To earn a Ph.D. in the United States, you have to complete multiple research projects that aim to answer different questions about a specific topic. Below are brief overviews of my different projects that aim to understand the genetic, physiological, ecological, and evolutionary origins of a color-behavior polymorphism in eastern mosquitofish (Gambusia holbrooki).
Aim 1: Does the frequency of melanism vary spatially and temporally? If so, what are the environmental sources of this variation?
Since the melanistic phenotype is rare in nature, the persistence of this color-behavior polymorphism implies that certain ecological conditions favor melanistic males over silver males. Alternatively, the polymorphism may be maintained by negative frequency-dependent selection across ecological conditions, meaning that melanism is only advantageous when it’s rare no matter what the environmental conditions are like. For this aim, I am examining a museum collection of eastern mosquitofish from a long-term study in the Everglades.
Aim 2: How does the development and expression of the color-behavior phenotype differ between silver and melanistic males?
Eastern mosquitofish populations differ in how they developmentally regulate the melanistic phenotype; expression of the melanistic phenotype can either be constitutively activated or temperature-sensitive and expressed only after exposure to cool water temperatures. I am breeding and raising silver and melanistic males from both populations. Currently, I am investigating how melanism and other traits (e.g. behavior) develop during a male mosquitofish’s lifetime. We are also examining how expression of those traits may be altered once the fish is an adult.
Aim 3: What are the genetic and physiological mechanisms of covariance between melanin expression and aggressive behavior in eastern mosquitofish?
The genetic and physiological mechanisms underlying the color-behavior covariance in eastern mosquitofish have yet to be identified. I have assembled a hypothetical network of genes and neuroendocrine modulators that may regulate both melanin and aggression. This network can be considered to consist of functional modules (i.e., multiple genes within a module interact together to produce a function in the body, such as melanism). Modules can overlap and share many genes or be connected to each other by only a few genes. Modules can also not overlap or connect at all. First, I am determining the identity of the melanism-aggression network’s genetic components. Then, I am analyzing gene expression levels to understand how the genes in the modules are interacting to produce the phenotypes. Once the gene network is defined, I will expand it to include small non-genetic molecules and other neuroendocrine modulators like hormones.