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. 2016 Oct 15;219(20):3190–3203. doi: 10.1242/jeb.127134

Fig. 8.

Fig. 8.

Comparison of oxygenation properties of the major Hb isoform (HbA) between pairs of high- and low-altitude birds in the Andes. O2 equilibria were measured at pH 7.40, 37°C in the presence and absence of allosteric effectors ([Cl−], 0.10 mol l−1; [Hepes], 0.1 mol l−1; IHP:tetrameric Hb ratio, 2.0: [heme], 0.3 mmol l−1). For each taxon, P50 values (±s.e.m.) are reported for stripped Hbs in the absence of added anions, in the presence of Cl− alone (added as KCl), in the presence of IHP alone, and in the presence of both anions combined. As explained in the main text, the ‘KCl+IHP’ treatment is most relevant to in vivo conditions in avian red blood cells, but measurements of O2 affinity under each of the four standardized treatments provide insights into the functional mechanism responsible for observed differences in P50(KCl+IHP). In each pairwise comparison shown here, slight differences in intrinsic Hb–O2 affinity (reflected by stripped P50 values) become more pronounced in the presence of IHP. (A) Comparison of HbA O2 affinities between high- and low-altitude hummingbirds in the Emeralds clade (Trochilidae: Apodiformes): the green-and-white hummingbird, Amazilia viridicauda, and the amazilia hummingbird, A. amazilia, respectively. (B) Comparison of HbA O2 affinities between high- and low-altitude hummingbirds in the Coquettes clade (Trochilidae: Apodiformes): the Andean hillstar, Oreotrochilus estella, and the speckled hummingbird, Adelomyia melanogenys, respectively. (C) Comparison of HbA O2 affinities between high- and low-altitude flowerpiercers (Thraupidae: Passeriformes): the black-throated flowerpiercer, Diglossa brunneiventris, and deep-blue flowerpiercer, D. glauca, respectively. (D) Comparison of HbA O2 affinities between high- and low-altitude populations of the house wren, Troglodytes aedon (Troglodytidae: Passeriformes). (E) Comparison of HbA O2 affinities between high- and low-altitude populations of the hooded siskin, Spinus magellanica (Fringillidae: Passeriformes). (F) Comparison of HbA O2 affinities between high- and low-altitude nightjars (Caprimulgidae: Caprimulgiformes): the band-winged nightjar, Hydropsalis longirostris, and Tschudi's nightjar, H. decussata, respectively. Data from Projecto-Garcia et al. (2013), Galen et al. (2015), and Natarajan et al. (2016).