Meeting Abstract
P1.64 Sunday, Jan. 4 Sexual Dimorphism of Syringeal Muscles in Songbirds UCHIDA, A.M.*; GREEN, J.; AHMAD, S.; GOLLER, F.; MEYERS, R.A.; Weber State University, Ogden, UT; Weber State University, Ogden, UT; Weber State University, Ogden, UT; University of Utah, Salt Lake City, UT; Weber State University, Ogden, UT rmeyers@weber.edu
Male songbirds typically sing more frequently and more complex songs than females; in some species females do not sing at all. This behavioral difference is paralleled by sexually dimorphic syringeal muscle mass, but whether it is also reflected in syringeal muscle architecture is unknown. Fiber type composition of these muscles was investigated using myosin ATPase and immunohistochemistry. Female and male members of 5 oscine species (European Starlings, Sturnus vulgaris; White-crowned Sparrows, Zonotrichia leucophrys; Red-winged Blackbirds, Agelaius phoeniceus; Brown-headed Cowbirds, Molothrus ater; and Bengalese Finches, Lonchura domestica) all showed similar syrinx muscle fiber morphology, with larger superfast fibers outnumbering smaller fast fibers (for starlings: superfast fiber mean diameter 31-38m and ~70% of fiber population; fast fiber mean diameter 14-20m and ~30% of fibers). In contrast, Zebra Finches (Taeniopygia guttata) showed pronounced sexual dimorphism, with males possessing a majority of superfast fibers (as in the other species examined) and females a majority of fast. This finding provides a structural explanation for equal twitch durations in male and female starlings and faster twitch times in male Zebra Finches relative to females. Whereas female starlings, sparrows, and blackbirds sing occasionally, female Zebra Finches, cowbirds and Bengalese Finches do not. Thus the presence of superfast fibers does not parallel the occurrence of singing in females. These findings suggest that superfast fibers may be a basal character of the oscine syrinx, or are essential for other vocal or non-vocal functions. Further investigation of closely related species and behavior is needed. Supported by NIH grant #DC004390 and WSU.
