6 - Speciation

Question 1

MIcroevolution

Answer 1

• Evolution within populations, within species
• Changes in allele frequencies and associated traits within populations

Question 2

Macroevolution

Answer 2

• Evolution of species, genera, families, and other higher order levels of classification
• Relevant to interpret the fossil record

Question 3

Species

Answer 3

A group of interbreeding organisms that is reproductively isolated from other such groups

Question 4

Reproductive isolation isolating mechanisms

Answer 4

• Geographical seperation
• Differences in behaviour
• Physical appearance
• Number of chromosomes
• Reproductive physiology

Question 5

Hybridisation

Answer 5

• Genetic exchange between distinct populations
• Die or are sterile
• Creates a barrier to gene flow

Question 6

Gene flow

Answer 6

• Movement of genetic material within or between populations
• Maintains similarities among members of the population
• Counters the effect of selection for different
  phenotypes (if alleles are selected against in one part of the population, they may still reappear through migration)

Question 7

No gene flow

Answer 7

• Migration not possible
• No gene flow
• Local adaptations favoured
• Phenotypes become
  distinct
• Species reproductively
  isolated

Question 8

With gene flow

Answer 8

• Migration possible between habitats
• Gene flow swamps local
  adaptation
• Phenotype intermediate

Question 9

Problems with the biological species concept

Answer 9

Many clearly distinct species are not reproductively isolated

Question 10

Does speciation appear in the fossil record

Answer 10

• No, too rapid
• Too slow to observe in living populations

Question 11

Two processes of speciation

Answer 11

• Anagenesis
• Cladogenesis

Question 12

Allopatric speciation

Answer 12

• Two or more populations of a single species become isolated geographically and then diverge to form two
  (or more) new species
• Mechanism of reproductive isolation
• Subjected to different selection pressures

Question 13

Two additional mechanisms that may increase reproductive isolation and facilitate speciation

Answer 13

• Character displacement
• Reinforcement

Question 14

Character displacement

Answer 14

• Competition for
  resources will promote greater morphological differences (niche
  separation)
• e.g. Competition from newly arrived big beaks causes small beaks to use wetter habitat (which then selects for even smaller beaks)
• When there is no geographic overlap
  (hence no competition), the two species will have more similar diets/beaks

Question 15

Reinforcement

Answer 15

• Parents initially adapted to different environments → hybrid offspring may have a mosaic of traits that make them less fit for either environment
• Hybrids selected against

Question 16

Reinforcement vs character displacement

Answer 16

• In both cases, these mechanisms increase
  reproductive isolation
• Via competition and niche partitioning (CD)
• Via selection against hybrids (R)
• Not mutually exclusive

Question 17

Allopatric speciation following recolonisation

Answer 17

• Reproductive isolation may be complete→speciation complete
• Isolation may be
  amplified via reinforcement and/or
  character displacement

Question 18

Parapatric speciation

Answer 18

• Limited overlap in ranges (no true barrier)
• Groups in different parts of the range experience different environments
• At boundaries, hybrids selected against
• Reproductive isolation not complete, but natural selection keeps populations separate

Question 19

Sympatric speciation

Answer 19

• Overlapping ranges
• Differences between sub-groups develop without geographic separation
• Selection against intermediate types will lead to two new species (disruptive selection)
• Different adaptations to SAME environment

Question 20

Ecological niche

Answer 20

How a species exploits its habitat

Question 21

Adaptive radiation

Answer 21

• Occurs when a species colonises a new habitat with many open niches
• With fewer competitors, species will differentiate, filling available niches relatively rapidly

Question 22

Phyletic Gradualism

Answer 22

• Tiny changes accumulate gradually via microevolution
• Gradual transformation of one species into another
• Rates of evolution are constant and slow
• Anagenesis

Question 23

Punctuated equilibrium

Answer 23

• Short periods of rapid change after long periods of
  little or no change (stasis)
• Rates vary
• New species arise through splitting (isolation)
• Can be fast
• Cladogenesis

Question 24

Tempo and mode in evolution

Answer 24

• Room for both modes!
• Depends on many factors, but especially the environment
• Fossil record is difficult to interpret but adaptive radiations a good example of punctuated events