Sexual Dimorphisms in Neuromuscular Junction Morphology in the Green Anole Lizard

O’BRYANT, E.L.*; WADE, J.: Sexual Dimorphisms in Neuromuscular Junction Morphology in the Green Anole Lizard

The green anole lizard exhibits seasonal courtship behavior that is sexually dimorphic. It consists of the extension of a bright red throat fan, called a dewlap, along with head-bobs and a push-up display. While males extend the dewlap in aggressive encounters as well as in courtship, females use their diminutive dewlap much less frequently, and in agonistic encounters only. In parallel, a number of components of the neuromuscular system controlling dewlap extension are sexually dimorphic during the breeding season. For example, length of the second ceratobranchial cartilage (which bows out to extend the dewlap), dewlap motoneuron soma size, as well as dewlap muscle fiber size and number are all greater in males than in females. In the present study, intact males and females were sacrificed during the breeding season and the dewlap muscle and surrounding cartilage pieces (ceratohyal and first ceratobranchial) were extracted and post-fixed for 1 hr. The length of the muscle was measured in two dimensions: (1) along fibers between the two cartilage pieces, and (2) along the muscle parallel to them. The muscle was then stained for acetylcholinesterase to visualize neuromuscular junctions (NMJ) on the fibers. The cross-sectional area and density of NMJ were then measured for each animal. NMJ were on average larger in males than in females (p=.022), but their density along each fiber was equivalent between the sexes (p=.094). In addition, the length of the overall muscle (p<.0001), but not individual muscle fiber length (p=.372) was larger in males than in females. These results are consistent with the idea that enhanced NMJ size either facilitates or is a consequence of increased use of a larger dewlap in breeding males compared to females. Supported by NSF IBN-9733074.

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