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Origins of Life and Other Revolutions. Key Events in Evolution of Life on Earth Origins of life Oxygen revolution Eukaryotes (Endosymbiogenesis) Multicellularity.

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Presentation on theme: "Origins of Life and Other Revolutions. Key Events in Evolution of Life on Earth Origins of life Oxygen revolution Eukaryotes (Endosymbiogenesis) Multicellularity."— Presentation transcript:

1 Origins of Life and Other Revolutions

2 Key Events in Evolution of Life on Earth Origins of life Oxygen revolution Eukaryotes (Endosymbiogenesis) Multicellularity Cambrian Explosion Major Habitat Transitions – Invasion of land

3 Millions of years ago (mya) 1.2 bya: First multicellular eukaryotes 2.1 bya: First eukaryotes (single-celled) 3.5 billion years ago (bya): First prokaryotes (single- celled) 535–525 mya: Cambrian explosion (great increase in diversity of animal forms) 500 mya: Colonization of land by fungi, plants and animals Present 500 2,000 1,500 1,000 3,000 2,500 3,500 4,000 Key Events in Evolution of Life on Earth

4 Outline Origins of life Evolution of Eukaryotes Evolution of Animals Major Habitat Transitions

5 Outline Origins of life Evolution of Eukaryotes Evolution of Animals Major Habitat Transitions

6 Fig. 26-21 Fungi EUKARYA Trypanosomes Green algae Land plants Red algae Forams Ciliates Dinoflagellates Diatoms Animals Amoebas Cellular slime molds Leishmania Euglena Green nonsulfur bacteria Thermophiles Halophiles Methanobacterium Sulfolobus ARCHAEA COMMON ANCESTOR OF ALL LIFE BACTERIA (Plastids, including chloroplasts) Green sulfur bacteria (Mitochondrion) Cyanobacteria Chlamydia Spirochetes

7 The 3 Domains of Life Phylogenetic relationships based on 18S rRNA sequences, showing clade separation of bacteria, archaea, and eukaryotes. Eukarya

8 The Earth was formed ~4.6 billion years ago Earth’s early atmosphere likely contained water vapor and chemicals released by volcanic eruptions (nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, hydrogen, hydrogen sulfide) Origins of Life (Herron & Freeman, Chapter 17)

9 What were the earliest life forms? Prokaryotes are the earliest life forms we know of, but what might have preceded them?

10 Fig. 25-3 (a) Simple reproduction by liposomes (b) Simple metabolism Phosphate Maltose Phosphatase Maltose Amylase Starch Glucose-phosphate 20 µm Protobionts are aggregates of abiotically produced molecules surrounded by a membrane or membrane-like structure Protobionts exhibit simple reproduction and metabolism and maintain an internal chemical environment Protobionts

11 Replication and metabolism are key properties of life Experiments demonstrate that protobionts could have formed spontaneously from abiotically produced organic compounds For example, small membrane-bounded droplets called liposomes can form when lipids or other organic molecules are added to water

12 Self-Replicating RNA and the Dawn of Natural Selection The early genetic material might have formed an “RNA world” The first genetic material was probably RNA, not DNA Early life forms might have consisted of protobionts with RNA as the genetic code Early protobionts with self-replicating, catalytic RNA would have been more effective at using resources and would have increased in number through natural selection

13 RNA World RNA can both serve as the genetic code (hereditary material) and also perform enzymatic functions (ribozymes) RNA molecules called ribozymes have been found to catalyze many different reactions – For example, ribozymes can make complementary copies of short stretches of their own sequence or other short pieces of RNA – Natural selection in the laboratory has produced ribozymes capable of self-replication (Herron& Freeman written prior to this discovery) News/2009/January/09010901.asp News/2009/January/09010901.asp

14 Self-Replicating RNA and the Dawn of Natural Selection Ribozymes (= RNA enzyme or catalytic RNA) RNA that can catalyze chemical reactions. Many natural ribozymes catalyze either the breaking or synthesis of phosphoester bonds in DNA or RNA. Such capacity would enable the capacity to self replicate and propagate life. The functional part of the ribosome, the molecular machine that translates RNA into proteins, is fundamentally a ribozyme



