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 effects in a statistically explicit framework.
My research spans spatiotemporal scales, ecosystems and organisms, but centers on the coevolutionary nature of Earth and life.
Long-term motivating questions:
- What are the first principles underlying Earth-life co-evolution over recent and deep time?
- What quantitative frameworks can we use to measure the relative importance of different co-occurring geo-climatic processes contributing to genomic divergence?
- How can we standardize and measure the relative contribution of neutral versus adaptive divergence within a lineage and compare these signals across species?
- How can we use genomic data to answer geologic questions?
- What quantitative approaches are most useful in integrating disparate types of data (among geology, physics, biology)?
Neutral and adaptive forcing of speciation in the southwest
Dozens of disparate species are thought to have speciated in isolation when initiation of the Colorado River bisected ancestral populations 5–6 million years ago (Ma). However,
the river itself and the southwest broadly has evolved dramatically over this timeframe. I led a meta-analysis of published literature and integrated these results with geologic data to develop co-evolutionary models (Dolby et al., submitted). Building on this, we are developing a second generation desert tortoise genome, and analyzing hundreds of low coverage genomes to ascertain how the
Colorado River has mediated gene flow since its inception, and test for signatures of differential adaptation to the onset of monsoonal conditions over this time period.
Top-down physical control of sea-level change as a driver of diversification in coastal species
Ice ages have majorly affected the distribution and genetic diversity of species on land. Our work shows, however, that this is true for coastal marine species as well. Using a Geographic Information System (GIS), sea level history, and geomorphology of the coastline, we predicted the change in distribution and size of estuaries as a function of sea-level change and assessed the genetic diversity and history of species living in those systems. Our articles in Molecular Ecology and Proceedings of the Royal Society B revealed that present-day genetic divergence results from sea-level driven elimination and reformation of habitats. We also showed that tectonic and sediment processes play a top-down role in controlling coastal geomorphology, the distribution of habitat, and mediates genetic divergence as a result. This combined ‘mechanism of divergence’ has potential global applications, as well as applications to diversification on deeper geologic timescales. We are currently working on: 1) applying this approach to coastlines globally in the context of regional tectonics, and 2) understanding how this mechanism works as a function of dispersal ability in order to apply this knowledge to diversification patterns in the fossil record.
Psuedocongruence, geo-genomics, and the drivers of endemism
Today the Baja Peninsula is a long, skinny protrusion into the Pacific Ocean, 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 or on the peninsula? And how has this complex geologic and climatic history affected its terrestrial and marine biota? We’ve written a comprehensive geo-bio synthesis of these patterns and processes in the Journal of the Southwest. We have a geo-genomic consortium under way to unite geologists and biologists in understanding the potentially psuedocongruent, co-occurring geo-climatic forces shaping divergence and endemism in this region.
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 and population changes 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 itself may have played in the rise of complexity (i.e. multi-trait life). In addition to learning more about these early living systems, thrusting such theory into a new setting, such as the origin of life, may also help contextualize the genomic evolution of extant life today and how genomes came to be such complicated things.
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