Speciation I (DONE) Flashcards
What is Mayr’s definition of the biological species concept?
One or more populations of potentially interbreeding organisms that are reproductively isolated from other such groups
Mayr 1942
What is the limitation with Mayr’s 1942 definition a biological species?
“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
What is the definition of speciation?
(Given by the lecturer)
The evolution of reproductive isolation between populations, leading to distinct species
What are the 2 types of isolating mechanisms?
Premating and postmating
What are 2 good examples of the evolution of reproductive isolation between populations?
Liger/Tion and Mule/hinny
both species’ offspring are sterile –> this is an example of postmating isolation
Define premating (prezygotic) isolation:
Mechanisms that prevent mating or fertilisation, such as behavioural isolation (e.g. different mating signals) & ecological isolation (e.g. pollinator preferences)
Define postmating (postzygotic) isolation:
Mechanisms that prevent hybrid offspring from surviving or reproducing, incl:
- Intrinsic isolation (genetic incompatibilities) &
- Extrinsic isolation (maladaptation to the environment)
What is another name for premating isolation?
Prezygotic isolation
Give 2 examples of premating/prezygotic isolation:
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)
Important note of isolating mechanisms in premating isolation:
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
What is another name for postmating isolating mechanisms?
Postzygotic isolation
What are the 2 subtypes of postmating/postzygotic isolation?
1 - Intrinsic or genetic postzygotic isolation
2- Extrinsic or ecological postzygotic isolation
Give an example of Intrinsic or genetic postzygotic isolation:
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
What is Holdanes rule?
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)
What is allopatric speciation?
Speciation caused by geographic isolation
e.g. shrimps separated by the Isthmus of Panama
What is sympatric speciation?
Speciations that occurs within the same geographic area, often driven by ecological divergence
eg apple maggot flies shifting from hawthorn to apple
What are ring species?
Pops that expand around a geographic barrier - diverging progressively until terminal populations cannot interbreed
e.g. Asian birds with song divergence
How does reproductive isolation change over time?
Prezygotic isolation evolves earlier (e.g. reinforcement in sympatric pops),
While postzygotic isolation evolves later due to genetic incompatibilities
What is the Dobhansky-Muller model?
Speciation occurs thru genetic incompatibilities that arise as populations diverge
What is reinforcement?
Selection against hybridisation due to reduced hybrid fitness, strengthening prezygotic isolation
What is an example of reinforcement in sympatric populations?
Pied & collared flycatchers evolving distinct male plumage to avoid hybridisation
What are the stages of speciation?
1 - Initial divergence (allopatry)
2 - Secondary contact (reinforcement strengthens prezygotic isolation)
3 - Sympatry (full reproductive isolation)
What is an example of sympatric speciation?
Chichild fishes in crater lakes evolving district feeding traits (benthic vs limnetic forms)
What is an example of temporal pattern in speciation?
In Drosophila, reproductive isolation strengthens as genetic divergence increases
What drives the speciation process?
Reproductive isolation thru spatial (allopatric/sympatric), temporal & ecological mechanisms, reinforced by hybridisation avoidance
What is intrinsic postzygotic isolation?
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)
What is extrinsic postzygotic isolation?
Isolation where hybrids are maladapted to their own environment & perform poorly
e.g. hybrids between maple- and willow-adapted beetles
How do larger areas affect allopatric speciation?
Larger areas (e.g. big islands) provide more opportunities for geographic isolation & subsequent divergence
What is the by-product mechanism in speciation?
Traits evolve to adaptation to different environments but also indirectly influence mate choice, driving reproductive isolation
What is a geographic mosaic of speciation?
Speciation dynamics vary across pops & regions due to local adaptations & environmental pressures
What is a real-world example of allopatric speciation?
Caribbean shrimp pairs show divergence after the closure of the Isthmus of Panama
What is the significance of child fishes in studying speciation?
They demonstrate sympatric speciation thru ecological divergence - evolving distinct feeding traits (e.g. benthic vs limnetic forms) in crater lakes
What evidence supports reinforcement in speciation?
Sympatric pops often show stronger mate choice preferences than allopatric pops to avoid hybridisation
How do ring species illustrate speciation?
Pops diverge gradually around a barrier & terminal pops fails to interbreed, as seen in Asian birds w song divergence
Why do sympatric pops develop prezygotic isolation earlier?
To avoid the costs of hybridisation (e.g. reduced hybrid fitness), a process called reinforcement
