L11. Diversification: Rates and Patterns of Evolution Flashcards
Trait vs. Taxon
trait:
- observable feature in the phenotype of an organism
- usually linked to the genome
- can also be considered behavioural in some instances
- ex. coloration, nocturnal, long neck, size
Trait evolution
- not all traits equally likely to have mutations, this is because mutations in critical organs typically do not increase fitness, also dependant on how many genes control the trait
- likelihood of mutation: severe mutations adding completely novel traits are extremely unlikely, most evolutionary changes are slight modifications on existing traits. Interestingly genes can be repurposed
- rate of evolution: can occur super gradually over time
Two time scales of evolution
Macroevolution
- evolution over geological time
- mainly observed through fossils
Microevolution
- evolution we can observe through a human generation
- mainly observed through genomic work
Trait evolution trends
- species becoming more complex over time (only agreed upon example is prokaryotes to eukaryotes, fossil rate shows more complexity and more simplicity over time)
- trend towards specialization in traits over time (to better fit a niche) (ex. Orchids are dependant on mycorrhizal fungi for reproduction)
- traits can regain a trait after it is lost through evolution (ex. viviparous lizard)
- irreducible complexity: some traits are so important to life it seems as if they will never be lost
Key innovations in trait evolution
novel and sudden phenotypic adaption to take advantage of niche
- ex. flight, hard bodies, seeds
Enables a linage to diversify greatly
- evolve into a large number of different lineages
- often occurs rapidly in the fossil record
Fosters Rule (Island Rule)
Species that evolve on islands typically get either smaller or larger than their mainland counterparts
ex. insular dwarfism
Insular Dwarfism
animals which are large on the mainland become smaller on an island
Occurs because:
- islands have limited resources and smaller animals need less food
- for herbivores large size is advantageous because it deters predators but on many islands there are no predators
- for carnivores prey tends to be smaller on islands, large size no longer needed
Insular Gigantism
Species which are small on the mainland tend to become large on islands
Occurs because:
- for carnivores because lack of large carnivores on island so can fill this niche of apex predator
- for herbivores because small size helps escape predation, it there are no effective predators they will get larger because selective pressure gone
Taxonomic rates of evolution
- rate at which taxa evolve
- most common general definition of evolution
- calibrated with the fossil record
Dating evolution: molecular clocks
background rate of mutation (often invisble) gets compared to the number of changes
- more similar = recent divergence
- more different = less recent
Creeps vs. Jerks
Creeps: gradual processes over time (gradual speciation)
- many morphological intermediates
- critiques: if intermediate worked why did evolution continue (ex. eye, why would an eye that didn’t yet work get selected for?)
Jerks: sudden abrupt changes (punctuated equilibrium)
- would be from a chance mutation
- after quick divergence, remain unchanged over long periods of time
- must have reproductive or geographic isolation between ancestral species and the new species
Is Gradual speciation or Punctuated equilibrium more common?
Fossil records lines of evidence suggests gradual speciation
- But, incomplete fossil record makes it hard to differentiate between the two(could be missing many intermediate forms in the fossil record)
When do species not change?
- no clear answer
- if habitats remain stable over time, species tend to remain stable
