The primary objective of this project is to understand the genetic and neurobiological mechanisms that give rise to natural variation in behavior. The research will focus on difference in burrowing behavior between two closely related species of North American mice (genus Peromyscus): oldfield mice consistently excavate long, multi-tunnel burrows, while a sister species, the deer mouse, builds short burrows with a single tunnel. This species-specific difference in burrow structure is heritable, and genes potentially involved in regulating in burrow architecture have been identified. This study proposes to manipulate gene expression in each species to determine how genes act in the brain to create behavioral difference leading to different burrow structures. A QTL has been isolated containing eight genes, including a gene, muscarinic acetylcholine receptor M5 (Chrm5), that has been associated with burrowing, likely acting in the reward system in the brain through dopamine release. Thus, increased digging could be caused by increasing the reward for digging.
This study has three aims: 1. To characterize expression levels of 7 additional genes in the QTL using quantitative RT-PCR; 2. To chararacterize the tissue-specific distribution of Chrm5 in brains of both species and hybrids using staining techniques; and 3. To introduce oldfield mouse Chrm5 into deer mouse brain using viral-vector-mediated gene transfer and to assay behaviors in the resulting mice. It is hypothesized that increasing Chrm5 expression level in the deer mouse should increase burrowing behavior.
By studying the precise mechanisms that produce behavioral changes between species, it should be possible to learn how behavior evolves as well as gain a better understanding of how the brain works. The outcomes of this research will improve our overall understanding of behavioral diversity in animals, and will be used to create educational materials for the Harvard Museum of Natural History. Finally, since Chrm5 is also implicated in nicotine use, studies of this receptor could potentially be applied to the general study of addiction.
What genes underlie changes in behavior between species? How do genetic mutations act in the nervous system (or elsewhere) to alter behavior? These fundamental questions in animal behavior remain inadequately understood, in part because most ecologically relevant behaviors are intractable for study at the genetic and molecular levels, particularly in mammals. However, details on the molecular underpinnings of natural variation in behavior can lead to a better understanding of brain function, as well as the constraints and forces shaping the evolution of behavioral traits. We have addressed these questions by studying burrowing behavior in deer mice (genus Peromyscus). Sister species P. polionotus (oldfield mouse) and P. maniculatus (deer mouse) dig burrows of dramatically different size and structure, and these differences have a strong genetic component. Burrow construction is a complex behavior that involves multiple motor patterns, circadian rhythms, and reward pathways. Thus, burrowing in Peromyscus is an ideal system for understanding the genetic and neurobiological bases of behavior. Because the two species can be crossed, we were able to use genetic mapping methods to locate the genomic regions that lead to differences in burrow construction. Next, we analyzed brain tissue from the two species to identify significant differences in the expression levels of genes. Our results from both genetic mapping and gene expression analysis both point toward a particular candidate gene, the muscarinic acetylcholine receptor M5. This receptor is known to regulate dopamine release and motivated behavior in mammals. Thus, our results suggested that differences in motivation to burrow may be partly responsible for the natural differences in burrow shape in these two species of wild mice. Our work has implications both for the understanding behavioral variation in animals and for human behavioral disorders, such as addiction. Beyond our research findings, our work has advanced the understanding of science more broadly. First, numerous undergraduate and graduate students have received mentoring and training by participating in this project, including training in genetic analysis software, molecular biology methodology, experimental design, and professional presentation of results. Most of these students have gone on to pursue careers in STEM and medical fields. Furthermore, we have used our work on burrowing behavior to develop behavior genetics lessons for high school students in collaboration with educators at the Meridian Academy in Boston, and we have hosted numerous student groups at our lab to learn about burrowing and behavioral genetics. Finally, our work has been featured on media sites such as National Geographic, the New York Times, and Nature News.
