Diversification & Diversification & ExtinctionsExtinctions

Macroevolution = Big Time Macroevolution = Big Time Change!Change!

• Changes occur to species to various degrees Changes occur to species to various degrees in response to environmental changes – in response to environmental changes – they may be drastic or hardly noticeable.they may be drastic or hardly noticeable.

• Sometimes, these changes within species Sometimes, these changes within species and populations are significant enough to and populations are significant enough to bring about new groups within a taxon or bring about new groups within a taxon or new taxa altogether.new taxa altogether.

• When new groups or levels arise due to When new groups or levels arise due to changes in a population or species – we say changes in a population or species – we say it is a case of it is a case of macroevolutionmacroevolution..

Endosymbiosis in Eukaryotic Endosymbiosis in Eukaryotic CellsCells

• Last time…We left off with an early Last time…We left off with an early prokaryotic cell being formed from the prokaryotic cell being formed from the “primordial soup” of a very young earth.“primordial soup” of a very young earth.

• These early prokaryotes would have given These early prokaryotes would have given rise to the two modern bacterial kingdoms rise to the two modern bacterial kingdoms – – archaebacteriaarchaebacteria and and eubacteriaeubacteria..

• One would think us eukaryotes would have One would think us eukaryotes would have arisen from the eubacterial lineage but arisen from the eubacterial lineage but this is not so…We actually have more this is not so…We actually have more similarities to the archaebacteria – the similarities to the archaebacteria – the bacteria that today live in the harshest bacteria that today live in the harshest areas on Earth.areas on Earth.

Prokaryote Prokaryote Eukaryote? Eukaryote?• Eukaryotes may have begun to develop from Eukaryotes may have begun to develop from

prokaryotes as the cell membrane may have prokaryotes as the cell membrane may have folded inward and formed the nucleus, folded inward and formed the nucleus, endoplasmic reticulum and vacuoles – all endoplasmic reticulum and vacuoles – all made of a phospholipid bilayer. Thus we have made of a phospholipid bilayer. Thus we have the beginnings of the first the beginnings of the first eukaryoticeukaryotic lineage. lineage.

• Researchers believe that the process of Researchers believe that the process of endosymbiosisendosymbiosis accounts for the presence of accounts for the presence of mitochondriamitochondria and and chloroplastschloroplasts. This would . This would only add to the abilities of early eukaryotic only add to the abilities of early eukaryotic cells.cells.

Endosymbiosis?Endosymbiosis?• Mitochondria and chloroplasts may Mitochondria and chloroplasts may

have been engulfed by the early have been engulfed by the early eukaryotes in a process similar to eukaryotes in a process similar to phagocytosisphagocytosis. They were seen as . They were seen as aerobic bacteria and photosynthetic aerobic bacteria and photosynthetic bacteria by the host cell respectively.bacteria by the host cell respectively.

• They would have been surrounded by They would have been surrounded by a a vesiclevesicle made of the host cell’s made of the host cell’s membrane. This would help to membrane. This would help to protect them inside the cell.protect them inside the cell.

Endosymbiosis?Endosymbiosis?

• A symbiotic relationship would have developed – A symbiotic relationship would have developed – energy rich molecules (ATP) would have been energy rich molecules (ATP) would have been supplied to the host and the “invader” would supplied to the host and the “invader” would have a nutrient-rich home in which to live – it’s have a nutrient-rich home in which to live – it’s win-win baby! This is known as win-win baby! This is known as mutualismmutualism..

• The mitochondria and chloroplasts would have The mitochondria and chloroplasts would have multiplied quite rapidly in their new nutrient-rich multiplied quite rapidly in their new nutrient-rich surroundings.surroundings.

• The The heterotrophicheterotrophic eukaryotes would have only eukaryotes would have only taken up the mitochondria while the taken up the mitochondria while the autotrophicautotrophic eukaryotes would have taken up both the eukaryotes would have taken up both the mitochondria and the chloroplasts.mitochondria and the chloroplasts.

