23 Mar 2015
Reintroduction programmes were created to reintroduce captive bred species back into a habitat. These are species that are originally endangered and at the risk of extinction. However there are many factors that affect the success of a reintroduction programme. These can include the expense of a reintroduction programme (Vickery et al. 2003). As many non-profit charities carry out the reintroduction programmes, there is a need to find support or outside funding to cover the costs of captive breeding for reintroduction and in some cases the programmes just aren't feasible (Kleiman, 1989), (to the process of captive breeding). This important process builds up species numbers for reintroduction, where individuals from a species are removed from their habitat and taken into captivity for breeding to take place. Captive breeding also acts as a way to help to conserve species that are unable to survive in their natural habitat such as the Arabian Oryx (Spalten et al, 1999). This leads into another issue which vitally needs to be addressed. The habitat in which a species will be reintroduced into needs to be carefully chosen, as there are many factors in the environment which could have possible adverse effects. To ensure the successful reintroduction of a species; first intrinsic factors need to be addressed, which would include the issue of carrying capacity. Carrying capacity is the number of organisms a habitat can sustain without a species being lost. For example, if the number of organisms released is below the carrying capacity, theoretically a positive growth should be observed (Newth, 1985). If the number of organisms is above the carrying capacity, the opposite will occur and a negative decline would be evident. Then the extrinsic factors need to be examined, these include abiotic and biotic factors of the habitat need to be closely explored. For example abiotic factors like storms, forest fires and floods can all have impacts on populations, although they are density independent. The biotic factors would include predation and the competition for resources. If a species is being reintroduced into its original habitat, then the causation of the decline needs to be addressed in order for the situation not to reoccur. For example, any genetic issues. These can arise as a consequence of captive breeding and subsequent species reintroduction. These include an inbreeding depression, loss of genetic variation, hybridisation (more commonly known as out breeding depression), potential adaptation to the captive environment, and even a potential for the accumulation of new deleterious alleles. Each of these in one way or another will impede the organism's successful reintroduction to the wild.
When it comes to biodiversity, humans have a negative effect, resulting in the decrease of natural areas. Human impact, overexploitation, habitat disturbance, habitat destruction, and climate change are the main issues that cause the decrease in the number of organisms throughout the world.
Reintroduction is the attempt of returning a species back into its native habitat where they were extirpated or where their numbers have become very low. This may involve captive breeding for release back into the wild or relocating wild caught individuals. With poor success rates being an issue it has led to greater monitoring of species and since 1990 it has seen an increase in peer-reviewed publications relating to reintroduction (Armstrong et al. 2008).
Reintroducing endangered species back into the wild is an attractive, yet expensive, approach to saving rare or endangered species currently maintained in captivity (Kleiman, 1989). As there are so many species today that are now classed as either vulnerable, endanger, critically endangered and even some that are now only found in captivity the idea of breeding animals in captivity for reintroduction into their natural habitat seems like a good idea, however these programmes are expensive and therefore need funding to be carried out as many wildlife conservation programs fall into the category of either governmental or non-governmental organizations (NGO) which are not-for-profit organizations. As some financial resources are limited it may result in the elimination of projects with lower priority because of prohibitive costs (Karesh, 1993).
A reintroduction program begins with captive breeding to ensure that the offspring is genetically healthy, well maintained and capable of self-sustaining reproduction. Captive breeding is carried out among several institutions to maintain high levels of genetic diversity (waza.org, 2011). This exchange of animals between regions is one of the areas that are costly.
816 species (plus many more un-described species) have become extinct within the last 500 years with thousands more being threatened with extinction. As the human population grew it resulted in a need for more space, an increased demand for natural resources such as food, energy, building supplies, and an increase in waste produced.
The human activities that have had a negative impact include; hunting and fishing, agriculture, industrialisation, urbanisation and sprawl, and international traffic and trade. These all created issues towards the environment, one being the impact on organisms and leading to the decrease in their numbers and even extinction. However not all human impact is bad for the environment; moderate levels of disturbance can create new diversity.
Since the 1600's, overexploitation of animals has resulted in many species becoming extinct or endangered. An early example of overexploitation can be seen throughout the history of the whaling industry where thousands of whales were killed, with the large whales being depleted first before moving on to the smaller species. Commercial whaling is now almost abandoned but the damage has already been done and we now have to live with the consequences. Another more modern example is over fishing which has now resulted in reduced catches as the species number have become significantly low.
Pollution (chemical and biological) often causes a subtle degradation and an impact through interference with ecosystem process and the fitness of individuals being reduced. Climate change can lower pH that is damaging to plants and aquatic organisms.
