Locust ear as frequency analyser Final lecture: Mar 31, 2011, Bio 325 James F.C. Windmill, Martin C. Gopfert and Daniel Robert 2004. Tympanal travelling waves in migratory locusts Journal of experimental Biology 208: 157-168 Locust ear as frequency analyser

Muller’s organ in a locust As with most ears those of the locust are bilateral, a right and a left, each situated within a recess in the first abdominal segment. The plane of the tympanum is angled to face backward slightly. The auditory ganglion of each ear is visible through the transparent tympanum, its nerve running anteromedially to join the metathoracic ganglion. Also visible through the tympanum are dark brown chitinous structures (e.g., pyriform vesicle) that lie on top of the tympanum. The chitinous parts of this organ are formed from exoskeleton: the tympanum (ear drum) is a very much thinned region of the cuticle. Behind the tympanum, applied (like a triggered air bag it takes the shape of its ‘container’) is an expanded tracheal sac. Backing the membrane with air is an important adaptation: if the tympanum were backed by haemolymph of the circulatory system the tympanum’s movements would be significantly damped by the blood.

Locust ear old professor’s lecture note

Locust ear: neurosensory cells transduce sound into nerve membrane depolarizations

Pyriform vesicle and higher frequencies discrimination

Travelling waves vs standing waves eardrum movement when subjected to four different frequencies; scanning laser videos show the complex movement of different regions; profiles: red is outward movement of the tympanum and green is inward movement

Mammalian ear

Stapedius muscle inserts on stapes originates on mastoid bone; tensor tympani inserts on manubrium of malleus. New Mexico Mining & Minerals Stapedius and tensor tympani very large in bats. Echolocation needs high hearing sensitivity to detect faint echoes. These muscles are adapted in all mammals to dampen ossicle movement, an involuntary reflex action: bats need them especially.

Cochlea: frequency analyser

Summing up the theme Structure is illuminated by behaviour: the jumping of a flea shows the Structures evolve as packages: owls combine feather adaptations for sound reflection and quiet flight, with tubular eyes and turnable heads etc., all shaped by the need to Structures evolve with trade-offs: tubular eyes limit ability to rotate in the skull eye socket: attractive peacock plumage reduces flight efficiency. Structures change their function over time: the tube feet of a starfish were originally filter feeding devices. Above all never look at an animal without puzzling about its form. The structure on the back end of this horseshoe crab is a telson. It is shaped like a spike. A rudder? Then why not side-to-side flattened in order to exert effective force against the water? A defense against something attacking from behind? A device for burrowing? Always regard an animal as a product of its history and think in terms of the selective forces that might account for its form.