Bio 325 Lect 11, 2014

1. Bio 325 Lect 11, 2014 Kelp and drag Swim bladder gas secretion, countercurrent Weberian Ossicles Sound in air and water Gas bag in a body: lung listening in frogs Muscle blocks

2. Thallus (body): stipes and blades, gas-filled pneumatocysts at base of blades contribute buoyancy. As a floating rope-like flexible structure, the stem goes with the wave in the direction of flow. Kelp is a brown alga growing in ‘forests’ in shallow seas “flexibility in combination with great length provides a mechanism of avoiding bearing large flow forces in habitats subjected to oscillating flow” (Vogel Cats’ Paws p. 94) holdfast Drag: retarding forces of fluids flowing relative to an object

3. Kelp is perhaps the fastest growing organism on earth. Half a metre a day and reaching lengths of 30-80 m. • See p. 94 Cats’ Paws: Flexibility can reduce drag: kelp (large seaweed) “When a wave comes crashing in to shore, a long flexible seaweed attached to the substratum moves with the water until it is strung out in the direction of flow: only then is there much water movement relative to the plant and does its thallus have to resist the significant flow forces. If an alga is long enough, the water that was rushing up the shore may be slowing down or starting to wash back down the shore before the plant is completely laid out with water moving past it. Therefore, flexibility in combination with great length provides a mechanism of avoiding bearing large flow forces in habitats subjected to oscillating flow.”

4. Swim bladder /Gas bladder Many bony fishes have a single median gas bag in their body used to change their density, giving neutral buoyancy at different levels in the water column. This bladder, situated just below the backbone and just above the viscera, contains oxygen at a high concentration; the oxygen is actively secreted from the blood. Fisheries & Oceans Canada

5. Univ. S. Dakota • A rete is a set of elongate parallel capillaries just ahead of the gas gland, some leading to it and some leading away: arterial blood to and venous blood from. • Tension of oxygen in the leaving venous capillaries is high, but by running these capillaries right beside the incoming arterial capillaries, oxygen can diffuse between them. • This is called a countercurrent exchange and the same morphological arrangement is also used by animals to conserve heat. • The oval is a separate chamber of the gas bladder that can be isolated by a sphincter muscle: it functions to permit diffusion back into the blood to reduce buoyancy.

6. “You strange, astonished-looking, angle-faced, Dreary-mouthed, gaping wretches of the sea, Gulping salt-water everlastingly, Cold-blooded, though with red your blood be graced, ---- And mute, though dwellers in the roaring waste.” James Henry Leigh Hunt • Its an effective poem, but Hunt couldn’t be more wrong. Fish are not mute, nor deaf. The difficulty with sound, in both air and water, is always in finding quiet. There is ‘too much’ sound in the sea [hence noise*]: fish make it just by moving about. It would be strange indeed if fishes had not evolved to gather information about their noisy environment. Indeed, fishes have elaborate systems for detecting sound waves in water and for many species their swimbladder has evolved an important sensory transducing function in addition to regulating body density.

7. Sound waves (compressional pressure waves) pass easily through the flesh of animals, flesh being mostly water anyway. A fish doesn’t need its generators or receivers on the body surface. But an interface with air, such as the gas bladder, is important in transduction of the water pressure wave: it is in effect, a way to make some part of the fish body move [oscillate] in order to extract frequency information from the sound waves. The pressure changes in the water wave are tracked as displacements of the swim bladder which moves a chain of specially evolved bones to impart frequencies to the otic capsule (membranous labyrinth) and brain.

8. Drums’ are an example of fishes that use the swim bladder to make sound signals • Sonic muscles investing the swim bladder are used by some fishes (family Sciaenidae: drums and croakers) to create sound signals: Aplodinotus The muscles squeeze the gas bladder, creating waves via animal tissue that radiate out into the sea. Freshwater carp Aplodinotus Freshwater drum Occurs in Lake Erie Inland fishes of NY

9. Sound in the fluids air and water: different physical features • Speed of sound in air can be taken as about 344 metres per sec [this is at 20 Celsius: it changes with temperature}. • In air can calculate: Wavelength (cm) = 34400 (cm per s) /frequency (cycles per s) • Middle C is 262 Hz (cycles/s); what is the wavelength of middle C in air? Ans. 344(100)/262 = 131.3 cm • What is the wavelength of the 4.7 kHz (4700 Hz) produced by a cricket as the fundamental of its calling song? Ans. 344(100)/4700 = 7.3 cm • What is the wavelength of 35000 produced by the katydid M. sphagnorum as part of its calling song? Ans. 344(100)/35000 = .983 cm • Calculate these WAVELENGTHS IN WATER: Speed of sound in water is 4-5 times faster than in air: 1430-1500 metres per sec. • So middle C is different in wavelength under water: 1500(100)/262 = 572.5 cm instead of 131.3 – and so would be the wavelengths of the katydids if they sang at the bottom of a pond.

