Review for Test #2
Review for Test #2 BIO 113
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This 12 page Study Guide was uploaded by Amanda Howard on Thursday February 25, 2016. The Study Guide belongs to BIO 113 at Wake Forest University taught by Anderson, Todd Michael and Clifford W. Zeyl in Spring 2016. Since its upload, it has received 40 views. For similar materials see Evolutionary and Ecological Biology in Biology at Wake Forest University.
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Date Created: 02/25/16
Disruptive Selection The main idea of disruptive selection is that two extreme traits are favored An example of this is forest birds o Birds with large beaks are selected for to crack large nuts o Birds with small beaks are selected for to eat smaller seeds o Birds with medium beaks are selected against because they are not specialized to a food source and don’t handle either type efficiently Simultaneous Selection Complication: What if the fitness of an allele at one loci is determined by the allele present at a different loci? o Consider two snakes: One has a bright yellow longitudinal stripes One has a checkered pattern One moves quickly and erratically One simply move away at a rapid pace o Which traits are better? The checkered pattern and erratic motion breaks up the visual outline of the snake The stripes and fast motion make it hard for predators to judge speed and location Any other combination of these traits would probably result in the snake being caught and eaten These traits are selected for dependent on each other Evolution of complex traits (eyes example) BG: traits like eyes are too complex to have arisen as one mutation Start from Scratch: o Detecting light o A single mutation can cause a mutation in a cell that causes a protein to change when a photon is detected o Many single celled photosynthesizing cells use this to detect light Incremental Improvements: o Multiple light detecting cells creating a patch o Dark membrane behind the photocells so that the light can only hit them from one side o Curve the patch so that the organism can detect which direction the light is coming from More Incremental Improvements: o Pinhole eye to focus the light in order to focus the image o Eyes protected by a layer of skin and filled with fluid o Lens to focus the image on the retina o Muscle attached to the lens to change its shape Final Product: o complex eyes with an iris, lens adjustable by muscles, the whole deal Evolution of Species Evolution of similar traits o Convergent Traits The evolution of a similar trait in two separate lineages An example would be wingsBirds are not most closely related to bats yet they both have wings o Homologous Traits Both species inherit the trait from a common ancestor An example of this would be forearms in tetrapods (vertebrates with limbs) all inherited from a common ancestor: Ichthyostega Evolution of lineages o Begins with a single species, gene, population, etc o Becomes a lineage as it is passed down and descends through time o A split occurs when the lineage splits into two new lineages o The two lineages continue to evolve independently of each other new traits emerge o The lineages continue to split off creating new lineages of their own o Monophyletic groups groups with one common ancestor which can therefore be removed from the tree with a single cut Organisms are classified in nested monophyletic taxa Phylogenics o Goal: to deduce the sequence of the branching events in the history of evolution o Approach: map the series of switches in homologous traits that occurred during the evolution of a group o A monophyletic group vs clade Monophyletic group only the ancestors descended from a common ancestor Clade all the descendants of that ancestor 14 Events first known biological activity: methanogens (Archaea) o 3.8 BYA o Hypothetically occurred at Hydrothermal vents o Prior to this life would have been impossible due to a lack of oxygen o Archaea however can process elements around the vents photosynthesis by cyanobacteria generates first oxygen o ~3.5 BYA o Stromatolites are fossilized alternating layers of mud and cyanobacteria with the living layer at the top o There are actually currently living cyanobacteria in a marine in Australia which is unusually salty o Cyanobacteria produced the first oxygen allowing for the development of life endosymbiotic origin of mitochondria o 1.2 BYA o Mitochondriondescended from bacteria o These organisms could survive on their own and are the early ancestors of the mitochondria found in many organisms today endosymbiotic origin of chloroplasts o 800 MYA o Again these organisms could survive on their own and are the ancestors of today’s chloroplasts found in plants origin of animals, multicellularity o 800700 MYA o The earliest animals were found in the ocean and were generally soft bodied Cambrian explosion o 540505 MYA o Sudden radiation of phyla (basic body plans) in less than 10MY o origin of major animal groupsnew clades evolve relatively quickly followed by slower diversification o millions of new organisms o beginning of diversity, new lineages have different niches in the environment o earliest predators earliest land plants o 470 MYA first known land vertebrates (amphibians) o 350 MYA Permian mass extinction o 250 MYA o Worst massextinction in history first flowering plants o 160 MYA o After a massive drop i2 O levels earliest mammals o ~160MYA end of Cretaceous mass extinction o 65 MYA o Ended the cretaceous o This is the extinction that wiped out the dinosaurs, really anything bigger than a dog was destroyed o Possible meteor his of the coast of the Yucatan major mammalian radiation o 6040 MYA o Possible because the dinosaurs were wiped out at the end of the cretaceous first grasslands o ~22 MYA o Developed to survive grazing mammals Plate Tectonics Land masses are plates of rock floating on magma o Magmamolten rock This is important because shifting plates change the climate o example Huge interior regions of the continent Selection for grasses Whole new ecosystem: grasslands Speciation The evolution of two species from one ancestral species Not necessarily associated with new adaptations in either species The problem: o if a single mutation causes genetic incompatibility with the rest of the species, that’s one lonely mutant...how does that mutation spread? o if multiple mutations are required, what prevents interbreeding between the initial mutants and the rest