Macroevolution

Question 1

what is macroevolution?

Answer 1

• large (time and taxonomic) scale patterns in evolution

- understanding changes in phenotypes and species richness, across species, clades, time and space

Question 2

what are the key questions in macroevolution?

Answer 2

• does change in one trait correlate with change in another trait?
• are there evolutionary correlations?
• why do some groups contain more species than others?
• does competition between groups limit diversity

Question 3

what are the sources of information for macroevolution?

Answer 3

• phylogenies, fossils and other traits

Question 4

do traits in insects show evolutionary correlations?

Answer 4

• looking at insect genomes, transition from solitary to group living
• transition to sociality could increase gene regultion because you need to create more specialised phenotypes
• they have genomes of 10 bee species
• gene regultion measured by the number and strength of transcription binding sites and the likelihood of gene methylation

Question 5

what were the results of the sociality trait in insects?

Answer 5

• looked for a correlation between social complexity measuring gene regulation
• saw a positive correlation
• the more social they are the more gene regulation there is

Question 6

what is independent contrast?

Answer 6

used when you have data on different species or other taxonomic groups that are related

Question 7

how do you calculate independent contrast?

Answer 7

1. get phylogeny of species represented in the data
2. estimate ancestral states by brownian motion
3. calculate raw contrasts between sister taxa
4. estimate the standard devisation of each contrast
5. standardize the contrasts by dividing each by its standard deviation
6. analyse them (regressions must be forced through the origin_

Question 8

what is raw contrast?

Answer 8

differences between their sister species

Question 9

why use independent contrasts?

Answer 9

• problem with raw species: it might be that some of the phylogeny is more highly related
• could have similarities because they are related so plain correlation doesnt mean much
• a regression assumes independence

Question 10

how can you tell when a species became independent from other sepcies?

Answer 10

• a phylogeny tells you this, you can then control for non-independence

Question 11

what do independent contrasts estimate?

Answer 11

the ancestors through averages

Question 12

how do you estimate what the ancestors are like if you need to calculate contrast between ancestors?

Answer 12

• have to assume a model of evolution

- brownian motion

Question 13

what is brownian motion?

Answer 13

• under this at any time step the same of evolution can happen but its random which direction
• traits will wander around through evolutionary time
• ancestors will have wandered the same distance from the original ancestor

Question 14

what are the assumptions about variation in brownian motion?

Answer 14

• the amount of variation in evolutionary trajectories is directly proportional to the time spent evolving
• variance increases in direct proportion to the sum of the branch length

Question 15

what is the framework for species richness between species?

Answer 15

• pattern (variation across taxonomic groups)
• proximate factors (Speciation rate, extinction rate and age)
• ultimate factors (operate via the intermediate of speciation and extinction: clade traits, behaviour, environmental chnages)

Question 16

what does the yule model of diversification assume?

Answer 16

no extinction and a constant rate of diversification

Question 17

what is the output of the yule model?

Answer 17

• get exponential growth of clades

- growth is linear when logged

Question 18

what can be estimated under the yule model?

Answer 18

• estimate the diversification rate using age and current species richness

Question 19

why are some clades more speciose than others?

Answer 19

• age or diversification rate?
• experiment that correlated age and diversification rate against species richness
• use PGLS
• correlated age and species richness - rubbish
• correlated diversification rate and species richness = explains a good chunk of species richness
• species richness varies because diversification rates vary

Question 20

what are PGLS?

Answer 20

• phylogenetic generalized least squares

- controls for phylogenetic relatedness looks for degree of variation from the expected

Question 21

how can we see diversification and extinction in the fossil record?

Answer 21

• originations = first appearances
• extinction = last appearances
• species hard to tell apart in the fossil record
• appear in layers of rock called strata (oldest at the bottom)
• can calculate species richness by counting the fossils in each strata

Question 22

what is the red queen hypothesis?

Answer 22

• competition between different groups which negatively effects the diversity of each group
• potentially the diversity of one group could negatively affect the other group
• biotic factors affecting extinction (always trying to evolve to outpace another group)

Question 23

what is the court jester hypothesis?

Answer 23

• abiotic factors could drive extinction and hence diversity
• opposite of the red queen hypothesis
• eg its thought that dinosaurs went extinct from an asteroid