I am fascinated by distributions, and how they change over time. Avian speciation requires isolation, and therefore distributional changes are fundamental to the diversification process. Broadly speaking, organism distributions change because of 1) underlying geological, environmental, or climate changes; 2) evolution of an organisms dispersal ability to maintain population connectivity and and colonize new areas, or are 3) mediated by these changes in other species. Determining how these factors influence distributional changes, and therefore geographic diversification, requires knowledge of how population history, geography, and selection intersect. To this end, I sample genome-wide genetic markers to infer historical relationships and functional changes among species and populations, and apply modeling approaches and phenotypic assessments in comparative hypothesis-testing frameworks. My work is inspired and heavily influenced by time spent and observations made in the field, particularly in the Asian and American tropics.
Avian phylogenetics and phylogeography
Well-resolved and exhaustively sampled phylogenetic hypotheses are the foundation for all comparative biology. Molecular systematic approaches have made great strides in developing a robust avian phylogeny, yet major challenges remain: 1) taxon sampling is sparse, approximately one-third of all recognized bird species are yet to be included, 2) most taxa are sampled for one or a few markers, deeper sampling is needed to improve confidence, and 3) recognized bird species diversity is rapidly increasing due to philosophical shifts in species concepts, growing use of genetic data, and a better understanding of tropical bird faunas.
To improve the resolution of our picture of the avian tree of life, I use both "root-to-tip" and "tip-to-root" strategies. The root-to-tip approach focuses on gathering massive amounts of DNA sequence data and testing and employing emerging analytical approaches to resolve uncertainties highlighted by previous research. The tip-to-root approach focuses on fine-scale study of structured populations and broad taxon sampling across landscapes, blurring the lines between phylogenetics and phylogeography.
Biogeography
Phylogenetic and phylogeographic studies provide the template to understand how physical geographical, environmental, and ecological factors limit avian distributions, promote diversification in allopatry, and regulate secondary contact. At deep time scales, I am interested in the relative roles of earth history, environmental change, and evolution of dispersal ability in determining global bird colonization history. At more recent time scales, I am interested in understanding the paradoxical role of geographic barriers in promoting diversification— that is, if organisms are mobile enough to colonize across geographic barriers, how are they subsequently isolated by them? Across time scales, I use genomic data to infer historical population and colonization history to understand the relative roles of isolation, divergence, specialization/adaptation, and gene flow in insular (or island model) diversification. These data also provide new insight into species limits, which are currently applied unevenly across the landscape (e.g., temperate vs. tropics), and among taxonomic groups, which may obscure our understanding of broad-scale macroevolutionary and macroecological processes underlying avian diversity.
Ornithological exploration
Genetic sample limitation is a major constraint in avian phylogenetic and phylogeographic research. Continued building of specimen and tissue resources are crucial to to add "missing" taxa to the tree of life and to test fine-scale phylogeographic hypotheses. Currently, the most pressing geographical sampling gaps are found in tropical regions. Habitat-wise, open landscapes are poorly sampled worldwide. Historically, closed-canopy forest habitats have received the bulk of study, and events driving avian diversification in grasslands, savannas, and dry forests are likely separate from those of forest populations.
Although considered by some to have the most well-developed vertebrate taxonomy, rates of descriptions of new birds species are holding steady or perhaps increasing because of continued ornithological exploration. To date, my research expeditions have led to the description of two new bird species (one in the Philippines and one in Peru), with several more new taxonomic descriptions in preparation. Additionally, these efforts have further elucidated the cryptic diversity which is widespread and common in tropical birds. Seeking out geographic regions of secondary contact among cryptic lineages will contribute to understanding the evolutionary significance of such patterns.
Specimen-based research
Biological collections are a fundamental resource in biology because they document and preserve the history of life.
A central argument for continued collection of biological diversity is the prospect of unexpected information—knowledge derived from specimens that was unforeseen by, and often unimaginable to) the original collectors. Collectors in the late 19th century could scarcely have imagined that toe pads from their study skins would yield the DNA used to resolve age-old debates on the relationships among lineages, nor that their egg collections would provide baseline comparisons leading to DDT bans. The usefulness of collections largely depends on collector ability to predict what specimen material will be useful in the future. Although we may not know the exact future use of specimens, we do know that preservation utilizing a wide variety of methods will be needed to answer different research questions, and that specimens with the most detailed associated data are the most useful over time.
With future applications in mind, my tissue collection efforts are shifting from DNA to RNA preservation, and towards preserving as many tissue types from the organism as possible. This includes those of associated parasites, pathogens, and microbes, where the majority of undiscovered "avian" diversity resides. Preservation of a greater diversity of tissue resources will also broaden use of biological collections among sub-disciplines of biology that have traditionally had little interaction with museum collections.
Monarch Flycatchers are broadly distributed from Africa to Oceania, but most of the phenotypic diversity resides in Pacific islands. This Short-crested Monarch is a species endemic to the Philippines. Mt. Cagua, Philippines
Buff-breasted Mountain-Tanager populations isolated across the Apurímac gap of Peru appear similar in plumage, yet have distinctly different songs. Is this an example of local song dialects maintained despite ongoing gene flow, or an example of diverging populations retaining pleisiomorphic plumage? Chupón, Ayacucho, Peru.
Resolving the relationships among the six crown lineages of trogons has been difficult with traditional markers, because they radiated extremely rapidly. However, thanks to massive amounts of data obtained from sequence capture, we now have a robust hypothesis. Philippine Trogon, Zamboanga, Philippines.
In nocturnal birds, vocalizations and genetic markers are often better at diagnosing lineages than plumage and morphological characters. In Philippine Frogmouths, vocal differences appear to be congruent with established biogeographical boundaries, but more study is needed. Zamboanga, Philippines.
This is the western "white-crowned" form of the Marcapata Spintail, a montane species from the Andes. Despite partial isolation by physical barriers, fine-scale collection efforts revealed introgression with the eastern "red-crowned" form, which was previously thought to be allopatric. Chupón, Ayacucho, Peru.
A mule train heading up a series of landslide-prone switchbacks, a scene typical of fieldwork in remote portions of the Andes. Paccaypata, Peru.
Geographic variation in Philippine "babblers." These specimens are a result of recent field work throughout the archipelago. University of Kansas Biodiversity Institute bird collection.