Chapter 25 The History of Life on Earth

Antarctica many millions of years ago Antarctica now… WOW!!

Past organisms were very different from today’s. The fossil record shows macroevolutionary changes over large time scales including –The origin of photosynthesis –The emergence of terrestrial vertebrates –Long-term impacts of mass extinctions

Prebiotic Chemical Evolution & the Origin of Life Hypothesis: First cells originated by chemical evolution -non living materials became organized into molecules; molecules were able to replicate & metabolize. -possible because atmosphere was really different; no O2, volcanoes, UV, lightning, etc. Four Main Stages of Cell Emergence: 1.small organic molecules are made abiotically 2.monomers  polymers (macromolecules) 3.protocells (droplets of aggregated molecules) 4.Origin of self replicating molecules/ beginning to heredity

Stage 1: Synthesis of Organic Compounds on Early Earth Earth formed about 4.6 bya Earth’s early atmosphere likely contained water vapor and chemicals released by volcanic eruptions (nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, hydrogen, hydrogen sulfide) TED Talk: The Line Between Life and Non- life

A. I. Oparin & J. B. S. Haldane hypothesized that the early atmosphere was a reducing environment (no oxygen) Stanley Miller and Harold Urey conducted lab experiments that showed that the abiotic synthesis of organic molecules in a reducing atmosphere is possibleStanley Miller and Harold Urey = Primeval Soup Hypothesis

Video: Hydrothermal Vent Video: Hydrothermal Vent OR… Organic compounds were created near hydrothermal vents OR… They rained down from outer space

What came first, the amino acid or the enzyme? –How would macromolecules form without enzymes/dehydration synthesis? Dilute solutions containing monomers dripped onto hot sand, clay, or rock vaporizes water –“Proteinoids” (proteins formed abiotically) were made this way Maybe waves splashed monomers onto hot lava? Stage 2: Abiotic Synthesis of Macromolecules

Stage 3: Protocells Replication & metabolism are key properties of life Protocellss are aggregates of abiotically produced molecules surrounded by a membrane or membrane- like structure Exhibit –simple reproduction –metabolism –maintain an internal chemical environment

(a) Simple reproduction by liposomes (aggregates of lipids) (b) Simple metabolism Possible to contain enzyme within; catalyze RXNs, give off product Phosphate Maltose Phosphatase Maltose Amylase Starch Glucose-phosphate 20 µm Protocells can behave similarly to a cell (osmotic swelling, membrane potential like nerve cell)

Stage 4: Self-Replicating RNA and the Dawn of Natural Selection RNA = probably the first genetic material, then DNA Ribozymes can make complementary copies of short stretches of their own sequence or other short pieces of RNA Base sequences provide blueprints for amino acid sequence (polypeptides)

Early protocells with self-replicating, catalytic RNA would have been more effective at using resources (“fitness”) & would have increased in # due to natural selection. RNA could have provided template for DNA (more stable, better at replicating) The stage has now been set for life!

Fig Animals Colonization of land Paleozoic Meso- zoic Humans Ceno- zoic Origin of solar system and Earth Prokaryotes Proterozoic Archaean Billions of years ago Multicellular eukaryotes Single-celled eukaryotes Atmospheric oxygen

Fig Present Dimetrodon Coccosteus cuspidatus Fossilized stromatolite Stromatolites Tappania, a unicellular eukaryote Dickinsonia costata Hallucigenia Casts of ammonites Rhomaleosaurus victor, a plesiosaur 100 million years ago ,500 1, cm 4.5 cm 1 cm

Table 25-1

Table 25-1a

Table 25-1b Animation: The Geologic Record Animation: The Geologic Record

Fig 25-UN2 Prokaryotes Billions of years ago

The First Single-Celled Organisms Oldest known fossils are stromatolites stromatolites –rock-like structures composed of many layers of bacteria and sediment –Dated 3.5 billion years ago Prokaryotes were Earth’s sole inhabitants from 3.5 to about 2.1 billion years ago

Fig. 25-4i Stromatolites 3.5 BYA Fossilized stromatolite

Fig 25-UN3 Atmospheric oxygen Billions of years ago

Photosynthesis & the Oxygen Revolution By about 2.7 bya, O 2 began accumulating in the atmosphere rusting iron-rich terrestrial rocks –O 2 produced by oxygenic photosynthesis reacted with dissolved iron and precipitated out to form banded iron formations “Oxygen revolution” = rapid increase in O2 around 2.2 bya –Posed a challenge for life; some microbes hid out in anaerobic environments –Provided opportunity to gain energy from light –Allowed organisms to exploit new ecosystems as old ones died, opening up new niches Source of O 2 was likely bacteria similar to modern cyanobacteria –Later rapid increase attributed to evolution of eukaryotes

Fig. 25-8

Fig 25-UN4 Single- celled eukaryotes Billions of years ago

Ancestral photosynthetic eukaryote Photosynthetic prokaryote Mitochondrion Plastid Nucleus Cytoplasm DNA Plasma membrane Endoplasmic reticulum Nuclear envelope Ancestral prokaryote Aerobic heterotrophic prokaryote Mitochondrion Ancestral heterotrophic eukaryote The First Eukaryotes Oldest fossils of eukaryotes go back 2.1 bya Endosymbiosis –mitochondria & plastids (chloroplasts & related organelles) were formerly small prokaryotes living within larger host cells –At first, undigested prey or internal parasites? –2 became interdependent; host + endosymbionts became a single organism

Evidence supporting endosymbiosis: –Similarities in inner membrane structures and functions between chloroplasts/mitochondr ia and prokaryotes –Organelle division is similar to prokaryotes –Organelles transcribe & translate their own DNA –Organelle ribosomes are more similar to prokaryotic ribosomes than eukaryotic ribosomes

