Christopher C. Witt

University of New Mexico | UNM · Department of Biology

Animals that sustain high levels of aerobic activity under hypoxic conditions (e.g., birds that fly at high altitude) face the physiological challenge of jointly optimizing blood-O2 affinity for O2 loading in the pulmonary circulation and O2 unloading in the systemic circulation. At high altitude, this challenge is especially acute for small endoth...

Significance Within a given gene, there may be many possible mutations that are capable of producing a particular change in phenotype. However, if some sites have especially high rates of mutation to function-altering alleles, then such mutations may make disproportionate contributions to phenotypic evolution. We report the discovery that a point m...

Significance Predictable evolutionary trends illuminate mechanisms that affect the diversity of traits and species on the tree of life. We show that when birds colonize islands, they undergo predictable changes in body shape. Small-island bird populations evolve smaller flight muscles and longer legs. These shifts in investment from wings to legs,...

Significance Interactions between hosts and parasites can reciprocally limit the ranges of individual species. But to what extent do they affect composition of communities? In the Andean biodiversity hot spot, we tested why host and parasite communities vary over spatial and temporal scales. Variation in rainfall was the predominant predictor of tu...

The ecoevolutionary drivers of species niche expansion or contraction are critical for biodiversity but challenging to infer. Niche expansion may be promoted by local adaptation or constrained by physiological performance trade-offs. For birds, evolutionary shifts in migratory behavior permit the broadening of the climatic niche by expansion into v...

Vertebrate lungs contain diverse microbial communities, but little is known the causes of community composition or its consequences for health. Lung microbiome assembly by processes such as dispersal, coevolution, and host-switching can be elucidated with comparative surveys. However, few comparative surveys exist for lung microbiomes, particularly...

Giant hummingbirds (Patagona spp.) are extraordinarily large hummingbirds whose taxonomy has been muddled for two centuries. Patagona systematics were recently redefined in a study of migration, physiology, and genomics, revealing two species: the Southern Giant Hummingbird and Northern Giant Hummingbird. Here, we re-evaluate taxonomy and nomenclat...

More than tools for managing physical and digital objects, museum collection management systems (CMS) serve as platforms for structuring, integrating, and making accessible the rich data embodied by natural history collections. Here we describe Arctos, a scalable community solution for managing and publishing global biological, geological, and cult...

Per- and polyfluoroalkyl substances (PFAS) in the environment pose persistent and complex threats to human and wildlife health. Around the world, PFAS point sources such as military bases expose thousands of populations of wildlife and game species, with potentially far-reaching implications for population and ecosystem health. But few studies shed...

Museum collections house millions of objects and associated data records that document biological and cultural diversity. In recent decades, digitization efforts have greatly increased accessibility to these data, thereby revolutionizing interdisciplinary studies in evolutionary biology, biogeography, epidemiology, cultural change, and human-mediat...

Natural history museums are vital repositories of specimens, samples and data that inform about the natural world; this Formal Comment revisits a Perspective that advocated for the adoption of compassionate collection practices, querying whether it will ever be possible to completely do away with whole animal specimen collection.

Per- and polyfluoroalkyl substances (PFAS) threaten human and wildlife health, but their movement through food webs remains poorly understood. Contamination of the physical environment is widespread, but particularly concentrated at military installations. Here we measured 17 PFAS in wild, free-living mammals and migratory birds at Holloman Air For...

Glaucia Del-Rio Carrie Branch The American Ornithological Society (AOS) is pleased to announce Glaucia Del-Rio, Carrie Branch, and Sara Lipshutz as the 2023 recipients of the society’s Early Professional Awards, the James G. Cooper Early Professional Award and the Ned K. Johnson Early Investigator Award. The James G. Cooper Early Professional Awar...

Predictable trait variation across environments suggests shared adaptive responses via repeated genetic evolution, phenotypic plasticity or both. Matching of trait–environment associations at phylogenetic and individual scales implies consistency between these processes. Alternatively, mismatch implies that evolutionary divergence has changed the r...

We explored the evolutionary radiation in the House Wren complex (Troglodytes aedon and allies), the New World’s most widely distributed passerine species. The complex has been the source of ongoing taxonomic debate. To evaluate phenotypic variation in the House Wren complex, we collected 81,182 single-nucleotide polymorphisms (SNPs) from restricti...

