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First published online October 19, 2007
Journal of Experimental Biology 210, 3780-3788 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.006288
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Modulation of flight muscle power output in budgerigars Melopsittacus undulatus and zebra finches Taeniopygia guttata: in vitro muscle performance

David J. Ellerby* and Graham N. Askew{dagger}

Institute of Integrative and Comparative Biology, University of Leeds, Leeds LS2 9JT, UK


Figure 1
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  		Fig. 1. Representative force–velocity relationships of zebra finch (B) and budgerigar (A) pectoralis muscle fascicles. Muscle fascicle velocity is expressed relative to resting muscle length, L0. Muscle fascicle force is expressed relative to maximal isometric force, P0.

 

Figure 2
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  		Fig. 2. Mechanical performance of a budgerigar pectoralis muscle fascicle in vitro. (A) Force production during strain and activation conditions measured in vivo at 4 m s–1 simulated flight speed. Length, unbroken lines; stress, broken lines. The bold line shows the timing of the stimulus relative to the strain cycle. (B) Work loops obtained by plotting fascicle stress against length for the data shown in A. Fascicle length is expressed relative to resting muscle length, L0. Muscle stress is expressed relative to maximal isometric stress, P0.

 

Figure 3
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  		Fig. 3. Mean stress difference {sigma} of zebra finch and budgerigar pectoralis muscle fascicles in relation to simulated flight speed. Values are means ± s.e.m. (budgerigars: N=11, 9, 9, 6, 9, 5, 7 for speeds 4, 6, 8, 10, 12, 14, 16 m s–1, respectively; zebra finches: N=7, 6, 3, 5, 4, 4, 7 for speeds 0, 4, 6, 8, 10, 12, 14 m s–1, respectively).

 

Figure 4
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  		Fig. 4. Relationship between mechanical power output of (A) zebra finch and (B) budgerigar pectoralis muscle fascicles and simulated flight speed. Open circles show the power output of supramaximally stimulated muscle measured in vitro. Open triangles show these values corrected to account for in vivo changes in EMG intensity with flight speed. Closed triangles show the values from supramaximally stimulated muscle corrected to account for changes in EMG intensity and the relative duration of non-flapping flight with flight speed. For each species and within each set of conditions (in vitro, estimated in vivo and flight power), mean values designated by the same number were not significantly different (Scheffé P>0.05). Values are means ± s.e.m. (budgerigars: N=11, 9, 9, 6, 9, 5, 7 for speeds 4, 6, 8, 10, 12, 14, 16 m s–1, respectively; zebra finches: N=7, 6, 3, 5, 4, 4, 7 for speeds 0, 4, 6, 8, 10, 12, 14 m s–1, respectively).

 

Figure 5
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  		Fig. 5. Relative changes in pectoralis power output (%{Delta}P) due to changes in muscle strain trajectory, recruitment intensity and intermittent flapping duration in (A) zebra finches and (B) budgerigars with flight speed. Values are means ± s.e.m. (zebra finches: N=6, 3, 5, 4, 4, 7 for speeds 4, 6, 8, 10, 12, 14 m s–1, respectively; budgerigars: N=11, 9, 9, 6, 9, 5, 7 for speeds 4, 6, 8, 10, 12, 14, 16 m s–1, respectively).

 

Figure 6
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  		Fig. 6. The effects of cycle shortening duration on work output for a range of aerobic power generating muscles. Data are from zebra finch Taeniopygia guttata pectoralis muscle (present study) and budgerigar Melopsittacus undulatus pectoralis muscle (present study); `birds in vivo' are European starling Sturnus vulgaris pectoralis muscle (Biewener et al., 1992Go), mallard Anas platyrhynchos pectoralis muscle (Williamson et al., 2001Go), cockatiel Nymphicus hollandicus pectoralis muscle (Hedrick et al., 2003Go) and pigeon Columba livia pectoralis muscle (Biewener et al., 1998Go); `flight muscles in vitro' are tettigonid (Neoconocephalus triops) wing muscles (Josephson, 1985bGo) and hawkmoth dorsoventral muscle (Stevenson and Josephson, 1990Go); `other muscles in vitro' are Hyla versicolor and H. chrysoscelis external oblique muscles (Girgenrath and Marsh, 1999Go), mouse (Mus) and rat (Rattus) diaphragm muscle (Altringham and Young, 1991Go), mouse soleus muscle (Askew and Marsh, 1997Go) and rat soleus muscle (Swoap et al., 1997Go). The solid line indicates scaling relationships for data excluding the data from the present study, and broken lines the upper and lower 95% confidence limits.

 




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