hungry predators.

There is a chemical on the eggs that makes them attractive to dumpers, Tallamy says, and scientists are working to determine whether that chemical is created by the mother-guard herself to invite the dumping of additional eggs.

"The females guard the eggs, but they are not very good at it," he says. "They tend to lose about 80 percent of their young. So, if a good number of eggs are being dumped, the mother-guard can save more of her own eggs."

The lace bug is of interest because maternal care-giving is a very primitive trait, one that dates to the ancient jellyfish, Tallamy says. Over time, the vast majority of insects have developed mechanisms that allow the mother to lay her eggs and then get on with life without long days of maternal care.

"Few species exhibit maternal care," Tallamy says. "In the insect world, thousands do it, but millions don't do it."

Not only is the egg-guarding behavior unusual in itself among insects, but researchers also find the lace bugs' low rate of success noteworthy. "It is an unusual trait, and we are interested in finding out why, if lace bugs are so ill-equipped to guard eggs, they bother," Tallamy says.

This latest BBC interest is not the first time Attenborough has filmed Tallamy's research, which previously was included in his 1990 film, The Trials of Life.

Attenborough, whose career in British broadcasting spans more than 50 years and who was knighted in 1985, has traveled the globe as narrator of such BBC series as Zoo Quest and Wildlife on One. More recently, he has made the films Life in the Freezer and The State of the Planet, which aired in 2000.

--Neil Thomas, AS '76