Boletín de la Unión de Ornitólogos del Perú (UNOP) ISSN 2220-9212

The extent to which species ranges reflect intrinsic physiological tolerances is a major question in evolutionary ecology. To date, consensus has been hindered by the limited tractability of experimental approaches across most of the tree of life. Here, we apply a macrophysiological approach to understand how hematological traits related to oxygen...

Animals developing at high elevation experience a suite of environmental challenges, most notably the low partial pressure of oxygen (PO2) in ambient air. In low PO2 , bird species with high-elevation ancestry consistently demonstrate higher hatching success than lowland counterparts, suggesting highland birds are adapted to restricted O2 (hypoxia)...

Vocal learning is thought to have evolved in 3 orders of birds (songbirds, parrots, and hummingbirds), with each showing similar brain regions that have comparable gene expression specializations relative to the surrounding forebrain motor circuitry. Here, we searched for signatures of these same gene expression specializations in previously unchar...

Stepfanie M. Aguillon Benjamin Freeman The American Ornithological Society (AOS) is pleased to announce Stepfanie M. Aguillon, Benjamin Freeman, and Allison Shultz as the 2022 recipients of the society’s Early Professional Awards, the James G. Cooper Early Professional Award and the Ned K. Johnson Early Investigator Award. The James G. Cooper Earl...

Nest stacking is a rarely reported phenomenon in birds. Here, we place the behavior within the broader context of nest functions, describe new observations of nest stacking within and between Neotropical marsh‐dwelling songbirds, and discuss the ecological significance of this behavior, including its role in interspecific facilitation. Abstract in...

Disentangling the factors underlying the diversification of geographically variable species with a wide geographical range is essential to understanding the initial stages and drivers of the speciation process. The Amazilia Hummingbird, Amazilis amazilia, is found along the Pacific coast from northern Ecuador down to the Nazca Valley of Peru, and i...

For endotherms with sustained high metabolism, like hummingbirds, blood-oxygen (O 2 ) carrying capacity should be finely tuned to supply O 2 to respiring tissues. Hematological adjustments are expected in response to changes in O 2 availability that occur along elevational gradients; however, eco-physiological rules by which this variation occurs h...

The extent to which species ranges reflect intrinsic physiological tolerances is a major, unsolved question in evolutionary ecology. To date, consensus has been hindered by the limited tractability of experimental approaches across most of the tree of life. Here, we apply a macrophysiological approach to understand how hematological traits related...

Plumage pigmentation is fundamental to a bird's phenotype, with pigment deposition causing relative crypsis or conspicuousness, depending on the environmental context. Geographic variation in plumage melanin tends to be predictable, suggesting that aspects of climate cause local matching of plumage to environment via genetic adaptation. Ecogeograph...

In most vertebrates, the demand for glucose as the primary substrate for cellular respiration is met by the breakdown of complex carbohydrates, or energy is obtained by protein and lipid catabolism. In contrast, a few bat and bird species have convergently evolved to subsist on nectar, a sugar-rich mixture of glucose, fructose, and sucrose.1-4 How...

Hummingbirds and other lightweight bird species are challenging to track because they have limited capacity to carry devices for data‐logging. We present a simple and customizable three‐loop ‘backpack' harness for studying hummingbird migration and movement, with step‐by‐step instructions for harness construction and attachment. The harness has neg...

Many paleognaths (ratites and tinamous) have a pair of homomorphic ZW sex chromosomes in contrast to the highly differentiated sex chromosomes of most other birds. To understand the evolutionary causes for different tempo of sex chromosome evolution, we produced female genomes of 12 paleognathous species and reconstructed the phylogeny and the evol...

Elevational migration can be defined as roundtrip seasonal movement that involves upward and downward shifts in elevation. These shifts incur physiological challenges that are proportional to the degree of elevational change. Larger shifts in elevation correspond to larger shifts in partial pressure of oxygen, air density, temperature, and ultravio...

Researchers seeking to generate genomic data for non‐model organisms are faced with a number of trade‐offs when deciding which method to use. The selection of reduced representation approaches versus whole genome re‐sequencing will ultimately affect the marker density, sequencing depth, and the number of individuals that can multiplexed. These fact...

A Correction to this paper has been published: https://doi.org/10.1038/s41586-021-03473-8.

