A childhood of violence can make humans and other animals violent later on. Now scientists unexpectedly find the same holds true for even the simple honeybee. Unlike people, however, greater aggression in honeybees was not associated with later health problems.
Study lead author Clare Rittschof, an integrative biologist at Penn State University, and her colleagues investigated the honeybee, which is known to perform coordinated acts of aggression when, for example, defending a hive. Honeybees and humans share aspects of their molecular responses to social aggression — for instance, both experience brain activity involving NF kappa B, a protein complex involved in cellular responses to stress — so research into the honey could provide earl clues as to the social roots of human aggression, says Rittschof, who’s also affiliated with the University of Illinois at Urbana-Champaign where she conducted some of the work. The scientists detailed their findings online October 23 in the journal Scientific Reports.
Researchers fostered juvenile honeybees in either high- or low-aggression colonies. They gauged colony aggression by first exposing colony entrances to pieces of paper covered in isopentyl acetate. The compound has the odor of banana and pear – it also happens to be one of the primary compounds found in a honey bee alarm pheromone that alerts honeybees to potential hive threats; previous research found that more aggressive colonies show a greater response to it. After exposure, the researchers then counted how many bees came out of the hive.
To see how aggressive these fostered honeybees were as eight-day-old adults, the researchers exposed individual bees to ones from other colonies, whose foreign scent naturally triggered aggressive responses. Honeybees raised in high-aggression colonies were 10 to 15 percent more aggressive than ones raised in low-aggression colonies based on behaviors such as biting and stinging attempts.
“I was surprised that we were able to discern an effect of early-life environment on aggression,” Rittschof said. “We were so surprised with the behavioral findings that we repeated the experiment two more times before we were convinced the effect was real.”
Behavioral ecologist James Nieh at the University of California, San Diego, who did not take part in this research, also found the results unexpected. “I would have thought aggression levels were more genetically programmed than they were subject to environmental changes,” he says.
But the results provided a further twist. In some animals, exposure to social aggression at an early age is often accompanied by health problems. In humans, for example, there’s an increased susceptibility to heart disease and other chronic diseases of aging. By some measures, this is not the case in the honeybees — those raised in high-aggression colonies were more tolerant of the pesticide acetamiprid and less susceptible to parasitic mites. “Aggression appears to be an indicator of resilience in general,” Rittschof says. This is the first time aggression has been linked to such resilience in bees.
“These findings might help explain why aggression seems to be such a dominant feature of Africanized honeybees,” says Nieh, referring to the invasive bees known for their belligerent behavior.
The researchers suggest that early social experiences may be crucial to the health of the ecologically threatened honeybee. “To improve honeybee health efficiently, it may be worthwhile to target potential problems at the larval stage, since environmental inputs at this stage appear to be long-lasting,” Rittschof says.
Rittschof would now like to see what features make bees reared in more aggressive colonies more resilient. She also wants to determine what specific aspects of aggression have an effect on larval bees, and why social effects during early life are so persistent. Rittschof wonders, for example, whether the early-life social environment affects brain development, or perhaps causes epigenetic changes that influence gene expression.