bioe 109 summer 2009 lecture 12- part ii the cambrian explosion
TRANSCRIPT
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BIOE 109Summer 2009
Lecture 12- Part IIThe Cambrian explosion
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The origin and early evolution of the eukaryotes
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The origin and early evolution of the eukaryotes
• unlike prokaryotes, eukaryotes 1. have much larger cell sizes. 2. possess nucleus and organelles. 3. are mainly aerobic. 4. have cilia and flagella with tubulin rather than flagellin protein.
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The origin and early evolution of the eukaryotes
• unlike prokaryotes, eukaryotes
5. have linear DNA molecules associated with histones. 6. are usually multicellular. 7. have both mitosis and meiosis. 8. have a cytoskeleton.
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When did eukaryotes evolve?
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When did eukaryotes evolve?
• between 1.9 – 1.3 BYA, “microfossils” increase in size from 1-25 m to 40-80 m.
How did the eukaryotes evolve??
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When did eukaryotes evolve?
• between 1.9 – 1.3 BYA, “microfossils” increase in size from 1-25 m to 40-80 m.
How did the eukaryotes evolve??
• Lynne Margulis has championed the serial endosymbiosis hypothesis.
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When did eukaryotes evolve?
• between 1.9 – 1.3 BYA, “microfossils” increase in size from 1-25 m to 40-80 m.
How did the eukaryotes evolve??
• Lynne Margulis has championed the serial endosymbiosis hypothesis.
• mitochondria and chloroplasts were once free-living bacteria that took up permanent residence in larger eukaryotic cells.
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Evolution of mitochondria and chloroplasts
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Primary endosymbiosis gave rise to mitochondria
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Secondary endosymbiosis gave rise to chloroplasts
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Transfer of mitochondrial and plastid genes to the nucleus
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Transfer of mitochondrial and plastid genes to the nucleus
• most chloroplasts now have ~100 genes, mitochondria typically has 37.
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Transfer of mitochondrial and plastid genes to the nucleus
• most chloroplasts now have ~100 genes, mitochondria typically has 37.
• ~ 630 genes in the yeast and human genomes have an -proteobacterial ancestry.
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Transfer of mitochondrial and plastid genes to the nucleus
• most chloroplasts now have ~100 genes, mitochondria typically has 37.
• ~ 630 genes in the yeast and human genomes have an -proteobacterial ancestry.
• vast majority of the original genes have been lost.
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Transfer of mitochondrial and plastid genes to the nucleus
• most chloroplasts now have ~100 genes, mitochondria typically has 37.
• ~ 630 genes in the yeast and human genomes have an -proteobacterial ancestry.
• vast majority of the original genes have been lost.
• the transfer continues – Nuclear mitochondrial DNAs (Numts) are common!
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Current examples of endosymbioses
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Current examples of endosymbioses
1. The ciliate Paramecium bursaria and green algae (Chlorella)
• the ciliate readily uptakes the algae which supplies carbon compounds from photosynthesis.
• similar to early chloroplast evolution?
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Current examples of endosymbioses
2. The anaerobic amoeba, Pelomyxa palustris (lacks mitochondria)
• readily uptakes aerobic bacteria and then requires oxygen.
• similar to early mitochondrial evolution?
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Biases in the fossil record
1. Geographic bias
• majority of compression and impression fossils come from marine sediments, lake beds, and floodplains.
• terrestrial environments, especially tropical ones, are poorly represented.
2. Taxonomic bias
• fossil record is dominated by marine species possessing shells.
• presently, marine organisms represent about 10% of all known species.
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Biases in the fossil record
3. Temporal bias
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Biases in the fossil record
3. Temporal bias
• this is called the “pull of the recent”.
• older rocks are much rarer than newer rocks!
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The Ediacaran and Burgess Shale faunas
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The Ediacaran and Burgess Shale faunas
Ediacaran Fauna
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The Ediacaran and Burgess Shale faunas
Ediacaran Fauna
• dates to about 560 MYA.
• are exclusively soft-bodied (sponges, jellyfish, comb jellies, etc) and non-burrowing.
