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Maynard Smith & Szathmary (1995) Walter Salzburger: Major Transitions in Evolution 1 from to 1 replicating molecule populations of molecules in compartments 2 independent replicators chromosomes 3 RNA as gene and enzyme DNA genes, protein enzymes 4 bacterial cell (prokaryotes) cells with nuclei, organelles (eukaryotes) 5 asexual clones sexual populations 6 protists (single-celled) animals, plants, fungi 7 solitary individuals colonies (non-reproductive casts) 8 primate societies human societies (language) Maynard Smith & Szathmary (1995) Major transitions in evolution 2 Major transitions in evolution molecules - populations of molecules ! The first objects with the properties of multiplication, variation and heredity were replicating molecules, similar to RNA but perhaps simpler ! These molecules were not informational, because they did not code for other structures ! In a protocell, populations of replicating molecules were enclosed within some kind of membrane (“compartment”) 3 Major transitions in evolution molecules - populations of molecules replicating molecule metabolic product 4 Major transitions in evolution molecules - populations of molecules protocell 5 Major transitions in evolution Stromatolites ! ...are witnesses of the oldest known fossils, dating back to up to 3.5 billion years ! ...are layered structures that have been formed by cyanobacteria and other microbes www.discoverwest.com.au ! ...are formed when cells grow on the sea surface, and sediments are deposited among or above the cells. The cells then grow up to the light, leaving a mineralized layer below them. ! Cyanobacteria were likely responsible for the creation of earth’s oxygen and, today, are nearly extinct www.futura-sciences.com 6 Major transitions in evolution replicators - chromosomes ! In living organisms, replicating molecules (“genes”) are linked together end to end to form chromosomes. Most simple organisms have a single chromosome per cell. ! This has the effect that when one gene is replicated, all are (coordinated replication) ! This situation favors co-operation between genes in a compartment. 7 Major transitions in evolution replicators - chromosomes chromosome cell gene protein 8 Major transitions in evolution RNA - DNA and proteins ! Today, there is a division of labor between two classes of molecules: nucleic acids (DNA, RNA) and proteins ! Nucleic acids store and transmit information, proteins catalyze chemical reactions and form structure (e.g., muscles, hair) ! I seems likely that, initially, this division did not exist and that RNA performed both functions ! The transition from this “RNA world” to the world of DNA and proteins required the evolution of the genetic code 9 Major transitions in evolution RNA - DNA and proteins ribozyme transfer RNA (tRNA) messenger RNA (mRNA) GC UGAUUGA AUAU CGUGUCA micro RNA (miRNA) ribosomal RNA (rRNA) images: www.whatislife.com, www.rothamsted.ac.uk, www.wikipedia.org, www.aps.anls.gov 10 Major transitions in evolution www.fig.cox.miami.edu RNA - DNA and proteins transcription 11 Major transitions in evolution www.fig.cox.miami.edu RNA - DNA and proteins translation 12 Major transitions in evolution Ridley (1996) RNA - DNA and proteins genetic code 13 Major transitions in evolution prokaryote - eukaryote • relatively simple • no nucleus (i.e., DNA lies in no particular region) prokaryote cell • a single circular chromosome (most often) • small ribosomes • in two of the three domains of life (bacteria, archaea) • complex internal structure • DNA is organized in the nucleus eukaryote cell • more than one chromosome • organelles (mitochondria, chloroplasts) • large ribosomes • in all complex multicellular organisms 14 Major transitions in evolution prokaryote - eukaryote endosymbiont hypothesis 15 Major transitions in evolution prokaryote - eukaryote three domains of life 16 Major transitions in evolution asexual - sexual reproduction Hydra 17 Major transitions in evolution asexual - sexual reproduction 18 Major transitions in evolution asexual - sexual reproduction Haplodiploid life cycle without fusion endomitosis One-step meiosis ! Genome duplication followed by a simple form of meiosis 19 Major transitions in evolution asexual - sexual reproduction Life cycle with syngamy and a one-step meiosis cell fusion One-step meiosis ! Endomitosis is replaced by fusion; this is a sexual cycle 20 Major transitions in evolution asexual - sexual reproduction Modern sexual life cycle cell fusion two-step meiosis ! Two-step meiosis is only found in eukaryotes 21 Major transitions in evolution protists - animals, plants, fungi ! Protists exist as single cells (or sometimes colonies) ! Animals, plants, fungi are composed of many different kinds of cells. Therefore, each individual carries many thousands to millions copies of the genetic information ! Although - in animals, plants and fungi - all cells contain the same information, they are very different in shape, composition, function, etc. ! Multicellularity most likely evolved three times in eukaryotes 22 Major transitions in evolution protists - animals, plants, fungi ephithelial cells macrophage cell muscle cells blood cells pigment cells images: www.nikonsmallworld.com, www.astrographics.com, www.dundee.ac.uk, www.esa.int, www.protist.biology.washington.edu nerve cell 23 true animals (metazoa) plants true fungi 24 Major transitions in evolution solitary individuals - colonies Social insects: www.apple.com Some animals, notably ants, bees, wasps and termites, live in colonies in which only a few individuals reproduce. Such colonies have been likened to a superorganism, analogous to a multicellular organism. The sterile workers are analogous to body cells, and the reproducing individuals to the cells of the germ line. www.epfl.ch It has been estimated that one-third of the animal biomass of the Amazon rainforest consists of ants and termites. The same might be true for other habitats as well. 25 Major transitions in evolution solitary individuals - colonies groups nr. of eusocial species Isoptera all termites Homoptera some gall aphids 40 Hymenoptera hover wasps (Stenogastinae) 50 independent-founding paper wasps (Polistinae) 630 swarm-founding paper wasps (Polybiini) 400 yellowjackets, hornets (Vespinae) 78 sweat bees (Halictinae) 400 bumble bees (Bombinae) 200 honey bees (Apini) 2200 5 stingless bees (Meliponinae) 280 ants (Formicidae) 9500 eusocial insects 26 www.nmnh.si.edu Major transitions in evolution www.nationalgeogrpahic.com solitary individuals - colonies www.cs.dartmouth.edu leaf cutter ant 27 Major transitions in evolution primate - human (language) chimpanzee human gorilla orangutan rhesus macaque evolution of language Was language the decisive step in the transition from an ape to a human society? images: National Geographic, Leonardo da Vinci 28