What factors cause genetic divergence between isolated populations?
Genetic drift
founder effect and population bottleneck
mutation
differential selection
What are some post zygotic barriers to reproductive isolation and what can we expect as the results of it?
post zygotic barriers means barriers that occur after fertilization
- Habitat isolation (they are physically all the the same habitat but mate in different areas of the habitat)
-behavioural isolation
( species closely related but have a slight different mating display) - Temporal isolation
-mechanical isolation (different sizes small mate large mate) - Gametic isolation (the gametes are chemically incompatible)
RESULT:
- hybrids
- the hybrid has a low fertility
- lower survival
- hybrids can mate but the offspring will have a low reduced fitness
-embryonic development of hybrids fails in early development
What are the two modes of speciation?
Allopatric speciation
sympatric speciation
After a population has diverged and renewed contact between two populations have occurred what are the three possible outcomes of the population?
- individuals can hybridize readily ( the species are now going to mate together and there traits start to blend which means they are going to merge and move forward as one species)
- Individuals do not hybridize at all
( none of the individuals can mate together) - individual’s hybridize but offspring have reduced fitness
(There is still enough hybridization but since there is still some similarities that might make them want to mate but the children will have low survival rates and low fertility)
what is allopatric speciation?
- speciation with no gene flow between diverging populations
-this is physical barriers that divide the population
(eg. rivers)
(vicariance event) (meaning splitting) - gene flow stops and the populations separate and the populations evolve independently
- overtime the alleles become fixed in place because of mutation and drift and natural selection
what is sympatric speciation? explain the course of it?
there is no geographic barrier to gene flow
-so there is gene flow between different populations
- process by which new species evolve from a single ancestral species while inhabiting the same geographic region
INITIAL STAGE: in a population some individuals develop polymorphism that affects there survival and fitness
- example: two organisms that are adapted to eat different foods, these differences lead to a reduced interbreeding between the two, eventually leading to a formation of two separate species
MATING IS DISCOURAGED: as the two forms become more and more different mating between them is discouraged either by pre-zygotic (before fertilization, such as behavioural differences) barriers or post-zygotic barriers (reduced viability of offspring)
- this causes speciation process, and leads to separate species even though they are in the same area
What is polyploidization?
- where the organism gains one or more additional chromosomes, which can lead to speciation, especially in plants or some animals like frogs.
- It can cause sudden speciation because offspring have more than one chromosome which can isolate them since they are reproductively isolated from the parent population
- Meiosis fails and organism produces 2n gamets
- autoploidization which is where a 2n gamete fertilizes with another 2n gamete producing a autoploid
allopolyploidization is similar but involves the mating of two closely related species, this results in hybrids that might have additional set of chromosomes from each parent species, also leading them to isolate from the parent population