The causes of habitat destruction include; agriculture (clearing of land for crops and pastures), industry and urban development (loss of wilderness, waste and pollution), global trade and traffic (modification of waterways, roads dissecting landscape, translocation of species into non-native ranges). An example of habitat destruction is deforestation where the rainforests are destroyed through large scale clearing for small scale agriculture or timber.
Very few studies actually show the estimated annual cost of their programmes, FIischer and Lindenmayer (2000) included some programmes and their costs in their review; an assessment of the published results of animal relocations. A programme for the reintroduction of the Californian condors (Gymnogyps californianus) in the US showed their annual costs to be $1,000,000 (Cohn, 1993). The cost of rehabilitating and reintroduction of the sea otter (Enhydra lutris) after the Exxon Valdez oil spill was estimated to have cost $80,000 per individual otter released and said to have totalled $17,000,000 altogether (Estes,1998). The cost of reintroducing the golden lion tamarin (Leontopithecus r. rosalia) was estimated at approximately $22,000 per individual that survived (Kleiman et al. 1991). Two projects that were carried out to reintroduce the grey wolf (Canis lupus) back into central Idaho and the Yellowstone National Park had an expected combined cost of $6,700,000 over approximately eight years (Bangs et al. 1996).
Apart from Kleiman et al. (1991) the studies that did provide an estimated cost did not include a breakdown of their prices and did not mention where they received their funding from (Fischer et al. 2000).
Ensuring that the most effective actions are taken for the lowest cost possible and not wasting any funds in the process. Cost efficiency in conservation can be determined in terms of units of an environmental goods conserved per unit money spent. Environmental goods could refer to the recovery of species numbers in a key habitat (Lindsey et. al, 2005). With the declining government budget allocations for conservation in many states and with aid budgets not rising to meet the shortfall has resulted in a need to ensure that the available funds are used efficiently (Mendelssohn, 1999). In order to increase the chances of receiving financial support conservation programs are designed for cost efficiency and it is now becoming an important issue when prioritising conservation (Lindsey et. al, 2005).
As many studies do not breakdown their expenditure, it is unclear exactly where the money goes. The cost of reintroduction can be divided into two areas; veterinary aspects and translocations. Translocation refers to the introduction of a species back into the wild that was originally in captivity. As a veterinarian would be required throughout the process of a reintroduction programme, from the beginning when the breeding process happens, on the actual reintroduction, and finally checking the animals in the wild to ensure it is healthy. With such a long period of time that a veterinarian would be required, the cost of covering wages and vaccinations could be high.
As government funding is low for reintroduction programmes then the funds may need to be found elsewhere. Donor funding is an important source of funding for conservation. The Global Environment Facility (GEF) is an independent financial organization that unites 182 member governments who work in partnership with international institutions, NGO's, and the private sector to address the global environmental issues, one being Biodiversity Conservation programmes (the GEF, 2010).Many zoos' fund their own conservation work from money earned from the public visiting the zoo; paying an entrance fee and through recreation.
Because humans are the main cause of species becoming extinct or endangered, ultimately we are also the only solution of helping solve the problem. This is why we have created reintroduction programmes, in hopes to change what we originally caused. However many still have different views on conservation, and with available funds declining it has fuelled such demands as reopening the international trade in elephant products such as ivory this is because they believe it would provide an additional source of revenue (Mendelssohn, 1999). A big issue is to ensure we prioritise conservation efforts and put the money where it is needed by creating reintroduction programmes for those species that if they became extinct would have an impact on the environment, for example we need pollinators as humans depend on plants along with many other species. But also a loss of one species could have an impact on a food chain meaning other species will eventual begin to lower in numbers and face the same fate.
The success rate of reintroduction needs to be addressed and finding the best way to go about reintroducing species back into the wild is important, with such issues as the expense, captive bred animals being more prone to disease and ensuring genetic variation is it really the best way to conserve a species?
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The process of moving individual animals from one site to another, such as from the wild to a zoo for the study of conservation is an increasing tool to re-establish threatened populations (Roe et al, 2010). There are a range of issues with the reintroduction of captive bred individuals in order to increase a wild population that is decreasing due to a range of factors. Ex situ conservation involves the removal of individuals or groups from the natural habitat into captivity. This is either to maintain a genetic stock or for a range of breeding programmes. Although it has been found that it is relatively easy to keep a range of animals in a captive environment, but there are large amounts of difficulty when it comes down to trying to breed them (Pullin, 2002). Until only recently zoos and other wildlife institutions have made conservation breeding programmes more important, and some of these breeding programmes have the intention to reintroduce the offspring back into the wild. The number of individuals released from captive breeding is normally quite small, although it is becoming more common in order to try and decrease the amount of inbreeding that may occur within the wild populations (Jamieson, 2011).