Researchers seeking to generate genomic data for non-model organisms are faced with a number of trade-offs when deciding which method to use. The selection of reduced representation approaches versus whole genome re-sequencing will ultimately affect the marker density, sequencing depth, and the number of individuals that can multiplexed. These fact...

Studying processes acting on differentiated populations upon secondary contact, such as hybridization, is important to comprehensively understand how species are formed and maintained over time. However, avian speciation studies in the tropical Andes have largely focused on the role of topographic and ecological barriers promoting divergence in all...

Populations along steep environmental gradients are subject to differentiating selection that can result in local adaptation, despite countervailing gene flow and genetic drift. In montane systems, where species are often restricted to narrow ranges of elevation, it is unclear whether selection is strong enough to influence functional differentiati...

Turnover in species composition between sites, or beta diversity, is a critical component of species diversity that is typically influenced by geography, environment, and biotic interactions. Quantifying turnover is particularly challenging, however, in multi-host, multi-parasite assemblages where undersampling is unavoidable, resulting in inflated...

Whole-genome sequencing projects are increasingly populating the tree of life and characterizing biodiversity1,2,3,4. Sparse taxon sampling has previously been proposed to confound phylogenetic inference5, and captures only a fraction of the genomic diversity. Here we report a substantial step towards the dense representation of avian phylogenetic...

Torpor is thought to be particularly important for small endotherms occupying cold environments and with limited fat reserves to fuel metabolism, yet among birds deep torpor is both rare and variable in extent. We investigated torpor in hummingbirds at approximately 3800 m.a.s.l. in the tropical Andes by monitoring body temperature (Tb) in 26 indiv...

The central Andean rainforests and the Atlantic Forest are two similar biomes that are fully isolated by xerophytic and open-vegetation regions (the Chaco and Cerrado, respectively). Even though there is evidence suggesting that these rainforests have been connected in the past, their dynamics of connection, the geographic areas that bridged these...

Background Human populations native to high altitude exhibit numerous genetic adaptations to hypobaric hypoxia. Among Tibetan plateau peoples, these include increased vasodilation and uncoupling of erythropoiesis from hypoxia. Objective/Methods We tested the hypothesis that these high‐altitude adaptations reduce risk for hypertension and diabetes‐...

Turnover in species composition between sites, or beta diversity, is a critical component of species diversity that is typically influenced by geography, environment, and biotic interactions. Quantifying turnover is particularly challenging, however, in multi-host, multi-parasite assemblages where undersampling is unavoidable, resulting in inflated...

Birds naturally maintain high glucose concentrations in the blood and tissues, even when relying on fat to meet the metabolic demands of flight or thermogenesis. One possibility is that high glucose levels might be needed to deal with these metabolic demands. Thus, we hypothesized that birds chronically exposed to colder temperatures and higher ele...

Metatranscriptomics is a powerful method for studying the composition and function of complex microbial communities. The application of metatranscriptomics to multi‐species parasite infections is of particular interest, as research on parasite evolution and diversification has been hampered by technical challenges to genome‐scale DNA sequencing. In...

Background: Birds of prey (raptors) are dominant apex predators in terrestrial communities, with hawks (Accipitriformes) and falcons (Falconiformes) hunting by day and owls (Strigiformes) hunting by night. Results: Here, we report new genomes and transcriptomes for 20 species of birds, including 16 species of birds of prey, and high-quality refe...

Sex chromosomes of mammals and most birds are heteromorphic, while those of many paleognaths (ratites and tinamous) are inexplicably homomorphic. To dissect the mechanisms underlying the different tempo of sex chromosome evolution, we produced high-quality genomes of 12 paleognathous species, and reconstructed their phylogeny based on alignments of...

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The breeding biology and phenology of the endangered hummingbird Purple-backed Sunbeam (Aglaeactis aliciae) are not well known. We report observations of nesting A. aliciae near El Molino, in La Libertad Department, Peru. On 11 March 2018, we found a female building a nest while on 10 March 2019 we found an incubating female. We describe specific c...

An underexplored question in evolutionary genetics concerns the extent to which mutational bias in the production of genetic variation influences outcomes and pathways of adaptive molecular evolution. In the genomes of at least some vertebrate taxa, an important form of mutation bias involves changes at CpG dinucleotides: if the DNA nucleotide cyto...

