13/ speciation Flashcards
1
Q
what counters disruptive selection and therefore speciation
A
- gene flow
- exchange of genes between populations as a result of movement and interbreeding of individuals
2
Q
2 main theories of speciation
A
- allopatric: geographical isolation and reproductive isolation 1st, then divergence
- sympatric speciation: divergence 1st, then reproductive isolation
3
Q
long term geographical isolation can result in phenotypic divergence due to…
A
- different environmental conditions, so dif selection pressures
- random genetic drift
3
Q
example of divergence in geographical isolation - birds
A
- chaffinches
- dif islands off the coast of n africa have dif bird characteristics
4
Q
disruptive selection - genetic crosses, post or pre zygotic isolation
A
- in pop AA/ AB/ BB
- homozygous AA and BB selected for
- AB against
- post zygotic - not less likely in early stages for fertilisation to occur
5
Q
4 requirements for evidence that sympatric speciation has occurred
A
- species must be largely sympatric - live in same area
- sympatric species must be reproductively isolated
- sympatric taxa must be sister species
- biogeographic and evolutionary history of the species must make it unlikely that they were ever allopatric
6
Q
sympatric speciation - fish sexual selection
A
- lake victoria over 600 species of cichlid fish
- pundamilia nyererei and p pundamilia
- preference for colours of same species in normal light but not in monochromatic light - female selection barrier to reproduction. but this can be breeched in lab
6
Q
sympatric speciation example - rhagoletis palmonella
A
- north american apple maggot fly
- native host plant is hawthorn
- then apple trees introduced
- pre-zygotic barrier between apple feeders and hawthorn feeders
- apples mature faster, so dif breeding times, 2nd pre-zygotic barrier
- palmonella on way to speciation, mendax feeds on blueberries - already achieved