10. Sound in air and water (continued) • Sound compression waves in both air and water have both displacement and pressure change. But water is much denser than air, so much less compressible: in water the amplitude of pressure oscillations for a given intensity is 60 times smaller but the sound pressure is 60 times greater. • One expects that sensory organs detecting underwater sound would transduce on the basis of pressure rather than displacement. (There are insect sensory transducers, Johnston’s Organ, that use the displacement rather than the pressure.) • Animal hearing organs that transduce waterborne sound must be stiffer than those of animals listening in air. • Lungs are a common air-filled cavity in many animals and lungs can play a role in sound transduction: an example is the co-qui treefrog.

11. Assigned reading: Narins P.M., Ehret G., Tautz J. 1988. Accessory pathway for sound transfer in a neotropical frog. PNAS 85: 1508- Eleutherodactylus coqui Body wall overlies lung cavity in this arboreal frog and with a laser vibrometer these authors show it vibrates in response to free-field sound in air. Pressure gradient system, i.e., sound reaches ear by both external and internal routes.

12. Fish muscles are of two colours: why? • The rate at which oxygen can be supplied to a muscle may become the limiting factor in the muscle’s activity during escape. So many animals have a separate set of anerobic muscles that work without oxygen limitation. These muscles convert glucose to lactic acid to get the energy for contraction. Energy thus obtained is via a less efficient metabolic process and the lactic acid that accumulates is yet another limitation, but where a burst of speed is important, anerobic muscles make this possible. Later the animal is able to oxidize the incompletely used products of anerobic metabolism.

13. Why are the axial muscles of fish so strangely shaped ? They look like zig-zag ‘W’s. Univ. of Michigan Museum of Zoology, UMMZ Adaptive fibre orientation in white muscle fibres in teleost fishes from p. 210-211, R. McNeill Alexander, 'Exploring Biomechanics', figure redrawn (gkm).

14. [“Aerobic axial muscles of fish, red muscles, run lengthwise along the sides of the body.“] • The white fibres (anerobic) " have different patterns in different fish species, "but the commonest pattern in teleost fishes... has white fibers running at angles of up to 35 degrees to the long axis of the body. The muscle is partitioned into segments called myotomes and each fiber runs only the length of a myotome, from one partition (septum) to the next. But if you follow a series of fibers, connected end to end through the partitions [from one myotome to the next] you will find a pattern: these chains of fibers run helically, like the strands of a rope." In other words these muscle fibre 'chains' lie at changing distances from the vertebral column. Zig-zag blocks of muscle myotomes separated by myocommas

15. "Imagine that the fibers were not so arranged, but instead all ran parallel to the long axis of the body. Imagine the fish bending to such an extent [in producing body waves] that the outermost fibers of the bend, just under the skin, had to shorten by 10 %. Fibers halfway between this peripheral position and the backbone would have to shorten by only 5% and fibers right alongside the vertebrae would have to shorten hardly at all. In each tail beat, the outermost fibers would have to shorten quite a lot and relatively fast, whereas the innermost fibers would shorten much less in the same time and therefore more slowly.“ This would be very inefficient.

16. "Now consider how the actual arrangement of white fibers affects the shortening of the muscles." Sequences ('chains') "of fibres run between muscle blocks helically, like the strands of a rope (represented as red ribbons in the illustration). Each chain lies close to the backbone for part of its course and nearer the skin of the fish's side for others. The result is that when the fish bends, say to the right, all the white fibers on the right side have to shorten by about the same percentage of their length."

17. Remember that the axial muscles on the left of the vertebral column are antagonized by those on the right and vice versa. These 'chains' of fibres (running across a series of 'zig-zag' myotomes) will all contract and shorten in phase with each other, reaching the same % shortening all at the same time and relaxing maximally at the same time. In other words they go through their cycle of contracting and relaxing together. But they are located at different points between the skin and the backbone as they follow their helical pattern. Thus at the time these 'functional myotome series' contract simultaneously they are at different phases of the body wave; if they were not at different phases they could not shorten by a uniform per cent.