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The Ediacaran and Burgess Shale faunas
Ediacaran Fauna
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Vernanimalcula, found in China in 2004
Dates to 40 – 55 million years before Cambrian
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Burgess Shale Fauna
Discovered byCharles WalcottIn 1909
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Burgess Shale Fauna
• found near Field, B.C., dates to 520 MYA (similar to Yunnan fossils in China) • all but one of the 35 existing phyla dramatically “appear” – this is the Cambrian explosion.
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Burgess Shale Fauna
• found near Field, B.C., dates to 520 MYA (similar to Yunnan fossils in China) • all but one of the 35 existing phyla dramatically “appear” – this is the Cambrian explosion. • entirely new modes of locomotion evolve (i.e., swimming, burrowing, climbing).
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Burgess Shale Fauna
• found near Field, B.C., dates to 520 MYA (similar to Yunnan fossils in China) • all but one of the 35 existing phyla dramatically “appear” – this is the Cambrian explosion. • entirely new modes of locomotion evolve (i.e., swimming, burrowing, climbing).
• first segmented body plans, external skeletons, appendages, and notochords
• the diversity of body plans is astonishing!
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Anomalocaris
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Wiwaxia
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Opabinina
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Hallucigenia
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Pikaia
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Stephen Jay Gould (1941-2002)
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What caused the Cambrian explosion?
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What caused the Cambrian explosion?
1. Increase in the oxygen content of seawater
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What caused the Cambrian explosion?
1. Increase in the oxygen content of seawater
• allowed organisms to achieve increased sizes and metabolic rates.
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What caused the Cambrian explosion?
1. Increase in the oxygen content of seawater
• allowed organisms to achieve increased sizes and metabolic rates. • large size is clearly a prerequisite for the evolution of predators.
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What caused the Cambrian explosion?
2. Origin of hard parts (shells and mineralized exoskeletons).
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What caused the Cambrian explosion?
2. Origin of hard parts (shells and mineralized exoskeletons).
• some of the earliest shells have holes bored through them by predators! • strong selection pressures by presence of predators would have favored mineralized shells.
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What caused the Cambrian explosion?
3. The evolution of eyes
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What caused the Cambrian explosion?
3. The evolution of eyes
• proposed by Andrew Parker in his 2003 book, “In the blink of an eye”.
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What caused the Cambrian explosion?
3. The evolution of eyes
• proposed by Andrew Parker in his 2003 book, “In the blink of an eye”.
• eyes first appear in trilobites about 543 MYA.
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What caused the Cambrian explosion?
3. The evolution of eyes
• proposed by Andrew Parker in his 2003 book, “In the blink of an eye”.
• eyes first appear in trilobites about 543 MYA.
• large predators with eyes make for better predators!
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What caused the Cambrian explosion?
4. Genetic changes
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What caused the Cambrian explosion?
4. Genetic changes
• did the diversification of homeotic genes drive the Cambrian explosion?
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What caused the Cambrian explosion?
4. Genetic changes
• did the diversification of homeotic genes drive the Cambrian explosion?
• homeotic genes encode for transcription factors.
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What caused the Cambrian explosion?
4. Genetic changes
• did the diversification of homeotic genes drive the Cambrian explosion?
• homeotic genes encode for transcription factors.
• they activate suites of genes that control body plans during early development.
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Macroevolutionary patterns
1. Adaptive Radiation
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Macroevolutionary patterns
1. Adaptive Radiation
Definition (Mayr 1963): evolutionary divergence of members of a single phyletic line into a series of rather different niches or adaptive zones.
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Some generalizations about adaptive radiation
1. Occur at edges of a species range
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Some generalizations about adaptive radiation
1. Occur at edges of a species range
2. Facilitated by the absence of competitors and predators
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Some generalizations about adaptive radiation
1. Occur at edges of a species range
2. Facilitated by the absence of competitors and predators
• island archipelagoes are prime areas for radiations.
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Some generalizations about adaptive radiation
1. Occur at edges of a species range
2. Facilitated by the absence of competitors and predators
• island archipelagoes are prime areas for radiations.
Examples: Hawaiian Drosophila and honeycreepers
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Hawaiian honeycreepers
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Some generalizations about adaptive radiation
3. May involve “general adaptations”
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Some generalizations about adaptive radiation
3. May involve “general adaptations”
• general adaptations enable exploitation of new adaptive zones.
