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Hummingbird blood traits track oxygen availability across space and time |
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| Authors: | Jessie L Williamson Ethan B Linck Emil Bautista Ashley Smiley Jimmy A McGuire Robert Dudley Christopher C Witt |
| Institution: | 1. Museum of Southwestern Biology, University of New Mexico, Albuquerque, New Mexico, USA;2. Museum of Southwestern Biology, University of New Mexico, Albuquerque, New Mexico, USA
Department of Biology, University of New Mexico, Albuquerque, New Mexico, USA;3. Centro de Ornitología y Biodiversidad (CORBIDI), Lima, Peru;4. Museum of Southwestern Biology, University of New Mexico, Albuquerque, New Mexico, USA Museum of Vertebrate Zoology, University of California, Berkeley, California, USA Department of Integrative Biology, University of California, Berkeley, California, USA;5. Museum of Vertebrate Zoology, University of California, Berkeley, California, USA Department of Integrative Biology, University of California, Berkeley, California, USA |
| Abstract: | 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 rules of trait–environment covariation. Here we tested whether species adaptation alters elevational variation in blood traits. We measured blood for 1217 Andean hummingbirds of 77 species across a 4600-m elevational gradient. Unexpectedly, elevational variation in haemoglobin concentration (Hb]) was scale independent, suggesting that physics of gas exchange, rather than species differences, determines responses to changing oxygen pressure. However, mechanisms of Hb] adjustment did show signals of species adaptation: Species at either low or high elevations adjusted cell size, whereas species at mid-elevations adjusted cell number. This elevational variation in red blood cell number versus size suggests that genetic adaptation to high altitude has changed how these traits respond to shifts in oxygen availability. |
| Keywords: | Andes blood blood–oxygen ecophysiology elevation haematology haemoglobin hummingbird phylogeny trait–environment association |