New evidence reveals that behavior may be predetermined by genetics. Generally, we consider behavior to be learned. By interacting with the world, different behaviors are reinforced or discouraged. A student who receives a high grade on a test will be more motivated to study and continue performing well. The reward of these habits creates a positive feedback loop. Studies suggest that our genes also influence our behaviors. Researchers in Germany studying the social behaviors of honeybee colonies found that DNA can predetermine certain behaviors. Understanding how these genes influence social interactions between bees may shed light on what drives some human behavior.
One way we acquire new behaviors is through observation. Social learning requires attention, retention, reproduction, and motivation. Attention must be focused on the behavior being observed, the memory of that behavior must be retained, and an individual must have the ability and motivation to replicate the behavior.
Genetics also plays a role in how we interact with each other. The oxytocin receptor gene (OXTR) and vasopressin receptor gene (AVPR1A) have been shown to mediate bonding behavior in various species, including humans. Variants in the oxytocin receptor gene, in fact, have been linked to autism spectrum disorder and depression. How an individual responds during a specific social experience, however, involves a complex interplay of genes and environmental factors. Having a gene attributed to a certain behavior does not guarantee that an individual will display it.
In bees, there is a clearer association between genes and social behavior. From gathering nectar to producing honey, each bee in the colony plays a role in supporting the hive. Alongside the queen bee, female worker bees comprise a majority of the colony. Young worker bees are generally those found inside the hive maintaining the honeycomb structure and attending to the queen. Older workers are relegated to tasks outside the hive, such as foraging for nectar, pollen, and water. The behavior of each bee must be coordinated within each colony to ensure that the hive survives. A new study by Sommer et. al provides evidence that these behaviors are genetically programmed into their development.
Bee colonies have a unique social structure split into three castes: the queen, workers, and drones. The all-male drone bees generally leave the hive to mate with queens in other colonies. Female bees, therefore, perform the vast majority of tasks in the hive. Only one female bee, however, is queen. The remaining are infertile worker bees. Whether a female becomes a queen and a worker bee is influenced by a gene called complementary sex determiner (Csd). This gene crucially regulates the feminizer (fem) gene, which mediates the female developmental pathway. Although every female bee produces feminizer proteins, diet early in life differentiates these two castes. Queen larvae are fed royal jelly, while worker larvae are given “bee bread”. Nutritional differences in these diets influence the expression of a gene further down in the female developmental pathway called doublesex (dsx). The doublesex gene is essential for differentiating a worker bee from the queen. This gene has been extensively studied in fruit flies for its role in determining sex, though it seems that it plays a greater role in bees. Recent evidence of doublesex proteins in the brains of worker bees suggests that this gene may also be involved in programming their behaviors.
The Doublesex Gene
The published study focused on identifying whether the doublesex gene is essential for coordinating bee behavior. Sommer began by investigating where doublesex proteins are expressed in the brains of worker bees. Attaching green fluorescent proteins to this gene allowed them to track its expression. What they found confirmed that the doublesex gene is highly expressed in the antennal lobe, known as the “smell hub” of a bee’s brain. Here, olfactory signals detected from their antennae are processed and identified. Bees rely on smell to perform many of their behaviors, including navigation, foraging for food, and defending against invaders. Investigators also found elevated doublesex expression in the worker bees’ ventral lateral lobe, which is the main area of the bee brain responsible for learning and memory. This region was also significantly larger in worker bees compared to queens and drones.
Next, technology enabled the team to mutate the doublesex gene and prevent its expression in select worker bees. Once in the hive, their behavior was monitored using a QR code attached to their backs. Video recordings from the hive were then analyzed by artificial intelligence, which tracked the behavior of individual bees. The computer-based algorithm calculated how often and much time each bee spent in areas containing food, the time they spent with the larvae, and their total distance traveled inside the hive.
Their observations confirmed that doublesex is critical for coordinating bee behavior. Worker bees that no longer expressed this gene stopped performing certain tasks as efficiently, even though their overall sensory and motor functions appeared to be intact. One of the key behaviors impaired was brood rearing. Normally, worker bees are responsible for tending to eggs produced by the queen bee. Brood rearing keeps these eggs at a constant temperature to enable larvae to develop into worker and drone bees. Investigators found that worker bees with the mutated doublesex gene nursed the larvae half as often compared to normal workers. For other behaviors, such as handling food and inspecting honeycombs, the mutated bees showed a 50% reduction in how often and how long these tasks were performed. Since these tasks require the cooperation of numerous bees, the reduced performance of a few workers likely had a substantial impact on the overall efficiency of the hive.
This study provides compelling evidence that some bee behaviors may be hardwired into their DNA, but what about humans? Humans have a gene similar to doublesex known as DMRT1 that plays a crucial role in sexual development. DMRT1 is primarily expressed in the testes where it facilitates the regulation of male sexual function. However, there is no evidence directly linking this gene to specific human behaviors. It is possible that DMRT1 may induce indirect influence not yet studied.
Understanding how genes like doublesex guide behavior in simpler organisms may offer valuable insights into the genetic underpinnings of social behavior across species, including humans. Future studies could offer new insights into why we act the way we do—whether we’re part of a bee colony or a human society.
