evolutionary Biology 5 Flashcards
Types of reproductive isolation
Prezygotic - before egg and sperm meet. e.g. Habitat, behavioural, morphological, temporal, gametic , mechanical.
Postzygotic - After egg and sperm meet. e.g. hybrid inviability, hybrid infetility , hybrid breakdown
Dobzhansky-Muller model
If an allele comes into contact with an allele from another population that is has never came into contact with before there is a chance of conflict and the disruption of each alleles function.
-increased chance of disruption as time increases before the alleles meeting
what is needed for reproductive isolation
assortaive mating
what is assortative mating
in which individuals with dissimilar genotypes and/or phenotypes mate with one another more frequently than would be expected under random mating.
Direct system
when the same gene that is adaptive also affects mating preference
Indirect system
The gene that is adapted is linked to one which affects mating preference. (adative train and male choice alleles appearing on linked loci )
Reinforcement hypothesis
If there is selection against hybrids due to them having a low fitness then there will be selection for prezygotic isolation.
e. g. Pied and collared flycatchers - normally live in allopatry but when they live in sympatry the males change their plumage so it is different to the collared flycatcher , this requires the females preference to change (reinforcement)
- direct system, the adaptive gene (plumage) is linked to mating preference
Haldanes rule
when a cross produces inviable or sterile offspring the hetero-gametic sex is more strongly affected e.g. males xy.
how do you know how long ago a species diverged
can look at genetic distances (how diverged) and the level of isolation between species
prezygotic isolation evolves quicker in which kind of pairs/speciation
symaptric, pairs in the same geographic area
How does the genome diverge
stage 1 - small (adaptive) divergence
stage 2 - Divergent areas grow via linkage
stage 3 - Genomes diverge so much that interbreeding is very reduced
stage 4 - isolation
Speciation genes
genes which cause reproductive isolation on their own
- thought to have evolved via gene duplication as duplicated genes have no function.
- Duplicated genes that are in the process of evolving into new functions at time of species separation are likely to contribute to species differentiation.
How quickly do barriers evolve
- very varied
- infertility/inviability tends to affect the heterogametic sex first
- tendancy for this process to happen fast in sympatry
Reproductive Character displacement
phenomenon where differences among similar species whose distributions overlap geographically are increased in regions where the species co-occur, but are reduced or lost where the species’ distributions do not overlap.
