Being male doesn't usually generate a lot of respect or status in the insect world. At worst, a male preying mantis can have his head chomped off by his mate, and some male spiders are devoured by less than devoted females. At best, male insects are merely tolerated and thoroughly dominated by females.
But now a University of Washington researcher has discovered the first species among social insects, a wasp, where males rule the nest, biting and sometimes chasing off females, including their queens. They also consume much of the food gathered by workers.
Sean O'Donnell, the UW assistant professor of psychology who studied the wasps in the cloud forests of Costa Rica, believes more examples of male dominance among social insects will be found as researchers focus on the tropics where most species live. In the past, researchers, who primarily live in temperate zones, have studied social insects that live nearby and where male dominance doesn't exist.
"Among social insects males just haven't received much attention. We have had the bias that males are not important and, to some extent, we have ignored them," said O'Donnell, whose discovery will be published in the journal Ethology.
That probably is about to change following his study of the species Mischocyttarus mastigorphorus, which lives at about 1,450 meters elevation in the cloud forests of Costa Rica and neighboring countries. The wasp, which is about half an inch long, lives in small colonies of two to three dozen individuals in dark and dank conditions. It comes in two color types that mimic other wasp species living on the margins of its habitat, and males frequently make up half or more of a colony's population.
O'Donnell studied 32 colonies of M. mastigorphorus, surveying the number of males present in each and collected detailed behavioral data on six of the colonies, tracking all individuals.
Dominance behavior or aggressive social interactions occur at a high rate in many insect societies, according to O'Donnell. Up to now, this behavior was only known to be expressed by females, both by queens and workers, who usually perform most of the risky tasks and labor in insect colonies. Queens dominate workers and workers dominate each other. Males were at the bottom of the pecking order.
Among the Costa Rican wasps, however, O'Donnell noted that males chased and lunged at females, sometimes biting or chewing on them, as well as chasing them off the nest. The females did not respond in kind or responded submissively to the male dominance. Instead workers and queens crouched, became immobile or fled the nest. Males also did not forage for food nor perform much labor for colonies, but they did consume a high percentage of the food brought to the nests by the females.
Why are males the "top dogs" among this species? O'Donnell believes it's a mating strategy for colonies. Unlike temperate zone male wasps, which have short life spans and even shorter opportunities - several days to several weeks - to mate, M. mastigorphorus males are relatively long lived. In population surveys over many months he observed males to be present at least 10 months of the year. Individual males may have the potential to be able to mate for several months.
"My best guess is that the function of dominance directs the food flow to the males and allows them to stay on the nest. This may increase their longevity, permitting males to mate over a longer part of the year," said O'Donnell.
Scientists study social insects because they are so ecologically successful, being the most abundant social organism on the planet. Researchers look for clues about how social behavior evolved and is maintained, hoping to learn about patterns that may apply to humans.
For more information, contact O'Donnell at 206-543-2315 or sodonnel@u.washington.edu
Digital images of the wasp studied by O'Donnell are available and can be downloaded from http://www.washington.edu/newsroom/news/
Journal
Ethology