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
Shift in floral traits that contribute to reproductive isolation when in contact with
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
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?
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.
What is it?
Why do we care?