17 RNA World RNA can both serve as the genetic code and also perform enzymatic functions (ribozymes) But, can RNA self replicate? If so, it would have all components to be considered “life”



20 Synthetic Life Humans can now create synthetic life, by constructing a genome on the computer, synthesizing the DNA and injecting the genetic code into a cell replicating-synthetic-bacterial-cell/overview/ mary

21 The First Single-Celled Organisms Stromatolites date back 3.5 billion years ago Prokaryotes were Earth’s sole inhabitants from 3.5 to about 2.1 billion years ago Prokaryotes Billions of years ago 4 3 2 1 The oldest known fossils are stromatolites, rock-like structures composed of many layers of bacteria and sediment

22 The oldest known fossils are of cyanobacteria from Archaean rocks of western Australia, dated 3.5 billion years old Stromatolites

23 Prokaryotes Prokaryote: – No internal membranes, organelles, nucleus – Bacteria + Archaea, not a Eukaryote – Not a coherent category – Archaea and Bacteria are not closer to each other than to Eukaryotes

24 Fungi EUKARYA Trypanosomes Green algae Land plants Red algae Forams Ciliates Dinoflagellates Diatoms Animals Amoebas Cellular slime molds Leishmania Euglena Green nonsulfur bacteria Thermophiles Halophiles Methanobacterium Sulfolobus ARCHAEA COMMON ANCESTOR OF ALL LIFE BACTERIA (Plastids, including chloroplasts) Green sulfur bacteria (Mitochondrion) Cyanobacteria Chlamydia Spirochetes


26 Incredible Metabolic Diversity Some can use inorganic chemicals as the electron donor in the redox reaction of making ATP (respiration) (animals use organic carbon, food, as the electron donor) Eukaryotes can use only oxygen as the terminal electron acceptor when making ATP in the electron transport chain (aerobic respiration) Prokaryotes can use NO 3 -, NO 2 -2, SO 4 -2, etc. (anaerobic respiration) Some are photosynthetic Some can fix nitrogen, converting atmospheric N 2  NH 3

27 Outline Origins of life Evolution of Eukaryotes Evolution of Animals Major Habitat Transitions

28 – O 2 in the atmosphere was generated by photosynthetic activity of cyanobacteria – Cyanobacteria were the first organisms to use H 2 O (instead of H 2 S or other compounds) as a source of electrons and hydrogen for fixing CO 2 – Photosynthesis: 6 CO 2 + 6 H 2 O + photons → C 6 H 12 O 6 + 6 O 2 Oxygen Revolution Atmospheric oxygen Billions of years ago 4 3 2 1 “Oxygen revolution” from 2.7 to 2.2 billion yrs ago

29 – O 2 allows the production of more energy and more efficient metabolism C 6 H 12 O 6 + 6 O 2 → 6 CO 2 + 6 H 2 O, ΔG = -2880 kJ per mole of C 6 H 12 O 6 Aerobic metabolism: 36 ATP molecules per glucose Anaerobic metabolism: 2 ATP molecules per glucose Aerobic and anaerobic metabolism share the initial pathway of glycolysis but aerobic metabolism continues with the Krebs cycle and oxidative phosphorylation. – However, Oxygen is also Toxic Oxygen is highly toxic to many species Electrons that escape from the electron transport chain can bind to oxygen and produce reactive oxygen species Reactive oxygen species (H 2 O 2, O 2 − ) can damage DNA and other molecules Oxygen Revolution

30 Evolutionary History dictates type of Metabolism The fact that much of prokaryotic life evolved BEFORE the oxygen revolution is reflected in the diverse forms of anaerobic metabolism – Most bacteria do not require oxygen, and for many it is toxic – Most bacteria use other molecules as the terminal electron acceptor when making ATP The fact eukaryotic life evolved AFTER the oxygen revolution is reflected in the fact that all eukaryotes use aerobic metabolism – They use oxygen as the terminal electron acceptor in energy production

