Speciation I (DONE)

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 is the limitation 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 –> not extinct or those who reproduce asexually

Question 3

What is the definition of speciation?

(Given by the lecturer)

Answer 3

The evolution of reproductive isolation between populations, leading to distinct species

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 (prezygotic) isolation:

Answer 6

Mechanisms that prevent mating or fertilisation, such as behavioural isolation (e.g. different mating signals) & ecological isolation (e.g. pollinator preferences)

Question 7

Define postmating (postzygotic) isolation:

Answer 7

Mechanisms that prevent hybrid offspring from surviving or reproducing, incl intrinsic isolation (genetic incompatibilities) & extrinsic isolation (maladaptation to the environment)

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)

Question 15

What is allopatric speciation?

Answer 15

Speciation caused by geographic isolation

e.g. shrimps separated by the Isthmus of Panama

Question 16

What is sympatric speciation?

Answer 16

Speciations that occurs within the same geographic area, often driven by ecological divergence

eg apple maggot flies shifting from hawthorn to apple

Question 17

What are ring species?

Answer 17

Pops that expand around a geographic barrier - diverging progressively until terminal populations cannot interbreed

e.g. Asian birds with song divergence

Question 18

How does reproductive isolation change over time?

Answer 18

Prezygotic isolation evolves earlier (e.g. reinforcement in sympatric pops),

While postzygotic isolation evolves later due to genetic incompatibilities

Question 19

What is the Dobhansky-Muller model?

Answer 19

Speciation occurs thru genetic incompatibilities that arise as populations diverge

Question 20

What is reinforcement?

Answer 20

Selection against hybridisation due to reduced hybrid fitness, strengthening prezygotic isolation

Question 21

What is an example of reinforcement in sympatric populations?

Answer 21

Pied & collared flycatchers evolving distinct male plumage to avoid hybridisation

Question 22

What is the formula for reproductive isolation over time?

Answer 22

RI = f(D)

D = genetic divergence

(Not sure this is necessary but I guess its good for context)

Question 23

What factors influence hybrid fitness in postzygotic isolation?

Answer 23

F h = f(E,P)

Where E: Environment (e.g., resource availability) and
P: Parental genetic contribution.

(Again not sure this is necessary but I guess its good for context)

Question 24

What are the stages of speciation?

Answer 24

1 - Initial divergence (allopatry)

2 - Secondary contact (reinforcement strengthens prezygotic isolation)

3 - Sympatry (full reproductive isolation)

Question 25

What is an example of sympatric speciation?

Answer 25

Chichild fishes in crater lakes evolving district feeding traits (benthic vs limnetic forms)

Question 26

What is an example of temporal pattern in speciation?

Answer 26

In Drosophila, reproductive isolation strengthens as genetic divergence increases

Question 27

What drives the speciation process?

Answer 27

Reproductive isolation thru spatial (allopatric/sympatric), temporal & ecological mechanisms, reinforced by hybridisation avoidance

Question 28

What is intrinsic postzygotic isolation?

Answer 28

Isolation caused by incompatibilities that result in hybrid sterility or inviability

e.g. Haldane’s rule, where hybrid sterility often affects the heterogametic sex (e.g. male mammals)

Question 29

What is extrinsic postzygotic isolation?

Answer 29

Isolation where hybrids are maladapted to their own environment & perform poorly

e.g. hybrids between maple- and willow-adapted beetles

Question 30

How do larger areas affect allopatric speciation?

Answer 30

Larger areas (e.g. big islands) provide more opportunities for geographic isolation & subsequent divergence

Question 31

What is the by-product mechanism in speciation?

Answer 31

Traits evolve to adaptation to different environments but also indirectly influence mate choice, driving reproductive isolation

Question 32

What is a geographic mosaic of speciation?

Answer 32

Speciation dynamics vary across pops & regions due to local adaptations & environmental pressures

Question 33

What is a real-world example of allopatric speciation?

Answer 33

Caribbean shrimp pairs show divergence after the closure of the Isthmus of Panama

Question 34

What is the significance of child fishes in studying speciation?

Answer 34

They demonstrate sympatric speciation thru ecological divergence - evolving distinct feeding traits (e.g. benthic vs limnetic forms) in crater lakes

Question 35

What evidence supports reinforcement in speciation?

Answer 35

Sympatric pops often show stronger mate choice preferences than allopatric pops to avoid hybridisation

Question 36

How do ring species illustrate speciation?

Answer 36

Pops diverge gradually around a barrier & terminal pops fails to interbreed, as seen in Asian birds w song divergence

Question 37

Why do sympatric pops develop prezygotic isolation earlier?

Answer 37

To avoid the costs of hybridisation (e.g. reduced hybrid fitness), a process called reinforcement