Abstract
We examined fiber capillarization and ultrastructure in the highly aerobic flight muscle of six gray crowned rosy finches ( Leucosticte arctoa; mass 22.9±0.5 (SE) g) living at altitude (A; White Mountains of Eastern California; 4000 m) compared to eight sea-level (SL) house finches ( Carpodacus mexicanus, mass, 19.8±0.6 g) of the same subfamily, Carduelinae. Capillary length per fiber volume (A, 10 400±409 mm −2; SL, 7513±423; P<0.001) and capillary-to-fiber ratio (A, 2.32±0.07; SL, 1.85±0.06; P<0.001) were significantly greater in A, with no difference in fiber cross-sectional area compared to SL. Capillary geometry was significantly different in A, yielding a greater contribution of tortuosity and branching to capillary length than in SL. Capillary-to-fiber surface ratio and fiber mitochondrial volume were both greater in A, but their ratio was similar to SL, indicating a proportional increase in the size of the capillary to fiber interface and fiber mitochondrial volume in A to sustain high levels of aerobic capacity while living at altitude.
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