Population Genomics of Range Expansions
The distribution of animals on the planet is always shifting, now with climate change more than ever. But we don't know what these changes do to the genetics of those species. My dissertation research focused on what happens to a species' genome during a geographic range expansion. Currently, I’m working on the issue of distributional shifts more broadly in a project focused on Arctic Fish species through the Fulbright Arctic Initiative Scholar program.
When a species invades or colonizes a new area, a number of forces are at work to alter the genetics of that species. These forces include natural selection and genetic drift, which when really strong is called allele surfing. These are the same forces that have shaped the diversity of life on earth since the first life forms arose. I'm searching for evidence of these forces in the genomes of two marine invasive species: the lionfish Pterois volitans and the Asian shrimp Palaemon macrodactylus.
Many people are familiar with the concept of natural selection: some individuals in a species will do better evolutionarily (have more offspring and therefore contribute more to the next generation) because of certain characteristics or traits. In the case of a species invasion, it's possible that selection acts to make an invader more successful in its new range either by selecting for individuals well-adapted to the local environmental pressures, or individuals that are better at eating the local cuisine. Additionally, selection might act on traits that make the species better at invading.
Fewer people are familiar with the concept of genetic drift. Genetic drift refers to a number of random processes by which the genetics of a species changes due to chance. Genetic drift depends on the number of individuals in a population and the way that population might change over time. Specifically, small "founder populations" that are involved in the expansion--small groups of individuals that disperse to a new location beyond the previous range boundary and reproduce there to create a new population--experience high levels of genetic drift because only a small subset of genes from the total population will be present in that new founder population. When this happens over and over again, it can lead to allele surfing, which is a process by which a single version of a gene (an allele) can become very common at the edges of an invasion because of repeated founder events.