January 29

1. January 29 Colonial hydrozoans of the Order Siphonophora Swim bladder functions Counter current retes Chaoborus: ghost midges Exoskeletons and levers Saltatoria: jumping animals

2. ~300 species live in the open ocean Siphonophora (Cnidaria)colonial Hydrozoa Colonial hydrozoa: what is a pneumatophore? A pneumatophore is an individual colonial zooid modified into a gas-filled float giving buoyancy to the colony below. Theyuse stinging nematocysts to capture fish prey. Zooids: nectophores: squirt out jets of seawater to propel the colony gastrozooids are sac-like, specialized for ingestion and distribution of nutrients to rest of colony dactylozooids with batteries of nematocysts etc.

3. Siphonophores have created “a complex metazoan body by making organs out of individual organisms” (p 386, Wilson) Velella: By-the-wind sailor from Meglitsch P.A. Invertebrate Zoology Wikkipedia Wilson, E.O. 1975. Sociobiology. Harvard, Cambridge Mass.

4. Buoyancy see Vogel Comparative Biomechanics p. 96 • Archimedes’ Law : objects heavier than the volume of water they displace will sink; objects lighter than the volume of water they displace will rise. A fish is buoyed up by a force equal to the weight of the water it displaces. It can change this force by changing its volume, i.e., displacing more or less water. Secreting oxygen gas into its swim bladder from the blood, the fish increases its volume and displaces more water, so increasing the force acting to make it rise in the water column. Conversely it can absorb oxygen gas from the bladder and so sink. Inland fishes of NY, Cornell Recall remarks last lecture re Buoyancy Compensators and the virtues of being neutrally buoyant.

5. 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. Ancestors of bony fishes, living in fresh water, evolved lungs to supplement their gills in times of drought. When some of these ancestors reinvaded the seas these lungs evolved into swim bladders. Fisheries & Oceans Canada

6. Univ. S. Dakota • How to keep oxygen tension high in the bladder when blood has a much lower tension: oxygen will tend to diffuse from the bladder into the blood*. Rete mirabile [Latin ‘rete’ is ‘net’, i.e., network of capillaries. • Rete is a set of relatively long parallel-lying capillaries just ahead of the gas gland, some leading to it and some leading away: ‘arterial’ blood to and ‘venous’ blood from (Red Body). • 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 is also used to conserve heat. • *The oval is a separate chamber of the gas bladder isolated by a sphincter muscle that allows diffusion back into the blood to reduce buoyancy. • (Tension: term applied to the partial pressure of a gas when in solution.)

7. Weberian ossicles • Sound waves travel well in water (and 4X faster than in air) and they pass easily through the flesh of animals. But they are interrupted by gas – e.g., swim bladder. So the swimbladder is a ‘bubble of gas’ that is readily vibrated by impinging sound waves. Some fish (freshwater carp – overgrown minnow -- have capitalized on this: special bones ‘Weber’s Bones’ connect the swim bladder to the internal ear. >speechlab.eece.mu.edu< Freshwater carp “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 Inland fishes of NY

8. ‘Drums’ are fishes that use the swim bladder to make sound signals • Sonic muscles investing the swim bladder can be used by some fishes (family Sciaenidae: drums and croakers) to create sound signals: Aplodinotus >speechlab.eece.mu.edu<. Aplodinotus Freshwater drum Occurs in Lake Erie

9. Summing up swim bladder functions • Imagine it as it isn’t. If you put the swim bladder elsewhere in the body, e.g., below the viscera, what would be the effect? • The fish would become unstable if its centre of mass was placed below its centre of volume (Wikkipedia). In other words the dorsal location of the swim bladder enables the fish to swim properly. • Fish swim bladders function to adjust body density (regulate buoyancy), and to establish stability. In some fishes it is important as a sensory organ both in listening for sound and making it.

10. A freshwater insect with adaptation for buoyancy control They dive very deep in lakes, apparently in contrast to other aquatic insects Chaoborus: ghost midge Phantom midges: Family Chaoboridae; these are insects, flies (Order Diptera), similar to mosquitoes as adults, but they don’t take blood. Larvae are aquatic and predaceous; their antennae are raptorial and they prey on mosquito larvae. Because they are so transparent they have the common name ghost or phantom midge. They regulate their depth with two pairs of bilaterally symmetrically placed gas-filled sacs. How appears unknown.

