21 st lecture 11/09/15

Transcription

1 21 st lecture 11/09/15 Vertebrate defining features- vertebrae (backbone) forms around notochord. The notochord is present during development. The nerve chord is on the dorsal surface. Vertebrates have an internal and elaborate skeleton (cartilage or bone). There is a defined head with braincase (skull), and sensory organs. There are two girdles- pectoral muscles, and arms come off these. We also have a pelvic girdle, where legs come. Vertebrates include jawless fish, cartilaginous fish [evolution of jaws], bony fish, amphibians [evolution of legs], mammals, turtles, lizards/snakes, crocodiles, dinosaurs, and birds. Evolution of jaws- jaws are derived from gill arches of chordates. Earliest jawed fish are from the late Silurian (420 mya). Some had dermal armourfor example, placoderm. Cartilaginous fish- cartilaginous skeleton, maintaining water balance is a major issue (high levels of urea in their blood), reproduction sexual and mostly internal, embryo encased in leathery egg case, and some sharks give birth to live young. Bony (ray finned) fish- rigid bony skeleton (cartilage replaced); paired fins (ray like structure), swim bladder for buoyancy, usually a single dorsal fin, incredibly diverse. The evolution of legs, and move onto land- Water gives buoyancy, but on land, you need to support your own body weight. This requires much adaptation. Most bony fishes have fins made of long rays of bone (rayfinned fishes); some fishes developed more substantial bones in the fins (lobe-finned fishes); for example, lungfish. The first tetrapods:amphibians- about 350 mya, some of these lobefinned fish, living in shallow lagoons, developed bones to be able to walk (paddle in shallow water). These early amphibians had both gills and lungs. They still needed water. Nowadays, water is critical for amphibians. Water is critical for reproduction. Eggs don t have shells. Some have ingenious ways to keep moist. The first tetrapods had unusual limbs- acanthostega had 8 digits. Reptiles- tetrapod vertebrates, evolved from advanced reptile-like amphibians, adapted to life on dry land, many extinct groups (dinosaurs, pterosaurs etc), and modern reptiles inhabit all continents except Antarctica. Key features: have scutes or scales, are cold blooded, most lay eggs, and there is no aquatic larval stage. Reptiles aren t a monophyletic group. Strictly speaking, reptiles should include birds. Reproduction is sexual and internal. Reptiles usually lay eggs, but some produce live young. Appearances of the major groups of tetrapods: amphibians 350 mya; reptiles 330 mya; mammals around 190 mya (mammal lineage [mammallike reptiles: 320 mya]); dinosaurs and crocodiles around 230 mya; birds 150 mya. Dinosaurs come from the same lineage as crocodiles (archosaurs). Unlike crocodiles, many walked upright.

2 Origin of birds- one group of small dinosaurs was the dromaeosaur dromaeosaur fossil had feathers, wings, and first evidence for evolutionary origin of birds from dinosaurs. Birds are in the group archosaur. Evolution of mammals- first mammal-like reptiles at 320 mya. At first were very reptile-like, such as the dimetrodon. Many were large and carnivorous, such as the gorginopsid. The thrinaxodon was a smaller mammal-like reptile possibly with fur and an upright stance with the legs tucked under the body. This is a change of stance. Lizards and crocodiles sprawl, while dinosaurs and mammals are erect. This change of stance requires a change of structure in the skeleton. The hip joints and upper limb bones changed. The stress will be on the knees of a crocodile. The mammals feel the stress on the pelvis. Change of stance enabled quicker locomotion with longer legs. Fish move their bodies from side to side; sprawling animals like crocodiles and lizards do the same; change of stance: mammals move the back half of the body forward and back (bend in different plane). Dolphins and whales swim the same way (different from fish). As mammal-like reptiles became more like mammals, jaw articulation changed. Reptiles have a quadrate, articular jaw, while mammals have a squamosal and dentary jaw. It is a shorter and more powerful jaw. There is a clear point of contact. Cynognathus had an intermediate jaw. Jaw became ear bones. Class mammalia- terrestrial, aquatic, flying, subterranean. There are about 5000 species. Key features are fur, warm-blooded, milk, and 3 inner ear bones. Split into 3 sub-classes. Prototheria (platypus, echidna). There was a prediction there was likely to be an egg-laying mammal. Metatheria (marsupials)- there is a very short gestation period. Eutheria (placental mammals). Eutherian mammals- prolonged gestation period, fed internally via a placenta, massive range of body size (2g- 200 million g), about 20 orders (including primates), some unexpected relationships. Bumblebee bat and blue whale. Unexpected relationships among mammals- DNA sequence analysiselephants and dugongs are close relatives, and are both closely related to golden moles. 22 nd lecture 14/09/15 Humans diverged from the species: orangutans- 15 mya; gorillas- 9 mya; chimps- 6 mya. These are all in the Family Pongidae, and humans are in Hominidae. The difference between humans and chimps is very small. The close relatives Drosophila melanogaster and D. ananassae: estimated divergence time is 12 mya, with same genus and subgenus. The chimps and humans share over 98% of coding DNA, but are in different class and family.

