HERMANSON, J.W.*; MITCHELL, R.M.; BETOF, A.S.; RISKIN, D.K.; Cornell Univ., Ithaca, NY: Muscle design and function in relation to locomotion: star-nosed moles and other “primitive” mammals.

Primitive placental mammals include shrews and moles, comprising the Insectivora of some authors. Shrews, considered to be relatively basal among living mammals, have been shown to contain locomotor muscles lacking type I, slow oxidative myofibers. One rationale proposed for this is that these mammals are lightweight and do not support their bodies off of the substrate for long periods of time. The question remains as to whether or not the muscles have been constrained (to lack type I fibers) by phylogeny assuming that the condition is a synapomorphy within Insectivora and other basal mammals. Thus, the evolution of type I fibers might be associated with derived mammals in response to functional demands. We analyzed the muscle architecture and histochemical properties, as well as myosin heavy chain isoforms in star-nosed moles (Condylura cristata) as one example of a primitive group of mammals despite their unique locomotor morphology and natural history. A suite of muscles including teres major and pectoralis contained all type II fibers that were of uniformly small diameter but that expressed a range of glycolytic potential as assessed with alpha-GPD reactions. Screening against two type I myosin antibodies yielded negative results in shrew and mole muscle. While birds and reptiles appear to have muscles containing type I fibers, we are intrigued at the absence of these fatigue resistant myofibers in these basal mammals. We extend this analysis to include functional interpretation of the forelimb and hindlimb muscles of the star-nosed mole and comparison with the short-tailed shrew (Blarina brevicauda).