Evolution Lecture 12: Reproductive Isolation

Individuals are unfit because of....

Mutation-selection balance, over dominant selection maintains delterious alleles, migrants introduce locally maladaptive alleles, genetic drift and reproductive isolation

Reproductive isloation

The inability of an individual to breed successfully to a related individual because of pre or post-zygotic barriers or differences

Points of reproductive isolation

Premating isolation, post mating prezygotic barriers and postzygotic barriers

Premating isloation

Potential mates do not meet(barriers like geographic, temporal, behavioral and mechanical) ; potential mates meet but do not mate

Post mating prezygotic barriers

Failure to fetilize

Postzygotic barriers

Offspring have low fitness; extrinsic and intrinsic

Extrinsic

Offspring have low fitness because of the environement

Intrinsic

Offspring have low fitness because of genetics

Masting

Mass flowering in a single cycle is thought to have evolved to overwhelm potential pests

Individual fitness increases if you flower/seed at the ____

Same time because you are less likely to be eaten by a predator; increases with mating every other year

Many species evolved strategies to reproduce very rapidly when food is ____ to capitalize on masting

Unlimited

Mautam/Thingtam

Cycles in Northwestern India "When the bamboo flowers, famine, death and destruction will soon follow"; Bamboo flowers so there is a lot of seeds, so a black rat population surges where they eat the seeds and move onto the plants

Fertilization failure

Can occur because of a mismatch between sperm and egg

Extrinsic barriers

The offspring have a combination of traits that don't work in a particular environment; can be behavioral or morphological

Intrinsic barriers

Offspring could have trouble finding mates, are sterile, or just die

In post-zygotic inviability, most offspring may not survive because of ____ issues

Developmental

Incompatible sets of alleles can evolve because of....

Underdominance, Dobzhansky-Muller Incompatibilities

Underdominance in incompatibility

Can lead to alternate alleles becoming fixed in different populations - crosses between those populations will reveal the unfit heterozygote

Dobzhansky-Muller Incompatibilities

Crosses of populations fixed for different alleles results in a combination of alleles that were "untested" in the wild, so it might have very low or no fitness(the Aa)

Even within species, some combinations of alleles may be....

Incompatible

DMIs and time....

Hybrid fitness is expected to decrease in the long run due to a build up of incompatibilities between highly diverged species

Reproductive isolation does seem to increase between distantly....

Related species

Heterosis/hybrid vigor

Hybrids outperforming either parent; not clear how diverged populations need to be for incompatibilities to outweigh this