Adaptations for rapid and forceful contraction in wing muscles of the male golden-collared manakin: sex and species comparisons

Abstract

The courtship display of the male golden-collared manakin (Manacus vitellinus) of Panamanian rainforests is noteworthy for several types of whipcrack-like sounds created by a rapid overhead¯ip of the wings. We have hypothesized that this courtship behavior, which is not performed by females, is associated with steroid-sensitive and sexually dimorphic neuromuscular systems. Presumably, muscles creating the motion of the wingsnap in males are specialized for greater force generation and speed of contraction. We tested this hypothesis by examining mass, ®ber diameter, metabolic enzyme activity, and myosin isoform expression in several muscles of male and female manakins and in both sexes of a non-wingsnapping bird, the zebra ®nch (Taenopygia guttata). We have identi®ed three wing muscles, the scapulohumeralis caudalis, the supracoracoideus, and the pectoralis major, that di er in one or more of these characteristics across sex and species, suggesting they are specialized for faster contraction and greater force production in male manakins. These muscles normally function to raise and lower the wings during¯ight. As this movement is the principal motion of the wingsnap, these adaptations presumably underlie the performance of the wingsnap display. Keywords Bird á Courtship á Myosin á Acoustic signals á Sexually dimorphicAbbreviations a-GPD a-glycerophosphate dehydrogenase á Itb m. iliotibialis lateralis á IHC immunohistochemistry á NADH nicotinamide adenine dehydrogenase á OD optical density á Pec m. pectoralis á Sc m. supracoracoideus á SH m. scapulohumeralis caudalis

High-speed video analysis of wing-snapping in two manakin clades(Pipridae: Aves)

“…The scapulohumeralis caudalis in particular exhibits the greatest disparity in mass and fiber type composition (Schultz et al, 2001), and in a manner consistent with those expected for increased force generation and muscle contraction speeds. While consistent with our predictions, this interspecific comparison (Schultz et al, 2001) was made between M. vitellinus and T. guttata, of which the former were wild-caught, and the latter were captive individuals of a distantly related, ecologically distinct species that does not perform physical courtship displays. Thus, the great differences between the comparative and control species allows for numerous alternative explanations for the morphological differences found.…”

“…Previous morphological work has uncovered striking modifications of the wing morphology of Manacus (Lowe, 1942;Schultz et al, 2001;Bostwick, 2002; K.S.B., unpublished data) and other species in the Pipridae, including P. mentalis (Bostwick, 2002; K.S.B., unpublished data). The wing kinematics described above provide a preliminary functional context in which to interpret the morphological modifications found in Manacus, but they also complicate morphological interpretation by showing that the snaps and rolls of Manacus are produced by fundamentally different wing kinematics than snorts and fanning (and presumably whirrs and rattles).…”

“…Together with the primary downstroke muscle, the pectoralis, these muscles have been quantitatively compared in terms of mass and physiology between male and female Manacus vitellinus and Taenopygia guttata (Zebra finch). Male M. vitellinus exhibit muscular modifications in males relative to females, and in M. vitellinus relative to the control species (Schultz et al, 2001). The scapulohumeralis caudalis in particular exhibits the greatest disparity in mass and fiber type composition (Schultz et al, 2001), and in a manner consistent with those expected for increased force generation and muscle contraction speeds.…”

“…Male M. vitellinus exhibit muscular modifications in males relative to females, and in M. vitellinus relative to the control species (Schultz et al, 2001). The scapulohumeralis caudalis in particular exhibits the greatest disparity in mass and fiber type composition (Schultz et al, 2001), and in a manner consistent with those expected for increased force generation and muscle contraction speeds. While consistent with our predictions, this interspecific comparison (Schultz et al, 2001) was made between M. vitellinus and T. guttata, of which the former were wild-caught, and the latter were captive individuals of a distantly related, ecologically distinct species that does not perform physical courtship displays.…”

“…Extreme modifications of wing morphology (Lowe, 1942;Schultz et al, 2001;Bostwick, 2002) and physiology (Schultz and Schlinger, 1999;Saldanha et al, 2000) have been documented in several sonating piprids, especially the genus Manacus, but the function of the morphological modifications has remained unexplained due to lack of information on the mechanisms of sound production. The goal of the research presented here was to test the mechanistic hypotheses delineated above in order to understand the functional role of the modified piprid wing morphology.…”