Author: Taylor Heuermann (undergraduate member of the lab), Dec. 2016
Something within the study of animal behavior that I find fascinating is the interplay between genetics and environment to create the expression of different behaviors. Although there is a significant collection of literature on how genes influence behavior, there are still many questions to be answered simply because the topic is so complex. A recent paper (Riyahi et al. 2016) provided insight into how the behavioral traits of Great Tits (Parus major) were influenced by their genetics, more specifically, by polymorphisms in the DRD4 gene. The paper outlines a lot of information and experimental design that could provide helpful information to me as I move towards conducting similar work in chickadees.
Riyahi et al. studied the personality differences, specifically differences in neophobia (fear/wariness toward novel objects), boldness, and exploratory behavior, of Great Tits that lived in urban, suburban, and rural areas in and near Barcelona City, Spain. The researchers defined personality as consistent individual differences in behavior related to exploration, caution, and neophobia. Because they knew from prior studies that personality is heritable in Great Tits, it is a good mechanism to study natural selection as it relates to their habitats of interest. A gene within Great Tits that is commonly associated with variation in personality is the SNP830 polymorphism of DRD4. Riyahi et al. focused on this region.
Riyahi et al. used two different tests to determine neophobia, boldness, and exploratory behavior in their Great Tits. To test neophobia and boldness, the researchers exposed birds to a novel object (a flashlight). They placed the flashlight in a bowl that had been the food delivery mechanism for 24 hours prior. Latency of the focal bird to approach the flashlight was the measure of neophobia and boldness. Riyahi et al. measured exploratory behavior by allowing the focal bird to enter an observational room attached to their holding cage; the researchers then counted all of the hops and flights occurring within the first 2 minutes of entry to the novel environment. Riyahi et al. assayed each bird individually for both boldness and exploratory behavior, using each individual only once. The researchers used DNA extractions and PCRs to determine and compare the genotypes of the birds after knowing their boldness and exploratory behavior.
The study revealed that urban birds were more explorative and bolder toward a novel object than forest birds, and exploration score was independent of the sex and age of the birds. Suburban birds showed intermediate exploratory behavior between city and forest birds, and heterozygotes for the gene of interest showed a higher exploration score than homozygotes. However, even though the genotype frequencies of SNP830 varied significantly between forest and urban birds, exploration score and latency to approach a novel object were not related to SNP830 polymorphisms.
Riyahi et al. developed several possible explanations for their findings. Urban habitats are now considered a selection pressure, and many different findings suggest that the novel selection pressures of the urban environment favor the decoupling of behavioral traits that commonly form behavioral syndromes in the wild. This decoupling could explain why, despite very apparent genetic difference, behavioral difference typically attributed to that gene might not be apparent. Behavior is also a very complex system pulled together by interactions between many different genes, so even extreme differences at one point in the genetic system may not be enough to visibly affect the phenotypic expression of behavior.
Even though the understanding of the genetic foundation of behavior is still incomplete, it is still relevant to note that phenotypic expression of behavior between urban and rural populations of Great Tits and many other animals are in many cases significantly different. It is therefore still very possible to locate where those differences come from genetically. Several studies involving different species have found that bolder and less neophobic conspecific individuals may be better competitors in urban habitats, meaning those individuals would be selected for and genetic divergence should start to occur.
This paper provided a lot of helpful insight into not only how to consider designing a similar study of my own using Black-capped or Carolina chickadees, but also gives a good reminder that it is going to take a lot of trial and error to find genes that may be in some part directly responsible for behavioral differences between individual conspecific chickadees. Even so, I will start by looking at different SNPs within the DRD4 gene of Black-capped or Carolina chickadees and comparing genetic differences I find with differences in behavior to see if they correlate, just as Riyahi did. Although I do find this topic intrinsically interesting on its own, I am excited to be able to better understand the genetics behind behavior in order to one day be able to apply it to human health. Chickadees are good model organisms to better understand the genes that may lead to Alzheimer’s, chronic depression, etc. in humans. Understanding further the workings of DRD4 in chickadees will improve basic knowledge of the gene and its homolog and serve as a foundation for further behavioral genetics research.
Riyahi, Sepand, Mats Björklund, Fernando Mateos-Gonzalez, and Juan Carlos Senar. 2016. Personality and urbanization: behavioural traits and DRD4 SNP830 polymorphisms in Great Tits in Barcelona City. Journal of Ethology. doi:10.1007/s10164-016-0496-2