Speciation & Adaptive Radiations Lec 15-16

Question 1

Speciation

Answer 1

the evolution of reproductive isolation within an ancestral species, resulting in two or more descendant species

Question 2

Allopatric speciation

Answer 2

• evolution of reproductive isolation because of a geographic barrier
• vicariance = both populations large
• peripatric = one population small
• gene flow = 0
• speciation by genetic drift, natural selection, drift + selection

Question 3

Evidence for allopatric speciation : Behavioural

Answer 3

• increase in divergence correlated between genetics and mating and distance
• suggests incremental evolutionary divergence with space and time

Question 4

Mechanisms of allopatric speciation (without gene flow)

Answer 4

• natural selection (from being in different environments) causes the evolution of genetic differences that create pre/postzygotic incompatibility (reproductive isolation)
• genetic incompatibility, when the “right” alleles for each species get mixed up “wrong” in the crossing between two divergent groups = Dobzhansky-Mueller incompatibility

Question 5

Parapatric speciation

Answer 5

• restricted gene flow and environmental differences between populations
• e.g. clines
• difficult to distinguish in nature from secondary contact
• range expansion leads to sympatry

Question 6

Evidence for parapatric speciation

Answer 6

• multiple cave species nested in spring (=surface) species
• repeated speciation into caves
• gene flow at cave-surface interface

Question 7

Sympatric speciation

Answer 7

-no geographic barrier
requires:
-disruptive selection
-reproductive isolation
-transmitting the force of disruptive selection to the genes responsible for speciation
-genetic differences result in reproductive isolation

Question 8

Ecological speciation

Answer 8

the process by which barriers to gene flow evolve between populations as a result of ecologically-based divergent selection

Question 9

Cytological divergence

Answer 9

• can be instantaneous speciation

- common in plants, rare in animals

Question 10

Recombinant speciation

Answer 10

=hybrid speciation

• F1 has high fitness and is fertile
• common in plants, rarer in animals
• may be an effect of changing environment

Question 11

Allopatric

Answer 11

vicariant , peripatric

Question 12

genetic modes of speciation involve cytoplasmic or genetic incompatibility between diverging populations

Answer 12

-can be slow (e.g. genetic drift) or can be instantaneous (e.g. polyploidy)

Question 13

Speed of speciation

Answer 13

• strength of prezygotic and postzygotic isolation increases gradually with time
• time to full reproductive isolation is variable

Question 14

Allopatric speciation

Answer 14

-expect that pre-zygotic and post-zygotic reproductive isolation accumulates gradually as populations diverge

Question 15

Time to speciation depends on geography

Answer 15

• prezygotic isolation arises earlier among sympatric than allopatric taxa
• reinforcement: the enhancement of prezygotic isolation in sympatry by natural selection
• postzygotic isolation does not differ between sympatry and allopatry

Question 16

Adaptive radiations

Answer 16

-all of evolution’s processes can be understood through the lens of adaptive radiation (GG Simpson)

Question 17

Adaptive trait =

Answer 17

-enhances fitness compared to some alternative trait

Question 18

Adaptation or Adaptive Evolution =

Answer 18

change in living organisms that allow them to live successfully in an environment

Question 19

What are radiations?

Answer 19

-high rates of speciation, diverse groups

Question 20

What are adaptive radiations?

Answer 20

=the evolution of ecological and phenotypic diversity within a rapidly multiplying lineage
-outcome of divergent natural selection from: environment, resources, resource competition

Question 21

Process of adaptive radiation

Answer 21

1. Phenotypic differentiation between populations/species caused by differences in their environment and resources
2. Divergence in phenotype resulting from resource competition
3. Ecological speciation = reproductive isolation associated with different ecologies; often overcoming gene flow

Question 22

How to test adaptive radiations? Comparative Method

Answer 22

=comparing sets of species to pose or test hypotheses on adaptation and other evolutionary phenomena

• takes phylogeny into account “historical”
• to test hypotheses about adaptation and adaptive radiation
  e. g. convergent evolution vs shared ancestry

Question 23

Common elements of adaptive radiation

Answer 23

Criteria:

• single common ancestor
• colonisation of new environments
• new niches
• outcome of competition
• “island” habitats (isolation)

Question 24

Criteria of adaptive radiation

Answer 24

• common ancestry
• phenotype-environment correlation
• trait utility
• rapid speciation

Question 25

Famous adaptive radiations include:

Answer 25

• darwins finches
• threespine stickleback
• cichlid fishes

Question 26

Criteria of adaptive radiation

Answer 26

• common ancestry
• phenotype-environment correlation
• trait utility
• rapid speciation

Question 27

Famous adaptive radiations include:

Answer 27

• darwins finches
• threespine stickleback
• cichlid fishes