Hybridization

Hybridization is mating between unrelated individuals.

In plant systems the term is most commonly used to mean mating between different species

 

Importance Impacts in plant Evolution

Source of novel gene combinations

Mechanism of speciation

Also important in plant breeding (move one trait from one plant into another)

 

Hybridization is associated with habitat disturbance

Species may be isolated by ecological adaptations

preventing gene flow between species, thus preventing hybridization

hybrid would likely have intermediate traits that are not adaptive to habitat and could not compete with parental types

Disturbances (natural and human) could break down these barriers to hybrid formation and establishment

Example Amelancier bartamiana and A. laevis

 

Evolutionary Consequences of Hybridization

Reinforcement of reproductive isolating mechanisms

Formation of a hybrid swarm through reproduction at one site

Fusion of two species through interspecific gene flow (introgression)

Creation of genetic diversity and adaptation

Evolution of new species

 

Reinforcement of Reproductive Isolating Mechanisms

Phlox drummondii and Phlox cuspidata are both Texas species that sometimes grow together

Shift in floral traits that contribute to reproductive isolation when in contact with

 

 

Hybrid Swarm

A hybrid swarm is a localized phenomenon of hybridization followed by backcrossing

Gene flow is limited to one or a few sites

Often referred to as local introgression

Some hybrids MAY have a higher fitness than parental types. This is known ad heterosis or hybrid vigor

 

 

Fusion of Species through introgression

Species fusion could occur if genes flow between two species is so common that all the individuals of contain genetic material of both ancestral species and can freely interbreed.

 

 

Creation of genetic diversity by introgression

Introgression is the permanent incorporation of genes of one species into another. This can happen in three ways:

Merging of different species

Transfer of genetic material without the merging of species

The stabilized introgressant may form a new species

 

Evidence for Hybridization

Morphological intermediacy

 

F1 generations are often intermediate in morphological characters WHY?

many genes control the traits, and they get some from each parent

Presence of hybrid swarms may confound identification of hybrids

phenotypes may span gaps of parents

Not always intermediate characters may be novel, parental, or extreme.

What are processes that other than hybridization that can lead to intermediate characters?

Mutation

phenotypic plasticity

evolutionary trend (going form large to small, or whatever)

 

Chemical and molecular characters

More likely to show predictable expression in hybrids

Nuclear DNA will show an inherited pattern that is additive

Chloroplast DNA is inherited by only one parent

Hybridization and phylogeny reconstruction

Hybridization can pose problems with phylogeny reconstruction

Phylogenies show a bifurcating pattern of evolution, but hybridization is reticulate

By adding in hybrids we may find reduced resolution in trees, increase homoplasy, or it may completely disrupt phylogeny

May be able to use phylogenies to elucidate hybrid speciation

Other Molecular Markers

RAPDs, AFLPs, etc.

 

ALLOPOLYPLOIDY

What is it?

Example Tragopogon

Why do we care?