Trumbo Studying Evolution of Social Behavior Among Insects
n the broadest sense, you might call Stephen Trumbo a behaviorist. But his science is biology and the society he studies is insects.
Trumbo, an assistant professor of ecology and evolutionary biology at the University's Waterbury campus, is a specialist on burying beetles - insects that provide parental care for their young that includes burying small dead animals to feed them.
Trumbo, who maintains a lab at the Waterbury campus to study the insects, is interested in studying how the beetles' social behavior evolved. There are some related beetles without social behavior. "We're trying to figure out which behaviors became adapted for social life," he says, "and what hormones control social behavior."
"There are many cases in which an insect group without social behavior gave rise to a group with social behavior," says Trumbo. "The burying beetles are one of the most accessible for study and therefore could become a model for how social behavior can evolve from behavior originally used in nonsocial contexts."
The burying beetles are found throughout much of the world, but not in Africa south of the Sahara or in Australia. There are seven species in Connecticut, mostly in woodlands, and one that is no longer found in the state.
Trumbo and Derek Sikes, a graduate student in ecology and evolutionary biology at the Storrs campus, have received grant support for their research from the National Science Foundation, the National Geographic Society and the UConn Research Foundation. The grants will allow Sikes to complete an evolutionary history of the group - determining which species are related to each other, which should suggest how social behavior developed in this group. As part of the research, Sikes traveled to Japan and to Nepal to collect burying beetles. The highlands of Asia have the greatest concentration of burying beetles but are some of the least studied areas.
The beetles are able to find through their sense of smell a small animal such as a mouse or bird that has recently died. They taste the animal, work themselves beneath it to "weigh" it, and work the ground to bury the animal after removing all its hair or feathers and shape it into a round ball of meat.
"They are very sensitive to decay odors of a dead animal," Trumbo says.
"c are helpful in cleaning up the environment," he said. "They cut down on the number of flies, because the carcass disappears underground by the next day."
He says the beetles seem to respond to the volume of the carcass.
"They match the number of their young with the size of the little carcass. They almost always lay too many eggs. The day the eggs hatch, the parents will kill larvae to match the number the carcass will support."
There are more burying beetles than carcasses, he says, so the insects compete for possession.
"The males and females may fight over a carcass until one male and one female work together on it.
"One group will find a carcass and start to bury it, and an intruder may come along and attempt to take away the carcass. If the intruder is not driven out, it will kill every larva on the carcass and then mate with the opposite sex and start over on the same carcass."
If a male finds something the size of a mouse, he will release pheromones - a chemical to attract other members of the same species - to attract a female, Trumbo says.
"If it's a larger carcass, the male will mate and then try to attract more females," he says. "That means the female will have to share, so she will try to prevent him from releasing more pheromones."
The result may be a domestic pushing match in which the female will try to knock the male from the tiny promontory he's chosen as a spot from which to do his calling.
Once the young are hatched, both male and female provide care. They regurgitate liquified carrion to the young, and if another beetle comes around they protect their larvae. At a certain point in the development of the young, the male will leave their care to the female, but if the female is removed, the male will stay with them until they mature.
Trumbo, who teaches undergraduate classes in introductory biology and biology for non-majors, first became interested in burying beetles when he was a graduate student at the University of North Carolina at Chapel Hill in the early 1980s.
He was particularly interested in parental care among animals and set out to study flying squirrels. Yet he was only able to trap one squirrel after a month of effort - a slow way to acquire a group large enough to study.
"Then I saw an article about burying beetles in Scientific American. I went out in the woods and put out a mouse carcass and sat down and waited. I caught one within 30 minutes and concluded that this would be a more accessible group to study."