Lecture 29 11 12 2012 The Doushantuo Microfossils Researchers identified cyanobacteria and multicellular algae in samples dated 570 580 Ma They also found what they concluded were animal embryos in early stages of development Edicaran Deposits and Fossils Fossils dating from 565 million years ago include animals a with simple radial forms and b with many body segments and legs Precambrian everything that was going on before the great diversity shown in pic a cambrian seascape Why is it that before the Cambrian explosion we don t see very much diversity The Cambrian Explosion records the radiation of animals with modern body plans that is the diversification of clades that diverged earlier No new distinct animal body plans phyla have evolved over the last half billion years Cambrian Explosion a series of concurrent adaptive radiations o Generation of many diversified species with distinct ecologies from a common ancestor o Adaptive radiations may be rapid and often occur when a few organisms colonize an isolated new habitat that is biotically impoverished few species already present o Perhaps once all the new body plans had evolved there was much less ecological space for innovations o The evolutionary potential for similar diversifications may still be there as in the continental tarweed but are the ecological opportunities constrained Post Cambrian animal diversity has been perturbed significantly by at least 5 mass extinction events There are two distinct patterns of extinction o Background extinction represents as a default rate 1 10 per million years of loss of species due to normal levels of ecological and biotic turnover The average rate of extinctions over all of Earth s history Reflect the loss of species due to normal levels of ecological and biological turnover o Mass extinction events reflect cataclysmic plant wide environmental perturbations Have occurred repeatedly throughout the history of life on earth They rapidly eliminate most of the species alive in a more or less random manner The big five End Cretaceous extinction The best studied Around 75 of species went extinct Dinosaurs Strong evidence that a 10 km asteroid struck the earth in the Caribbean region Late Triassic extinction End Permian extinction 250 mya Worst in Earth s history Over 90 of species died Flood basalts add enormous quantities of heat CO2 and sulfur dioxide to the atmosphere as molten rock flows across the earth s surface The Siberian traps are end permian flood basalt deposits covering up to 7 million km 2 Volcanism caused warming increased CO2 and toxic gas increases Late Devonian Extinction End Ordovician Extinction The second worst in Earth s history Global cooling may have been responsible as evidenced by glacial deposits in then tropical Australia These mass extinctions stand out against the background extinction rate Intervals in which 50 of all species alive at the time go extinct in the span of just a few million years Reflects cataclysmic planet wide environmental catastrophes usually associated with abrupt changes in Why study Bacteria and Archaea climate All life on this planet shares a common prokaryotic ancestor Bacteria and archaea affect your life Photosynthetic bacteria were responsible for the evolution of the oxygen atmosphere on which we depend Bacteria and archaea play key roles in decomposition and cycle key nutrients through both terrestrial and aquatic environments thus sustaining the food webs on which we depend Only small fraction of bacterial species cause disease in humans Assaying prokaryotic diversity was until recently limited by what we could grow in culture this is no longer the case Scientists have finally acquired an arsenal of molecular DNA based techniques that allow them to study the organisms in their natural environments Archaea were identified in 1977 by Carl Woese based on their phylogenic distinctiveness He went on to propose the 3 domain model of life Archeans are found in all habitats many are extremophiles live in extreme environments none are known to be pathogens they are by far the least understood domain of life Roles of all bacterial species in humans are still not understood Some help the body reabsorb water Others aid in vitamin D synthesis Others promote healthy GI tract Most bacteria are not pathogenic Some bacteria are o Streptococcus pyogenes o Stephyloccus aureus o Treponema spp o Correlia burgdorferi o etc The average human body has about 10 trillion human cells and about 10X that many bacterial cells from over 900 different bacterial species Genetic Interchange Many bacteria have plasmids in addition to chromosomes Plasmids independent circular DNA molecules separate from the chromosomal DNA that carry only a few genes and that can replicate autonomously o Often contain genes that confer a selective advantage such as the ability to make the organism resistant to antibiotics o May be transferred among bacteria by a form of mating behavior called conjugation Conjugation has promoted the rapid spread of antibiotic resistance among many bacterial pathogens o Plasmid transfer via conjugation 1 Two bacterial cells come into contact One cell contains a plasmid 2 Copy of plasmid is transferred from donor cell to recipient cell through a conjugation tube 3 Recipient cell contains plasmid Diversity in prokaryotes also includes metabolic diversity in terms of how ATP is produced and how building block molecules are synthesized 6 examples of metabolic diversity o cyanobacteria o clostridium aceticum o nitrifying bacteria o heliobacteria o escherichia coli e coli o beggiatoa Electron Donor Receptor Diversity In cellular respiration a molecule with high potential energy serves as an electron donor and is oxidized whereas a molecule with low potential energy serves as a final electron acceptor and is reduced The potential energy difference is converted into ATP o Electrons pass from an electron donor through an electron transport chain to a final electron acceptor By donating an electron electron donor becomes By accepting an electron election acceptor becomes oxidized reduced o The electron transport chain is organized in a series of multi molecular complexes in the plasma membrane Bacteria and Archaea can exploit a wide variety of electron donors and Bacteria and Archaea live in virtually every habitat including extreme acceptors environments Extremophiles lovers of extreme conditions Extreme thermophiles thrive in very hot environments Archaean