L11 - Diversification: Rates & Patterns of Evolution

Question 1

What is macroevolution?

Answer 1

• Evolution over geological time
• Mainly observed through fossils

Question 2

What is microevolution?

Answer 2

• Evolution we can observe within a human generation
• Mainly observed through genomic work

Question 3

Define trait?

Answer 3

• 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

Question 4

How might traits evolve?

Answer 4

• 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

Question 5

What is the likelihood of mutation?

Answer 5

• Severe mutations adding completely novel trait are extremely rate
• Most evolutionary changes are slight modifications on existing traits

Question 6

What is gene duplication?

Answer 6

• 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

Question 7

At what rate does trait evolution occur?

Answer 7

• Very very slowly
  
  • Only over 1.6 M years have horses molars gradually enlarged

Question 8

Some trends in trait evolution?

Answer 8

• 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

Question 9

Why make yourself dependent on another species for germination?

Answer 9

• Smaller energy investment required for seeds
• Mycorrhizae fungi likely only found in optimal habitats for orchid growth

Question 10

Can a species regain a trait if it is lost through evolution?

Answer 10

• 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.

Question 11

Define irreducible complexity

Answer 11

Traits whose functions have become so essential to life, losing them through evolution seems impossible

Question 12

What are some key evolutionary innovations?

Answer 12

• 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

Question 13

What is the Island Rule (or Fosters Rule)?

Answer 13

Species that evolve on islands typically get either larger or smaller than their mainland counterparts

Question 14

What is insular dwarfism?

Answer 14

• 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.

Question 15

What is insular gigantism?

Answer 15

• 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

Question 16

What are taxonomic rates of evolution?

Answer 16

The rate at which taxa (species, genus, famiy…) evolve

Question 17

How do we date evolution?

Answer 17

• 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

Question 18

What are creeps and jerks?

Answer 18

• 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

Question 19

What are some issues with phyletic gradualism?

Answer 19

• 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

Question 20

Which is more likely to occur in nature? Creeps or jerks?

Answer 20

Fossil records lines of evidence suggests gradual speciation is more common

Question 21

What are some challenges between distinguishing the two in the fossil record?

Answer 21

• 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

Question 22

Why do some species remain morphologically unchanged? What drives rapid evolution or stabilization?

Answer 22

• 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