Current Research

Evolutionary applications Climate change is exerting an enormous selective gradient on natural populations. Since the response to changing environments can involve both physiological and evolutionary components, we will need to know much more about the quantitative genetics of “non-model” systems at the population level. Evolutionary quantitative genetics provides a framework to predict how populations will respond to new selection pressures, and to understand the genetic architecture (number of loci and their effects) of traits the reduce physiological stress. Yet for many of the species that provide ecosystem services, act as ecosystem engineers, or bring so much aesthetic value to our lives, the laboratory crosses of traditional quantitative genetics are impossible or impractical. A solution to this problem is to link natural genetic variation in the wild with next generation sequencing approaches to uncover hidden natural variation that is key to the climate change response. At Bowdoin College, I have been collaborating with Sarah Kingston, who is the current Doherty Marine Biology Postdoc. Sarah and I have been exploiting a hybrid zone in the Gulf of Maine between two blue mussels: Mytilus edulis X Mytilus trossolus, as a model system to identify the genes that determine calcification rates. Our approach is to subject wild caught mussels to simulated climate change in the lab and use the individual variation in the stress response as a stress phenotype. Genotype by sequencing (GBS) approaches, combined with gene expression profiles generated by RNA seq, provide the data to identify genomic regions linked to stress phenotypes.

Conservation genetics The molecular tool kit plays an increasingly important role in identifying fundamental units of conservation. Some examples from my lab include John Fitzpatrick’s thesis work (Fitzpatrick et al, 2011), which strongly suggests new species or sub-species in Hawaii and the Eastern Pacific within the species formerly described as S. rubroviolaceus. As in other fisheries stocks, efforts are under way to document life history and phenotypic evolution among these distinct populations. A second interesting example from my lab comes from a collaborative study of a flycatcher complex (the “Elepaio” or Chasiempis sandwichensisis) in which divergence in phenotypic traits and song variation has been well described among the Main Hawaiian Islands by Eric Vanderwerf and colleagues. Two mitochondrial genes suggest a complex of at least three sibling species each endemic to different island (Vanderwerf et al. 2009). Recognizing the conservation and evolutionary significance of the Oahu species is particularly timely. Relentless urban and agricultural development during the last century has reduced population size to < 2000 birds which occupy an estimated 4% of its former range. In addition to identifying the spatial distribution of potential conservation units, there is historical information contained in DNA sequence data that can greatly informs the design of parks and reserves. Maturing coalescent-based population genetic approaches can evaluate models that include both isolation and gene flow. Thereby providing more biological reality and more robust estimates of connectivity among populations or species than traditional frequency-based methods. I am keen to collaborate with ecologists and systematic biologists who are interested in the application of these kinds of approaches to their particular system.

Speciation I am interested in what Darwin called that “mystery of mysteries” or how populations make the transition to new species. Recently, my group has been integrating the fossil record with molecular phylogeny to deconstruct rapid speciation and adaptive radiation (Schwartz et al. 2012). We also take a microevolutionary view of speciation by capitalizing on incipient species of corals and parrotfish in order to understand contemporary forces that drive reproductive isolation, including natural selection, sexual selection, and genetic drift. I gave a STRI Tupper Seminar last May that summarized my micro-evolutionary work across three systems, inducing parrotfish