INCREASED FIBER CAPILLARIZATION IN-FLIGHT MUSCLE OF FINCH AT ALTITUDE

We examined fiber capillarization and ultrastructure in the highly aer obic flight muscle of six gray crowned rosy finches (Leucosticte arcto a; 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 fi nches (Carpodacus mexicanus, mass; 19.8 +/- 0.6 g) of the same subfami ly, Carduelinae. Capillary length per fiber volume (A, 10400 +/- 409 m m(-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 grea ter 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 interfa ce and fiber mitochondrial volume in A to sustain high levels of aerob ic capacity while living at altitude. (C) 1998 Elsevier Science B.V. A ll rights reserved.