Editing Species reintroduction (section)

== Genetic considerations ==
When a species has been extirpated from a site where it previously existed, individuals that will comprise the reintroduced population must be sourced from wild or captive populations. When sourcing individuals for reintroduction, it is important to consider [[local adaptation]], adaptation to captivity (for [[ex situ conservation|''ex situ'' conservation]]), the possibility of [[inbreeding depression]] and [[outbreeding depression]], and [[Taxonomy (biology)|taxonomy]], [[ecology]], and [[genetic diversity]] of the source population.<ref name=":0" /> Reintroduced populations experience increased vulnerability to influences of [[Genetic drift|drift]], [[Natural selection|selection]], and [[gene flow]] evolutionary processes due to their small sizes, climatic and ecological differences between source and native habitats, and presence of other mating-compatible populations.<ref name="Frankham 2008" /><ref>{{Cite journal |last1=Latch |first1=Emily K.|last2=Rhodes|first2=Olin E.|date=2006-01-21 |title=The effects of gene flow and population isolation on the genetic structure of␣reintroduced wild turkey populations: Are genetic signatures of source populations retained? |journal=Conservation Genetics |language=en |volume=6 |issue=6 |pages=981–997 |doi=10.1007/s10592-005-9089-2 |s2cid=19523834 |issn=1566-0621}}</ref><ref>{{Cite journal |last=Sork |first=Victoria L. |author-link1=Victoria Sork |date=2015-11-03 |title=Gene flow and natural selection shape spatial patterns of genes in tree populations: implications for evolutionary processes and applications |journal=Evolutionary Applications |volume=9 |issue=1 |pages=291–310 |doi=10.1111/eva.12316 |pmc=4780383 |pmid=27087853 |language=en}}</ref><ref>{{cite journal |last1=Brekke |first1=Patricia |title=High genetic diversity in the remnant island population of hihi and the genetic consequences of re-introduction |journal=Molecular Ecology |date=2011 |volume=20 |issue=1 |pages=29–45 |doi=10.1111/j.1365-294X.2010.04923.x |pmid=21073589 |bibcode=2011MolEc..20...29B |s2cid=25508833 |url=https://kar.kent.ac.uk/27513/1/Brekke%20et%20al%202011%20Molecular%20Ecology.pdf}}</ref>

If the species slated for reintroduction is rare in the wild, it is likely to have unusually low population numbers, and care should be taken to avoid [[inbreeding]] and [[inbreeding depression]].<ref name=":0" /> Inbreeding can change the frequency of allele distribution in a population, and potentially result in a change to crucial genetic diversity.<ref name=":0" /> Additionally, [[outbreeding depression]] can occur if a reintroduced population can hybridize with existing populations in the wild, which can result in offspring with reduced fitness, and less adaptation to local conditions. To minimize both, practitioners should source for individuals in a way that captures as much genetic diversity as possible, and attempt to match source site conditions to local site conditions as much as possible.<ref name=":0" />

Capturing as much [[genetic diversity]] as possible, measured as [[heterozygosity]], is suggested in species reintroductions.<ref name=":0" /> Some protocols suggest sourcing approximately 30 individuals from a population will capture 95% of the genetic diversity.<ref name=":0" /> Maintaining genetic diversity in the recipient population is crucial to avoiding the loss of essential local adaptations, minimizing inbreeding depression, and maximizing fitness of the reintroduced population.

=== Ecological similarity ===
Plants or animals that undergo reintroduction may exhibit reduced fitness if they are not sufficiently adapted to local environmental conditions. Therefore, researchers should consider ecological and environmental similarity of source and recipient sites when selecting populations for reintroduction. Environmental factors to consider include climate and soil traits (pH, percent clay, silt and sand, percent combustion carbon, percent combustion nitrogen, concentration of Ca, Na, Mg, P, K).<ref name=":1" /> Historically, sourcing plant material for reintroductions has followed the rule "local is best," as the best way to preserve local adaptations, with individuals for reintroductions selected from the most geographically proximate population.<ref>{{Cite journal |last1=Havens |first1=Kayri |author-link=Kayri Havens |last2=Vitt |first2=Pati |last3=Still |first3=Shannon |last4=Kramer |first4=Andrea T. |last5=Fant |first5=Jeremie B. |last6=Schatz |first6=Katherine |date=2015-01-01 |title=Seed Sourcing for Restoration in an Era of Climate Change |journal=Natural Areas Journal |volume=35 |issue=1 |pages=122–133 |doi=10.3375/043.035.0116 |issn=0885-8608 |s2cid=86349716 |doi-access=free}}</ref> However, geographic distance was shown in a [[common garden experiment]] to be an insufficient predictor of fitness.<ref name=":1" /> Additionally, projected climatic shifts induced by [[climate change]] have led to the development of new seed sourcing protocols that aim to source seeds that are best adapted to project climate conditions.<ref>{{Cite journal|last1=Breed|first1=Martin F.|last2=Stead|first2=Michael G.|last3=Ottewell|first3=Kym M.|last4=Gardner|first4=Michael G.|last5=Lowe|first5=Andrew J.|date=2013-02-01|title=Which provenance and where? Seed sourcing strategies for revegetation in a changing environment|journal=Conservation Genetics|language=en|volume=14|issue=1|pages=1–10|doi=10.1007/s10592-012-0425-z|bibcode=2013ConG...14....1B |s2cid=12813499|issn=1566-0621}}</ref> Conservation agencies have developed seed transfer zones that serve as guidelines for how far plant material can be transported before it will perform poorly.<ref>{{Cite book|title=Genetically appropriate choices for plant materials to maintain biological diversity|last1=Rogers|first1=D. L.|last2=Montalvo|first2=A. M.|publisher=Report to the USDA Forest Service, Rocky Mountain Region, Lakewood, CO.|year=2004|location=University of California|pages=103–129}}</ref> Seed transfer zones take into account proximity, ecological conditions, and climatic conditions in order to predict how plant performance will vary from one zone to the next. A study of the reintroduction of ''[[Castilleja levisecta]]'' found that the source populations most physically near the reintroduction site performed the poorest in a field experiment, while those from the source population whose ecological conditions most closely matched the reintroduction site performed best, demonstrating the importance of matching the evolved adaptations of a population to the conditions at the reintroduction site.<ref>{{Cite journal|last1=Lawrence|first1=Beth|last2=Kaye|first2=Thomas|date=2011|title=Reintroduction of Castilleja levisecta: Effects of Ecological Similarity, Source Population Genetics, and Habitat Quality|journal=Restoration Ecology|volume=19|issue=2|pages=166–176|doi=10.1111/j.1526-100x.2009.00549.x|bibcode=2011ResEc..19..166L |s2cid=85653946 }}</ref>

