chapter 24 - speciation

Question 1

define sympatric speciation

Answer 1

when speciation occurs in the same geographical space

Question 2

why does sympatric speciation occur? give an example

Answer 2

species may be isolated by factors such as preferences for different habits, mating, natural selection

eg. disruptive selection and assortative mating could lead to reproductive isolation

Question 3

define polyploidization

Answer 3

• instant speciation!
• genetic isolation created by formation of polyploid individuals that can breed only with each other

Question 4

define autopolyploidy

Answer 4

• polyploids that have duplicate chromosome sets from SAME species
• spontaneous gene duplication

(eg. chromosome doubling to produce a tetraploid)

Question 5

define allopolyploidy

Answer 5

• polyploids that have duplicate chromosome sets from DIFFERENT species
• hybridization event, followed by chromosome doubling

Question 6

name the 2 types of polyploids

Answer 6

autopolyploids and allopolyploids

Question 7

tetraploids

Answer 7

autopolyploidy: offspring of a parent that produced diploid gametes and then SELF FERTILIZED

allopolyploidy: error in meiosis or mitosis

Question 8

explain how allopolyploid species form (requires hybridization event)

Answer 8

• 2 species mate
• error in meiosis or mitosis leads to UNREDUCED GAMETES (with more than one set of chromosomes)
• if egg is fertilized, results in polyploid offspring

Question 9

why can polyploidy lead to reproductive isolation?

Answer 9

• diploid + tetraploid = TRIPLOID
• uneven (dysfunctional) amounts of chromosomes when gametes combine
• offspring can’t survive

Question 10

why is polyploidization more common in plants than animals?

Answer 10

• plant somatic cells undergo MORE rounds of MITOSIS making it more common that errors would occur
• self-fertilization more common

Question 11

define hybrid zones

Answer 11

zones where hybrids are made

diverged species/populations that come together to produce cross-fertilized offspring

Question 12

what can happen when isolated populations come in contact?

Answer 12

• when prezygotic isolation does not exist, populations may interbreed, produce hybrids
• gene flow may cause homogenization between populations
• gene flow may result in adaptive introgression (advantageous genes transferred across species)

Question 13

define adaptive introgression

Answer 13

advantageous genetic variation is transferred from one species (or population) to another

the good stuff gets shared

Question 14

name outcomes of hybridization

Answer 14

• homogenization (via gene flow)
• adaptive introgression (good genes transferred)
• reinforcement (NS for reproductive isolation)
• development of hybrid zones
• speciation by hybridization

Question 15

define reinforcement

Answer 15

selection for traits that isolate populations reproductively

• if two populations of different species are very diverged, their hybrid offspring may have lower fitness
  = incomplete postzygotic isolation
• if hybrid fitness low, may be strong NS against interbreeding

Question 16

can hybrids speciate?

Answer 16

yes!

and sometimes they actually have higher fitness

Question 17

define the biological species concept (BSC) and its issues

Answer 17

• assigns individuals to the same species if they actually or potentially interbreed
• populations evolutionarily independent if they are reproductively isolated from each other (NO GENE FLOW)

ISSUES:
- difficult to apply to natural systems (seemingly different species can still interbreed)
- asexual organisms?

Question 18

what mechanisms stop gene flow between populations?

Answer 18

PREZYGOTIC or POSTZYGOTIC mechanisms

Question 19

List and describe mechanisms of reproductive isolation

Answer 19

PREZYGOTIC (can’t mate)
- temporal: diff breeding times
- habitat: diffbreeding habitats
- behavioural: diff mating rituals
- gametic barrier: eggs + sperm incompatible
- mechanical: genitalia incompatible

POSTZYGOTIC (offspring die or have low fitness)
- hybrid variability: offspring don’t develop normally, die as embryos
- hybrid sensitivity: sterile offspring

Question 20

define the morphospecies concept (MSC) and its issues

Answer 20

• morphological traits distinguish species
• based in idea that distinguishing features more like to happen with no gene flow

ISSUES:
- features are subjective

Question 21

define the phylogenic species concept (PSC) and its issues

Answer 21

• species defined as smallest monophyletic group on a tree that compares populations

ISSUES
- may end up over diagnosing species (not all clades are really species)

Question 22

define allopatry

Answer 22

populations or species that live in different places

Question 23

OVERALL THEME:
name the ways genetic isolation can happen

Answer 23

ALLOPATRIC SPECIATION (physically separated)
- allopatry (physical separation)
- geographic distance (change of mating over long distance)

SYMPATRIC SPECIATION (in one physical space)
- reproductive isolation (pre/postzygotic)

Question 24

define the two types of allopatry and why they occur

Answer 24

DISPERSAL
- population moves to new habitat, colonizes, forms new population
- age of barrier pre-dates speciation event

VICARIANCE
- physical barrier splits population into isolated groups
- age of barrier ~same as speciation event

genetic isolation happens because of
- genetic drift
- natural selection
- mutation
- NOT gene flow

Question 25

how to find out which species are more closely related on phylogenic tree

Answer 25

find most recent common ancestor!

Question 26

mechanisms of sympatric speciation

Answer 26

• disruptive selection + assortative mating
• polyloidization (auto/alloploidy)

Question 27

what is a polyploid?

Answer 27

species with more than 2 sets of homologous chromosomes

Question 28

what is assortative mating?

Answer 28

biased mating with other individuals with similar traits

Question 29

define allopatric speciation

Answer 29

solation happening when species become physically separated

• DISPERSAL (one group of pop moves away)
• VICARIANCE (physical barrier of separation)