CHAPTER 26 LECTURE SLIDES Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The Tree of Life Chapter 26

Origins of Life Cell is the basic unit of life Today all cells come from pre-existing cells The Earth formed as a hot mass of molten rock about 4.5 billion years ago (BYA) As it cooled, chemically-rich oceans were formed from water condensation Life arose spontaneously Ocean’s edge, hydrothermal deep-sea vents, or elsewhere

Fundamental Properties of Life Cellular organization Sensitivity Growth Development Reproduction Regulation Homeostasis Heredity

Frozen water found on Mars Panspermia Earth may have been “infected” with life from some other planet Meteor or cosmic dust may have carried complex organic molecules to earth Kicked off evolution of life Frozen water found on Mars

Conditions on Early Earth Seems likely that Earth’s first organisms emerged and lived at very high temperatures First organisms emerged between 3.8 and 2.5 BYA Early atmosphere composition not agreed on May have been a reducing atmosphere Would have made it easier to form carbon-rich molecules

In 1953, Miller and Urey did an experiment that reproduced early atmosphere Assembled reducing atmosphere rich in hydrogen with no oxygen gas Atmosphere placed over liquid water Temperature below 100ºC Simulate lightning with sparks

Found within a week that methane gas (CH4) converted into other simple carbon compounds Compounds combined to form simple molecules and then more complex molecules Later experiments produced more than 30 carbon compounds including amino acids Adenine also produced

RNA may have been first genetic material Ribozyme activity Amino acids polymerized into proteins Metabolic pathways emerged Primitive organisms may have been autotrophic – built what they needed Lipid bubbles could increase the probability of metabolic reactions Leads to cell membranes Other innovations contributed to diversity of life

11 Periods Eons Eras North and South America joined by land bridge. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Periods Eons Eras North and South America joined by land bridge. Uplift of the Sierra Nevada. Worldwide glaciation. Present Quaternary Appearance of humans First primate Cenozoic Tertiary 50 MYA Bird radiation Mammal radiation Pollinating insects Cretaceous 100 MYA Diversification of flowering plants Gondwana begins to break apart; interior less arid. First flowering plants, birds, marsupial mammals Mesozoic 150 MYA Jurassic Gondwana Gondwana Pangea intact. Interior of Pangea arid. Climate very warm. 200 MYA First dinosaurs Phanerozoic Triassic First gymnosperms Pangea Pangea 250 MYA Permian 300 MYA First reptiles Carbonife- rous Supercontinent of Laurentia to the north and Gondwana to the south. Climate mild. 350 MYA First amphibians Laurentia Laurentia Paleozoic Devonian Gondwana Gondwana 400 MYA Bony fish, tetrapods, seed plants, and insects appear Silurian Early vascular plants diversify 450 MYA Ordovician Invertebrates dominate First land plants Cambrian Cambrian explosion; increase in diversity 500 MYA 11

12 Periods Eons Eras Supercontinent of Gondwana forms. Oceans cover Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Periods Eons Eras Supercontinent of Gondwana forms. Oceans cover much of North America. Climate not well known. 500 MYA Late Appearance of animals and plants Gondwana Gondwana First multicellular organisms 1000 MYA Middle Proterozoic 1500 MYA Oldest definite fossils of eukaryotes Most of Earth is covered in ocean and ice. Early 2000 MYA Appearance of oxygen in atmosphere Cyanobacteria 2500 MYA Late Precambrian 3000 MYA Archaean Middle 3500 MYA Oldest fossils of prokaryotes Early Molten-hot surface of Earth becomes somewhat cooler 4000 MYA Oldest rocks Hadean 4500 MYA Formation of Earth 12

Classification of Organisms More than 2000 years ago, Aristotle divided living things into animals and plants Later, basic units were called genera Felis (cats) and Equus (horses) In the 1750s, Carolus Linnaeus instituted the use of two-part names, or binomials Apis mellifera the European honeybee Genus name capitalized, all in italics

Taxonomy is the science of classifying living things A classification level is called a taxon Scientific names avoid the confusion caused by common names

The Linnaean Hierarchy Taxa are based on shared characteristics Domain → → → Species Early taxonomists not aware of distinction between derived and ancestral traits Many hierarchies now being re-examined Categories at the different levels may include many, a few, or only one taxon Limitations Many higher ranks are not monophyletic Linnaean ranks not equivalent in any meaningful way

Grouping Organisms Carl Woese proposed a 6-kingdom system Eukaryotes Prokaryotes Eukaryotes

6-kingdom system 4 eukaryotic kingdoms 2 prokaryotic kingdoms Plantae Fungi Animalia Protista – did not fit into 3 other kingdoms Probably paraphyletic 2 prokaryotic kingdoms Archaea Bacteria Each fundamentally different Each probably monophyletic

3 domain system Domain Archaea Domain Bacteria Domain Eukarya Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Domain Bacteria (Bacteria) Domain Archaea (Archaebacteria) Domain Eukarya (Eukaryotes) Common Ancestor a. 3 domain system Domain Archaea Domain Bacteria Domain Eukarya Each of these domains forms a clade

