Macroevolution Flashcards
what is macroevolution?
- large (time and taxonomic) scale patterns in evolution
- understanding changes in phenotypes and species richness, across species, clades, time and space
what are the key questions in macroevolution?
- 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
what are the sources of information for macroevolution?
- phylogenies, fossils and other traits
do traits in insects show evolutionary correlations?
- 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
what were the results of the sociality trait in insects?
- 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
what is independent contrast?
used when you have data on different species or other taxonomic groups that are related
how do you calculate independent contrast?
- get phylogeny of species represented in the data
- estimate ancestral states by brownian motion
- calculate raw contrasts between sister taxa
- estimate the standard devisation of each contrast
- standardize the contrasts by dividing each by its standard deviation
- analyse them (regressions must be forced through the origin_
what is raw contrast?
differences between their sister species
why use independent contrasts?
- 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
how can you tell when a species became independent from other sepcies?
- a phylogeny tells you this, you can then control for non-independence
what do independent contrasts estimate?
the ancestors through averages
how do you estimate what the ancestors are like if you need to calculate contrast between ancestors?
- have to assume a model of evolution
- brownian motion
what is brownian motion?
- 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
what are the assumptions about variation in brownian motion?
- 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
what is the framework for species richness between species?
- 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)
what does the yule model of diversification assume?
no extinction and a constant rate of diversification
what is the output of the yule model?
- get exponential growth of clades
- growth is linear when logged
what can be estimated under the yule model?
- estimate the diversification rate using age and current species richness
why are some clades more speciose than others?
- 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
what are PGLS?
- phylogenetic generalized least squares
- controls for phylogenetic relatedness looks for degree of variation from the expected
how can we see diversification and extinction in the fossil record?
- 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
what is the red queen hypothesis?
- 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)
what is the court jester hypothesis?
- abiotic factors could drive extinction and hence diversity
- opposite of the red queen hypothesis
- eg its thought that dinosaurs went extinct from an asteroid