High-elevation organisms experience shared environmental challenges that include low oxygen availability, cold temperatures, and intense UV radiation. Consequently, repeated evolution of the same genetic mechanisms may occur across high-elevation taxa. To test this prediction, we investigated the extent to which the same biochemical pathways, genes...

Background: Birds of prey (raptors) are dominant apex predators in terrestrial communities, with hawks (Accipitriformes) and falcons (Falconiformes) hunting by day, and owls (Strigiformes) hunting by night. Results: Here, we report new genomes and transcriptomes for 20 species of birds, including 16 species of birds of prey, and high-quality refere...

Variation in susceptibility is ubiquitous in multi‐host, multi‐parasite assemblages, and can have profound implications for ecology and evolution in these systems. The extent to which susceptibility to parasites is phylogenetically conserved among hosts can be revealed by analysing diverse regional communities. We screened for haemosporidian parasi...

Haemosporidian parasites of birds are ubiquitous in terrestrial ecosystems, but their coevolutionary dynamics remain poorly understood. If species turnover in parasites occurs at a finer scale than turnover in hosts, widespread hosts would encounter diverse parasites, potentially diversifying as a result. Previous studies have shown that some wide-...

An underexplored question in evolutionary genetics concerns the extent to which mutational bias in the production of genetic variation influences outcomes and pathways of adaptive molecular evolution. In the genomes of at least some vertebrate taxa, an important form of mutation bias involves changes at CpG dinucleotides: If the DNA nucleotide cyto...

Avian malaria and related haemosporidians (Plasmodium, [Para]Haemoproteus, and Leucocytoozoon) represent an exciting multi‐host, multi‐parasite system in ecology and evolution. Global research in this field accelerated after 1) the publication in 2000 of PCR protocols to sequence a haemosporidian mitochondrial (mtDNA) barcode, and 2) the developmen...

Variation in susceptibility is ubiquitous in multi-host, multi-parasite assemblages, and can have profound implications for ecology and evolution. The extent to which susceptibility is phylogenetically conserved among hosts is poorly understood and has rarely been appropriately tested. We screened for haemosporidian parasites in 3983 birds represen...

Avian malaria and related haemosporidians (Plasmodium, [Para]Haemoproteus, and Leucocytoozoon) represent an exciting multi-host, multi-parasite system in ecology and evolution. Global research in this field accelerated after 1) the publication in 2000 of PCR protocols to sequence a haemosporidian mitochondrial (mtDNA) barcode, and 2) the developmen...

Genetic introgression among closely related species is a widespread phenomenon across the Tree of Life and could be an important source of adaptive variation during early stages of diversification. In particular, genomic studies have revealed that many rapidly radiating clades tend to have complex, reticulate evolutionary histories. Although rapid...

The selection of species and individuals for molecular analyses critically affects inferences in various fields of systematic biology including phylogenetics, phylogeography, and species delimitation. Especially in areas like the Neotropical region where molecular analyses have recovered substantial within-species divergence and unexpected affiniti...

Haemosporidian parasites of birds are ubiquitous in terrestrial ecosystems, but their coevolutionary dynamics remain poorly understood. If species turnover in parasites occurs at a finer scale than species turnover in hosts, widespread hosts would encounter diverse parasites and potentially diversify as a result. Previous studies have shown that so...

Blood glucose is a circulating fuel source for animals. However, species vary in glucose requirements due to distinct fuel physiology . Birds naturally have higher plasma glucose concentrations (PGlu) by a factor of 1.5–2 compared to mammals when adjusted for body mass. Currently, the physiological and evolutionary cause of the high PGlu is unknown...

Hummingbirds show remarkable adaptation to high altitude hypoxia whereas humans are imperfectly adapted to high altitude living. Here we compare hemoglobin levels and metabolism derived from growth rhythms in hummingbirds and humans. To compare growth rhythms, we analyzed growth intervals in hummingbird tail feathers and human growing tissues such...

Most tropical bird species have narrow elevational ranges, likely reflecting climatic specialization. This is consistent with Janzen's Rule, the tendency for mountain passes to be effectively “higher” in the tropics. Hence, those few tropical species that occur across broad elevational gradients (elevational generalists) represent a contradiction t...

Flying animals of different masses vary widely in body proportions, but the functional implications of this variation are often unclear. We address this ambiguity by developing an integrative allometric approach, which we apply here to hummingbirds to examine how the physical environment, wing morphology and stroke kinematics have contributed to th...