6. Feb 2011

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  1. Lecture 8: Animals
  2. What is an animal? Multicellular eukaryotes Chemoheterotrophs- digest food inside body Sexual reproduction Muscles and nerves
  3. Animal Ancestry Colonial flagellate hypothesis Ancestor was colony of flagellates in a sphere > cells became specialized > infolding created two layers of cells Supported by fact that many tissues develop this way embryonically Supported by implication that radial symmetry preceeded bilateral symmetry Supported by choanoflagellates- closest protist relative of animals
  4. Colonial Flagellate • This is an illustration of Proterospongia. The cells are embedded in a jelly- like matrix. Whether this is a colonial choanoflagellate or a very simple animal depends upon whom you ask.
  5. Evolution Many kinds arose during Cambrian explosion, happened so fast the origin of many is murky DNA evidence points to the tree we currently use See pg. 312
  6. Terms Used for Classification Germ layer: tissue layers found in embryos; develop into different tissue types Endoderm: Innermost germ layer- gives rise to lining of digestive tract, etc. Ectoderm: Outermost germ layer- gives rise to nervous system and outer integument Mesoderm: Middle germ layer- gives rise to many organs, muscle, connective tissue
  7. Terms Used for Classification Radial symmetry: organized circularly Bilateral symmetry: left- right symmetry (like us) Cephalization: localization of brain and sensory organs
  8. Terms Used for Classification Protosomes: the first embryonic opening becomes the mouth Deuterosomes: the first embryonic opening becomes the anus Coelom: Body cavity where the organs are located
  9. Terms Used for Classification Acoelomates: do not have a coelom Pseudocoelomates: have a partial coelom Coelomates: have a true coelom Segmentation: repetition of body parts along the length of the body
  10. Classification Animals are classified based on the characteristics we just listed We will now examine different groups
  11. Sponges Phylum Poriphera Base of evolutionary tree of animals - collar cells at pores are basically identical to choanoflagellates Cellular level organization Multicellular, but lack organized tissues Filter feeders, can filter huge amounts of water per day Can reproduce both sexually and asexually Asexually: budding Sexually: eggs and sperm released into central cavity
  12. Cnidarians Phylum Cnidaria, sea anemones and jellyfish Have radial symmetry Have two germ layers: ecto and endoderm Capture prey with tentacles that have stinging cells Have tissue level of organization
  13. Flatworms Phylum Platyhelmenthes Bilateral symmetry Have all 3 germ layers Acoelomates Have cephalization- small brain, eyespots, chemosensitive organs Captures food by wrapping it up and covering it in mucus, then tearing and sucking up
  14. More flatworms Digestive tract only has one opening Hemaphrodites; sexual reproduction Free living are called planarians Parasitic are tapeworms and flukes Have hooks and suckers on mouth to hold onto host tissues Can live for years
  15. Roundworms Phylum Nematoda Have a body cavity- Pseudocoelomates, because not completely surrounded by mesoderm Complete digestive tract- open on both ends Nonsegmented Many are free living and live in a variety of habitats and eat a variety of food Many parasites as well: roundworm, hookworm, Elephantiasis, Trichinosis
  16. Hookworms and the American South People in the South after the Civil War seen as lazy Study of people and hygiene habits Trees instead of latrines used Hookworms! Can travel up to 6’ after being deposited- were causing large infections Just digging a hole that was 6’ deep solved the problem
  17. Molluscs Phylum Mollusca, snails, octopuses, scallops, clams, nautiluses Have a coelom, proteosomes Have 3 parts: Visceral mass: contains organs Foot: used for locomotion Mantle: covers the visceral mass- may secrete exoskeleton to form shell Also may have a radula: like a toothy tongue
  18. Molluscs There are 3 types of molluscs:gastropods, cephalopods, bivalves Gastropods: Conchs, snails, nudibranchs Foot ventrally flattened, muscle contractions pass along the foot to move it Terrestrial snails use the mantle as a lung
  19. Molluscs Cephalopods: Octopus, Squid, Nautilus “Head-footed” - the foot is the tentacles around the head Have a beak- use tentacles to seize prey and beak and radula to tear it up Complex nervous and sensory systems Can move quickly by jetting water out of the mantle
  20. Molluscs Bivalves: Clams, oysters, scallops, mussels Shell has two parts, foot projects ventrally from shell Filter feeders, water enters through a siphon and food adheres to the gills; food then moved to the mouth by cillia
  21. Annelids Phylum Annelida, worms Has coelom and are segmented, proteosomes Coelom is filled with fluid; it is divided by septa which make it more rigid- facilitates movement Complete digestive tract; have crop, gizzard, intestine, accessory glands, etc. Circulatory system to carry blood Have a brain Remove waste by nephridia- ducts that carry waste to pores in the skin
  22. Annelids Again, 3 main groups: Polychaetes, oligochaetes, leeches Divided by how many setae (=bristles) on each body segment- these bristles anchor the worm and help it move Polychaetes: have many setae, are predatory Oligochaetes: Have a few- decomposers that live in soil: earthworms leeches: No setae - have suckers to attach to food
