Lecture 8 Evolution III

Question 1

what is the biological species concept?

Answer 1

• a species consists of a group of actually or potentially interbreeding individuals that are reproductively isolated from other groups
• based on potential to interbreed rather than on physical similarity
• problems: can’t be applied to fossils, asexual species, emphasizes absence of gene flow - but gene flow can occur between distinct species

Question 2

what is the morphological species concept?

Answer 2

• defines a species by structural features

- applies to sexual and asexual species but relies on subjective criteria

Question 3

what is the biological species concept?

Answer 3

• species is a set of organisms adapted to a particular set of resources, called a niche, in the environment
• based on ecological niche
• applies to sexual and asexual species
• emphasizes the role of disruptive selective

Question 4

what is the phylogenic species concept?

Answer 4

• defines species as the smallest group of individuals on a phylogenic tree
• based on evolutionary history
• applies to both sexual and asexual characteristics
• can be difficult to determine degree of difference required for separate species

Question 5

what is reproductive isolation?

Answer 5

• existence of biological factors/barriers that impede two species from producing viable, fertile offspring (hybrids)

Question 6

what are hybrids?

Answer 6

• OFFSPRING of crosses between different species

Question 7

what are the two types of reproductive isolation?

Answer 7

• prezygotic

- postzygotic

Question 8

what are the five prezygotic isolation mechanisms?

Answer 8

• habitat/ecological isolation: 2 species encounter each other rarely/not at all bc they occupy different habitats, even though not isolated by physical barrier
• temporal isolation: breed at different times of day/season/years
• behavioural isolation: courtship patterns and other behaviours unique to a species are barriers
• mechanical isolation: morphological differences can prevent successful mating - anatomically impossible
• gametic isolation: sperm of one species may not be able to fertilize eggs of another species

Question 9

what is prezygotic isolation?

Answer 9

block fertilization by

• impeding different species from attempting to mate
• preventing the successful completion of mating
• hindering fertilization if mating is successful

Question 10

what is postzygotic isolation?

Answer 10

prevent the hybrid zygote from developing into a viable, fertile adult

Question 11

what are 3 postzygotic isolation?

Answer 11

• reduced hybrid viability: genes impair hybrid’s development - DEATH
• reduced hybrid fertility: even if hybrids are vigorous, they are sterile
• hybrid breakdown: some 1st gen hybrids are fertile, but next gen are feeble/sterile

Question 12

what are the two types of speciation?

Answer 12

• allopatric

- sympatric

Question 13

what is allopatric speciation?

Answer 13

• gene flow interrupted when pop’n is divided into geographically isolated subpopulations
• regions with more barriers typically have more species
• ex: ensantina salamanders

Question 14

what is sympatric speciation?

Answer 14

• speciation takes place in geographically overlapping populations
• NO geographic separation

Question 15

how does sympatric speciation occur?

Answer 15

• habit differentiation, sexual selection, polyploidy

Question 16

what is habitat differentiation?

Answer 16

sympatric speciation

• appearance of new ecological niches
• ex NA fly can live on native hawthorn trees as well as recently introduced apple trees

Question 17

what is an example of sexual selection re: sympatric speciation?

Answer 17

• mates of different colour - cichlid fish in L. Victoria

Question 18

what is polypoidy?

Answer 18

• presence of extra chromosomes sets due to accidents during cell division
• more common in plants than in animals

Question 19

what is autopolyploid?

Answer 19

• individual with more than 2 chromosome sets derived from one species
• failure of cell division leads to doubles, triples, etc
• plants may be self-compatible but isolated from parents

Question 20

what is allopolyploid?

Answer 20

• species with multiple sets of chromosomes derived from different species
• ex: wheat

Question 21

what are hybrids?

Answer 21

result of mating between species with incomplete reproductive barriers

Question 22

what is a hybrid zone?

Answer 22

region in which members of different species mate and produce hybrids - often have reduced fitness compared w parents

Question 23

what are 3 hybrid zone outcomes?

Answer 23

reinforcement
stability
fusion

Question 24

what is reinforcement?

Answer 24

HZ

• hybrids less fit than parents
• over time hybridization decreases
• NS favours genes that cause individuals to avoid mating with hybrids
• reproductive barriers should be stronger for sympatric than allopatric species

Question 25

what is stability?

Answer 25

HZ - continued formation of hybrid individuals - extensive gene flow from outside hybrid zone can overwhelm selection for increased reproductive isolation inside the hybrid zone

Question 26

what is fusion?

Answer 26

HZ - weakening reproductive barriers - if hybrids are as fit as parents there can be substantial gene flow between species - potential for parent species can fuse into a single speceis ex: coywolf

Question 27

what are the two models of speciation?

Answer 27

- punctuated equilibrium | - gradualism

Question 28

what is punctuated equilibrium?

Answer 28

- speciation happens rapidly, followed by relatively long periods of stasis (no change)

Question 29

what is gradualism?

Answer 29

- slow differentiation by NS over many generations