Understanding Social Behaviour
What is the biological foundation for sociality?
Understanding how genes and neural circuits control complex behaviors is one of the most challenging questions in neuroscience. Social behavior consists of interactions between individuals of the same species both competitively and cooperatively. A wide range of sociality occurs among animals. The evolution of social behavior at its most developed form is found in eusocial animals, including ants and termites, bees and wasps, and a few other organisms. Since many of these species lack powerful genetic techniques, the genetic basis of social behavior has remained enigmatic. Analyzing social behavior at the molecular level through the use of behavioral genetics will provide insight into how complex and highly derived patterns of social behavior evolved from simpler ancestral behavior. Moreover, it can explain the evolutionary relationships between apparently similar behaviors across distantly related taxa.
Insect societies are often described as the pinnacles of social evolution since the majority of eusocial animals are insects. Therefore understanding the molecular mechanisms of eusociality depends on developing simple models systems suitable for studies involving both genetics and neuroscience. The model organism, Drosophila melanogaster fits these criteria. Furthermore, the fruit fly is evolutionarily closer to eusocial insects than humans. Combining this fact with the strong Drosophila genetic tools will present the opportunity to understand and formulate the genetic and neural network controlling eusociality.
Although the evolution of eusociality has been intensively studied, the genetic and physiological changes involved in the evolution of eusociality are largely unknown. Many species do not live in societies, but they sometimes aggregate and exhibit behaviors such as mating and aggression, which is relevant to the study of sociality. These programme of behaviors, for both logistical and conceptual reasons could be utilized to the study of sociality since these behaviors has been readily studied in simple genetic model organisms, especially in Drosophila melanogaster through the powerful molecular techniques that are available. In addition, sociality probably evolved through modifying the molecular and neural mechanisms that are associated with the perception of environmental stimuli by solitary organisms. Therefore analyses of certain behaviors exhibited by solitary animals can enhance our understanding of social life.
Other researchers and myself identified that male Drosophila invest more time mating when they are exposed to potential rivals, so called ‘Longer-Mating-Duration (LMD)’. We successfully delineated the underlying physiological mechanisms, genetic components, and crucial neural circuits of LMD summarized below.
- Rival-indeuced prolonged mating (Longer-Mating-Duration: LMD)
- LMD requires only visual input, especially red eyes in motion, which is enough to induce LMD.
- Circadian clock genes period/timeless are involved but Clock/cycle are not. This indicates that clock genes can also modulate relatively short time sequences and the function of clock gene components can act differently on each behavioral phenotype such as circadian clock vs. learning and memory, habituation, sleep, drug sensitization, and mating duration.
- Among 150 clock neurons, only lateral neurons including LNd, l-LNv, and s-LNv are involved with LNd neurons.
- This indicates that specialized neurons exist which modulate specific behaviors.
- LMD also requires long-term memory persisting up to 12 hours. Ellipsoid body neurons and the genes rutabaga and amnesiac are involved in this process.
Recently, we discovered that sexually experienced males shorten their mating duration. This indicates that males respond to different social-contexts (not only potential rivals but also sex partners) and modulate their mating behavior. We named this behavior ‘Shorter-Mating-Duration (SMD)’. The manuscript explaining this newly identified behavior is ready for submission. Interestingly, SMD requires very different genetic components, physiological inputs, and neural circuitry as delineated below.
- Sexual satiety-mediated shortened mating
- SMD requires gustatory and mechano-sensory stimuli.
- Circadian clock genes Clock/cycle not period/timeless are required for SMD.
- SMD requires mushroom body not ellipsoid body neurons for memory.
In summary, we discovered an interesting behavioral phenotype that can be a useful model for studying social behavior in Drosophila melanogaster, and I identified genetic components and neural circuits regulating such behaviors. I believe that my work provides considerable mechanistic insights to a very interesting plastic social behavior of Drosophila melanogaster.
Useful Links and Articles
Establishing Behavioural Paradigms
The extreme altruism exhibited by eusocial insects was one of the most perplexing traits that Darwin encountered when developing his theory of natural selection.
Scientists describe the genetic changes associated with solitary-to-social transitions throughout bee evolution.
Spectacular progress in molecular biology, genome-sequencing projects and genomics makes this an appropriate time to attempt a comprehensive understanding of the molecular basis of social life. Promising results have already been obtained in identifying genes that influence animal social behaviour and genes that are implicated in social evolution. These findings — derived from an eclectic mix of species that show varying levels of sociality — provide the foundation for the integration of molecular biology, genomics, neuroscience, behavioural biology and evolutionary biology that is necessary for this endeavour.