large enough, selective pressure acting on each generation can restore fitness. Unless the F1 hybrid generation is sterile or very low fitness, selection will act in each generation using the increased diversity to adapt to the environment. This can lead to recovery in fitness to baseline, and sometimes even greater fitness than original parental types in that environment. However, as the hybrid population will likely to go through a decline in fitness for a few generations, they will need to persist long enough to allow selection to act before they can rebound. Examples The first mechanism has the greatest effects on fitness for polyploids, an intermediate effect on translocations, and a modest effect on centric fusions and inversions. Generally this mechanism will be more prevalent in the first generation (F1) after the initial outcrossing when most individuals are made up of the intermediate phenotype. Examples of the second mechanism include stickleback fish, which developed benthic and limnetic forms when separated. When crosses occurred between the two forms, there were low spawning rates. However, when the same forms mated with each other and no crossing occurred between lakes, the spawning rates were normal. This pattern has also been studied in Drosophila and leaf beetles, where the F1 progeny and later progeny resulted in intermediate fitness between the two parents. This circumstance is more likely to happen and occurs more quickly with selection than genetic drift. For the third mechanism, examples include poison dart frogs, anole lizards, and cichlid fish. Selection over genetic drift seems to be the dominant mechanism for outbreeding depression. In plants For plants, outbreeding depression represents a partial crossing barrier. Unfortunately, outbreeding depression is not understood well in angiosperms. After observing Ipomopsis aggregata over time by crossing plants that were between 10–100m apart, a pattern was noticed that plants that were farther away spatially had a higher likelihood of outbreeding depression. Some general takeaways from this were that spatial patterns of selection on plant genotypes will vary in scale and pattern, and outbreeding depression reflects the genetic constitution of "hybrid" progeny and the environments in which the parents and progeny grow. This means that although outbreeding depression cannot be predicted in angiosperms yet, the environment has a role in it. See also Dominance versus overdominance Haldane's rule Heterozygote advantage Inbreeding depression References Breeding Population genetics