3 Order Primates- fourth largest of all animals after rodents, bats, and insectivores. Includes great apes, humans; there are over 250 species, and most are arboreal. Features of primates- 1. Plantigrade feet- most mammals walk on tips of feet (on their toes). This is digitigrade. Primates walk on their entire feet right up to the heel. This is Plantigrade. Others are bears and hedgehogs. 2. Grasping digits- primates have prehensile (grabbing) digits and opposable thumbs. Also finger nails (not claws). Adaptation for arboreal existence, and important in evolution of tool use. 3. Binocular vision- forward facing eyes (often enormous), increased visual sense (including colour vision) at the expense of sense of smell, adaptation for nocturnal existence and judging distances. 4. Increased brain size- particularly in great apes and humans; visual and locomotory areas are greatly enlarged. 5. Shoulder anatomy- a well-developed clavicle (collar bone); very flexible rotating shoulder joint; good for movement through trees. 6. Upright posture- most primates can sit upright, some can walk short distance on hind legs; humans do it habitually. How do humans differ from other great apes? 1. Bipedalism- humans walk upright habitually, great apes typically knuckle walk, and human foot becomes less grasping with the great toe straightened. 2. Skeletal differences with upright walking- big toe reduced, pelvis shortened, more bowl-like than blade-like (helps support base of spine), femur bends inwards, knee straightened, patella central to joint, connection with spinal column (foramen magnum) on underside of skull, less robust upper arms. 3. Consequences of upright walking- upright walking freed hands for other purposes; humans have greater manual dexterity, and have greater tool use, and ability to throw accurately (important in hunting). 4. Diet- humans are highly omnivorous (generalists), but with a much higher meat intake than other apes. We also eat higher amount of processed food (cooked, pickled, fermented). 5. Brain size- humans have a greatly increased brain size compared to our nearest relatives. World population of great apes- 50 thousand-60 thousand orangutans, 110 to 120 thousand gorillas, 150 thousand to 200 thousand chimpanzees, 30 thousand to 50 thousand bonobos, and 7.2 billion humans. Majority of hominid fossils are found in East Africa, mostly in the Rift Valley. Lots of lakes, and human fossils found in same deposits as lake dwelling creatures. Early hominids must have spent some time around water. There are about 20 species of hominids. 3 main genera: Australopithecus (7 species), Paranthropus (3 species), and Homo (7 species). It is thought the Sahelanothropus tchadensis was the first hominid. Discovered in 2001, nicknamed Toumai, 6 to 7 million years old, chimps

4 and humans may have common ancestor earlier than thought, skull only, location of foramen magnum on base of skull suggests it was bipedal. Australopithecus afarensis- Lucy- lived 3-4 million years ago; skeleton includes jawbone, part of pelvis, and entire femur. Enables great interpretation of the way we lived. First solid evidence for the transition from four to two legs (bipedalism). The shape of the pelvis is very similar to humans. The angle of the femur and articulation with knee joint indicates bipedalism. Bones suggest A. afarensis was only 1.2m tall. There are footprint fossils: heel to toe, parent and child possibly. Facial features were more chimp-like. A complete juvenile skull from 3.3 mya suggests a more adult-like appearance (but chimp dentition); adult cranial capacity is 440mL (comparable with chimp). There is no increase in brain size in this genus. The earliest humans- the appearance of Homo- the earliest species of Homo was likely Homo habilis (handy man). They lived mya, and often found with simple stone tools. Cranial capacity is around 600mL (larger than chimps, and A. but still much smaller than humans). Homo erectus- lived around 1.8mya to 300 thousand years ago. More complex stone tools, and increased cranial capacity (900mL in early specimens, and 1100mL in later specimens). They built simple dwellings, and used fire 300 thousand years ago. Fire was used for warmth, and for processing food. Homo sapiens- appeared thousand years ago. First found on Omo River, Ethiopia. The cranial capacity is 1300 ml. Homo neanderthalis- the nearest relative of H. sapiens. Lived between 130 thousand years to 30 thousand years ago. Found in Europe and Middle East. Very similar societies to sapiens (hunter/gatherer), and may have been outcompeted by H. sapiens (may have interbred). They shared up to 99.5% of genes. Homo floresiensis- discovered in Flores, Indonesia, around 18 thousand years ago, thought to have descended from H. erectus ancestor, tiny skull and skeleton hence nicknamed hobbit. 23 rd lecture 16/09/15 Ecology is the way in which organisms interact with their environment (including other organisms). It is also the name for the study of these interactions. These processes drive evolution by natural selection. Evolution refers to the change over time of inherited traits found in populations of individuals. Evolution is a genetic change that is maintained in a population over time. Evolution isn t design, so isn t predetermined by the organism. For example, the snail didn t decide to make a shell to avoid predation. However, one with a shell may have had an advantage and reproduced more etc. These adaptations are inherited by offspring. Interactions with other animals can drive evolutionary changemales are often very colourful, and the most colourful males attract females, but also predators. Streams with high numbers of predators have

