Current Research
Epigenetic Mechanisms Underlying Environmentally-Induced Developmental Plasticity
Among natural populations, the ability for a single genotype to produce multiple phenotypes in response to environmental variation (phenotypic plasticity) is widespread. While there has been a great deal of work outlining the proximate causes and consequences of phenotypic plasticity, the mechanistic link between ecological inputs and organismal phenotypes remains largely unknown. To better understand how, at the molecular level, the environment influences downstream phenotype, I am focusing on patterns of DNA methylation (an environmentally-sensitive gene regulatory mechanism) in Spea multiplicata (the New Mexico spadefoot toad) in collaboration with David Pfennig at UNC Chapel Hill and Jenny Tung at Duke University. S. multiplicata tadpoles exhibit dramatic phenotypic differences based on their diet, and these differences have longterm fitness implications that can change based on environmental conditions. Using both wild-caught and lab-reared individuals, I am comparing patterns of DNA methylation across the genome between tadpole morphs, examining how these patterns change over time, and using differentially-methylated sites to better understand the genes responsible for this polyphenism.
The Phylogeography of Peromyscus maniculatus Across the California Channel Islands
Islands have been a source of inspiration for biologists for over 200 years, acting as natural laboratories for the study of evolution and ecology. The Channel Islands off the coast of southern California provide an excellent opportunity for studying evolutionary divergences, occupying a unique position as recent, temperate continental islands that have never been connected to the nearby mainland. By integrating bathymetry data, archaeological records and molecular data, previous researchers have produced hypotheses about the expected patterns of divergence we would expect to see across the islands, and I am testing these hypotheses using deer mice (Peromyscus maniculatus), the only mammal native to all eight of the Channel Islands. Using data from mitochondrial sequences and microsatellite loci, I am reconstructing the evolutionary history of mice across the islands, reconciling it with what is known about the arrival of early humans on the islands, and comparing the findings with what has been proposed for other native mammals.
Factors Influencing the Coevolution of Peromyscus maniculatus and its Ectoparasites
Studies examining the congruence between host and parasite phylogenetic trees have found that a shared evolutionary history is most often observed between highly host-specific parasites and their hosts, with generalist parasites evolving almost independently from their hosts. A suite of traits have been proposed that are hypothesized to increase host-parasite co-structure, but the importance of these traits, which include low parasite mobility, high host specificity and a vertical transmission of parasites between hosts, remains to be quantified. Islands, with their clear geographic barriers and low species richness limit opportunities for migration and host switching, creating a simplified system that can better address questions of host-parasite coevolution. The California Channel Islands are particularly well suited for this type of investigation on mammalian hosts and their ectoparasites, with differing numbers of host species on different islands allowing for comparisons to be made between a single parasite on multiple islands as well as between different parasites on the same island. Using the deer mouse, Peromyscus maniculatus, I am examining how alternative host availability on different islands impacts host-parasite co-structure for fleas, a highly mobile, generalist parasite.
Previous Research
Factors Influencing Insular Body Size Change in Rodents
The "island rule", the tendency for mammals to undergo dramatic size shifts when colonizing an island, is one of the most striking patterns in nature, exemplified by Mediterranean elephants 1/10 the mass of their mainland counterparts and Carribean rodents 2-3 times larger than their extant relatives. Despite these dramatic examples, the phenomenon remains controversial. In fact, there are many examples of differences in the degree and direction of size change observed between populations of the same species on different islands, especially among insular rodents. As part of my dissertation, I used museum records and a database of island body sizes to test whether insular variation in rodent body sizes was significantly different from the variation found on the mainland, and I explored the factors producing the body size differences observed on islands. When examining all records of insular rodents, there was no clear pattern of body size change. However, focusing on populations that were significantly larger/smaller than expected produced a striking pattern of insular size increase for rodents, with the few examples of size decreases explained largely by resource limitations on those particular islands.