Show Me The Money!Show Me The Money!• What evidence is there that this What evidence is there that this

endosymbiotic thing even happened?...endosymbiotic thing even happened?...• They have two membranes – no other They have two membranes – no other

organelles do. The two membranes organelles do. The two membranes differ from one another based on their differ from one another based on their make-up.make-up.

• Both chloroplasts and mitochondria Both chloroplasts and mitochondria replicate their own DNA which replicate their own DNA which resembles eubacterial DNA. This resembles eubacterial DNA. This division is independent of the host cell’s division is independent of the host cell’s division.division.

Unicellular Unicellular Multicellular! Multicellular!

• Archaebacteria gave rise to Archaebacteria gave rise to methanogens, thermophiles and methanogens, thermophiles and halophiles.halophiles.

• Eubacteria were aerobic and others Eubacteria were aerobic and others were autotrophic (photosynthetic).were autotrophic (photosynthetic).

• As more and more photosynthesis took As more and more photosynthesis took place the content of the atmosphere place the content of the atmosphere went from one dominated by carbon went from one dominated by carbon dioxide to one with a greater oxygen dioxide to one with a greater oxygen content.content.

Mass Extinction = Mass Extinction = Diversity?!?!Diversity?!?!

• Mass extinctions are events that Mass extinctions are events that dramatically alter the environment dramatically alter the environment and lead to the death of an incredible and lead to the death of an incredible number of species in a large number of species in a large geographical area.geographical area.

• After every mass extinction you see After every mass extinction you see a noticeable increase in the diversity a noticeable increase in the diversity of the subsequent geological period.of the subsequent geological period.

• Why is this? How does a lot of death Why is this? How does a lot of death lead to an abundance of life?lead to an abundance of life?

Mass Extinction = Mass Extinction = Diversity?!?!Diversity?!?!

Life After Death!!!Life After Death!!!

• Not everyone is killedNot everyone is killed – there are surviving – there are surviving species that are capable of coping in the new species that are capable of coping in the new environment. They have been naturally environment. They have been naturally selected and are seen as fit to continue.selected and are seen as fit to continue.

• These These fit survivorsfit survivors now have whatever now have whatever resources are available to themselves with resources are available to themselves with little or no competition – life is good and little or no competition – life is good and numbers go way up! This could be a source numbers go way up! This could be a source of competition!of competition!

• The new environment has many The new environment has many unfilled unfilled nichesniches whose species have gone extinct – whose species have gone extinct – there was a mass extinction after all!there was a mass extinction after all!

Life After Death!!!Life After Death!!!

• If you need to switch to a new resource If you need to switch to a new resource (because of (because of intraspecific competitionintraspecific competition) or ) or you desire something that was previously you desire something that was previously unavailable because you weren’t the best fit unavailable because you weren’t the best fit at attaining it – well now you are in luck!at attaining it – well now you are in luck!

• Nobody else is around so get it done! Go Nobody else is around so get it done! Go forth and move into a new role.forth and move into a new role.

• Think – it’s like Darwin’s finches – move in Think – it’s like Darwin’s finches – move in from South America as a single species and from South America as a single species and evolve into many different species in the evolve into many different species in the absence of other birds.absence of other birds.

The Rate of EvolutionThe Rate of Evolution• There are two main ideas – There are two main ideas – gradualismgradualism

and and punctuated equilibriumpunctuated equilibrium..

• GradualismGradualism states that evolution takes states that evolution takes place over long periods of time and that place over long periods of time and that changes accumulate slowly over this changes accumulate slowly over this time.time.

• The environment is slow in changing and The environment is slow in changing and so is the divergence within a species.so is the divergence within a species.

The Rate of EvolutionThe Rate of Evolution

• Punctuated EquilibriumPunctuated Equilibrium states that states that speciation and change occurs in very short speciation and change occurs in very short spurts and then is followed by long periods spurts and then is followed by long periods of little or no significant change.of little or no significant change.

• So who is the winner???So who is the winner???

• They both are! With evidence (the fossil They both are! With evidence (the fossil record) being incomplete – you could not record) being incomplete – you could not say which is more accurate because there say which is more accurate because there is evidence for both theories at work.is evidence for both theories at work.

Both Views Presented…Both Views Presented…

FINFIN