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.
Broad, long-term questions:
- What quantitative frameworks can help us disentangle the relative impact of co-occurring geo-climatic processes in shaping evolution of a species?
- How can we measure the relative contribution of neutral versus adaptive processes in diverging a lineage, and can we standardize this measure across taxa?
- How can we use evolutionary patterns and genomic data specifically to answer geologic questions?
- Are there ‘laws’ governing the interplay of geological and evolutionary processes, and what roles do genomic information and population genetic theory play?
Geologic control on desert tortoise speciation
Gopherus agassizii and G. morafkai speciated ~5 Ma and thought to be a result of the Colorado River bisecting the ancestral population. The Colorado River region itself, however, has evolved dramatically over this timeframe. We are using volcanic, sediment, and tectonic data to model how physical evolution of the lower Colorado River region has mediated gene flow and neutral divergence since the late Miocene to understand how much of this process was mediated by landscape evolution. To do this, we are comparing modern genomic diversity patterns against data simulated under different geologically-parameterized historical scenarios of this iconic example of vicariant speciation.
Paleomonsoon and niche divergence in desert tortoises
In addition to being (mostly) separated by the Colorado River today, these desert tortoises exhibit different ecological preferences, and with their hybrids exhibiting an intermediate tolerance. Many of these variables, however, are factors relating to monsoonal precipitation, which begs the question of what role differential selection pressures played in driving divergence of these iconic species. We are working to identify the genes and genomic variants that that underlie these ecological preferences, and determine whether the timing of divergence is explained by the onset of the paleomonsoon. By combining this with information about neutral divergence of the genome, we aim to develop a metric to reflect the relative amount of adaptive versus neutral change in explaining how these species differ. We hope this metric can be compared across species to garner a real understanding of the relative external drivers of species divergence.
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.
Sea-level change and the top-down physical control on diversification of coastal fishes
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 proposed 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.
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.
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