Lecture 12 - Speciation

Question 1

Mechanical isolation

Answer 1

Structural incompatibility of the reproductive organs between two species

Question 2

Copulatory behavioral isolation

Answer 2

Behaviour of individual during copulation is insufficient to allow normal fertilisation

Question 3

Gametic isolation

Answer 3

Transferred gametes cannot effect fertilization

Question 4

What are the 3 different types of post-mating pre-zygotic barriers?

Answer 4

Mechanical isolation

Copulatory behavioural isolation

Gametic isolation

Question 5

Example of mechanical isolation

Answer 5

The males of two species of Japanese carabid beetles have different shape and size of copulatory pieces causing tearing of the females reproductive organs and sometimes killing her (65% reproductive isolation)

Question 6

How common is mechanical isolation in animals?

Answer 6

Not very common

Question 7

What is an example of copulatory behavioral isolation?

Answer 7

Males of different species of drosophila have different shaped posterior lobe of the genital arch

Stimulates the female differently

If the female is not stimulated correctly the sperm is expelled

Question 8

What are the two different types of gametic isolation?

Answer 8

Non-competitive gametic isolation (intrinsic factors)

Competitive gametic isolation: conspecific sperm precedence

Question 9

Example of conspecific sperm/pollen precedence

Answer 9

D.Simulans female inseminated by both D.simulans and D.mauritania males produced almost no hybrdis (even when hetero-specific male is secound to mate)

Question 10

Hybrid inviability

Answer 10

The hybrid zygote dies due to genetic incompatibilities

Question 11

Hybrid sterility

Answer 11

The hybrid zygote survives, but is unable to produce viable progeny

Question 12

Two types of post-zygotic barriers?

Answer 12

Extrinsic - isolation depends on environment
Intrinsic - developmental problem in hybrids that is independent from the environment

Question 13

What are the two types of Extrinsic post-zygotic barriers?

Answer 13

Ecological inviability and behavioural sterlitiy

Question 14

Ecological inviability

Answer 14

Hybrids suffer lower viability because cannot fin an appropriate ecological niche

Question 15

Behavioral sterility

Answer 15

Hybrids are less fertile than the parental species because cannot obtain mates

Question 16

Two types of intrinsic post-zygotic barriers

Answer 16

Hybrid inviability - developmental difficulties cause hybrid lethality

Hybrid sterility - physiological or behavioural

Question 17

Example of ecological inviability in plants

Answer 17

Sagebush has two types: one that grows in the mountains and one that grows in the basin

hybrids show a lower fitness in both environments

Question 18

Example of ecological inviability in animals

Answer 18

butterflies H.melpomene and H.cydno

Have colors that show they are unpalatable

Hybrids change this colour pattern and means they are eaten more

Question 19

Example of behavioral sterility

Answer 19

Hybrids of Chrysoperla sps. will produce intermediate songs that are discriminated against by the females of both parental species

Question 20

is extrinsic isolation fixed? give an example

Answer 20

No

Darwin’s finches in the Galapagos, before and after el nino even. The climactic phenomenon had an impact on the seed size on the islands and therefore altered beak morphology

Question 21

How easy is it to distinguish between extrinsic and intrinsic post-zygotic isolation? give an example

Answer 21

Hard

Two species of mouse hybrids more prone to intestinal parasites (extrinsic) due to reduced genetic resistance (intrinsic) to parasitism

Question 22

Examples of hybrid sterality

Answer 22

Mule (horse and donkey)

Zedonk (zebra and donkey)

Question 23

Haldanes rule

Answer 23

If the reproductive isolation barriers are incomplete, the heterogametic (XY) sex will show the strongest isolation

The male is XY in mammals and most insects

The female is XY in butterflies and birds

Question 24

Dominance theory

Answer 24

Hybrid heterogametic are affected by X-linked incompatible genes either dominant or recessive (see example in notes)

Question 25

What are the 3 genetic basis for reproductive barriers of intrinsic sterility

Answer 25

Sequences divergence

Structural differences between chromosomes

Disharmonious interaction

Question 26

Sequences divergence as an intrinsic barrier

Answer 26

Sequence divergence leads to a lack of recombination and lack of correct pairing of homologous chromosomes in meiosis I

Question 27

Relationship between the strength of isolation and genetic distance

Answer 27

The strength of isolation increase gradually with genetic distance

Question 28

Structural differences between chromosomes as an intrinsic barrier

Answer 28

Differences in chromosomes can cause quadrivalent structures to form instead of bivalents which can undergo two separate outcomes:

Alternate segregation which generates two viable wild type gametes and 2 viable T type gametes

Adjacent segregation which generates 4 dead gametes

Question 29

Dobzhanski-muller incompatibility

Answer 29

Negative epistatic interactions between loci: genes contributing to hybrid sterility/inviability do not have this effect in non-hybrid individuals

Two populations can diverge and become fixed, if the two species then hybridise the two genes will work together and cause death

Question 30

Example of D-M incompatibility

Answer 30

Two species of flies have diverged (D.melanogastor and D.simulans)

Hybrid is inviable because Hmr and Lhr genes have diverged in the two species, and when together cause the death of hybrid males

Question 31

What theory underlies Discharmonious interaction

Answer 31

Dobzhanski-Muller incompatibility