Fig. 25-4h Tappania, a unicellular eukaryote 1.5 BYA

Multicellular eukaryotes Billions of years ago The Origin of Multicellularity eukaryotic cells allowed for a greater range of unicellular forms Once multicellularity evolved then… algae, plants, fungi, and animals Ancestor appeared rougly 1.5 bya, though oldest fossil is algae dated to 1.2 bya

Ediacaran biota (Proterozoic Eon) –large & more diverse soft-bodied organisms that lived from 565 to 535 mya after snowball Earth –Thaw opened up niches that allowed for speciation

Fig. 25-4g Dickinsonia costata 2.5 cm 565 MYA

Fig 25-UN6 Animals Billions of years ago

The Cambrian Explosion sudden appearance of fossils resembling modern phyla in the Cambrian period (Phanerozoic Eon, 535 to 525 mya) first evidence of predator-prey interactions; claws, hard-shells, spikes, etc. Burgess Shale

Fig. 25-4f Hallucigenia 1 cm 525 MYA

Fig. 25-4e Coccosteus cuspidatus 4.5 cm 400 MYA

Fig Sponges Late Proterozoic eon Early Paleozoic era (Cambrian period) Cnidarians Annelids Brachiopods Echinoderms Chordates Millions of years ago Arthropods Molluscs

Fig (a) Two-cell stage 150 µm 200 µm (b) Later stage

Fig 25-UN7 Colonization of land Billions of years ago

The Colonization of Land Fungi, plants, and animals began to move to land 500 mya Plants & fungi 420 mya: adaptations to reproduce on land Arthropods & tetrapods are the most widespread and diverse land animals –Tetrapods evolved from lobe-finned fishes around 365 million years ago –Amphibians, reptiles, then birds and mammals

Fig 25-UN8 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

Major Influences on Life on Earth Continental Drift: 3 occasions of formation, then separation of supercontinents; next one will occur in roughly 250 million years. –Collision and separation of oceanic and terrestrial plates shape mountains, cause earthquakes –Pangaea (250 mya) caused drastic changes in habitats = evolution! Mass extinctions: 5 major ones in Earth’s historyMass extinctions –Opens up niches for future species –Usually takes 5-10 million years to return diversity to its pre- extinction levels Adaptive Radiation : Periods of evolutionary change in which groups of organisms form many new species whose adaptations allow them to fill different niches (with little competition)

Adaptive Radiation –Occur after mass extinctions Rise of mammals after Cretaceous extinction –Colonized regions (i.e. new islands) Hawaiian Islands

How can evolutionary novelties/major changes in form come about? Evolutionary developmental biology, or evo- devo, is the study of the evolution of developmental processes in multicellular organisms Genomic information shows that minor differences in gene sequence or regulation can result in major differences in form …think fruit flies with legs instead of antennae

Evo-devo Changes in rate and timing (regulation) of developmental genes is called heterochrony –Accelerated growth in bone structures (finger bones to wings in bats) or slowed growth (reduction in leg bones in whale ancestors) –Paedomorphosis: fast development of reproductive system compared to other development; leads to maintenance of juvenile features though sexually mature (phenotypic variation) (a) Differential growth rates in a human (b) Comparison of chimpanzee and human skull growth Newborn Age (years) Adult Chimpanzee fetus Chimpanzee adult Human fetus Human adult allometric growth Gill s

Changes in spatial pattern of developmental genes (homeotic genes = master regulatory genes)homeotic genes –determine where, when, and how body segments develop –Small changes in regulatory sequences of certain genes lead to major changes in body form More Evo-devo Fig Adult fruit fly Fruit fly embryo (10 hours) Fly chromosome Mouse chromosomes Mouse embryo (12 days) Adult mouse Hox genes of the fruit fly and mouse show the same linear sequence on the chromosomes

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 Change in location of two Hox genes in Crustaceans led to the conversion of swimming appendage to feeding appendage Duplications of Hox genes in vertebrates may have influenced the evolution of vertebrates from invertebrates Homeobox/Hox genes code for transcription factors that turn on developmental genes in embryos The expression of 2 Hox genes in snakes suppresses the development of legs…the same genes are expressed in chickens in the area between their limbs

Even more Evo-devo Changes in genes and where they are expressed –Differing patterns of Hox gene expression = variation in segmentation –Suppression of leg formation in insects vs. crustaceans –Change in expression, not gene, can cause differences in form Fig Hox gene 6 Hox gene 7 Hox gene 8 About 400 mya Drosophila Artemia Ubx Ubx gene expressed in Abdomen – supressing leg formation Ubx gene expressed In main trunk – doesn’t supress legs insect crustaceans Fig Thorax Genital segments Thorax Abdomen Brine shrimp Artemia in comparison to grasshopper Hox expression

Test of Hypothesis A: Differences in the coding sequence of the Pitx1 gene? Result: No Marine stickleback embryo Close-up of ventral surface Test of Hypothesis B: Differences in the regulation of expression of Pitx1 ? Pitx1 is expressed in the ventral spine and mouth regions of developing marine sticklebacks but only in the mouth region of developing lake stickbacks. The 283 amino acids of the Pitx1 protein are identical. Result: Yes Lake stickleback embryo Close-up of mouth RESULTS Fig

Fig (a) Patch of pigmented cells Optic nerve Pigmented layer (retina) Pigmented cells (photoreceptors) Fluid-filled cavity Epithelium (c) Pinhole camera-type eye Optic nerve Cornea Retina Lens (e) Complex camera-type eye (d) Eye with primitive lens Optic nerve Cornea Cellular mass (lens) (b) Eyecup Pigmented cells Nerve fibers Eye Evolution Video Evolutionary “Novelties” are actually just new forms arising by slight modifications of existing forms