chapter 25 the history of life on earth. antarctica many millions of years ago antarctica now…...
TRANSCRIPT
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 possible
= Primeval Soup Hypothesis
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
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. 25-7
Animals
Colonizationof land
Paleozoic
Meso-
zoic
Humans
Ceno-zoic
Origin of solarsystem andEarth
ProkaryotesProterozoic Archaean
Billions of years ago
1 4
32
Multicellulareukaryotes
Single-celledeukaryotes
Atmosphericoxygen
Fig. 25-4Present
Dimetrodon
Coccosteus cuspidatus
Fossilizedstromatolite
Stromatolites Tappania, aunicellulareukaryote
Dickinsoniacostata
Hallucigenia
Casts ofammonites
Rhomaleosaurus victor, a plesiosaur
10
0 m
illi
on
ye
ars
ag
o2
00
17
53
00
27
04
00
37
55
00
52
55
65
60
03
, 500
1, 5
0 0
2.5 cm4.5 cm
1 cm
Table 25-1
Table 25-1a
Table 25-1b
Animation: The Animation: The Geologic Record
Fig 25-UN2
Prokaryotes
Billions of year
s ag
o
4
32
1
The First Single-Celled Organisms
• Oldest known fossils are 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
Atmosphericoxygen
Billions of year
s ag
o4
32
1
Photosynthesis & the Oxygen Revolution• By about 2.7 bya, O2 began accumulating in the atmosphere rusting iron-rich terrestrial rocks– O2 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 O2 was likely bacteria similar to modern cyanobacteria– Later rapid increase attributed to evolution of eukaryotes
Fig. 25-8
Fig 25-UN4
Single-celledeukaryotes
Billions of year
s ag
o
4
32
1
Ancestral photosyntheticeukaryote
Photosyntheticprokaryote
Mitochondrion
Plastid
Nucleus
Cytoplasm
DNA
Plasma membrane
Endoplasmic reticulum
Nuclear envelope
Ancestralprokaryote
Aerobicheterotrophicprokaryote
Mitochondrion
Ancestralheterotrophiceukaryote
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/mitochondria 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
Multicellulareukaryotes
Billions of
year
s ag
o
4
32
1
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 year
s ag
o
4
32
1
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. 25-10
Sp
on
ge
s
LateProterozoiceon
EarlyPaleozoicera(Cambrianperiod)
Cn
idar
ian
s
An
nel
ids
Bra
ch
iop
od
s
Ec
hin
od
erm
s
Ch
ord
ate
s
Mill
ion
s o
f y
ears
ag
o
500
542
Art
hro
po
ds
Mo
llus
cs
Fig. 25-11
(a) Two-cell stage 150 µm 200 µm(b) Later stage
Fig 25-UN7
Colonization of land
Billions of year
s ag
o4
32
1
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 increasein diversity ofanimal forms)
500 mya:Colonizationof land byfungi, plantsand animals
Pre
sen
t
500
2,00
0
1,50
0
1,00
0
3,00
0
2,50
0
3,50
0
4,00
0
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 history– 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
NewbornAge (years)
Adult1552
Chimpanzee fetus Chimpanzee adult
Human fetus Human adult
•allometric growth
Gills
• Changes in spatial pattern of developmental genes (homeotic genes = master regulatory 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-devoFig. 21-17
Adultfruit fly
Fruit fly embryo(10 hours)
Flychromosome
Mousechromosomes
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 earlyvertebrates (jawless)with two Hox clusters
Hypothetical vertebrateancestor (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. 25-22
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 expressedIn main trunk – doesn’t supress legs
insectcrustaceans
Fig. 21-18
ThoraxGenitalsegments
Thorax Abdomen
Abdomen
Brine shrimp Artemia in comparison to grasshopper Hox expression
Test of Hypothesis A:Differences in the codingsequence of the Pitx1 gene?
Result:No
Marine stickleback embryo
Close-up of ventral surface
Test of Hypothesis B:Differences in the regulationof expression of Pitx1 ?
Pitx1 is expressed in the ventral spineand mouth regions of developing marinesticklebacks but only in the mouth regionof developing lake stickbacks.
The 283 amino acids of the Pitx1 proteinare identical.
Result:Yes
Lake stickleback embryo
Close-upof mouth
RESULTSFig. 25-23
Fig. 25-24
(a) Patch of pigmented cells
Opticnerve Pigmented
layer (retina)
Pigmented cells(photoreceptors)
Fluid-filled cavity
Epithelium
Epithelium
(c) Pinhole camera-type eye
Optic nerve
Cornea
Retina
Lens
(e) Complex camera-type eye
(d) Eye with primitive lens
Optic nerve
CorneaCellularmass(lens)
(b) Eyecup
Pigmentedcells
Nerve fibers Nerve fibers
Eye Evolution Video
Evolutionary “Novelties” are actually just new forms arising by slight modifications of existing forms