  23. Polychaetes
  24. Oligochaetes Giant earthworm!
  25. Leeches
  26. Arthropods Phylum Arthropoda: Over one million species! Insects, crustaceans, arachnids Coelom, segmented, proteosomes Have six characteristics: 1. Jointed appendages- hollow tubes moved by muscles 2. Exoskeleton- made of chitin, rigid and jointed 3. Segmentation- Some repeated, some fused in to head, abdomen and thorax only 4. Well-developed nervous system- Brain and ventral nerve cord, eyes, many other senses 5. Variety of respiratory organs- Gills, book lungs, or trachae, also open circulatory system 6. Metamorphosis- reduces competition of various age classes
  27. Arthropods Crustaceans: lobsters, crabs, barnacles, shrimp Mostly marine, but also freshwater (crayfish) and terrestrial (pillbugs) Head has 5 pairs of appendages: antennae, antennules- sensory, 3 mouthparts Thorax has 5 pairs of walking legs, first is the claw Abdomen has swimmerets- like small paddles and tail Hugely important in food chain - krill, etc
  28. Arthropods Arachnids: Spiders, scorpions, ticks, mites, harvestmen Spiders- Have cephalothorax and abdomen, kill prey with venom, use silk Scorpions- oldest terrestrial arthropods, nocturnal Ticks- are parasitic Horseshoe crabs- grouped with arachnids, but very unique in many ways
  29. Arthropods Insects: Largest group of animals Have head, thorax, and abdomen Can have wings- one or two pairs Live in huge variety of environments and eat huge variety of food
  30. Echinoderms Phylum Echinodermata: sea stars, sea urchins, sea cucumbers Deuterosomes; bilaterally sym. as larvae but radially sym. as adult No head, brain or segmentation No advanced nervous or circulatory system These seem so primitive, why discuss them here? They are closely related to Chordates!