of the population from spreading them throughout the population? Explanations: o allopatric speciation: interbreeding is prevented by some physical obstacle two groups are separated by geography for a period in which they differentiate even if the groups come back together they are no longer compatible the “DobzhanskyMuller model” (a form of allopatric speciation) after populations are separated, different mutations spread through each new lineage those mutations turn out to be genetically incompatible – combinations other than the ones that evolved have low fitness after that, if contact between the populations is restored, there is selection against individuals that choose the wrong (genetically incompatible) mate o sympatric speciation: selection somehow favors both different traits (usually ecological, e.g. avoiding competition) and mating preferences (individuals avoid mates with traits different from their own) for example: bird beaks in the rainforest there are birds with both very large and very small beaks this is an example of two extremes of the mutations for beak size, however both are favored because they are specialized for a specific type of food the reason a bird with a big beak would not have mated with a bird with a small beak is that the offspring would have been in the midsized beak range which is not specialized for either type of food another example: flowers some flowers are developed to attract humming birds red tube shaped flower developed to fit the beak of the hummingbird large volume of nectar others are developed to attract bees pink place to land concentrated nectar here, pollinators are both an ecological resource for which plants compete, and a genetic isolation mechanism attracting different pollinators requires different combinations of floral traits because reproduction requires pollen from another plant, specialization for different pollinators also prevents crosspollination – genetic isolation o recent evidence suggests that in at least some lineages this is not as hard to explain as evolutionary biologists have thought all along o temporal isolation if species have allopatric speciation they are in different locations so they can breed any time of year with no overlap however if two species are in the same location they will often mate at different time to decrease the chances of overlap o examples of convergence: cichlids (will be continued next class) o different groups of fish in ponds have similar features in terms of mouth adaptations in different ponds, however they are not as closely related to each other as to very different fish in the same pond from which they descended Convergence in cichlids radiation in different lakes All the fish in a lake have a common ancestor separate from that of the fish in another lake However, fish in the two lakes who are specialized to eat the same food closely resemble each other This is an example of convergence in that In addition disruptive selection is at work similar to that found in forest birds in that mutants become more specialized for specialized food types One of the possible reasons for cichlid radiation is that they have two sets of jaws which can have many uses in the different types of fish o In clam eaters for example the oral jaws may grab the clam and the second set may grind the shell o In predators may use their oral jaws to catch fish while the pharyngeal jaws may grind the prey o These two sets of jaws may allow speciation to occur more quickly by allowing rapid specialization o This trait is passed on even if one group of fish dies out: For example: if the algae eaters die due to chemical runoff, the pharyngeal jaw is still present in other cichlids meaning that the algae eating adaptations have the potential to reevolve later Genes Replication DNA RNA Protein “gene regulation” = how it is determined when and in what cells a gene actually produces the Protein (and thus the trait) it encodes o for many genes, regulation = whether or not transcription is initiated o genes in different parts of the body contain the DNA for all parts of the body, however regulation prevents an eye from developing in the stomach o however it is possible for there to be mutations or mistakes in transcription Here’s how transcription is initiated for a typical gene o Once a gene is replicated it takes transcription factors to turn it to RNA o “transcription factor”= a protein that affects the initiation of transcription, by binding to either a promoter, other TFs, or both o The RNA polymerase will only bind to a transcription factor after transcription factors are present, but the RNA can be blocked if too many transcription factors are present o Basically it is a question of whether or not transcription factors are present to allow for RNA transcription o In the case of cichlids and the second set of jaws: The fish had already evolved to be able to create bone, teeth, and jaws The process of creating a second set of jaws was not another long slow evolution The only requirement was that the gene for jaws was turned on or transcribed somewhere it wasn’t necessarily supposed to be Examples: o If you look at mice, flies, sharks, and squids, all three have similar genes to code for the placement of eyes meaning they are homologous o However the genes for the eyes themselves are completely different o This means that though the animals all share a common ancestor from who they got the gene that regulates were eyes develop for eye placement even before the evolution of eyes o However the eyes themselves evolved completely independently Abstract of Homeotic Gene Regulation Simultaneously turns on and off sections of DNA so that eyes, ears, etc. develop in the correct location Regulation of development is hierarchical: a few key transcription factors regulate the expression of many genes, which themselves regulate other genes Because homeotic genes control many other genes, one or two homeotic mutations can affect multiple features Because such mutations don’t alter the proteins produced by those “modules” of other genes, the features they produce (e.g. legs) can come out quite normally...just, in a new place or with different timing Once a complex trait is developed it requires far fewer mutations for the trait to appear in a new location or duplicated o Ex: cichlids Teeth are a complex trait that took millions of years to evolve Only took a single mutated Homeotic gene for a second set of jaws to evolve o Fly: Though all the genes necessary to produce wings are present in all parts of the body, homeotic genes regulate wing production to the correct location If there is a mutation, say an extra leg on a fly, will look normal since the genes necessary to produce the structure are present, however things like blood flow and muscle attachments will not be present so the leg will be useless o (Possible test use) o The homeotic gene that coded for many legs in centipedes is regulated suddenly which created the new groupinsects Example: o BMP4 causes cell death in the tissue between toes o This occurs in chickens which is why they have separated toes o In ducks there’s another gene called Gremlin which prevents BMP4 from doing its job which is why ducks have webbed toes Cichlid example continued: o Jaw length corresponds to the food type they are adapted to: elongated jaws for suction feeding in the water column short, blunt jaws for scraping food off rocks and the lake bottom o It is thought that BMP4 is involved in the development of the jaws of cichlid embryo o o Though there is a split in the ancestory of the fish at the red and blue locations (in cichlids these two branches develop in two separate lakes o However there is a species in each lake at the green location which is highly similar in appearance and is adapted to each snails. This fish is more closely related to the fish in its own lake than the very similarly adapted fish in the other lake Behaviors Example: in some seabird colonies parents will murder the chicks of their neighbors while the adults are off hunting. Why? o It seems like this would hurt the species o It gives the bird’s chicks a better chance because there’s more food for their own chicks if the neighbor’s chicks are dead o How would this trait evolve? o Imagine if this trait developed in a mutant in a group of birds where the entire population helps each other The mutant’s chicks would benefit from the help from the other birds The mutant’s chicks would also benefit from the fact that their parent would kill off rivals for food This would theoretically cause this mutation to spread Altruismbehavior that reduces the fitness of the individual performing it and increases the fitness of a different individual. o Examples: Mother frogs carry tadpoles which takes energy and could risk attracting predators Mother gators stay with their eggs until they hatch and risk starvation o Alleles encoding altruism seem to contradict the principle of selection acting directly on alleles: the phenotype encoded by an allele for altruism would directly reduce its own transmission to future generations. o But altruism is common in nature o Altruism comes in many forms, but one is especially common: parents (especially mothers) in many species risk or shorten their own lives caring for offspring o Explanations of altruism: group selection: selection for traits (e.g. altruism) based on a population or specieslevel effect e.g. parents risk/shorten lives to increase the survival rates of their offspring because that’s required to keep the species fit and ensure its future, or to maintain population size not realistic, like in the birds individuals don’t really care about the group as a general rule kin selection: selection favoring an allele for greater altruism directed specifically towards close relatives (which carry other copies of that same allele encoding the increased altruism) e.g. parents risk/shorten lives to increase the survival rates of their offspring because those offspring also carry the allele(s) that encode that behavior; their success transmits copies of that allele to future generations ex: Florida scrub jays the young from the year before don’t reproduce their first year, instead they help their parents raise a new group of young. The birds gain experience from this and the chance of the allele for altruism being passed down increases ex: how closely related two Beeeaters are determines their likelihood to help each other because the closer the relationship the more likely they share genes which can be passed down Test Prep Key terms: Disruptive selection Simultaneous selection Complex traits Convergent traits Homologous traits Phylogenics Clade Monophyletic group Plate tectonics Speciation Allopatric speciation DobzhanskyMuller model Sympatric Speciation Temporal isolation Convergence Gene regulation Transcription Homeotic gene regulation BMP4 and Gremlin Altruism Group Selection Kin Selection Practice Questions: 1. Would selection that favors cats with long claws be considered disruptive selection? Why or why not? 2. There are flowers that are colored to attract butterflies and also shaped to allow for butterflies to land on the plants. Another type of flower is shaped to allow for hummingbirds to hover and feed, in addition, their color attracts the birds. What kind of selection is this? 3. Which trait would be more likely a complex trait: color or an organ such as the lungs? Explain. 4. Is the similar coloring found in both alligators and river fish be more likely a convergent or homologous trait? 5. Frogs and toads are similar in appearance, however, they do not interbreed. What explanations can be offered for this? 6. Why are cichlids such a good example of convergent speciation? Answers 1. No. This selection is simple directional selection where one extreme is selected for. 2. Simultaneous selection 3. The lungs. While color can be changed by altering a single allele traits such as the lungs went through many intermediate stages of development. 4. Convergent. The two have highly separated lineages but share a similar habitat. 5. More than one possible answer: a. Allopatric speciation: the two groups were separated by some physical obstacle and developed into two species too different to breed b. Sympatric speciation: the traits that make them different are both favored in different ways and interbreeding would not be beneficial c. Temporal isolation: they breed at different times 6. All the fish in a lake have a common ancestor separate from that of the fish in another lake. However, fish in the two lakes who are specialized to eat the same food closely resemble each other in their adaptations. The reason these fish speciate so rapidly is that they have two sets of jaws which make mutating for different food types easier as each set of jaws must only accomplish one purpose instead of adapting to many new conditions,
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