The Tree of Life: An Introduction to Biological Diversity Chapter 26 The Tree of Life: An Introduction to Biological Diversity

Overview: Changing Life on a Changing Earth Life is a continuum extending from the earliest organisms to the variety of species that exist today Geological events change the course of evolution Conversely, life changes the planet that it inhabits

Geologic history and biological history have been episodic, marked by revolutions that opened many new ways of life

Concept 26.1: Conditions on early Earth made the origin of life possible Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages: 1. Abiotic synthesis of small organic molecules 2. Joining of these small molecules into polymers 3. Packaging of molecules into “protobionts” 4. Origin of self-replicating molecules

Synthesis of Organic Compounds on Early Earth Earth formed about 4.6 billion years ago, along with the rest of the solar system Earth’s early atmosphere contained water vapor and chemicals released by volcanic eruptions Experiments simulating an early Earth atmosphere produced organic molecules from inorganic precursors, but such an atmosphere on early Earth is unlikely

LE 26-2 CH4 Water vapor Electrode NH3 H2 Condenser Cold water Cooled water containing organic molecules H2O Sample for chemical analysis

Video: Hydrothermal Vent Instead of forming in the atmosphere, the first organic compounds may have been synthesized near submerged volcanoes and deep-sea vents Video: Hydrothermal Vent Video: Tubeworms

Extraterrestrial Sources of Organic Compounds Some organic compounds from which the first life on Earth arose may have come from space Carbon compounds have been found in some meteorites that landed on Earth

Looking Outside Earth for Clues About the Origin of Life The possibility that life is not restricted to Earth is becoming more accessible to scientific testing

Abiotic Synthesis of Polymers Small organic molecules polymerize when they are concentrated on hot sand, clay, or rock

Protobionts Protobionts are aggregates of abiotically produced molecules surrounded by a membrane or membrane-like structure 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

LE 26-4 Glucose-phosphate 20 mm Glucose-phosphate Phosphorylase Starch Amylase Phosphate Maltose Maltose Simple reproduction Simple metabolism

The “RNA World” and the Dawn of Natural Selection The first genetic material was probably RNA, not DNA RNA molecules called ribozymes have been found to catalyze many different reactions, including: Self-splicing Making complementary copies of short stretches of their own sequence or other short pieces of RNA

Complementary RNA copy 5¢ 5¢ Ribozyme (RNA molecule) 3¢ Template 3¢ Nucleotides Complementary RNA copy 5¢ 5¢

Early protobionts with self-replicating, catalytic RNA would have been more effective at using resources and would have increased in number through natural selection

Concept 26.2: The fossil record chronicles life on Earth Fossil study opens a window into the evolution of life over billions of years

How Rocks and Fossils Are Dated Sedimentary strata reveal the relative ages of fossils

Index fossils are similar fossils found in the same strata in different locations They allow strata at one location to be correlated with strata at another location Video: Grand Canyon

The absolute ages of fossils can be determined by radiometric dating The magnetism of rocks can provide dating information Magnetic reversals of the magnetic poles leave their record on rocks throughout the world

Ratio of parent isotope LE 26-7 Accumulating “daughter” isotope Ratio of parent isotope to daughter isotope 1 2 Remaining “parent” isotope 1 4 1 8 1 16 1 2 3 4 Time (half-lives)

The Geologic Record By studying rocks and fossils at many different sites, geologists have established a geologic record of Earth’s history

The geologic record is divided into three eons: the Archaean, the Proterozoic, and the Phanerozoic The Phanerozoic eon is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic Each era is a distinct age in the history of Earth and its life, with boundaries marked by mass extinctions seen in the fossil record Lesser extinctions mark boundaries of many periods within each era

Animation: The Geologic Record Mass Extinctions The fossil record chronicles a number of occasions when global environmental changes were so rapid and disruptive that a majority of species were swept away Animation: The Geologic Record

LE 26-8 Millions of years ago 600 500 400 300 200 100 100 2,500 100 2,500 Number of taxonomic families 80 2,000 Permian mass extinction ) Extinction rate 60 1,500 Number of families ( Extinction rate ( 40 1,000 Cretaceous mass extinction ) 20 500 Cambrian Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous Paleogene Proterozoic eon Neogene Ceno- zoic Paleozoic Mesozoic