11. Maddrell (1998) has a theory about why there are no insects in the sea: he thinks their tracheal system is inconsistent with going to depth – pressure at depth would so reduce the volume of their tracheae that these would collapse -- diurnal migration to depth is critical to avoiding predation in the sea he says; crustaceans can do it since not having gas-filled tubes for breathing (they use gills), but insects can’t. • But Chaeoborus appears to falsiby his hypothesis -- because of its unusual ability to dive deeply and successfully in freshwater lakes. • “A major but apparently solitary exception to this [ability to dive deeply] is found with larvae of the midge Chaoborus, which can occur in enormous numbers in very large lakes. However, this hides the facts that it avoids predation exactly as advocated above, i.e., it dives down to 70 m in this case (Green et al. 1973), and that it is a highly unusual insect. It can avoid the limitation that its tracheal system must fail at these depths from the fact that it is reduced to two pairs of gas-filled spherical sacs used to provide variable buoyancy...” (Seems a poorly developed ‘explanation’; there must be more to the buoyancy chambers of Chaoborus.) • Green J. et al. 1973. Ecological studies... J. Zool. Lond. 170: 299-308. Maddrell S.H.P. 1998. Why are there no insects in the open sea? J. exp. Biol. 201: 2461-2464.

12. Levers • A lever is a machine that moves (translocates) forces from one place to another, at the same time changing the force magnitude and direction. • Lever arm of the force-in is the shortest distance from the axis of rotation to the load. • Lever arm of the force-out is the shortest distance from the axis of rotation to where the load is considered to act (i.e., it’s centre of gravity). • Force advantage of a lever: the factor by which the force in is changed: FORCE OUT/FORCE IN • Distance advantage of a lever: the factor by which the distance moved is changed: DISTANCE (speed) OUT/DISTANCE (speed) IN • [Since both effort (force in) and the load (force out) must move their distances in the same time: distance advantage is the same thing as speed advantage.] • Force advantage and distance advantage have a reciprocal relationship: a lever with a good force advantage must have a poor distance advantage; a lever with a poor force advantage will have a good distance advantage. • Muscles often have to work with a poor force advantage, but they can have a large distance advantage.

13. 3 classes of lever: classified on the basis of the sequencing of force in, force out and fulcrum (axis) • FIRST EFFORT FULCRUM LOAD • SECOND FULCRUM LOAD EFFORT • THIRD FULCRUM EFFORT LOAD • One of the commonest arrangements in animal muscle systems is a first, together with a third-class, lever acting as an antagonistic pair. • Remember to consider the centre of gravity. • First class levers: force advantage is usually >1, speed advantage can be very good (wing of a fly for example) • Second class levers: force advantage is always >1, speed advantage is always <1 • Third class levers: force advantage is always <1 • distance advantage >1

16. Scallop as a 2nd class lever The load is assumed to be acting through the centre of gravity of the bivalve; the force out lifts this load.

19. Saltatorial: animals modified for leaping tracks in snow Forelimbs small, hindlimbs enlarged

20. Sources re jumping • Heitler, W.J. 1974. The locust jump, specialisations of the metathoracic femoral-tibial joint. Journal of comparative Physiology 89: 93-104. • Bayley, T.G. 2012. A buckling region in locust hindlegs contains resilin and absorbs energy when jumping or kicking goes wrong. J. exp. Biol. 215: 1151-1161. • Patek, S.N. et al. 2011. From bouncy legs to poisoned arrows: elastic movements in invertebrates. J. exp. Biol. 214: 1973-1980. • Gordon, J.E. 1978. Structures or why things don’t fall down. Penguin. • Sutton, G.P. & Burrows, M. 2011. Biomechanics of jumping in the flea. J. exp. Biol. 214: 836-847.

21. A bow should never be ‘shot’ without an arrow (Gordon 1976, p.92): this is because there is no way of getting rid of stored strain energy. It is possible to shatter a bow in this way. The strain energy stored in the bent bow can no longer be dissipated in the kinetic energy of the arrow and is used to make cracks in the substance of the bow. • A bow makes a nice example of tension and compression surfaces in a ‘beam’ (Vogel 1988, p. 202). Bending an object of thickness has the effect of tensing on the outside of the curve and compressing on the inside. In the middle there will be a neutral plane where there is no stress in either tension or compression (but not in shear). From this plane toward the surfaces stresses increase. This means that central regions contribute less strength; it is the reason why bones can be nearly as strong when hollow.

22. Special shock aborbers for kicks gone astray • Gordon’s comments about bows needing arrows apply readily to locust kicks that go wrong . • From the abstract of Bayley et al. 2012. “If a hindleg of a locust slips during jumping, or misses its target during kicking, energy generated by the two extensor tibiae muscles is no longer expended in raising the body [jumping] or striking a target.” • Bayley found a special region of the proximal hind tibia that is adapted to buckle under these conditions through the presence of a special rubbery cuticular protein, resilin. • As we now analyse in some detail the jumping of several insects, resilin will be seen to play an important role.