Current Research
My research program is focused on coevolutionary interactions, particularly host-parasite interactions. I'm interested in the effect spatial structure in biotic interactions.
In my current postdoctoral position, I develop mathematical models and computer simulations to understand the coevolution of hosts and symbionts. My goal is to gain a better understanding of how transmission strategies evolve and how different strategies may be favored by host-parasite interactions. In a broader context, having a thorough understanding of evolutionary forces may help us better understand the conditions for disease emergence and perhaps disease virulence evolution.
Dissertation Research
My dissertation research spanned both empirical and theoretical work in understanding the impact of spatial structure in biotic interactions.
Theoretical analysis of the evolution of migration or dispersal
The focus of my theory work was on the mechanisms by which abiotic and biotic interactions drive the evolution of dispersal or migration. I explored how the spatial variation in environmental quality as well as population density regulation modifies the immediate way that genetic structure drives the evolution of dispersal (Drown et al, in prep). I provided a mechanistic understanding of the way that genetic structure and variation in carrying capacity are correlated across space can reverse or magnify the effects of genetic structure alone. In a second model (Drown et al, in prep), I studied how host-parasite interactions drive the evolution of dispersal or migration. Antagonistic coevolutionary interactions have been used as an explanation of continual change in the context of the evolution of sex (i.e. the Red Queen Hypothesis). I developed mathematical theory that models a specific interaction between a host and parasite and described the forces that cause migration rate to evolve. I used a variety of techniques (individual based simulations, analytical solutions and approximations) to understand the model dynamics. I found that that the current conditions of local adaptation can determine the direction of evolutionary change. However when interactions have large fitness consequences for the host and parasite, then a pattern of escalation of migration rates can emerge. Many investigators have studied the role of relative migration rates among host and parasite in determining the outcome of a coevolutionary interaction. One major result that has some consensus (both from theory and empirical verification) is that the player with the largest migration rate should "win" in the interaction. Most often this has been expressed as the player will show local adaptation and the "loser" will be maladapted. The model that I have built can be used to understand these coevolutionary dynamics when migration itself evolves.
Empirical research using an aquatic invader as a natural experiment in range expansion
The final two chapters used a worldwide aquatic invasive snail, Potamopyrgus antipodarum (New Zealand Mud Snails), as a natural experiment in range expansion. We have seen a rapid spread from initial points of introduction in the Western United States. Montana State University has an excellent set of resources on the web detailing the spread across the Western United States.
I collected sequence data from over 1000 individuals to construct a detailed phylogeography across all of New Zealand. I described the worldwide distribution of P. antipodarum to address how differences among lineages may have affected the range and distribution across the globe. Clades that produced successful invasive populations globally were also widespread across the ancestral range showing that they may have general qualities that enable them to expand their ranges. (Drown and Dybdahl, in prep). Originally found in New Zealand, this freshwater snail has rapidly spread across western United States within the last 25 years. To determine the potential sources in New Zealand as well the patterns of range expansion across the western states, I conducted an extensive molecular analysis of diversity using sequence and microsatellite data (Dybdahl and Drown 2011). This research found that a single highly successful genotype has colonized nearly this entire region.
I also characterized the shape of phenotypic plasticity of fitness related traits by comparing invasive and ancestral range lineages. Invasive lineages were opportunistic specialists with increased fitness at higher salinities compared to ancestral range lineages. (Drown et al 2011)
Predissertation Research
Boston University
At Boston University I worked on several projects. My main focus was analyzing nearly 6000 larval fish from a reef on former US base at Johnston Atoll. My supervisors, Phil Lobel and Paul Barber, were interested in the physiological impacts on the marine fish of various contaminants (e.g. PCBs) present on the reef. Collections of larvae from a damsel fish (Abudefduf sordidus) from nests were made during two breeding seasons and I used newly developed microsatellite markers to infer parentage.
I also worked on two substantial side projects while at Boston University. In collaboration with Paul Barber and Elizabeth Jones, we made a comparison of selective mortality and genetic identity (Meekan et al 2007). In collaboration with Jason Philibotte and Paul Barber we conducted a study of the population structure of the reef fish Plectroglyphidodon imparipennis.
University of Utah
At the University of Utah my thesis project focused on the host specificity of feather feeding lice on their North American Dove hosts. North American Doves are host to two genera of feather feeding lice (Columbicola or “Wing lice” and Physconelloides or “Body lice”). Based on previous research they differed in their host specificity with body lice being more host specific (usually one host per species). I spent three years collecting preliminary data for my thesis project, getting real estimates of host specificity and abundance records of the different lice on the hosts of interest (Moyer et al 2002). The work was a combination of lab studies and field work. Most of the field work was conducted in Southern Texas (Weslaco) or in Southern Arizona (Tucson) where I spent my time mist netting doves and collecting lice. A major project that I worked on was comparing methods of quantifying lice on avian hosts (Clayton and Drown 2001) where I was able to use the ultimate tool in removing lice from deceased birds, a paint shaker!
I also worked with Kevin Johnson during my time at Utah. We started several projects in theoretical phylogenetics eventually working on a new method of cophylogenetic analysis (data based, rather than tree based) (Johnson et al 2001). It was during this time, that I became very interested in theoretical work and computer simulations. I also started to change the focus of my research interests to the population level (Johnson et al 2002).
Grinnell College
At Grinnell College I conducted a year long independent project on the molecular phylogenetics of North American oak galling Cynipid Wasps. For the project, I collected mtDNA sequence data from COI via manual sequencing (no fancy capillary machines then, just lots of hand poured acrylamide gels and radioactivity) and used this to infer the phylogenetic relationships of several genera within a family. I was also interested in testing the monophyly of these genera as they were being using in a ecological study of host specificity. This work was a collaborative project between Jackie Brown and Warren Abrahamson. This was an excellent experience for me as an undergrad. Through this project, I went to my first Evolution Society meeting and was able to attend several other meetings in the course of the year. I presented the final work at the 2nd International Symposium on the Biology of Gall-Inducing Arthropods in Hungary.