Week 7 Lectures
Week 7 Lectures GE 70B
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General Education Cluster 80A Frontiers in Human Aging
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This 7 page Class Notes was uploaded by Sarah Doberneck on Monday February 22, 2016. The Class Notes belongs to GE 70B at University of California - Los Angeles taught by Dr. Friscia in Winter 2016. Since its upload, it has received 27 views. For similar materials see Evolution of Life and the Cosmos in General at University of California - Los Angeles.
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Date Created: 02/22/16
Macroevolution Tuesday, February 16, 2016 10:22 AM Anagenetic- continuous change occurring within lineages Cladogenetic- most change associated with speciation events Phyletic gradualism model Punctuated equilibrium model o Some say that evolution is gradual o Proponents of this model claim that the changes take place in bursts and we can't see that in the fossil record because they happen so quickly o The answer is probably my that there is a combination of both methods o Speciation happens in peripheral populations. Not in large ones Cambrian explosion Who?? o Cambrian life! o Brachiopods, archaeocyathids, mollusks, crustaceans, aquatic and terrestrial worms, Amphioxus- a modern primitive vertebrate o Has all the characters of a vertebrate (notochord, neutral tube, pharynx, endostyle, post-anal tail, segmented muscles Trilobites There are some specimens so primitive we don’t have any modern analogs for them Predators emerged for the first time The Burgess Shale is a place where there is a large amount of life from this time period was preserved. o However, even before this was discovered, scientists knew that there was a large amount of life during this period but no one knew where it came from. This was a problem for Darwin's theory When? 500 ma Burrows indicate that there was life at this time simply because the sediment was moved around. Embryos fossilized The explosion begins to look less and less like an explosion The explosion had to have roots farther back is seen by looking at molecules and divergence times of organisms A duplication of hox genes probably allowed for more complex bodies in vertebrates Life seemed to suddenly become more complex right at the time of the Cambrian explosion The species started to have hard parts that allowed them to fossilize more easily. Why? Embryonic layers from which other structures are derived Sponges have one Cnidarians (jelly fish and medusas) and ctenophores (comb jellies) have two o This is a blind gut, where food goes into a sack basically then waste goes out the same way it came in All other animals have three o Allows for more specialized cells and a gut that goes through your body More complex environment because life got more complex o There are things in the water, things burrowing, etc. o Niches form and there is a snowball effect of life becoming too complex too fast o Part of this is the evolution of predators, which lead to increased evolution as the predators and prey evolve in an arms race Snow ball earth? o Possibly a complete global glaciation in the pre Cambrian era that affected diversity Long Term Trends in the Fossil Record Graph by Sepkoski: Increase in diversity over time Extinction events o 5 major ones o End Ordovician o End Devonian o End Permian o End Triassic o End Cretaceous What does it show? o First, it is increasing diversity over the entire Phanerozoic o Pull of the recent: artifcatual, sampling and interest bias. Small part of a much larger problem with paleontology-taphonomy o Ecological diversification: positive feedback, also escalation due to predator prey interactions Mass Extinctions Defined by: o Being global in extent o Affecting both marine and terrestrial organisms o Being brief in duration Causes o Major climatic change o Sea level changes o Volcanism o Plate tectonics o Extraterrestrial A Paradigm shift in Science Previously, historical scientists followed a fairly strict uniformitarian stance- the processes happening now were the same in the past Catastrophism was associated with deluvian ideas Now we have neo-catastrophist/uniformitarian view which allows for unique events in the past and future Isotopic evidence and mass death suggests environmental turmoil o Oxygen ratio syndicate an approximate six degree Celsius increase I global temperature o Carbon isotope ratios reveal a dramatic increase in atmospheric and oceanic The Permo-Triassic Mass Extinction The land was very diverse, the sea was teeming with life Who died? o 49% of all marine families o 63% of all terrestrial families