General Neuroscience

The Brain of a Honeybee

Vilena Lee


Abstract

Honeybees differentiate themselves from other insects due to their ability to practice advanced cognition. Scientists have determined this by studying  honeybees’ process of “foraging”. Worker bees are able to communicate to other bees in the hive the distance and angle at which a food source is found. By being able to communicate the location of the food source, honeybees have proven to have advanced memory skills relative to other insects. Honeybees, unlike humans, do not have a hippocampus or a prefrontal cortex, so scientists believe that honeybees exhibit these higher cognitive functions through their Mushroom Bodies, which are bilateral anatomical structures that are packed with neurons.

 

General Overview

     Honeybees, unlike other insects, are known for their high intellect and advanced cognitive ability. Honeybees have approximately 1 million neurons despite having a brain the size of a sesame seed [1]. This allows their brain to have a greater density relative to other insects and their nervous system to be complex for such a small size.  It is because of this that scientists have begun to use honeybees to conduct research on the brain. Bees have demonstrated strong cognitive ability with advanced learning and memory skills. “Foraging,” which is the process when bees exit the hive to gather nectar, is a distinct trait of honeybees, where worker bees that are older than 21 days are sent out to collect food for the hive [2]. There are two types of worker bees who forage for the hive: scout bees, and reticent bees. Scout bees go outside the hive and search for the best food source. When they return to the hive, it is critical that scout bees communicate to reticent bees information on the food source through a dance.

 

Communication Through Dance

     After a scout bee evenly distributes nectar into honeycombs, she will acquire an audience [3]. With the attention of the audience, she will do one of two dances: either a round dance or a waggle dance. The dance that she decides to do will tell the bees the quality and quantity of the food source. If it’s a strong, rich food source, all of the foraging bees will dance with great enthusiasm each time they return to the hive. On the contrary, if the food source is weak, the dance will not be as vigorous.

     A round dance is used for food sources that are fewer than 100 meters from the hive. The scout bee will distribute her newly acquired nectar to other bees in the hive and will then begin to “run” in small circles. She will switch directions every few minutes, and the dance will be repeated no more than 3 times. A waggle dance is for a more distant food source. Because the food source is farther away, it is more likely than not that the food source is stronger than a round dance food source. The “waggle” comes from the fact that the worker bee will dance in a figure-eight or sickle shaped pattern. The waggle dance tells the bees about the direction and energy required to reach the food source. The distance is given by how long it takes the bee to complete one “circuit” in 15 seconds. For example, if a bee completes 8-9 circuits in 15 seconds, the food source is approximately 200 meters away. However, if a bee completes 2 circuits in 15 seconds, it is estimated that the food source is about 2000 meters away. Direction is given to the hive by the direction of the dancer as she does her “waggle” dance. If the worker bee completes her “waggle” while upwardly facing the audience, then the hive can assume that the food source is facing towards the direction of the sun. On the other hand, if a worker bee does a “waggle”, and she completes the dance at 70 degrees upward to the left of the audience, then the hive will assume that the food source is 70 degrees to the left of the sun.

 

The Honeybee Brain

     Honeybees are able to learn and make complex decisions that will benefit their hive. According to research completed by Dr. Karl Von Frisch, it was disproven that honeybees are “hardwired” to be able to calculate distances and communicate the information to the hive. Individual bees are unable to program themselves to memorize locations, flower quality, and hive sites; they only live for 7 weeks during the summer time [4]. Rather, honeybees are able to complete such monumental tasks through their advanced observational learning. Honeybees are able to learn taste, smell, and touch information through the process of foraging. With this information, bees are able to generalize sites for food sources beyond simpler categories [5]. This ability for bees to learn and adapt through what they’ve seen and encountered have caused scientists to hypothesize that bees are able to adjust to their environment through neuroplasticity just like humans [6]. Scientists have attempted to classify bees in behaviorist terms; however, bees are too complex to define as a classical term, since they have the anatomical structure of insects, yet the cognitive ability of mammals.

     Bees are also able to take time of day, location, and several different sensory stimuli into account when deciding to forage. This has allowed scientists to also hypothesize that bees are able to show integrated memory. Bees have demonstrated short-term memory (lasting a couple of days) as well as long-term memory (lasting their whole lifespan). In humans, the prefrontal cortex is the place for higher order cognition and reasoning ability. Bees, and insects as a whole, do not have anything that resemble a prefrontal cortex. Bees do, however, use epigenetic methods for memory [7]. For long-term memory, bees are believed to use DNA methylation.

      DNA methylation is a molecular mechanism used to regulate memory specificity through the experiences and environments that an organism has accumulated over their lifetime [8]. These mutations occur in DNA and not within the DNA sequence. It is also possible for the mutations to be inherited. There is a hypothesis that DNA methylation correlates to the storage of memories through activating the transcription of genes that encode for proteins whose function is to regulate memory [9]. DNA methylation is believed to be a key mechanism for governing synaptic plasticity as well as long term storage in cortical regions of the brain [10]. This has led scientists to hypothesize that epigenetic regulation in cortical brain sites are able to be directed by memory-based plasticity within the hippocampus. Unfortunately, bees have nothing within their nervous system resembling a hippocampus either.

 

Mushroom Bodies

     Mushroom Bodies (MBs) are an anatomical structure containing densely packed neurons [11]. MBs are comparable to the cortex and hippocampus of humans because these structures are what give honeybees their advanced cognition. They are found in the anterior regions of insect brains, most notably with flies and honeybees [12]. MBs are a center of associative learning and behavior (e.g. olfactory learning, habituation, temperature regulation, and sleep). MBs are constructed through major intrinsic neurons called Kenyon cells as well as 50 other types of extrinsic and intrinsic cells. Kenyon cells are critical for receiving olfactory projection neurons and other critical sensory inputs. Honeybees have a much larger and complex MB system than other insects or other bees for that matter. French biologist Felix Dujardin was credited with accumulating a large body of evidence that demonstrated the idea of MBs being a multisensory brain region critical for the formation, storage, and retrieval of associative memories [13].

 

     Signs of neuroplasticity have been demonstrated within the MBs of honeybees. The mushroom body is believed to act as a combination of the human hippocampus and sensory cortex. This advanced neurological integration of signals develops into memories over time, increasing the honeybee’s ability to navigate in different situations. The MBs of honeybees have been proven to exhibit structural plasticity during adult behavioral development. However, neurogenesis is a rare occurrence in honeybees of all ages. Therefore, scientists believe that while honeybees are able to rewire their existing neurons to allow them to adapt to learning and memory, they are not, or typically not, capable of birthing and proliferating new neurons [14]. Because honeybees are able to adapt their currently existing neurons as a response to stimuli, yet are not able to generate new neurons, scientists prefer to claim that honeybees exhibit synaptic plasticity rather than neuroplasticity.


References


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Vilena Lee

Vilena Lee


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