=== Adaptation to captivity ===
Some reintroduction programs use plants or animals from captive populations to form a reintroduced population.<ref name=":0" /> When reintroducing individuals from a captive population to the wild, there is a risk that they have adapted to captivity due to differential selection of genotypes in captivity versus the wild.
The genetic basis of this adaptation is selection of rare, [[Dominance (genetics)|recessive]] [[allele]]s that are deleterious in the wild but preferred in captivity.<ref name="Frankham 2008" /> Consequently, animals adapted to captivity show reduced stress tolerance, increased tameness, and loss of local adaptations.<ref>{{Cite journal|last=Frankham|first=Richard|date=2008|title=Genetic adaptation to captivity in species conservation programs|journal=Molecular Ecology|volume=17|issue=1|pages=325–333|doi=10.1111/j.1365-294x.2007.03399.x|pmid=18173504|bibcode=2008MolEc..17..325F |s2cid=8550230}}</ref> Plants also can show adaptations to captivity through changes in drought tolerance, nutrient requirements, and seed dormancy requirements.<ref>{{Cite journal|last1=Ensslin|first1=Andreas|last2=Tschöpe|first2=Okka|last3=Burkart|first3=Michael|last4=Joshi|first4=Jasmin|date=2015-12-01|title=Fitness decline and adaptation to novel environments in ex situ plant collections: Current knowledge and future perspectives|journal=Biological Conservation|volume=192|pages=394–401|doi=10.1016/j.biocon.2015.10.012|bibcode=2015BCons.192..394E }}</ref> Extent of adaptation is directly related to intensity of selection, genetic diversity, [[effective population size]] and number of generations in captivity.
Characteristics selected for in captivity are overwhelmingly disadvantageous in the wild, so such adaptations can lead to reduced fitness following reintroduction.
Reintroduction projects that introduce wild animals generally experience higher success rates than those that use captive-bred animals.<ref name="Frankham 2008" /> Genetic adaptation to captivity can be minimized through management methods: by maximizing generation length and number of new individuals added to the captive population; minimizing effective population size, number of generations spent in captivity, and [[Natural selection|selection]] pressure; and reducing genetic diversity by [[Fragmentation (reproduction)|fragmenting]] the population.<ref name=":0" /><ref name="Frankham 2008" /> For plants, minimizing adaptation to captivity is usually achieved by sourcing plant material from a [[seed bank]], where individuals are preserved as wild-collected seeds, and have not had the chance to adapt to conditions in captivity. However, this method is only plausible for plants with [[seed dormancy]].<ref name="Frankham 2008" />

=== Genetic trade-offs ===
In reintroductions from captivity, translocation of animals from captivity to the wild has implications for both captive and wild populations. Reintroduction of genetically valuable animals from captivity improves genetic diversity of reintroduced populations while depleting captive populations; conversely, genetically valuable captive-bred animals may be closely related to individuals in the wild and thus increase risk of inbreeding depression if reintroduced.
Increasing genetic diversity is favored with removal of genetically overrepresented individuals from captive populations and addition of animals with low genetic relatedness to the wild.<ref>{{Cite journal |last=Earnhardt |first=Joanne M. |date=November 1999 |title=Reintroduction programmes: genetic trade-offs for populations |journal=Animal Conservation |language=en |volume=2 |issue=4 |pages=279–286 |doi=10.1111/j.1469-1795.1999.tb00074.x |bibcode=1999AnCon...2..279E |s2cid=84850782 |issn=1367-9430}}</ref><ref name=":3">{{Cite book |title=Introduction to conservation genetics |author=Frankham, Richard |date=2010 |publisher=Cambridge University Press |author2=Ballou, Jonathan D. |author3=Briscoe, David A. |isbn=978-1-139-19024-4 |edition=2nd |location=Cambridge, UK |oclc=774393970}}</ref> However, in practice, initial reintroduction of individuals with low genetic value to the captive population is recommended to allow for genetic assessment before translocation of valuable individuals.<ref name=":3" />