DISSERTATION RESEARCH: The role of Maternal Hormones in Programming Offspring Aggression

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A mother's hormonal response to her current environment can cause permanent changes in her developing offspring, potentially determining whether those offspring live or die in their future environment. Females breeding in more competitive environments tend to transfer more testosterone to their offspring prenatally, which permanently makes offspring more aggressive. This maternal effect may help offspring adapt to competitive environments, yet it is still unclear how maternally derived testosterone permanently impacts offspring behavior. Without knowing how it happens, it is difficult to characterize the heritability of this maternal effect and how it fits into larger evolutionary frameworks. This research is among the first to test if molecular mechanisms, such as changes in gene expression and control, mediate the effects of maternal testosterone on offspring aggression using birds, in which this maternal effect is best studied. This research will take a novel approach by exploring differences in aggression-related genes from several brain pathways. The results of this research will help clarify what contributes to long-lasting variation in aggressive behaviors and why differences in animal behaviors exist. The researchers will also train undergraduate students in laboratory methods and bioinformatics. Additionally, this research has lent itself to a citizen science project with songbird breeders throughout the United States to explore factors influencing avian reproduction. Specifically, the researchers will experimentally determine if an epigenetic mechanism (i.e., DNA methylation) underlies the programming of offspring aggression by maternal hormones in songbirds. Birds are excellent models for maternal effects because their young develop externally in eggs and females allocate substantial amounts of testosterone to their egg yolks. The researchers will inject zebra finch eggs with a control vehicle or testosterone and measure aggressive and competitive behaviors (i.e., growth rate and begging rate) in the resulting offspring. In a subset of these offspring, the researchers will test for evidence of epigenetic programming. Aggressive behaviors are initiated across many interacting genes (i.e., steroid receptors, histamine, dopamine, somatostatin, arginine vasotocin, etc.). Thus, the researchers will use RNA-seq and methyl-seq analyses to explore genome-wide differences in mRNA expression and site-specific methylation patterns of aggression-related genes in two socially-relevant brain regions, the telencephalon and diencephalon. This research will greatly expand our knowledge of how different gene networks interact across brain regions to express aggression and will provide one of the first avian DNA methylomes. All data generated in this project will be archived in appropriate electronic repositories.