o Surviving families squeaked through at low diversity o This can be used to estimate that 80-95% of all marine species were lost o Bioturbation: the disturbance of sedimentary deposits by living organisms. For example, worm burrows. How fast did it happen? o In the marine realm, very fast. In less than 1 million years about 94% of species disappear from this well-studied deposit in Chine Possible causes of the end Permian extinction o Formation of Pangea o Marine anoxia: oxygen levels greatly depleted in oceans o Sea level falls about 100 meters o Volcanic activity: huge basalt flow in Siberia about 251 Ma What could account for global warming and the increase in 12C? o 1. Bolide? Doubtful and there is no definitive evidence yet for a bolide impact at or near the PTR boundary. o 2. Marine regression? Unlikely. Also, it does not explain terrestrial extinctions and the rapidity of the extinctions. o 3. Volcanism: maybe. The Siberian traps o Largest known volcanic eruption o 2 million km2 of basalt that today's over 1.6 km2 of eastern Russians the depth of 400-3000 meters o Occurred over the span of about a million years o Flood basalts are thought to result from plumes that rise within the mantle and emerge on the surface in fissures, creating successive layers of lava. Basically huge hot spots o Volcanic eruptions produce: Ash---global cooling Carbon dioxide---global warming Sulfur dioxide---ozone destruction and acid rain Water vapor---global cooling Various other gases---global warming Coevolution Monday, February 22, 2016 9:52 PM Species interactions o A species constantly interacts with its environment, which includes many other species o Species interactions can be good, bad, r neutral for one or more involved o Mutualism +/+ Interaction that has a positive effect on both species involved E.g. pollination, seed dispersal, single celled algae in corals, microbiota in animals Anemones protect clown fish, which are immune to its sting. Clown fish do a wiggle danger that oxygenates water for anemones o Commensalism +/neutral Interaction benefits one species, little to no effect on other E.g. remoras on sharks Some examples may actually be unrecognized mutualism o Predator/prey or host/parasite +/- Eating is good, being eaten is bad Parasites need hosts to live but they sicken or kill their hosts From interaction to coevolution Coevolution: reciprocal evolutionary change between interaction species driven by natural selection o Reciprocal selection: selection that occurs in two species due to their interactions with each other (critical prerequisite of coevolution) o Selection in one direction doesn’t count, must be reciprocal o Could be mutual or antagonistic o Species interactions do not necessarily lead to coevolution, but all coevolution requires species interactions Mutualistic coevolution o Leaf-cutter ants + fungus Ants cut leaves, bring them to colony Worker ants chew leaves to a pulp that feeds resident fungus Fungus breaks down leaves, producing sugars and proteins that feed ants Mutual codependence- neither species can live without the other Antagonistic coevolution o Negative frequency-dependent selection in host- Red Queen effect Host mutation resists infection, selection favors this mutation and increases its frequency Parasite counters with its own mutation, which selection also favors (so then it also increases in frequency with some lag time behind host) Causes first host mutation to lose resistance, so its frequency decreases Decrease in parasite mutation follows, cycle continues o Often leads to an "arms race" E.g. prey gains adaptation to evade predation, predator adapts to defense Tradeoffs of coevolution o Parasites vs. hosts High virulence advantageous for resource competition or between species Low to moderate virulence better for host to host transmission Coevolutionary theory helped Darwin predict the existence of a moth that had not yet been discovered o Foot long spur of Madagascan star orchid holds nectar at the bottom o Positive frequency dependent selection drives evolution of longer spurs and longer proboscis Geographic Mosaic of Coevolution o Strength of selection and gene flow can disrupt what might otherwise be a strict pattern of coevolution Drift may overcome selection in small populations Predators may have more options in some populations but not in others o Geographic mismatches between newt toxicity and garter snake resistance likely due to interplay between tradeoffs and environments variation Tetrodotoxin is energetically costly for newts to produce, and more production requires more mutations Just one mutation gives snakes immunity so resistance is more