Tree based on rRNA analysis Archaea and Eukarya are more closely related to each other than to bacteria

Bacteria Most abundant organisms on Earth Key roles in biosphere Extract nitrogen from the air, and recycle carbon and sulfur Perform much of the world’s photosynthesis Responsible for many forms of disease Highly diverse Most taxonomists recognize 12–15 different groups

Archaea Shared characteristics Divided into three general categories Cell walls lack peptidoglycan (found in bacteria) Membrane lipids are different from all other organisms Distinct rRNA sequences Divided into three general categories Methanogens Extremophiles Nonextreme archaea

Methanogens Extremophiles Nonextreme archaea Use H2 to reduce CO2 to CH4 Strict anaerobes that live in swamps and guts Extremophiles Thermophiles – High temperatures (60–80ºC) Halophiles – High salt Acidophiles – Low pH (pH = 0.7) Nonextreme archaea Grow in same environments as bacteria Nanoarchaeum equitens – Smallest cellular genome

Eukarya Prokaryotes ruled the earth for at least one billion years Eukaryotes appeared about 2.5 BYA Their structure and function allowed multicellular life to evolve Eukaryotes have a complex cell organization Extensive endomembrane system divides the cell into functional compartments

Mitochondria and chloroplasts most likely gained entry by endosymbiosis Mitochondria were derived from purple nonsulfur bacteria Chloroplasts from cyanobacteria

Red algae Ancestral eukaryotic cell Purple bacteria Other bacteria Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Archaebacteria Animalia Fungi Protista Plantae Bacteria Brown algae Red algae Green algae Photosynthetic protists Nonphotosynthetic protists Chloroplasts Mitochondria Ancestral eukaryotic cell Halophiles Photosynthetic bacteria Thermophiles Methanogens Purple bacteria Other bacteria

Key Eukaryotic Characteristics Compartmentalization Allows for increased subcellular specialization Nuclear membrane allows for additional levels of control of transcription and translation Multicellularity Allows for differentiation of cells into tissues Sexual reproduction Allows for greater genetic diversity

Viruses Are literally “parasitic” chemicals DNA or RNA wrapped in protein Cannot reproduce on their own Not considered alive – cannot be placed in a kingdom Viewed as detached fragments of a genome Tobacco mosaic virus (TMV) first discovered in 1933

Vaccinia virus (cowpox) Influenza virus T4 bacteriophage Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Vaccinia virus (cowpox) Influenza virus T4 bacteriophage Herpes simplex virus HIV-1 (AIDS) Tobacco mosaic virus (TMV) Rhinovirus (common cold) Adenovirus (respiratory virus) Poliovirus (polio) 100 nm Ebola virus

Making Sense of the Protists Represents tension between traditional classification and use of evolutionary relationships Eukaryotes diverged rapidly as atmosphere shift from anaerobic to aerobic May never be able to sort out relationships during this time Protist is a catchall for eukaryotes that are not plant, fungus, or animal

6 main branches of protists are current working hypothesis At least 60 protists do not fit into these groups New kingdom called Viridiplantae would include all green algae and land plants

Origin of Plants Land plants arose from an ancestral green alga only once during evolution Green alga consist of 2 monophyletic groups Chlorophyta Streptophyta Composed of seven clades, including land plants Kingdom Viridiplantae would include Chlorophyta and Streptophyta

Mesostigma represent the earliest Streptophyte branch Charales is the sister clade to land plants Split 420 MYA

Some land plants show evidence of horizontal gene transfer Amborella has some mitochondrial genes from moss Close contact with epiphytes increases the probability of HGT

Sorting Out the Animals Origins of segmentation Used in the past to group arthropods and annelids close together rRNA sequences now suggest that these two groups are distantly related Segmentation likely evolved independently in these two groups, as well as in chordates

Division based on embryonic development Protostomes develop the mouth before the anus in embryonic development Annelids and arthropods among others Deuterostomes develop the anus first Chordates including humans Protostomes divided further into Lophotrochozoans Flatworms, mollusks, and annelids Ecdysozoans Roundworms and arthropods

Segmentation is regulated by the Hox gene family Hox ancestral genes already present in ancestor to all groups Members were co-opted at least three times

– Uniramous vs. biramous appendages Within the arthropods, insects have traditionally been separated from the crustaceans – Uniramous vs. biramous appendages However, molecular data is questioning this classification – Distal-less, a Hox gene, initiates development of both types of appendages

The Mammalian Family Tree Over 90% of mammals are eutherians or placental mammals Now divided into four major groups First major split occurred 100 MYA when Africa split from South America

Origin of whales and hippos debated for 200 years Whales thought to be relatives of pigs based on skull and teeth DNA sequences reveal a close relationship between whales and hippos Some adaptations to aquatic origins had a common origin Recent fossil finds confirm the artiodactyl origin

Understanding evolutionary relationships among organisms accomplishes these things Provides an orderly and logical way to name organisms Allows researchers to ask important questions about physiology, behavior, and development using information already known about a related species Provides insights in understanding the history of major features and functions