Biogeography & Phylogeography
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A central theme of my research is understanding the historical and ecological processes that shape patterns of population structure. I approach these questions using a range of phylogenetic and population genetic methods on molecular data ranging from mitochondrial DNA to whole genome datasets. Central questions my collaborators and I aim to address with this work, include: (1) what are the relative roles of ecological versus geological history in shaping patterns of phylogenetic diversity (e.g. Benham et al. 2015)? (2) How does introgression influence phylogenetic patterns and adaptation (e.g. Beckman et al. 2018)? (3) How does demographic history shape patterns of population structure across fine spatial scales (e.g. Mikles et al. 2020 ). And (4) how do different evolutionary and ecological mechanisms generate discordant patterns between mitochondrial (mtDNA) and nuclear datasets (Benham & Cheviron 2019)? My work tackles these questions in a number of species from Metallura hummingbirds in the Andes to Tailorbirds in southeast Asia.
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Adaptation across ecological gradients
I am broadly interested in the physiological mechanisms contributing to increased performance and fitness in different environments (e.g., Galen et al. 2015; Stager et al. 2015; Benham & Witt 2016). Although divergent selective pressures will be the main driver of adaptive physiological divergence between environments, a variety of additional factors, such as plasticity, demography, or genomic architecture, can influence adaptive outcomes in critical, but poorly understood ways. To address these questions, my research focuses on tidal marsh sparrows. Daily inundations of seawater into tidal marshes presents a major challenge for terrestrial vertebrates as much of the available drinking water will be three times the salinity levels they need to maintain internally. Adaptation to high salinity environments drives divergence between tidal marsh and freshwater-adapted sparrow populations in several physiological and behavioral traits that increase osmoregulatory performance through increased salt excretion and water retention. My work explores the processes underpinning divergence in tidal marsh environments from genotypic variants (e.g., Walsh, Benham et al. 2019) to physiological performance (e.g, Benham & Cheviron 2020).
Population responses to anthropogenic change
How organisms persist in the face of human-mediated ecological change is a central question in conservation biology. Increasingly, I am applying analytical approaches from my work investigating adaptive divergence at deeper time scales to understand how populations have responded to recent and ongoing anthropogenic change. I am currently involved in a large scale conservation genomics initiative, the California Conservation Genomics Project (CCGP: https://www.ccgproject.org). I focus on eight bird species for which we are generating high quality references to align lower coverage genomes from 150 individuals per species from across California. This will provide an unprecedented window into patterns of gene flow, genetic diversity, and adaptation across the ecologically diverse state of California. Even with the large genomic datasets generated by the CCGP, a persistent challenge will be linking evidence for population declines in the genomes of contemporary animal populations to past human activities. Museum collections are increasingly accessible as immense repositories of baseline genetic data that can be used to better pinpoint the anthropogenic drivers of population declines (Benham & Bowie 2023). I take advantage of these extensive collections to investigate how tidal marsh sparrows in California responded to >90% habitat loss over the past 100 years (Benham et al. 2022).
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Building, maintaining, and using natural history collections
"With enormous series of wide-ranging species at their command, the ornithologist is in possession of material to determine the character and extent of variation in color and in size... When to this intensive laboratory investigation they add a knowledge of the environmental conditions under which the species exists, they can often definitely correlate effect and cause."
-F.M. Chapman, 1923 Much as Chapman recognized the research value of large series of bird specimens, all aspects of my research rely on both specimen collection and utilizing the existing trove of specimens in natural history collections. Associated with these specimens is a wealth of genetic, physiological, and ecological data that I integrate into research investigating the evolutionary processes that shape patterns of avian diversity. I began working in collections as an undergraduate at the Louisiana State University Museum of Natural Science and I continued my involvement in building and curating collections during my graduate and post-doctoral studies at the University of New Mexico, Museum of Southwestern Biology, University of Montana, and now the Museum of Vertebrate Zoology at the University of California Berkeley. Many aspects of my research depend on the use of museum specimens, such as measuring spatial and temporal variation in morphology and sequencing tissues associated with voucher specimens. To contribute to these collections I have participated in 13 general collecting expeditions on four continents and I have prepared over 2100 specimens that include associated tissues and a range of ancillary data. |