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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Assisted gene flow | 2/3 | https://en.wikipedia.org/wiki/Assisted_gene_flow | reference | science, encyclopedia | 2026-05-05T14:17:36.560692+00:00 | kb-cron |
== Risks and limitations == Introducing foreign genotypes into a new population always runs the risk of reducing genetic integrity. For AGF, outbreeding depression, or a reduction in the fitness of offspring genotypes relative to parental lineages, is the most significant risk. Outbreeding depression can be caused by negative epistasis, chromosomal incompatibilities, and loss of locally adapted alleles within the recipient population. Results of these incompatibilities can lead to detrimental effects such as phenological mismatch. For example, research has shown that AGF has the potential to shift the timing of flowering in plants, which poses a threat to plant pollinator relationships. Additionally, while AGF can introduce beneficial alleles, pre-adapted to certain climate conditions, it can also introduce deleterious alleles which are maladapted to other environmental factors. Lastly, AGF risks genetic swamping if the proportion of introduced individuals or the fitness of new individuals is too high. In both AGF and genetic rescue strategies, foreign genotypes could outcompete local genotypes and lead to the loss of unique genetic lineages. In addition to the limited parameters on the size and current range of the target species, AGF may be difficult to achieve in long lived species. Successful implementation of AGF often takes several generations for beneficial adaptations to accrue and make an impact. This process may be too slow among species with long generation times, an important consideration for applications in forestry. Another important consideration is the accuracy of projected climate conditions. Climate projections can be uncertain and many variables must be accounted for. While the purpose of AGF is to conserve species threatened by changing climate, offspring still need to be able to establish and survive under typical conditions. Experts recommend that AGF management plans match the environment of source populations with intermediate climate projections to maximize survival.
== Identifying source and target populations == A key factor in determining potential source populations for AGF is a strong history of local adaptation to desired climate conditions. For plant species, this can be determined experimentally through transplanting in common gardens or controlled greenhouse experiments and assessing phenotypic trait inheritance. However, indicators of a viable source population are not limited to ecological factors. Genomic analysis can identify adaptive genetic variation and reveal which populations are best adapted to desired conditions, as well as which populations are most at risk. This can be especially helpful when assessing potential AGF strategies for small populations of endangered species. Genomic offset has become a promising method of genomic analysis that identifies adaptive genetic variation in populations of candidate species for AGF. This method uses a genotype-environment analysis of a population's genomic data to establish a statistical relationship between allele frequencies and environmental factors. This model is then used to measure the mismatch between current genetic composition and the composition needed for adaptation to projected climate conditions. A genomic offset approach called "risk of nonadaptedness" or RONA, which predicts the required allele frequency shift needed in a population to adapt to future environmental conditions, is an analytical tool that has been recommended for use in AGF strategies.
== Research examples ==
=== Successful AGF ===
==== Elkhorn coral (Acropora palmata) ==== A successful implementation of AGF was accomplished in 2018 on populations of Acropora palmata or elkhorn coral. Gene flow was initiated by in vitro fertilization of freshly collected coral eggs from Curaçao using cryopreserved sperm from Florida, Puerto Rico, and Curaçao. Despite these coral populations being genetically isolated after more than a 95% decline in population, the risk of outbreeding depression in corals is considered low because they have retained high genetic diversity and exhibit an outcrossed population genetic structure. Researchers found that genetically distinct populations of A. palmata could produce a successful population of offspring and that AGF is a viable option for the conservation of endangered coral populations.
==== Montane cushion plant (Silene ciliata Pourr.) ==== An example of AGF for a perennial plant species across an elevational gradient was tested by researchers in 2014. Silene ciliata is a perennial flowering plant species that grows in Mediterranean mountain ranges across Southern Europe. Since plant populations grow across steep elevational gradients, plants at lower elevations are projected to experience earlier snowmelt and onset of the summer drought period. Prior experimentation showed that plants from higher elevations flowered earlier when planted at lower elevation, suggesting that AGF from high to low populations may help advance flowering time to increase reproductive success and seedling survival ahead of the drought period. However results from the researchers' ex situ common garden experiment showed the opposite; gene flow from higher elevation populations delayed flowering time. The researchers suggested that because expression of flowering time is polygenic, the gene flow treatments may have led to a disruption of coadapted genes and the unexpected delay was the result of outbreeding depression.
==== Günther's toadlet (Pseudophryne guentheri) ==== Researchers in Australia set up a breeding experiment to assess methods of targeted gene flow in crawling frog species Pseudophryne guentheri, commonly known as Günther's toadlet. In 2017, adult frogs were collected in the field while the simulation of gene flow was conducted in a lab setting using in vitro fertilization of egg clutches. The results suggested that the risk of outbreeding depression increased with genetic, geographic and environmental distance between the source populations of breeding individuals.
=== Genomic offset ===