L11 - Diversification: Rates & Patterns of Evolution Flashcards
What is macroevolution?
- Evolution over geological time
- Mainly observed through fossils
What is microevolution?
- Evolution we can observe within a human generation
- Mainly observed through genomic work
Define trait?
- Observable feature in the phenotype (gene expression) if an organisms
- Generally physical/physiological (body functions) characteristics
- Sometimes, behavioural traits
- Organ presence, organ/body size, color, homeo/heterothermy, live birth, migration
How might traits evolve?
- Traits are generally linked to the genome (genes of the organism)
- A RANDOM mutation can create new/altered genes
- Some mutations will be expressed as new phenotypes
- Natural selections acts on the phenotype
What is the likelihood of mutation?
- Severe mutations adding completely novel trait are extremely rate
- Most evolutionary changes are slight modifications on existing traits
What is gene duplication?
- Can have duplication of genes/large sections of a chromosome
- In this case, there is a redundancy
- The duplicate mutates and acquires a new function
At what rate does trait evolution occur?
- Very very slowly
- Only over 1.6 M years have horses molars gradually enlarged
Some trends in trait evolution?
- Species become more complex over time
- E.g., unicellular species to multicellular eukaryotes
- However, no evidence of this in the fossil record
- General trend towards specialization in traits over time
Why make yourself dependent on another species for germination?
- Smaller energy investment required for seeds
- Mycorrhizae fungi likely only found in optimal habitats for orchid growth
Can a species regain a trait if it is lost through evolution?
- E.g., will orchids ever reproduce independently again?
- Rare, but not impossible
- Viviparous Lizard: tend to reproduce with live births, however some isolated populations do lay eggs.
Define irreducible complexity
Traits whose functions have become so essential to life, losing them through evolution seems impossible
What are some key evolutionary innovations?
- Evolution of seeds in plants
- First land plants reproduced mainly by spores
- Seeds allowed plants to reproduce away from water and experience dormancy
- Allowed greater provisioning and dispersal
What is the Island Rule (or Fosters Rule)?
Species that evolve on islands typically get either larger or smaller than their mainland counterparts
What is insular dwarfism?
- Animals which are large on the mainland become smaller on an island
- Islands have limited resources: SMALLER ANIMALS NEED LESS FOOD, NOT ENOUGH FOOD FOR THE LARGER ANIMALS TO SURVIVE
- For herbivores: their initial large size deters predators. Since there are few to no predators on island, they don’t need to be large anymore
- For carnivores: their prey tends to be smaller on islands and thus, they don’t need to be so big anymore.
What is insular gigantism?
- Species which are small on the mainland tend to become large on islands (E.g., Haast eagle New Zealand)
- Carnivores: Often lack of large carnivores on islands
- New carnivore species can become larger to fill the niche of apex predator
- Herbivores: Small herbivores stay small to
escape predation- If there are no effective predators (selective pressure), they will become larger
What are taxonomic rates of evolution?
The rate at which taxa (species, genus, famiy…) evolve
How do we date evolution?
- The background rate of mutation (often of “invisible” mutations, ones that don’t change the phenotype)
- Compare the number of changes and the intervals between changes
- More similar changes = recent divergence
- More drastic differences = less recent
What are creeps and jerks?
- Creeps: gradual speciation over time (phyletic gradualism)
- Observe intermediate forms
- Jerks: punctuated equilibrium (sudden abrupt changes)
- Random chance mutation
- Stabilizing selection: after quick divergence, remain unchanged over long periods of time
- Must be reproductive or geographic isolation between the ancestral species and the new species
What are some issues with phyletic gradualism?
- If intermediate forms are adaptive, why doesn’t evolution move towards stabilizing selection instead of changing traits over time?
- Evolution is not linear, does not have a goal to move toward the most optimal version of the species
- Some perceived low functioning traits are beneficial to some species
Which is more likely to occur in nature? Creeps or jerks?
Fossil records lines of evidence suggests gradual speciation is more common
What are some challenges between distinguishing the two in the fossil record?
- Assessment of the relative frequency between phenotypic changes may be biased by an incomplete fossil record
- Lack of many intermediate forms may mislead one to think that gradual speciation is actually punctuated equilibrium
Why do some species remain morphologically unchanged? What drives rapid evolution or stabilization?
- Climate and environmental conditions can slow processes of evolutionary change (e.g., very little change in the deep ocean)
- Species are adapted to their habitat: if their habitats remain stable over time, species tend to remain stable
