Societal rank, by general definition, refers to social status depending on cultural standards and behavior. In a new study, findings suggest that there may also be a molecular basis of social status in the genes.
Dominance has multiple definitions in the animal kingdom. For example, the dominant male is easily identified as the largest in size or the most aggressive. On the other hand, nondominant males are less aggressive and have fewer or no chances to mate. In other social hierarchies, some non-dominant animals can become dominant when given the opportunity such as the death or injury of an alpha male.
Researchers from Stanford University, the University of Houston, and Lynbrook High School published their study in the journal Proceedings of the National Academy of Sciences. "Despite the links identified between social status, physiology, and behavior, the molecular basis of social status is not known," wrote the authors.
Genetically Engineered Fish
During the study, they analyzed the genetic structure of African cichlid fish Astatotilapia burtoni using the CRISPER-Cas9 gene-editing tool. They discovered two receptor genes that control social status.
Androgen receptor (AR) paralogs are duplicate genes that regulate hormones such as testosterone which are necessary for male sexual development. The two AR genes identified by the researchers are behind the aggressive and reproductive behaviors of dominant A. burtoni males.
In the laboratory, the team generated two groups of genetically engineered African cichlid fish. AR-alpha mutants had 50 deleted base pairs and AR-beta mutants had five deleted base pairs.
Experimenting with the AR-alpha and AR-beta genes guided the team in understanding how they affect male behavior. Results showed that each gene is responsible for specific social status aspects.
For example, only AR-beta "is required for testes growth and bright coloration." On the other hand, only AR-alpha is needed for reproductive and aggressive behavior. Together, the two receptor genes are required to attract females and ultimately, mating success as well as dominance over other males.
Genes Affecting Social Dominance
"Testosterone binds to androgen receptors to exert its effects," explained Professor Beau Alward from the University of Houston. Dominant animals, wrote the authors, tend to have higher levels of testosterone compared to nondominant species. How genetics affect social status "may be fundamental across species that rely on social information to optimally guide physiology and behavior."
Specific regulation of each AR paralog suggests that there are independent mechanisms in the brain, noted the team. "The fact that these are independent implies that this is how flexible social status could be regulated by similar independent mechanisms in other species, including humans," said Alward.
The findings also suggest that manipulating testosterone signaling could enhance the motivation of species to seek higher social status. However, this would be complex due to factors such as whole-genome sequences of multiple species have revealed that some vertebrates have two ARs while others have only one AR. Also, multiple receptors have also been observed to bind to the same steroid.
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