The Permian extinction killed about 96% of marine animal species and 8 out of 27 orders of insects It may have been caused by volcanic eruptions The Cretaceous extinction doomed many marine and terrestrial organisms, notably the dinosaurs It may have been caused by a large meteor impact

LE 26-9 NORTH AMERICA Chicxulub crater Yucatán Peninsula

Mass extinctions provided life with unparalleled opportunities for adaptive radiations into newly vacated ecological niches

A clock analogy can be used to place major events in the context of the geological record

LE 26-10 Ceno- zoic Meso- zoic Humans Paleozoic Land plants Animals Origin of solar system and Earth 1 4 Proterozoic Eon Archaean Eon Billions of years ago 2 3 Multicellular eukaryotes Prokaryotes Single-celled eukaryotes Atmospheric oxygen

Concept 26.3: As prokaryotes evolved, they exploited and changed young Earth The oldest known fossils are stromatolites, rocklike structures composed of many layers of bacteria and sediment Stromatolites date back 3.5 billion years ago

The First Prokaryotes Prokaryotes were Earth’s sole inhabitants from 3.5 to about 2 billion years ago

Electron Transport Systems Electron transport systems were essential to early life Some of their aspects may precede life itself

Photosynthesis and the Oxygen Revolution The earliest types of photosynthesis did not produce oxygen Oxygenic photosynthesis probably evolved about 3.5 billion years ago in cyanobacteria

Effects of oxygen accumulation in the atmosphere about 2 Effects of oxygen accumulation in the atmosphere about 2.7 billion years ago: Posed a challenge for life Provided opportunity to gain energy from light Allowed organisms to exploit new ecosystems

Concept 26.4: Eukaryotic cells arose from symbioses and genetic exchanges between prokaryotes Among the most fundamental questions in biology is how complex eukaryotic cells evolved from much simpler prokaryotic cells

The First Eukaryotes The oldest fossils of eukaryotic cells date back 2.1 billion years

Endosymbiotic Origin of Mitochondria and Plastids The theory of endosymbiosis proposes that mitochondria and plastids were formerly small prokaryotes living within larger host cells

The prokaryotic ancestors of mitochondria and plastids probably gained entry to the host cell as undigested prey or internal parasites In the process of becoming more interdependent, the host and endosymbionts would have become a single organism

LE 26-13 Cytoplasm DNA Plasma membrane Ancestral prokaryote Infolding of plasma membrane Endoplasmic reticulum Nuclear envelope Nucleus Engulfing of aerobic heterotrophic prokaryote Cell with nucleus and endomembrane system Mitochondrion Mitochondrion Engulfing of photosynthetic prokaryote in some cells Ancestral heterotrophic eukaryote Plastid Ancestral photosynthetic eukaryote

Key evidence supporting an endosymbiotic origin of mitochondria and plastids: Similarities in inner membrane structures and functions Both have their own circular DNA

Eukaryotic Cells as Genetic Chimeras Endosymbiotic events and horizontal gene transfers may have contributed to the large genomes and complex cellular structures of eukaryotic cells Eukaryotic flagella and cilia may have evolved from symbiotic bacteria, based on symbiotic relationships between some bacteria and protozoans

LE 26-14 50 mm

Concept 26.5: Multicellularity evolved several times in eukaryotes After the first eukaryotes evolved, a great range of unicellular forms evolved Multicellular forms evolved also

The Earliest Multicellular Eukaryotes Molecular clocks date the common ancestor of multicellular eukaryotes to 1.5 billion years The oldest known fossils of eukaryotes are of relatively small algae that lived about 1.2 billion years ago

Larger organisms do not appear in the fossil record until several hundred million years later Chinese paleontologists recently described 570-million-year-old fossils that are probably animal embryos

150 mm 200 mm Two-celled stage of embryonic development (SEM) Later embryonic stage (SEM)

The Colonial Connection The first multicellular organisms were colonies, collections of autonomously replicating cells

