I study how species evolve in response to physical changes in the landscape over time. To do this I integrate population genetics and genomics with paleoclimatology, sea-level change, and earth surface and coastal processes to study these processes in a statistically explicit framework.
My research spans spatiotemporal scales and organisms, but centers on the coevolutionary nature of Earth and life.
Geological control underlying desert tortoise speciation
Gopherus agassizii and G. morafkai speciated ~5 Ma and are primarily separated by the Colorado River today, but the Colorado River region itself, has also been evolving. I am using volcanic, sedimentologic, and tectonic data to reconstruct the physical constraints on gene flow during this speciation event. I will compare these geologic-based estimates with demographic reconstructions using genomic data to piece together the speciation history of this iconic example of vicariant speciation.
Genes underlying niche adaptation in desert tortoises
Species distribution models were recently developed to differentially describe the niche of Agassiz’s desert tortoise (Gopherus agassizii), Morafka’s desert tortoise (Gopherus morafkai), and their interspecific hybrids. I’m working with others to identify the genes and genomic variants that that underlie these ecological preferences. Together we are using range-wide genomic sequencing, physiology, and modern and paleo-niche models to determine: 1) how these species have differentially adapted to the Mojave a Sonoran deserts? 2) what is the history of introgression between these species? 3) how do differentially adapted genes manifest in hybrid individuals?
Population genetics, origin(s) of life, and the rise of complexity
Origin of life research is often considered the nexus between biology, physics, and chemistry. Longstanding debates about the rise of metabolism, replication, and the role of cooperation continue. Population genetics, however, is the foundation of evolutionary biology, and we can assume the earliest Darwinian life probably played by the same mathematical rules governing species today. Based on this assumption, I’m using in silico evolution to explore what we can learn about earliest life on Earth (prebiotic –> RNA transition) based on population genetic theory, and the role natural selection may have played in the rise of complexity (i.e. multi-trait life). Thrusting theory into a new setting, such as the origin of life, may also help contextualize the genomic evolution of extant life today.
Sea level, coastal geomorphology, and recent evolution of fishes (California & Mexico)
Ice ages have majorly affected the distribution and genetic diversity of species on land. We’ve expanded this knowledge to show this is true for coastal marine species as well. By using a Geographic Information System (GIS), sea level, and morphology of the coastline we predicted the change in distribution and size of estuaries since the last ice age with millennial-scale resolution. We statistically assessed the affect of such habitat change on its inhabitants by evaluating the patterns of genetic diversity in fishes inhabiting these estuaries. Our article in the Proceedings of the Royal Society B revealed sea-level change has structured the genetic diversity and distribution of coastal marine species along Alta and Baja California coastlines.
Additional work we’ve done has shown tectonic and sedimentological processes to play a top-down role in controlling coastal topography, and in turn habitat connectivity and genetic divergence.
Tectonic and Climatic drivers of Gulf of California and Sonoran Desert biodiversity
Today the Baja Peninsula is a long, skinny protrusion into the Pacific Ocean, and a barrier between the Pacific and Gulf of California, but it wasn’t always that way. The peninsula rifted from mainland Mexico and translated northwest, and the Gulf only flooded ~6–8 million years ago. How did so many species come to be found only in the Gulf? And how has this complex geologic and climatic history affected its terrestrial and marine biota? These questions and others have attracted scientists such as myself for decades. Collaborators and I authored a comprehensive geo-bio synthesis of these patterns and processes here.
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