When it comes to architectural accomplishments, humans like to think they stand at the top of the pyramid. That’s to underestimate the astonishing achievements of social insects: termites build skyscraper nests and bees create mesmerizing geometric combs. The true master builders of the insect world, however, are the hundreds of species of stingless bees found in the tropics and subtropics, weaving combs of unrivaled variety and complexity inside hollow tree trunks or other cavities.
Now a group of evolutionary biologists led by Viviana Di Pietro at KU Leuven in Belgium reports that, like humans, these small-brained creatures are able to build according to a variety of architectural traditions, which are then passed down through generations.
The discovery, published in Current Biology, is the clearest demonstration yet of spontaneous cultural differences in insects. Insect culture was once thought to be impossible, says Andrew Whiten, a behavioural biologist at the University of St Andrews who was not involved in the research. “Less than a century ago, culture was thought to be uniquely human.”
To collect their data, Ms. Di Pietro and her colleagues observed more than 400 colonies of the stingless bee species Scaptotrigon depilis at a large apiary center in Brazil over two extended periods in 2022 and 2023. About 95% of the colonies showed combs built in horizontal layers, like a layered wedding cake, while the remainder adopted a spiral structure. In each case the tradition was maintained for several generations of worker bees.
Since S. depilis shows a strong preference for the horizontal-layer comb structure, it is surprising that the spiral comb occurs at all. Capturing the insects’ behaviour on video, the team established that there was no difference in the average cell-building rate between the two styles, and therefore no efficiency advantage to either.
To rule out genetic explanations for the different styles, the researchers transplanted workers from colonies built in one tradition to colonies built in another, first emptying the host structures of their indigenous adults. The imported workers soon adopted the local style, which was then maintained by the colony’s own larvae as they eventually matured into workers.
Tom Wenselaars, who runs the lab in which Ms. Di Pietro is a doctoral student, hypothesized that bees might change styles as a way to deal with building up small construction errors made by their predecessors. Such a process, in which multiple organisms indirectly influence each other’s behavior through the marks they leave on their environment, is known as stigmargy. To test whether stigmargy was indeed responsible for stylistic division among bee colonies, the researchers looked for a signal of helicity in otherwise perfect horizontal-layer combs, and found that it did indeed drive the bees to build spirals. This is strong evidence in favor of Dr. Wenselaars’ hypothesis.
These results have astonished observers of animal culture, because they suggest that stingless bees can transmit distinct building traditions across generations, without any individual needing to be instructed by its peers. This is a more expansive way of thinking about culture, which is often rigidly defined as behavior transmitted directly from individual to individual until it becomes a characteristic of a group.
According to Dr. Whiten, the new discovery suggests that more complex animal behaviors – for example dam building by beavers or nest building by chimpanzees – may also have arisen through such indirect transmission. Although scientists say it is too early to know for sure, it is possible that some human traditions may also have their roots in stigma.
Bees can’t afford to defy expectations. In recent lab experiments with bumblebees, behavioral ecologist Lars Chittka of Queen Mary University of London found that they are capable of learning cumulatively—that is, adopting and expanding upon the innovations of previous generations. The team trained “demonstrator bees” to open a complex two-step puzzle box (which requires removing blue and red tabs to reveal a sucrose solution), and then watched other insects learn the correct technique from the demonstrators. Such cumulative culture, which requires social learning, was previously thought to be unique to humans. The time for bumblebees to take a place at the top of that pyramid has long passed.
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Published: July 03, 2024, 05:09 PM IST
