B2 Major Transitions & Cooperations

What are the examples of major transitions in earth’s history?

1. assembly of genes into genomes

2. eukaryogenesis

3. multicellularity

4. eusocial organisms

Who wrote the first book on major life transitions?

1. John Maynard Smith

2. Eörs Szathmary

Summarize what it means to be a major transition

When two individuals join forces to form a higher-level unit

• Higher levels have their own fitness // lower levels lose autonomy

What are the three listed Major Transitions

1. Eukaryogenesis

2. Multicellularity

3. Cooperation (altruism)

What are the two benefits of major transitions?

1. Economies of scale

2. Division of labor

Economies of scale

The principle that certain tasks are impossible to complete alone or that there is more efficiency in groups

What does the surface-area-to-volume ratio tell us?

When dimensions double, volume increases faster than surface area

• Larger organisms have a SMALLER SA:vol ratio to retain more heat

• Smaller organisms have a LARGER SA:vol ratio to lose more heat

Division of labor

Specialized functions for efficiency; division of labor allows natural selection to specialize

Tradeoffs

If you optimize one trait, you may have to sacrifice another

Eukaryogenesis; who proposed the theory?

The origin of eukaryotes; the transition from two formerly independent organisms to a more complex organism

• Lynn Margulis

Conflict mediation

Genes transferred from mitochondria to the nucleus

• now mitochondria cannot live by itself

• Once the two cells fused together, they now have ONE common goal

List the two types of multicellularity

1. Clonal multicellularity (“staying together”)

2. Aggregate multicellularity (“coming together”)

Clonal multicellularity

Where cells have one parent cell and they divide and stay together

• Individual cells do not have their own fitness (division of labor)

Aggregate Multicellularity

Freely living individuals come together

• freely living individuals have their own fitness

What is the difference between germ and soma cells?

Germ:

• fxn: growth and reproduction

• no flagella

• fewer

Soma:

• fxn: motility

• 2 flagella

• more

What was the Volvox algae example?

Volvox algae exhibit clonal multicellularity via germ and soma cells

• Germ and soma cells cannot exist without each other; their cooperation increases the fitness of both

What was the Dictyostelium (slime mold) example?

Slime mold individuals aggregate into a slug when predators (nematodes) are around

• They do this to decrease their SA-Vol ratio when secreting mucus to protect from nematode attack

Kin selection; who proposed it?

Inclusive fitness (proposed by W.D. Hamilton) is altruistic behavior performed by individuals to increase the fitness of their offspring and the offspring of their kin (cousins, brothers, etc)

what was the belding ground squirrel example?

Females will give alarm calls to alert neighboring squirrels of predators

• females are more likely to give an alarm call because they are consistently near her kin, whereas males go off to join other colonies and are not near kin

What is group selection?

Tying your fitness to someone else’s fitness

• The principle of groups having high fitness based on the characteristics possessed by individuals in the group

Unit of selection

An individual natural selection is acting on

Where do chloroplasts and mitochondria descend from?

Chloroplasts: ancestors of cyanobacteria

Mitochondria: ancestors of alpha-proteobacteria

What are the “cheaters”?

Cheaters are the individuals who contribute little fitness to the group but they are at a higher level because of who they’re paired with