Some cells in the colonies became specialized for different functions The first cellular specializations had already appeared in the prokaryotic world

The “Cambrian Explosion” Most of the major phyla of animals appear in the fossil record of the first 20 million years of the Cambrian period Two animal phyla, Cnidaria and Porifera, are somewhat older, dating from the late Proterozoic Molecular evidence suggests that many animal phyla originated and began to diverge much earlier, between 1 billion and 700 million years ago

LE 26-17 500 Sponges Cnidarians Echinoderms Chordates Brachiopods Annelids Molluscs Arthropods Early Paleozoic era (Cambrian period) Millions of years ago 542 Late Proterozoic eon

Colonization of Land by Plants, Fungi, and Animals Plants, fungi, and animals colonized land about 500 million years ago Symbiotic relationships between plants and fungi are common today and date from this time

Continental Drift The continents drift across our planet’s surface on great plates of crust that float on the hot underlying mantle These plates often slide along the boundary of other plates, pulling apart or pushing each other

LE 26-18 Eurasian Plate North American Plate Philippine Plate Juan de Fuca Plate Caribbean Plate Arabian Plate Indian Plate Cocos Plate South American Plate Pacific Plate Nazca Plate African Plate Australian Plate Scotia Plate Antarctic Plate

Video: Volcanic Eruption Many important geological processes occur at plate boundaries or at weak points in the plates Video: Lava Flow Video: Volcanic Eruption

Volcanoes and volcanic islands Trench Oceanic ridge Subduction zone LE 26-19 Volcanoes and volcanic islands Trench Oceanic ridge Subduction zone Oceanic crust Seafloor spreading

The formation of the supercontinent Pangaea during the late Paleozoic era and its breakup during the Mesozoic era explain many biogeographic puzzles

LE 26-20 By about 10 million years ago, Earth’s youngest major mountain range, the Himalayas, formed as a result of India’s collision with Eurasia during the Cenozoic. The continents continue to drift today. Cenozoic North America Eurasia By the end of the Mesozoic, Laurasia and Gondwana separated into the present-day continents. 65.5 Africa South America India Madagascar Australia Antarctica Laurasia By the mid-Mesozoic Pangaea split into northern (Laurasia) and southern (Gondwana) landmasses. 135 Gondwana Millions of years ago Mesozoic At the end of the Paleozoic, all of Earth’s landmasses were joined in the supercontinent Pangaea. 251 Pangaea Paleozoic

Concept 26.6: New information has revised our understanding of the tree of life Molecular data have provided insights into the deepest branches of the tree of life

Previous Taxonomic Systems Early classification systems had two kingdoms: plants and animals Robert Whittaker proposed five kingdoms: Monera, Protista, Plantae, Fungi, and Animalia

LE 26-21 Plantae Fungi Animalia Eukaryotes Protista Prokaryotes Monera

Reconstructing the Tree of Life: A Work in Progress The five kingdom system has been replaced by three domains: Archaea, Bacteria, and Eukarya Each domain has been split into kingdoms

LE 26-22a Chapter 27 Chapter 28 Red algae Chlorophytes Charophyceans Proteobacteria Chlamydias Spirochetes Cyanobacteria Gram-positive bacteria Korarchaeotes Cercozoans, radiolarians Diplomonads, parabasalids Euglenozoans Euryarchaeotes, crenarchaeotes, nanoarchaeotes Alveolates (dinoflagellates, apicomplexans, ciliates) Stramenopiles (water molds, diatoms, golden algae, brown algae) Domain Archaea Domain Eukarya Domain Bacteria Universal ancestor

LE 26-22b Chapter 29 Chapter 30 Chapter 28 Chapter 31 Chapter 32 Chapters 33, 34 Chytrids Angiosperms Zygote fungi Sac fungi Club fungi Sponges Choanoflagellates Cnidarians (jellies, coral) Arbuscular mycorrhizal fungi Seedless vascular plants (ferns) Gymnosperms Bryophytes (mosses, liverworts, hornworts) Amoebozoans (amoebas, slime molds) Bilaterally symmetrical animals (annelids, arthropods, molluscs, echinoderms, vertebrates) Plants Animals Fungi