31 Certain organelles originated as free-living bacteria that were taken inside another cell as endosymbionts. Mitochondria developed from proteobacteria (in particular, Rickettsiales or close relatives) and chloroplasts from cyanobacteria Both mitochondria and plastids contain DNA that is different from that of the cell nucleus and that is similar to that of bacteria (in being circular in shape, its size, and DNA composition) Endosymbiotic Theory Lynn Margulis Wrote the seminal paper “The Origin of Mitosing Eukaryotic Cells” 1966

32 The organelles (mitochondria and chloroplasts) greatly aid in energy production in eukaryotes. Probably Archaea Covered in Chapter 15, Freeman and Herron

33 Given the evolutionary history of endosymbiosis (or endosymbiogenesis) leading to eukaryotes, eukaryotes will inevitably share traits with both archaea and bacteria

34 Outline Origins of life Evolution of Eukaryotes Evolution of Animals Major Habitat Transitions

35 65 mya: Cretaceous Extinction (dinosaurs go extinct) 230 mya: Permian Extinction 570 mya: Cambrian Explosion

36 Burgess Shale (3) Origins of Animal Phyla Cambrian Explosion (570 MYA)

37 Radiations: Evolution of hard body parts Diversification of body forms Radiation of Invertebrates Extinctions???? (1) Precambrian-Paleozoic (570 MYA) Boundary Cambrian Explosion



40 What is an Animal?

41 Multicellular (metazoan) Heterotrophic (eat, not photo or chemosynthetic) Eukaryote No Cell Walls, have collagen Nervous tissue, muscle tissue Particular Life History-developmental patterns (this lecture) What is an Animal?

42 Origins of Multicellularity It is thought that metazoans arose from Colonial flagellate protists Oxygen Revolution: allow higher metabolic rate larger body size powered motion

43 Cells of sponges are similar to flagellate protists

44 Doushantuo formation Southern China Fossilized metazoan embryo at the 256 cell stage 570 million years ago Clusters of cells (embryos?) Sponges

45 Burgess Shale Fossils Marrella Canadia Aysheaia Hallucigenea

46 WHY?

47 Ecological arms race? Increase in oxygen? (higher energy, larger animals possible)

48 The Paleozoic Sea

49 When?

50 Are Genetic Distances and fossil record roughly congruent?

51 Was the Cambrian Explosion an Explosion? Geology: YES Sudden Appearance of Animal Fossils Genetics: NO DNA Divergences Predate Cambrian

52 Precambrian Cambrian 1400 1200 1000 800 600 Mollusca Annelida Arthropoda Echinodermata Agnatha Gnathostomata 200 0 Million Years Ago Wray et al. 1996 Based on phylogeny of animals based on DNA sequence data, the radiation of animals predates the geological record of the Cambrian Explosion

53 Fossil Record vs Molecular Clock Molecular clock and fossil record are not always congruent – Fossil record is incomplete, and soft bodied species are usually not preserved – Mutation rates can vary among species (depending on generation time, replication error, mismatch repair) But they provide complementary information – Fossil record contains extinct species, while molecular data is based on extant taxa – Major events in fossil record could be used to calibrate the molecular clock

54 Fossil Record vs Molecular Clock So it’s highly likely that the divergence of animal lineages (phyla) was more gradual than the fossil record would suggest and that the time of divergence happened earlier

55 Evolution of Animal Body Plans True Tissues Tissue Layers (Diplo vs Triploblasts) Body Symmetry Evolution of body cavity (Coelom) Evolution of Development

56 Cambrian Explosion

57 But major body plans evolved within a short period of time Of course, evolution continued after the Cambrian Explosion

58 How could this happen? (genetic mechanism?)

59 We talked about how selection and drift could result in speciation The formation of novel body plans calls for changes (mutation, selection, drift) at loci that cause fundamental morphological changes Genetic Mechanisms?

60 The Evolution of Development (Freeman& Herron, Chapter 19) The tremendous increase in diversity during the Cambrian explosion appears to have been caused by evolution of developmental genes Changes in developmental genes can result in radically new morphological forms Developmental genes control the rate, timing, and spatial pattern of changes in an organism’s form as it develops into an adult

61 Changes in a few regulatory genes could have big impacts Most new features of multicellular organisms arise when preexisting cell types appear at new locations or new times in the embryo. Changes in the specification of cell fates is a major mechanism for the evolution of different organismal forms.

