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First published online February 15, 2006
Journal of Experimental Biology 209, 965-977 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02066

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Syringeal muscles fit the trill in ring doves (Streptopelia risoria L.)

C. P. H. Elemans^1,2,*, I. L. Y. Spierts¹, M. Hendriks¹, H. Schipper¹, U. K. Müller¹ and J. L. van Leeuwen¹

¹ Experimental Zoology Group, Wageningen University, Marijkeweg 40, 6709 PG, Wageningen, The Netherlands
² Department of Biology, University of Utah, 257S 1400E, UT 84112, Salt Lake City, USA

View larger version (61K): [in a new window]   Fig. 1. Syrinx morphology. (A) Morphology of the fresh syrinx of a male ring dove. The m. tracheolateralis (TL) inserts on the lateral tympaniform membrane (LTM). Because the TL muscle fibers seemingly overlap rostrally with fibers of the m. trachealis (TR), the origin of the TL cannot be determined exactly in vivo. The left and right m. sternotrachealis (ST) run together in several layers of fascia from their origin around tracheal ring T17–T19. The muscle fibers of the left ST overlap the fibers of the right ST. Around T12, the two muscles split, run through the interclavicular air sac (ICAS) separately and insert bilaterally on two protuberances of the sternum (not shown). (A different version of the image in A was also provided in the supplementary information accompanying Elemans et al., 2004.) (B) Sections through the trachea and syrinx using Masson's Trichrome stain. Muscle fibers of the TL and TR can be distinguished by following the sarcolemma in subsequent sections. The ST runs in the midline of the body, because the syrinx is tilted considerably with respect to the body. B1, B2, bronchial rings; LTM, Lateral tympaniform membrane; T1–T11, tracheal rings; prefix r and l indicate right and left, respectively.

View larger version (49K): [in a new window]   Fig. 2. Muscle preparations and measurements on muscle performance. (A) Ring dove syrinx. The dotted lines indicate dissection cuts for whole muscle preparations (1 and 2). (B) Twitch characteristics of a single-pulse muscle stimulation. Arrow indicates the onset of the stimulus. F10, F50 and F90 are defined as 10%, 50% and 90% of the maximum force Fmax. ton, time between stimulus and onset of muscle contraction; t10–90, time to ascend from F10 to F90; t90–10, time to descent from F90 to F10; t50–50, half-twitch time. (C) Muscle preparations were subjected to a sinusoidal length change with cycle frequency f and strain amplitude Lmax. The stimulus pulse train started at phase (degrees) in the cycle. (D) Example of force development during cycle. (E) Instantaneous power during cycle, indicating maximum instantaneous power (MIP). (F) Workloop with shaded area W represents work. C–F are presented as mean (solid lines) ± s.d. (dotted lines) over three cycles of one series. The s.d. values are too low to be clearly discernable.

View larger version (20K): [in a new window]   Fig. 3. Sound and muscle activity during the ring dove coo. (A,B,E,F,I,J) Typical results of (A,E,I) sound oscillograms and (B,F,J) spectrograms of the stereotyped ring dove coo, which consists of two syllables (S1, S2), followed by an inspiratory note (arrow in B) of three individuals D#1–3. Syllable S2 starts with a trill (tr). The result of the fundamental frequency analysis is superimposed on the spectrogram. The colour of the trace indicates the RMS value of the corresponding bin (yellow–red; low–high). (D,C,G,H,K,L) Electromyographic recording of TL (C,G,K) and (D,H,L) ST. EMG signal: upward, rectified and integrated with time-constant of 1 ms; downward, rectified. The part of the coo in the rectangle of dove D#1 is shown enlarged in Fig. 4. The timescale is the same for all panels.

View larger version (63K): [in a new window]   Fig. 4. Sound and muscle activity during the trill. (A) Sound oscillogram and (B) fundamental frequency of the trilled part of the coo from dove D#1. (C) TL and (D) ST EMG patterns during the trill. TL activation (red boxes) precedes the corresponding trill elements (gray boxes). Arrow shows TL burst associated with the first trill pulse (tr 1). ST activity shows no obvious temporal pattern. EMG signal: upward, rectified and integrated with time-constant of 1 ms; downward, rectified. This figure is modified from a previous version (Elemans et al., 2004).

View larger version (48K): [in a new window]   Fig. 5. Relationship between fundamental frequency and muscle activity during the coo. (A–C) Results of measurements in 16 544 calculated bins of 11 coos from different bouts for individual D#3 and (D–F) 9 435 calculated bins of 5 coos from different bouts for individual D#1. (A,D) Frequency–time relationships, linearly colour coded with time. Yellow corresponds to the start of the coo, red to the end of the coo. (B,E) Bins of integrated TL EMG activity normalised to maximal amplitude vs fundamental frequency of the sound with the same colour-coding as A and D, respectively. (C,F) The corresponding bin connections in time of the same bins in B and E, respectively. The dotted lines in C and F indicate regions where the relationship between TL activity and fundamental frequency of the sound differs.

View larger version (21K): [in a new window]   Fig. 6. Muscle performance. Muscles were stimulated at different phases () in the sinusoidal shortening–lengthening cycle. Normalized power as a function of stimulation at different phases () for (A) TL and (B) ST. Lines represent means ± s.d. (N=7). Cycle frequency is 10 Hz; strain, 5%. The duty factor is 25% of the strain cycle.

View larger version (51K): [in a new window]   Fig. 7. Work loop results. Normalized contour plots of (A) mean power and (B) mean maximal instantaneous power (MIP) for TL preparations. (C) Mean power and (D) mean MIP for ST preparations. Insets depict the corresponding standard deviations. Values are normalized per preparation. Asterisks show local maxima. The dots show the data points measured in the strain vs cycle frequency parameter space.

View larger version (79K): [in a new window]   Fig. 8. In situ shortening of TL. In situ length of TL when (A) not stimulated and (B) under full stimulation. The length change is about 10%.