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Physical drivers of spatiotemporal genetic patterns and evolutionary processes among and within species of the North American southwest


Over 150 years of investigation has yielded knowledge of the patterns and mechanisms of biological evolution. Yet rarely do such studies integrate the physical mechanisms that drive this evolution on a timescale that is biologically meaningful. Without integrating physical and biological processes, we risk overlooking the co-evolutionary nature of Earth and life. This thesis presents first a broad synthesis of how geologic, climatic, and environmental mechanisms drive patterns of evolution on long (> 5 Myr), medium (1–2 Myr), and short (10s–100s kyr) timescales. It secondly presents a detailed assessment of how estuaries and their inhabitants co-evolve through time and space in response to changing sea levels and the physical landscape. Chapter 1 is a meta-analysis and review of the biological and geological histories of the Sonoran Desert and Gulf of California (Gulf) from 15 Ma to present. We suggest a middle-Miocene marine embayment could explain the deposition of reworked marine microfossils and speciation ages and distributions of Gulf endemics. Assessment of the Pleistocene-age mid-peninsular seaway hypothesis reveals that the uplift age of the Baja peninsula and strong genetic discordance of highly dispersive taxa render this hypothesis unlikely. Finally, we document the distribution patterns of 527 plants disjunct between the mainland and Baja California peninsula and suggest postglacial responses that underlie these patterns. In Chapters 2 and 3 I develop a paleohabitat modeling technique that estimates the size and distribution of estuarine habitat from 20 kya to present on a near-millennial timescale using physical parameters. I apply this model to ~4,600 km of coastal distance from San Francisco, USA to Sinaloa, MX. Independent of this is an assessment of the genetic history of 524 individuals of three co-distributed fishes using mtDNA and large microsatellite datasets. Together, there is statistically significant agreement from these findings; lowstand greatly reduced estuarine habitat and individuals evolved independently in these isolated refugia. Tectonic and oceanographic processes have shaped the regional geomorphology of coastlines and thus the degree to which these refugia and refugial populations are isolated. This isolation-recolonization pattern is likely global, and is not restricted to glacier-adjacent coastlines at high latitudes.

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