L24 Genetics of Speciation

Question 1

Gouldian Finches

Answer 1

see onenote

• 3 colour morphs
• head colour determined by genetic polymorphism in a single gene, “red”, on the Z chromosome

male - ZZ
female - ZW

Question 2

Change in Australian climate

Answer 2

0.5 mya
widespread desertification

Populations got separated by the three peaks due to desertification, allowed the 3 population to become genetically distinct => slightly different phenotypes

Question 3

1.5 mya

Answer 3

savannah grasslands cover the north

Question 4

recent years

Answer 4

deserts recede again

Secondary contact between black and red morphs after the desert receded but they were slightly incompatible

Question 5

Allopatry

Answer 5

Occurring in separate, nonoverlapping geographic areas.
Allopatric populations of related organisms are unable to interbreed because of geographic separation. ♦ The development of new species as a result of the geographic separation of populations is called allopatric speciation. Compare sympatric.

Question 6

Present range

Answer 6

• Geographic isolation caused by desertification
• Evolution in allopatry
• Secondary contact when the deserts receded
• Different populations became the red and black morphs or “sub-species”

Question 7

Why do allopatric populations become genetically incompatible?

Answer 7

see onenote

Dobzhansky-Muller model of hybrid incompatibility

“speciation genes” - underlie genetic incompatibilities

Question 8

Haldane’s rule

Answer 8

see onenote

when in the offspring of two different animal races one sex is absent, rare, or sterile, that sex is the heterozygous (heteroagametic) sex

Question 9

what might explain haldane’s rule - hypothesis 1

Answer 9

see onenote

maybe each species’ X and Y chromosome carry incompatible alleles?

not really supported

Question 10

what might explain haldane’s rule - hypothesis 2

Answer 10

see onenote

Maybe the larger sex chromosome (X or Z) carries recessive “speciation genes”. Having hybrid autosomes might be fatal unless on has two copies of certain X-linked genes

Supported pretty well - Haldane’s rule often breaks down in species where females inactivate one of their X chromosomes e.g. mammals

Question 11

Reinforcement

Answer 11

evolution of mechanisms that reduce the frequency of hybridisaiton

prefer those that are like them e.g. red with red…

Question 12

Reinforcement in island Drosophila

Answer 12

see onenote

If they’ve never mated with the wrong population, will happily mate with the wrong species the first time

sympatry selected for mate choice against the wrong species, which avoids wasteful mating that would not produce any viable offspring - this is reinforcement

sympatry selected for post-mating mechanism that allow females to avoid wasting their eggs on allo-specific sperm - reinforcement

Question 13

Sympatry

Answer 13

both species living together

Question 14

Matute’s experiment

Answer 14

see onenote

Sympatry group evolved better discrimination over time

Controlled group (allopatry) stayed the same over time

Question 15

Ecological speciation

Answer 15

see onenote

speciation resulting from speciation on two different niches

Question 16

Issues with ecological speciation

Answer 16

3 points

Question 17

Magic traits

Answer 17

see onenote

trait that is subject to divergent selection and also causes assortative mating

• Divergent selection: adapt to ecological factors
• Assortative mating: Assortative matingis amatingpattern and a form of sexual selection in which individuals with similar phenotypes mate with one another more frequently than would be expected under a randommatingpattern.

E.g. coiling trait in snails
To avoid eaten by snakes some snails coil the other way

Snails can only mate with other snails that coil the same way
Coiling the other way may you snake-proof but also affects mating

Question 18

Speciation by autopolyploidy

Answer 18

new species with doubled genome - new tetraploids can breed with each other but not with dipoids

Question 19

Speciation by allopolyploidy

Answer 19

see onenote

hybrid mating coupled with weird meiosis