How do organisms living in temperate environments predict and respond to seasonal changes? I am using a combination of quantitative, population, and functional genetics to understand seasonality in the model fruit fly, Drosophila melanogaster. D. melanogaster originated in tropical Africa but now lives in temperate climates alongside humans. During the winter, cold temperatures trigger some flies to undergo diapause: an arrest of development of the ovaries that conserves energy. However, not all flies have this response, so we are using this natural genetic variation to study the genetic basis of this trait. I am using a genome-wide association study to understand how temperature (and perhaps light) induces this response in the lab (bottom photo). I am also tracking genetic changes in flies that been placed in outdoor cages to overwinter here in Virginia (top photo).
I examined the developmental and genetic basis of morphological differences in locally adapted freshwater and marine populations of threespine stickleback fish. Marine sticklebacks have repeatedly colonized freshwater habitats where they independently evolved changes in the head skeleton as adaptations to consume larger freshwater prey. My work used quantitative trait locus mapping to uncover the genetic basis of skeletal variation, focusing on bones involved in feeding. In collaboration with Dr. Dolph Schluter at the University of British Columbia, I studied crosses of three independent lake populations with convergent phenotypes,. We found that four shared genomic regions contributed to skeletal evolution in all three populations, but most genetic loci affecting skeletal morphology were unique to a single lake. These results suggest that the genetic basis of convergent phenotypic evolution is only partially predictable, with a limited number of shared evolutionary events.
Additionally, my work identified one genomic region that controls tooth number and bone length in several freshwater populations, indicating a single pleiotropic locus might underlie both phenotypes. However, using recombinant fine-mapping, I found that tooth number mapped near Bmp6, whereas bone length mapped to the nearby gene Tfap2a. Close linkage of these alleles may facilitate rapid local adaptation upon colonization of freshwater habitats. Further genetic mapping and genome editing suggested multiple regulatory changes in Tfap2a likely underlie bone length differences.
I also studied how the candidate gene Bmp6 is regulated in developing teeth. I identified a short, conserved enhancer upstream of Bmp6 that responds to TGFß signaling. When this enhancer is mutated, expression of Bmp6 is severely reduced and tooth number is increased, mirroring the evolved phenotype in freshwater fish. Collectively, these findings highlight how fine-tuning the regulation of existing developmental pathways can generate novel adaptive and ecologically relevant phenotypes. My research also led to the publication of a protocol for transgenesis and genome editing in threespine stickleback.
Finally, I collaborated with Dr. Chris Martin at UNC Chapel Hill to help generate the first linkage map and QTL mapping experiment to study jaw evolution in an adaptive radiation of Caribbean pupfish.