62 Hox genes are a class of homeotic genes that provide positional information during development If Hox genes are expressed in the wrong location, body parts can be produced in the wrong location For example, in crustaceans, a swimming appendage can be produced in a segment instead of a feeding appendage Example of Evolution Developmental Genes that could result in radically new body forms

63 Mutations in a Hox gene causing legs to grow out of the head In this case, the identity of one head segment has been changed to that of a thoracic segment.

64 Hox Clusters Gene family formed by gene duplication events Hox genes, usually found clustered next to each other along animal chromosomes Hox gene products are regulatory proteins that bind to DNA and control the transcription of other genes



67 Christiane Nüsslein-Volhard and Sean Carroll

68 Hox genes specify the developmental fate of individual regions within the body (modules), and usually the genes are activated and expressed in the body in the same order as their position in the cluster These genes regulate timing and location of gene expression during development Hox Clusters

69 Example: Hox Genes


71 Evolution of Hox clusters HOX-clusters undergo essential rearrangements in evolution of main taxa Duplication, deletion, divergence of the genes lead to differentiation in body plans Other regulatory genes/gene families are also important

72 Animal body plans

73 Evolutionary changes in Hox Genes New morphological forms likely come from gene duplication events that produce new developmental genes A possible mechanism for the evolution of six- legged insects from a many-legged crustacean ancestor has been demonstrated in lab experiments Specific changes in the Ubx gene have been identified that can “turn off” leg development

74 Hox gene 6 Hox gene 7 Hox gene 8 About 400 mya Drosophila Artemia Ubx


76 Differences in Hox gene expression distinguish the various arthropod segmentation patterns

77 Evolution of vertebrates from invertebrate animals was associated with alterations in Hox genes Two duplications of Hox genes are thought to have occurred in the vertebrate lineage These duplications may have been important in the evolution of new vertebrate characteristics Evolution of Vertebrates (Phylum Chordata)

78 Polyploidization is probably the single most important mechanism for the evolution of major lineages and for speciation in plants Multiple rounds of polyploidization might have occurred during the early evolution of vertebrates

79 Vertebrates (with jaws) with four Hox clusters Hypothetical early vertebrates (jawless) with two Hox clusters Hypothetical vertebrate ancestor (invertebrate) with a single Hox cluster Second Hox duplication First Hox duplication

80 Outline Origins of life Evolution of Eukaryotes Evolution of Animals Major Habitat Transitions

81 Habitat Transitions Freshwater invasions Invasion of Land Key innovations with the invasion of land

82 Geological record of timing of terrestrial invasions

83 Transitions between Saltwater  Freshwater and Water  Land Constitute Major Evolutionary Transitions in the History of Life Example of extraordinary environmental change:

84 SeaFreshLand ProtistaXX PoriferaXX CnideriaXX CtenophoraX PlatyhelminthesXXX NemerteaXXX RotiferaXX GastrotrichaXX KinorhynchaX NematodaXX NematomorphaXX EntoproctaXX AnnelidaXXX MolluscaXXX PhoronidaX BryozoaXX BrachiopodaX SipunculidaX EchiuroidaX PriapulidaX TardigradaXX OnychophoraX ArthropodaXXX EchinodermataX ChaetognathaX PogonophoraX HemichordataX ChordataXXX Life evolved in the sea, and freshwater and terrestrial habitats impose profound physiological challenges for most taxa (Hutchinson 1957; Lee & Bell 1999) Of ~40 Animal Phyla, only 16 invaded fresh water, and only 7 invaded land

85 SeaFresh waterSoilLand ProtistaXXX PoriferaXX CnideriaXX CtenophoraX PlatyhelminthesXXXX NemerteaXXX RotiferaXXX GastrotrichaXX KinorhynchaX NematodaXXX NematomorphaXX EntoproctaXX AnnelidaXXXX MolluscaXXXX PhoronidaX Habitat Invasions

86 SeaFresh waterSoilLand BryozoaXX BrachiopodaX SipunculidaX EchiuroidaX PriapulidaX TardigradaXXX OnychophoraXX ArthropodaXXXX EchinodermataX ChaetognathaX PogonophoraX HemichordataX ChordataXXXX Habitat Invasions

87 Osmoregulation The regulation of water and ions poses among the greatest challenges for surviving in different habitats. Marine habitats pose the least challenge, while terrestrial habitats pose the most. In terrestrial habitats must seek both water and ions (food). In Freshwater habitats, ions are limiting while water is not.

