T3 - Speciation 1

Question 1

What is Mayr’s definition of the biological species concept?

Answer 1

One or more populations of potentially interbreeding organisms that are reproductively isolated from other such groups

Mayr 1942

Question 2

What was the issue with Mayr’s 1942 definition a biological species?

Answer 2

“Reproductively isolated from other such groups”

It is hard to tell if a species are reproductively isolated from one another if u only have a gene seq/taxonomic character and/or they’re dead

Definition basically only works for living species

Question 3

What is the definition of speciation?

(Given by the lecturer)

Answer 3

The evolution of reproductive isolation between populations

Question 4

What are the 2 types of isolating mechanisms?

Answer 4

Premating and postmating

Question 5

What are 2 good examples of the evolution of reproductive isolation between populations?

Answer 5

Liger/Tion and Mule/hinny

both species’ offspring are sterile –> this is an example of postmating isolation

Question 6

Define premating isolation:

Answer 6

Species that choose not to mate w each other/cannot mate with each other

the isolation occurs b4 mating

Question 7

Define postmating isolation:

Answer 7

The cross does not work/the hybrid offspring do not work

Isolation occurs after they mate

Question 8

What is another name for premating isolation?

Answer 8

Prezygotic isolation

Question 9

Give 2 examples of premating/prezygotic isolation:

Answer 9

Pundamilia fish & Aquilegia flowers

(Pundamilia fish –> closely related species, however females choose mates based on colourings, this determines species - remove the choice of colour & females would make mistakes)

(Aquilegia flowers –> 2 diff species have diff nectar spurs, one is pollinated by hummingbirds & other by hawkmoth, due to differing pollinators, there is limited exchange of pollen between the species - however not entirely limited as bees and flies do interact w both)

Question 10

Important note of isolating mechanisms in premating isolation:

Answer 10

Isolating mechnsims are not perfect - esp not to begin with

In the beginning therefore there will still be some gene flow between things that are diverging to become species

Question 11

What is another name for postmating isolating mechanisms?

Answer 11

Postzygotic isolation

Question 12

What are the 2 subtypes of postmating/postzygotic isolation?

Answer 12

1 - Intrinsic or genetic postzygotic isolation

2- Extrinsic or ecological postzygotic isolation

Question 13

Give an example of Intrinsic or genetic postzygotic isolation:

Answer 13

Species of heliconias butterfly

Study of hatching rates in a lab –> bred H. melpomene and H. cydno with own species & cross bed them, v successful in all 3 conditions

Then tried to crossbreed the F1 cross generation w a male cydo –> absolutely no hatching occurred

2nd gen offspring are completely sterile

Question 14

What is Holdanes rule?

Answer 14

In hybrid sterility, it is common that the heterogametic sex suffers

e.g. butterflies have ZW sex determination so tends to be female that is affected (sterile)

However mammals it will be males affected (XY)