Lecture 17 Suspension-feeding birds: duck & flamingo Comparing the cicada and aphid clypeus Gut tube adaptations: discontinuous feeders and crops, gizzards, shunts, rumens, etc. Ennos Roland 2012. Solid biomechanics. Princeton Univ. Press, Princeton, Oxford. Added to reserve list in library. A very good resource for concepts you don’t understand or where you wish for more insight. For example see his Chapter 2 Biological Materials, Biological Protein Rubbers, Resilin, Abductin, Elastin. Chapter 1 deals with Newton’s laws, stress, strain, Young’s modulus Compliance is the inverse of stiffness; stiff materials have a high Young’s modulus, compliant materials (like resilin) have a low Young’s modulus. p. 36 he deals with the prealar arm. Mallard duck is a suspension-feeder: there are rows of projections called lamellae on the bill. “…when the mouth is closed, the large upper bill completely covers the lower …and when the mouth is slightly ajar, the adjacent lamellae of the upper and lower bills can act together as a sieve.” They must interdigitate. The tongue (hydrostat, blood) powers this filter via swellings. “…anterior swelling [drops] away from the roof of the mouth when the tongue moves forward, allowing water to enter the mouth from the front. When the tongue is drawn back, the front swelling presses against the roof of the mouth [like a piston], forcing the water backward and out the sides of the bill through the lamellae.” “… [a] rear swelling has projections called lingual scrapers on both sides; as the tongue moves back and forth these scrapers act to dislodge food particles from the lamellae and draw them [back] to the oesophagus. In mallard ducks, the tongue tip moves forward about 11 mm and then back again every 60 to 70 milliseconds. This rapid oscillation moves the water at high velocity, and so the lamellae may capture food particles by inertial impaction as well as by sieving.” Inertial impaction: Aerosol Impaction is the process in which particles are removed from an air stream by forcing the gases to make a sharp bend. Particles above a certain size possess so much momentum that they can not follow the air stream and strike a collection surface which is available for later analysis of mass and composition. (Wikki) Upside down: changes In upper jaw to improve its mobility ‘ultimate suspension-feeding bird’ The face of a flamingo is dominated by the filter on its face. https://web.stanford.edu/group/stanfordbirds/ text/essays/Flamingo_Feeding.html Comparing frons (face) of aphid and Cicadidae or Cicadellidae Sparky’s ice cream, Columbia Mo. USDA, Clemson Shape of a cicada’s face is determined by a cibarial pump; cicada is a fluid feeder that needs to create its own pressures to suck sap. Cibarial dilator muscles contract, dropping internal relative to external pressure: this pressure differential moves fluid up stylet bundle*. *Stylets are modified mandibles, maxillae, labium, elaborately lengthened and forming collective tubes for sap transfer. The cicada pictured is one of the 17-year ‘locusts’ that emerges in large numbers: a periodical cicada. Where a pump is needed, because the fluid food is not itself under pressure, a plant feeding insect may evolve one: pharyngeal or cibarial. Is this why cicadas, spittle bugs etc. have such a dilated face? Heads of aphid and cicada/spittlebug compared: cicadellids and cicadids have a disproportionately large cibarial pump. Why? • • • • • • Vascular plants, vascular tissue: phloem and xylem. Phloem is to the outside in most vascular plants; just beneath the bark of a tree. Phloem transports sap which contains sugars, the products of photosynthesis, direction of flow can be up or down, depending on to where the sugar is being transported. Aphids feed on phloem and obtain so much sugar it becomes a waste product. The aphid is dealing with a food which it concentrates in order to filter out food substance other than sugars. For this purpose it has a shunt in its gut. Xylem is vascular tissue that has always an upward directional flow and is associated with transpiration. It is mostly dead cells. Does xylem have sugars (when one taps a maple is it the xylem that is tapped? Is it worth feeding on?) Do cicadas feed on xylem; is xylem mostly at lower pressures than phloem, creating the need for a strong cibarial pump? A problem? • • • Aphid mouthparts (mandibles, maxillae, labrum and labium) are greatly lengthened, the first two drawn out into a long slender ‘stylet bundle’, the labrum and labium supporting the bundle base against the head. Each stylet is moved by retractor and protractor muscles situated in the head. The insect has channels within the adpressed maxillae, one to convey phloem sap up and in and one to carry saliva downward to lubricate bundle penetration with glandular secretion (i.e., aphid spit). Two grooves on the inner face of each maxillary stylet (blue) make up the two halves of a salivary canal and a food canal. Maxillary stylet Working its way down through the plant tissue, the stylet bundle gains support from the cellulose cell walls like a ‘worm’ used to clear blocked drains; confined laterally it cannot bend very far before being pushed forward; the insect takes many minutes (up to an hour) to reach the phloem and begin feeding. Phloem pressure pushes the sap up the maxillary food canal; apparently no need to pump/suck the fluid: note small head and thorax suggesting absence of a pump. transverse section stylet bundle ghppr head Rosy Apple Aphid with stylets inserted in plant mpts frons tissue colour coded Mandibular stylets (red) do the work of piercing the plant tissue, a right is thrust out a short distance (protracted) and penetrates down; then the left pushed until its tip meets that of the first; then the two maxillary stylets are lowered together into the created space: this is repeated between the walls of adjoining plant cells until the pholoem bundle is reached. Aphids are used to collect Plants in action phloem sap samples. Top photograph: a feeding aphid with its stylet embedded in a sieve tube (phloem). [scl, sclerenchyma; st, stylets; x, xylem; p, phloem. Note the Droplet drop of ‘honeydew’ being of ‘honey dew’ excreted from the aphid’s body. (a) to (e) show stylet cutting (microcautery) at about 3-5 s intervals (a to d) followed by a two-minute interval (d,e) where exudate accumulates. The stylet has just been cut in (b); droplets of hemolymph (aphid origin) are visible in (b) and (c); once the aphid moves to one side the first exudate appears (d), and within minutes a droplet (e) is available for microanalysis. Winged aphids can appear in populations and are the basis of dispersal The aphid needs to filter phloem and perhaps because of the pressure needs to secure a quiet backwater in its gut for secretion of enzymes and absorption of the products of digestion. The pressure pushes the fluid through at a high rate. Its gut loops back on itself and then is turned in ‘switchbacks’ overtop of the anterior midgut. This ‘filter chamber’ also functions a shunt: it allows for certain portions of the fluid to bypass the posterior midgut; through differential absorption the two overlain gut walls filter the wanted out of the unwanted. Gut tube adaptations • Inferring function from gross form may be more intuitive with guts than other body parts. Suppose you’re an animal with no teeth (because you’re a bird) and you also need a place to hold food while you travel (because you’ve got wings instead of hands, because you’re a bird), and you’ve got a lot of food available all at once? • You need to evolve a sac-like gut region with progress regulated by a sphincter muscle valve: need a crop or a pharynx . • The gut of animals is a long tube, with regions specialized for different assembly-line functions: regions specialized to: store, grind, churn, ferment, secrete enzymes and resorb digestive products and water, ultimately to accumulate and egest waste*. Gut diverticulae and storage: sacculate crop of leech: extreme downtime between blood feedings: adaptiveness of a crop. The leech (Annelida) has a disproportionately large crop in which it stores blood; this crop is comprised of many blindly ending lateral sacs that increase its capacity. Leeches feed on a food that is ready to digest so no teeth are required to ‘chew’ it. But the leech does have teeth to make the entry wound in its host. Diagram from sharon-taxonomy on the web McGill Office Science & Society Discontinuous feeding Mosquito (Culicidae): its crop rleates to the function of the insect abdominal tagma. • • Why don’t aphids have a crop? Another highly discontinuous fluid feeder, one finding a blood source only on occasion, the mosquito must often get all its food intake from just one feeding event. It uses piercing and sucking mouthparts elongated into a ‘straw’, halfgrooved appendages adpressed to make composite channels for fluid feeding (just like the aphid). This insect takes in a large quantity of blood and has to store it for later digestion. For this it needs a crop. Why no dilated face? Diverticulae of the gut tube arise in the thorax; but the thorax is a locomotory tagma, its volume mostly occupied by flight muscle. No room for blood storage in the thorax. On the other hand the abdomen’s telescoped segments are designed for expansion. Need to prevent blood coagulation during storage. Some mosquitoes feed on frog blood. • So the main crop (red) extends into and occupies the mosquito abdomen. It receives the blood as ingested (a valve shuts off the midgut) and the abdomen expands greatly. So one of the abdomen’s functions as a tagma is illustrated: allowing expansion to accomodate food intake. Ennos p. 80: chapter on polymer composite materials • • • • • • The problem of using vascular plants as food is cell walls and lignification. [Similarity of plant cell walls to arthropod cuticle) “Like cuticle, the plant cell wall is a composite of fibres of a straight-chain sugar” – cellulose fibrils. The cellulose “occurs within a matrix made of branched hemicellulose molecules.” “The mechanical properties of the cell-wall material is strikingly similar to that of cuticle.” “The high compliance of the matrix allows developing cells to stretch their cell wall using turgor pressure, just as insects stretch their skeletons at molt.” “Another similarity of cell walls to insect cuticle is the way that many of them are stiffened and strengthened by the process of lignification , which is very similar to the process of sclerotization. During lignification the complex polyphenol molecule lignin is incorporated into the cell wall…resulting in cell-wall material that is stiffer and stronger [with]…a lower breaking strain. The cell wall of plants becomes a major problem for herbivores in getting at the cell content as food. Bird gizzard Rocking T Ranch • An organ thickly invested with muscle that requires ingested gravel to ‘mill’ the food into smaller particles. Notice the peculiar form of the lining tissue. And birds also have a crop: useful for storage: it takes more time to digest than ingest. Teeth specialized with a high crown for grinding. Major tooth materials:. 1) enamel, shinny hard thin layer over the tooth surface: almost completely inorganic. “Two-thirds of its substance consists, as seen in mammals, of long prisms of calcium phosphate, arranged with their axes at right angles to the surface...” (Romer); 2) dentine, softer, wears more easily, forms main bulk of tooth. 3) cement. These 3 materials, differing in wear rates, keep tooth from becoming smooth through wear Grazing hoofed mammals have plant-wall chewing problems. Hypsodont teeth: high-crowned, protrude well above the gum, creating length for uneven wear during a lifetime of grazing (grasses with silica being an adaptation of the plant to protect itself from such grazers). Ruminants and horses have hypsodont dentition. The opposite condition is called brachydont. Hypsodont teeth may also be selenodont (see next slide). A cow’s teeth continue to grow through life. prehistoric gazelle Greece Museum Paleontology Geology Diastema: tooth series separation; function in the horse? Lets tongue out?