title: Structure and electrical properties of eye muscles in cave- and surface-dwelling crayfishes.
abstract: The morphologies and passive electrical parameters of fibres in two eye muscles of a surface- and a cave-dwelling crayfish were compared. In the cave-dwelling form the muscles contained fewer fibres, of less diameter, and hence had a smaller cross-sectional area. Current-voltage relationships were similar in both species. Input resistance was higher in the cave-dweller, but the difference was not as great as would be expected on the basis of geometry alone. Accordingly, the specific membrane resistance of muscle fibres in the cave-dweller is 50-60% smaller than that in the surface-dweller. This may account partially for the observation that identified excitatory junctional potentials in muscles of cave- and surface dwellers have similar amplitudes. We conclude that a functional oculomotor system is maintained in cave-dwelling crayfish, and that this system confers some positive selective advantage.
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D003400:Astacoidea / Q000033:anatomy & histology / Q000502:physiology*; D003624:Darkness; D004777:Environment; D005123:Eye / Q000033:anatomy & histology; D008564:Membrane Potentials; D009801:Oculomotor Muscles / Q000033:anatomy & histology* / Q000502:physiology