L5 Reproductive isolation

Question 1

What is the basic definition of a species?

Answer 1

A group of successfully interbreeding individuals

Question 2

What is the problem with the species definition?

Answer 2

At what point does a species become isolated and become separate from another

Question 3

What is prezygotic reproductive isolation?

Answer 3

Keeps the individuals apart, stopping them from mating and forming a zygote

Question 4

What are the mechanisms of prezygotic isolation?

Answer 4

Via:
Habitat - won’t meet
Behaviour - mechanisms like mating rituals won’t match
Morphological - the choosier sex may not be attracted to a trait in another species
Temporal - breeding times don’t correlate
Mechanical - sex organs don’t fit together
Gametic - sperm and egg match is inviable, can’t be fertilised

Question 5

What is postzygotic reproductive isolation?

Answer 5

Happens after fertilisation, but is still a barrier

Question 6

What are the mechanisms of post zygotic reproductive isolation?

Answer 6

Hybrid inviability - doesn’t survive
Hybrid infertile - can survive but can’t reproduce itself
Hybrid breakdown - hybrid is less fit than parental population

Question 7

What happens to populations without gene flow?

Answer 7

Should diverge, background genetics will change,

Question 8

What is the genetic basis of a barrier?

Answer 8

the obvious answer is if selection is acting on different alleles in different alleles in different environments. However, selection may not be involved, and so barriers arise by other mechanisms

Question 9

What is the Dobzhansky-Muller model?

Answer 9

model of the evolution of genetic incompatibility, important for understanding the evolution of reproductive isolation during speciation. Based around the idea that the background genomes of two separate populations can diverge by chance due to mutation, when not under selection. If two alleles that have never met are exposed to one another, may cause conflict

Question 10

How is mating preference linked to diverging traits?

Answer 10

You have to have a mating preference linked to an adaptive trait to reach reproductive isolation. Only get divergence once individuals start choosing mates within, over between, populations

Question 11

What are direct systems?

Answer 11

One gene that is adaptive, but also effects the mating preference , e.g. feather colour.

Question 12

Give an example of a direct system

Answer 12

Chichlids living in different levels of lake Victoria coloured differently, adaptive as masks from predators as different light levels. Female preference for males is based on the same trait. Females at the top of the lake choose males of the phenotype correlating to the top of the lake

Question 13

What is indirect selection?

Answer 13

Adaptive trait may not have any influence of the mating preference on the choosy sex. Selection should act for a mate preference allele linked at adaptive trait, against recombination

Question 14

What is reproductive character displacement?

Answer 14

differences in sexually selected traits among similar species in the same area are accentuated or altered when species co-occur, stops interbreeding from occurring

Question 15

What is the reinforcement hypothesis?

Answer 15

When there is a postzygotic barrier, selection will act on a prezygotic barrier to stop less fit hybrids from being created, occurs in sympatric populations - most obvious in sexually selected traits, but can be others

Question 16

In what situation would reinforcement take place?

Answer 16

When the species are in sympatry, allopatric populations don’t meet, and so need for selection to favour a prezygotic barrier

Question 17

What is an example of reinforcement in a population?

Answer 17

Flycatchers, pied and collard occur in sympatry in area of Europe. Males appear similar, whereas females are brown. In sympatry, male pied become brown so as to be distinguished. However, females have preference for black feathers, and so there is a change in the mate preference allele for black feathers, so pied females, when in sympatry, will select for brown feathers. This means populations won’t interbreed, this is the prezygotic barrier put forward by reinforcement.

Question 18

What happens as you get further away in relatedness?

Answer 18

Increased failure to reproduce

Question 19

What is the relationship between divergence and fitness?

Answer 19

Can be calculated by studying the cytochrome clock, which is based on Mitochondrial DNA. Differs in species

Question 20

What is Haldane’s rule?

Answer 20

When a cross produces inviable or sterile offspring, the heterogametic sex is strongly affected as they only have one copy of the allele

Question 21

What determines how quickly reproductive isolation takes place?

Answer 21

Depends on the processes taking place and whether the species are interacting. more likely to be faster in sympatry, as selection can act. In allopatry, relies on changes in the background genetics etc.

Question 22

How much does the genome need to differ to cause isolation?

Answer 22

Need two different genomes that are evolving differently enough for populations to diverge. Overtime chance of having a genome that differs, increases with selection. Eventually interbreeding is affected, leading to reproductive isolation.

Question 23

What are speciation genes?

Answer 23

Hypothetical, could be genes that cause reproductive isolation their own