Post on 28-Dec-2015
BIOE 109Summer 2009
Lecture 12- Part IIThe Cambrian explosion
The origin and early evolution of the eukaryotes
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.
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.
When did eukaryotes evolve?
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??
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.
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.
Evolution of mitochondria and chloroplasts
Primary endosymbiosis gave rise to mitochondria
Secondary endosymbiosis gave rise to chloroplasts
Transfer of mitochondrial and plastid genes to the nucleus
Transfer of mitochondrial and plastid genes to the nucleus
• most chloroplasts now have ~100 genes, mitochondria typically has 37.
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.
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.
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!
Current examples of endosymbioses
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?
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?
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.
Biases in the fossil record
3. Temporal bias
Biases in the fossil record
3. Temporal bias
• this is called the “pull of the recent”.
• older rocks are much rarer than newer rocks!
The Ediacaran and Burgess Shale faunas
The Ediacaran and Burgess Shale faunas
Ediacaran Fauna
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.
The Ediacaran and Burgess Shale faunas
Ediacaran Fauna
Vernanimalcula, found in China in 2004
Dates to 40 – 55 million years before Cambrian
Burgess Shale Fauna
Discovered byCharles WalcottIn 1909
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.
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).
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!
Anomalocaris
Wiwaxia
Opabinina
Hallucigenia
Pikaia
Stephen Jay Gould (1941-2002)
What caused the Cambrian explosion?
What caused the Cambrian explosion?
1. Increase in the oxygen content of seawater
What caused the Cambrian explosion?
1. Increase in the oxygen content of seawater
• allowed organisms to achieve increased sizes and metabolic rates.
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.
What caused the Cambrian explosion?
2. Origin of hard parts (shells and mineralized exoskeletons).
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.
What caused the Cambrian explosion?
3. The evolution of eyes
What caused the Cambrian explosion?
3. The evolution of eyes
• proposed by Andrew Parker in his 2003 book, “In the blink of an eye”.
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.
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!
What caused the Cambrian explosion?
4. Genetic changes
What caused the Cambrian explosion?
4. Genetic changes
• did the diversification of homeotic genes drive the Cambrian explosion?
What caused the Cambrian explosion?
4. Genetic changes
• did the diversification of homeotic genes drive the Cambrian explosion?
• homeotic genes encode for transcription factors.
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.
Macroevolutionary patterns
1. Adaptive Radiation
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.
Some generalizations about adaptive radiation
1. Occur at edges of a species range
Some generalizations about adaptive radiation
1. Occur at edges of a species range
2. Facilitated by the absence of competitors and predators
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.
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
Hawaiian honeycreepers
Some generalizations about adaptive radiation
3. May involve “general adaptations”
Some generalizations about adaptive radiation
3. May involve “general adaptations”
• general adaptations enable exploitation of new adaptive zones.
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)
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.
2. Punctuated equilibrium (PE)
• first proposed by Stephen Jay Gould and Niles Eldredge in 1972 to account for “gaps” in the fossil record.
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:
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. 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”.
Punctuated Equilibrium Phyletic Gradualism
3. Mass extinctions
3. Mass extinctions
• identified when extinction rates rise well above normal “background extinction”.
3. Mass extinctions
• identified when extinction rates raise well above normal “background extinction”.
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)
What caused the end-Permian mass extinction?
What caused the end-Permian mass extinction?
• in the Permian, the supercontinent Pangaea formed
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.
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.
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.
The K-T mass extinction
The K-T mass extinction
• proposed by Louis Alverez in 1980 because of thin layer of iridium at the K-T boundary.
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.
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.
Killing mechanisms:
1. Atmospheric debris
2. Acid rain
3. Widespread wildfires
4. Earthquakes of magnitude 13 on Richter scale
5. Tsunami 4 km high
Who survives mass extinctions?
Who survives mass extinctions?
1. Widespread/generalist species outsurvive endemic/specialized species.
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.
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.