widespread, but it also slows them down Mutualism to mimicry o Various species have evolved to mimic dangerous traits of other species in order to help evade predators Key Concepts Coevolution results from species interactions that create selective pressure on the two species involved Intensity & specificity among coevolving species may vary across time & space Negative frequency-dependent selection between hosts and parasites leads to Red Queen effect, cycling of genotype frequencies Antagonistic interactions may lead to coevolutionary arms races Mutualistic interactions may lead to positive frequency-dependent selection – instead of cycling, each mutation sweeps to fixation (characters become more extreme) and the two species become codependent) Mutualistic interactions are vulnerable to cheaters, but cheaters must remain relatively rare in order to be successful (Batesian mimicry) Symbiosis Dependent interaction (usually mutualistic, but could also be commensal or even parasitic) between two unrelated species living in very close physical association Coral reefs are dependent upon photosynthetic algal symbionts o Coral can eat plankton, but it’s not enough for many species o Algae can be free-living but receive protection and CO2 from coral Coral bleaching o If conditions don’t improve quickly enough for recolonization of Symbiodinium, algal cover can take over a reef o This is a mutualistic relationship Endosymbiosis Endosymbionts can only survive inside their hosts o Leads to the most extreme forms of coevolution o High levels of codependence o Association can last for tens or even hundreds of millions of years Sharpshooters feed on xylem for woody plants and trees o Require bacterial symbionts to supplement poor nutrition provided by xylem o Have developed special organs (bacteriomes) to house symbionts Coevolution of sharp shooters + two genera of bacterial symbionts o Sulcia acquired ~270 million years ago, long before first sharpshooter ancestor arose o Common ancestor of sharpshooter then acquired Baumannia ~50 million years ago o Vertical transmission of symbionts- basically "inherited" each generation o All three species have been coevolving ever since Endosymbiosis of chloroplasts o Single- celled ancestor engulfed in a photosynthetic bacterium- eat + photosynthesize Diversified into green and red algae, abandoned eating and just photosynthesize Plants still rely entirely on photosynthesis Endosymbiont has become an organelle (chloroplasts) Chloroplasts have their own genomes but highly simplified The oldest known endosymbiont o Mitochondria are found in all eukaryotic cells, convert O2 & sugar into energy Highly simplified genome, more similar to bacteria than any eukaryote Most closely related to group called SAR11 Metabolize oxygen, make up ~25% of all marine bacteria Endosymbiotic event occurred over 2 billion years ago Mitochondrial genome has mutated so much (many genes lost) that it took scientists decades to figure this out Coevolution and Biodiversity Coevolution can facilitate species diversification Escape and radiate model- ex. Milkweed and beetles o Milkweed develops toxic defense against herbivorous beetle o Beetle evolves enzyme to neutralize toxicity o Milkweed responds by becoming more toxic Different populations of milkweeds develop different types of toxins Different populations of beetles adapt specifically to each toxins Specificity of toxins and the beetles resistance to them causes both milkweed and beetle to speciate Coevolution may also facilitate extinction o Coral species with photosynthetic symbionts disappeared at a higher rate than those without symbionts K-T extinction o Codependence created by mutualistic coevolution makes one partner vulnerable to another’s extinction Key Concepts Symbiosis generates some of the tightest coevolutionary relationships Endosymbiosis has occurred multiple times on a variety of temporal and taxonomic scales Endosymbionts are typically transmitted vertically (parent to offspring) Plants owe their photosynthetic ability to endosymbionts acquired ~1.6–0.6 billion years ago Eukaryotic mitochondria descended from most ancient known endosymbiotic event over 2 billion years ago Coevolution may generate biodiversity (i.e. facilitate speciation), but can also make co-dependent species more vulnerable to extinction - the former is more likely with antagonistic relationships, the latter with mutualistic associations o Coevolution is all over the place and has been happening forever. It’s an incredibly important aspect of evolution so you should respect it and recognize its awesomeness
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