  31. Chordates Phylum Chordata: Fish, amphibians, reptiles, mammals Coelom, deuterosomes, segmented 4 characteristics: 1. Notochord: Dorsal supporting rod 2. Dorsal tubular nerve cord: contains a tube filled with fluid 3. Pharyngeal pouches: in many, seen only in the embryo- become gills in larval amphibians and fish, in humans become auditory tubes, tonsils, thymus and parathyroids 4. Tail: A postanal tail
  32. Chordates Most chordates are vertebrates, in which the notochord has been replaced by the vertebrae (backbones) which protect the nerve cord (spinal cord) However, there are a few chordates that are invertebrates: the Tunicates and the Lancelets Marine organisms- sea squirts
  33. Vertebrates Series of evolutionary advances used to characterize the verts- See evolutionary tree on pg. 325 for a list of these advances
  34. Here, Fishy, Fishy, Fishy Jawless fish: the first vertebrates No jaws- they are cylindrical, do not have paired fins- they undulate through the water Two groups today: hagfish and lampreys- they have a circular mouth Jaws are thought to have evolved from the first pair of gill arches
  35. Fish- Sharks! Sharks, rays and skates are Cartilaginous fish, they have a skeleton made of cartilage instead of bones Great predators: they can sense electrical currents, pressure changes, and have a great sense of smell
  36. FISH Bony fish: most numerous and diverse, two types: Ray-finned: Like trout, perch, etc., very diverse group Have swim bladder to control buoyancy, skin covered by bony scales Respire by having water flow through the mouth over the gills Single circuit circulatory system- Heart pumps blood to gills and then directly to body
  37. FISH Lobe-finned: Have fleshy fins Ancestors of amphibians Most have lung- so can breathe air
  38. Amphibians Frogs, toads, salamanders, cecilians Have jointed limbs so can walk on land, also eyelids to keep eye moist, ears, larynx, larger brain Need water to reproduce Most have lungs, also respire through skin 3 chambered heart, blood from body and lungs is sent out to body and lungs Most show metamorphosis
  39. Reptiles Dinos, snakes, lizards, turtles, crocs, birds Body covered in scales 3 chambered heart Can reproduce on land without water- amniote egg- provides embryo with food, water and oxygen, protects it from drying Except for birds (and some dinos?) are ectothermic- body temp controlled by environment
  40. Birds Really, birds are reptiles- feathers are just modified scales However, some differences- egg is hard instead of leathery, endothermic Flying- many many adaptations to allow flight Hollow bones, front legs are wings 4 chambered heart Well-developed brains, good vision
  41. Mammals Mammals have mammary glands that produce milk for offspring, and hair First mammals were monotremes and marsupials- monotremes lay eggs, marsupials have pouch Placental mammals evolved later, but are most diverse group today Embryo develops inside uterus, maternal blood provides nutrients and oxygen It is the same membranes that do this in the egg that do this in the uterus- what the afterbirth is Mammals have big brains and are very active
  42. Humans Humans are Primates- includes monkeys, apes and humans This does not mean monkeys apes humans Rather, it means that all primates share a common ancestor
  43. Primates Primates primarily adapted to arboreal life- limbs are mobile, have 5 digits, have opposable thumb and frequently big toe Trend is towards larger and more complex brain Humans most closely related to African apes- chimps, gorillas last common ancestor ~ 7 MYA
  44. Hominids Humans, apes and human-like ancestors are the hominids Can stand erect and walk on two feet We will discuss some human ancestors
  45. Hominids Early fossils, around 7 MYA, the time of the ape- hominid split: Sahelanthropus tchadensis: opening for spine suggests bipedalism, smaller canines Ardipithicus ramidus: 4 MYA, teeth less apelike, only fragments found so far
  46. Hominids Australopithecines- group of hominids that diversified in Africa about 4 MYA A. afarensis- Lucy- stood upright, bipedal, but small brain (3.18 MYA) One of these species may be the direct ancestor of humans
  47. Hominids Homo habilis- ~2 MYA, larger brain, used tools, smaller teeth skulls seem to indicate that the speech centers of the brain were enlarged- could probably communicate and co-operate to gather food Co-operation may have led to H. habilis out-competing the Australopithecines
  48. Hominids Homo erectus- 1.9- 0.3 MYA, fossils found in Africa, but also Asia and Europe Probably several species included in this group Still larger skulls, flatter face, taller Fossils found in many sites- were able to travel long distances First to use fire, made advanced tools
  49. Hominids Homo neandertalensis- 200,000 YO, found in Germany Short, stocky, heavy build, prominent brow Culturally advanced- lived in caves, may have made houses, made many tools Hunted large animals Buried their dead
  50. Hominids Cro-Magnons- oldest fossils to be designated as our species, Homo sapiens Fossils from France Compound tools, great hunters Had language, lived in groups Had art- cave drawings
  51. Hominids Homo sapiens- how did first humans evolve? We’re not sure- there are two theories: Out of Africa: H. sapiens evolved in Africa, migrated to Europe and Asia and replaced hominids already there Multiregional continuity hypothesis: evolved independently in several regions In the MCH- different regions would be genetically dissimilar, OOA would be more genetically alike Thus far it seems that the OOA is the most supported

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