88 The invasion of land occurred relatively recently (late in the history of life on earth)

89 The Colonization of Land Precambrian: c olonization of land by bacteria Late Ordovician–Late Devonian: Terrestrial ecosystems of plants, fungi, arthropods and eventually vertebrates Late Silurian: vascular plants Devonian: evidence of interactions among groups (fungal-plant symbiosis, arthropod herbivory) Late Devonian: Two major megaclades that were major participants in the Cambrian explosion appear on land – The lophotrochozoans: gastropod and bivalve mollusks, oligochaete annelids, rotifers, etc. – The ecdysozoans: arthropods, nematodes, etc. Invasion of land by crustaceans  origin of insects (Hexapods) Early Carboniferous: radiation of tetrapods (vertebrates with 4 legs)

90 Major Transitions of the Paleozoic

91 The invasion of land by crustaceans (terrestrial crustaceans = insects)

92 Questions What are some of the key biological revolutions that occurred during the history of life on earth, and how did they come about? Why is it hypothesized that early life on earth was in the form of RNA? How did the Oxygen Revolution come about? What are the implications of a high oxygen atmosphere for organismal physiology? How were Eukaryotes created? What are animals? About when did animals evolve? Is there congruence between fossil estimates versus molecular clock estimates of the timing? How did animals diversify (Cambrian Explosion)? Where did life evolve (land, sea)? About when did organisms begin to live on land? What are some challenges of living on land (relative to the sea)?

93 1.Which of the following is MOST likely to be true regarding evolutionary relationships among the major domains of life? (A) Bacteria and Archaea are both grouped into the category of “Prokaryotes” because they are more closely related to each other than to Eukaryotes (B) Archaea are ancestral to all other forms of Life (C) The Oxygen Revolution defines the emergence of life on Earth (D) Eukaryotes arose from a symbiotic relationship among prokaryotes (E) Eukaryotes evolved from Prokaryotes through Horizontal Gene Transfer

94 2. Which of the following is Least likely to be true regarding Prokaryotic Metabolism and the Oxygen Revolution? (A)The oxygen revolution led to the proliferation of diverse types of prokaryotic metabolism (B) The oxygen revolution enabled the preponderance of more efficient metabolism that could produce more ATP per unit glucose (C) The oxygen revolution altered the atmosphere of the Earth (D) The oxygen revolution created an inhospitable habitat for many classes of prokaryotes that use molecules other than oxygen as their terminal electronic acceptor for energy production (E) The oxygen revolution was caused as a byproduct of photosynthetic activity of cyanobacteria

95 3. Which of the following does NOT make RNA a good candidate for early life on earth? (a) RNA could act as an enzyme (b) RNA could serve as the genetic code (c) RNA is much more stable than DNA in our current atmosphere (d) RNA can catalyze chemical reactions that break or synthesize phosphodiester bonds in RNA or DNA (e) Recent studies suggest that RNA is capable of self replication

96 4. Which is the following is NOT a consequence of the Oxygen Revolution? (a) The ability of organisms to metabolically produce more ATP by using oxygen as the terminal electron acceptor during respiration (b) Eukaryotes, which evolved after the Oxygen Revolution, all use aerobic metabolism (c) The transformation of the earth's atmosphere ~2.5 billion years ago from one that was chemically reducing to one that is oxidizing (d) The heightened risk of DNA and cellular damage in organisms through oxygen free radicals (e) The proliferation of bacteria that use oxygen as the terminal electron acceptor during respiration, such that nearly all bacterial species are aerobic

97 Answers 1D 2A 3C 4E

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