5 dull males. Dull male population introduced into predator-less stream becomes brightly coloured within two generations. Ecology at three different levels- 1. Ecosystem- an entire environment, its physical properties, and all the organisms and communities found there, for example, coral reef and tropical rainforest. 2. Community- any groups of species that live in the same place and potentially (or actually) interact with each other. It can refer to a collection of related species in an area, for example Darwin s finches. They can describe interactions between just a few (even two) species in the same area. An example is the ragwort: aphids feed on ragwort, and ants feed on the aphid honeydew. Cinnabar moth caterpillars feed on ragwort, but damage it. Damaged ragwort is bad for aphids and bad for ants, so are a cascade. The ants attack the moth caterpillars, and remove them from the ragwort, causing the community to persist. 3. Population- a group of individuals of the same species. Population ecology involves understanding why species numbers vary, and the causes of variation within species. Symbiosis is when two species interact closely together in a way that is beneficial to one or both. Interaction can either be essential to existence of one or both species (obligate), or not (facultative). Three types of symbiosis include: mutualism, commensalism, and parasitism. Mutualism- both species in the relationship benefit from the association: obligate- corals have symbiotic algae (zooxanthellae); facultativeoxpeckers feed off ticks and fly maggots on buffalo skin. Commensalism- one species benefits, the other appears unharmed. For example, barnacles on whales. Parasitism- one species benefits. The other is harmed. Ectoparasites are on the outside of a host. For example, lampreys on fish, parasitic isopod (crustacean). Endoparasites are inside the body of the host. Cestode tapeworms are in vertebrates, and parasitoid of leaf-roller caterpillar. Brood parasites for example cuckoos on other birds. Parasitoid- some animals (mostly insects) are parasites in the larval form, but not as adults. Parasitoid flies and wasps lay eggs inside other animals. Their larvae then eat the hosts from within. Predators- another form of interaction where one species benefits and one is harmed. Prey evolve traits to avoid being caught by predators. They can run faster, develop defences (shells, toxins), or become better at hiding (camouflage), deception (mimicry). These are adaptations; characteristics of an organism that have evolved because it provides a survival benefit to that organism. Species evolve means to evolve means to avoid parasites. Improved immune systems or means of removing them; behavioural adaptations (such as avoiding possible areas of infection). Kangaroos avoid places where there are a lot of faeces. Blue tits line their nests with aromatic herbs to deter parasites. Counter adaptations- further adaptation to overcome prey defences. For example, fox needs to run faster, and cuckoo needs to develop egg

6 mimicry. There will then be more counter adaptations. The prey/host will evolve more strategies to avoid the improved abilities of the predator. Both species have to continue evolving in response to each other s counter adaptations. This is the Red Queen hypothesis, or the evolutionary arms race. Evolutionary arms races- one side wins (can drive the other to extinction, or the side in which winning is less important drops behind); both sides reach a stable optimum (they evolve the optimum strategy they can afford); they don t (the arms race just keeps on changing, which is the ultimate red queen scenario). Co-evolution- evolutionary arms races are an example of co-evolution. Evolutionary changes in one species influences evolutionary changes in other species. The example is the orchid that mimics female wasps visually and chemically. As a wasp species evolves, its orchid mimic has evolved with it. Fig wasps pollinate figs. They develop in fig fruit; when females emerge they pick up pollen; females move to a new fig tree with pollen, and fertilise new fruits and lay eggs; fig phylogeny mirrors fig wasp phylogeny Competition- if there is a limited supply of a biologically important resource (food, habitat, mates) then there will be competition. Competition results in the evolution of characters that make individuals better at competing. For example, body size in male elephant seals. Competition may take place between individuals of the same species: intraspecific competition. Interspecific competition- competition between two or more species. Coal tits feed on outer branches, and willow tits on the inside. On trees without willow tits, coal tits eat inside as well. Removal of willow tits has the same effect. Willow tits competitively exclude coal tits. This is niche separation. Niche- a niche describes the position a species has in a community (that is the way it makes its living in the community). If two species with the same niche overlap, this is sympatry, and there will be competition. There may be a behavioural change so that there is niche separation. Alternatively, there may be a change in physical characteristics (character separation) so that there will be niche separation. For example, Darwin s finches. Daphne Major in the Galapagos- medium ground finches had a range of beak sizes. In 1982, a new species with a big beak invaded the island. After a drought in 2003, only the small beaked finches survived. They were able to avoid interspecific competition.