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Some generalizations about adaptive radiation
3. May involve “general adaptations”
• general adaptations enable exploitation of new adaptive zones. Example: evolution of flight (in insects, birds, bats)
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Some generalizations about adaptive radiation
3. May involve “general adaptations”
• general adaptations enable exploitation of new adaptive zones. Example: evolution of flight (in insects, birds, bats)
• there are ~1,500,000 insects, ~10,000 birds and ~1,100 bat species.
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2. Punctuated equilibrium (PE)
• first proposed by Stephen Jay Gould and Niles Eldredge in 1972 to account for “gaps” in the fossil record.
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2. Punctuated equilibrium (PE)
• first proposed by Stephen Jay Gould and Niles Eldredge in 1972 to account for “gaps” in the fossil record. Two characteristics:
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2. Punctuated equilibrium (PE)
• first proposed by Stephen Jay Gould and Niles Eldredge in 1972 to account for “gaps” in the fossil record. Two characteristics: 1. Periods of rapid morphological change co-occur with periods of rapid speciation.
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2. Punctuated equilibrium (PE)
• first proposed by Stephen Jay Gould and Niles Eldredge in 1972 to account for “gaps” in the fossil record. Two characteristics: 1. Periods of rapid morphological change co-occur with periods of rapid speciation. 2. After species are formed they exhibit “stasis”.
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Punctuated Equilibrium Phyletic Gradualism
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3. Mass extinctions
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3. Mass extinctions
• identified when extinction rates rise well above normal “background extinction”.
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3. Mass extinctions
• identified when extinction rates raise well above normal “background extinction”.
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The “Big Five”
Mass Date % families % speciesExtinction (MYA) lost lost
end-Ordovician 439 26 85
late-Devonian 367 22 83
end-Permian 250 52 96
end-Triassic 215 22 80
Cretaceous- 65 16 76Tertiary (K-T)
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What caused the end-Permian mass extinction?
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What caused the end-Permian mass extinction?
• in the Permian, the supercontinent Pangaea formed
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What caused the end-Permian mass extinction?
• in the Permian, the supercontinent Pangaea formed
1. A dramatic fall in sea level
• only 10% of shallow continental seas covered.
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What caused the end-Permian mass extinction?
• in the Permian, the supercontinent Pangaea formed
1. A dramatic fall in sea level
• only 10% of shallow continental seas covered.
2. The oceans apparently turned anoxic
• Pangaea may have disrupted patterns of oceanic circulation.
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What caused the end-Permian mass extinction?
3. Increased volcanic activity
• the Siberian flood basalts are 400 to 3,000 m thick and cover 1.5 million km2 in NE Asia.
• these combined effects have been called the “world-gone-to-hell” hypothesis.
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The K-T mass extinction
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The K-T mass extinction
• proposed by Louis Alverez in 1980 because of thin layer of iridium at the K-T boundary.
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The K-T mass extinction
• proposed by Louis Alverez in 1980 because of thin layer of iridium at the K-T boundary.
• the Chicxulub impact crater was discovered in 1993 on the Yucatan peninsula.
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The K-T mass extinction
• proposed by Louis Alverez in 1980 because of thin layer of iridium at the K-T boundary.
• the Chicxulub impact crater was discovered in 1993 on the Yucatan peninsula.
• formed by a meteorite ~10-15 km in diameter traveling at 10 km/s.
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Killing mechanisms:
1. Atmospheric debris
2. Acid rain
3. Widespread wildfires
4. Earthquakes of magnitude 13 on Richter scale
5. Tsunami 4 km high
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Who survives mass extinctions?
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Who survives mass extinctions?
1. Widespread/generalist species outsurvive endemic/specialized species.
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Who survives mass extinctions?
1. Widespread/generalist species outsurvive endemic/specialized species.
2. Temperate marine species out-survive tropical species.
• sometimes the “nowhere-else-to-go” hypothesis.
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Who survives mass extinctions?
1. Widespread/generalist species outsurvive endemic/specialized species.
2. Temperate marine species outsurvive tropical species.
• sometimes the “nowhere-else-to-go” hypothesis.
3. Small-bodied species outsurvive large-bodied species.