Captive breeding has both a range of advantages and disadvantages (table 1), including the need to increase a species population size and reducing the risk of extinction within the wild. By using captive breeding within zoos, means that there is less of a need to remove individuals from the wild to study as it allows people to understand the species without removing large amounts of individuals from the wild causing a decrease in population size. Unfortunately there is a large amount of disadvantages with captive breeding compared to the advantages. This includes removing the last few remaining individuals from the wild, which could cause the species to become extinct in the wild even if the idea was for the reintroduction of the animal. Also getting the animals to breed in the first place is also very expensive; this is to ensure that the facilities are appropriate for the animals. Because the animals are bred in captivity it means that there is a large chance of the animals inbreeding together if breeding wasn't controlled, this could also affect the natural selection of the species and means that the genetic stock is reduced. The main objective should be for all captive breeding programmes, is the reintroduction of the offspring into the natural habitat but only if it will provide a chance that a viable population will be established (Pullin, 2002). Captive breeding for the reintroduction back into the wild is mainly used as a partial recovery of declining populations (Grimwood, 1962). This means that captive breeding alone would not work on its own, but only when it is put together with the conservation or reconstruction of a habitat where reintroduction is a possibility. When thinking about releasing captive bred offspring, there is a need for the individual to have learned some survival behaviours as juveniles in order to live successfully once released. These animals should be given the chance to learn this behaviour through a range of training within the captive habitat, so that the probability of survival in the wild would be roughly equal to that of wild animals of the same species (IUCN, 2008). Also there must be a large amount of care taken so that the larger animals (mainly carnivores and other large mammals etc) do not become too confident around humans, as this could cause them to be a danger to the local inhabitants and the local livestock as well as to themselves once in the wild.
Building up numbers for reintroduction
Initial source of stock can endanger remaining small wild populations
Enables research on the biology of species
Facilities in which to do the breeding are needed
Can eventually reduce the need to collect individuals from the wild
Maintaining a large enough population size to prevent problems of genetic drift and loss of variability
Captive colonies can be used to educate the public about the species
Captive populations may undergo selection, adapting them to their captive conditions and leaving hem maladapted to their natural environment
Loss of learned behaviour can occur due to unnatural behaviour under captive conditions
Susceptibility to disease due to artificially high concentration of individuals
It may be difficult to get the species to breed under captive conditions.
Table 1. From Pullin, 2002
It has been found that one of the biggest problems for captive breeding and the reintroduction of the offspring into the wild is that sometimes the process has been found to have been too successful. Therefore there is an excess stock of bred offspring ready to be reintroduced but without a location to release them at. This excess stock could be relocated to other zoos to improve their genetic pool or in very few cases there may be the urge to reintroduce this excess stock into the wild even if the habitat and environment isn't up to standards, which could mean that the individuals are more likely to have a shorter life span than if they were reintroduced into a more appropriate habitat (Pullin, 2002). Some of the disadvantages of the reintroduction of captive bred populations have some concerns with the possibility of interbreeding within captivity, the chance that there could be some domestication of the captive population by human impact which could cause issues in the wild, and there is the fear that any offspring of mating captive and wild individuals could lose adaptations to the local environment / habitat (Roldán et al, 2011). Due to the range of these different disadvantages in the reintroduction of captive bred individuals, it is sometimes seen as a last resort when it comes down to trying to increase wild population size. There have been many successful releases of captive bred individuals into the wild (Wilson et al, 2010). But the release programmes have very little monitoring of the species after the release of the captive bred animals, which means that there isn't very much research into the success of the reintroduction process which should be evaluated in order to improve the efficiency of these programmes.
One study by Roldán et al (2011) looked into the declining levels of the Greater Rhea (Rhea americana) in wild populations, especially the declining levels found in Central Argentina. The Greater Rhea at the moment is found in the Near Threatened category in the IUCN red list (IUCN, 2008), this is at this level due to the fact that the species levels are going to continue to decrease due to the loss of genetic variability. This is why the release of captive bred populations in to the wild has been seen as a way to increase local wild populations which will also increase the genetic variability. This shows that captive bred populations have a very significant role within reintroduction in to the wild. Roldán et al said that the similarity that has been found between wild and captive populations could be due to three different factors. These factors were: 1. that the short amount of time since farms of the Greater Rhea were established and the adult life expectancy of captive bred individuals released, 2. that the breeding stocks in the wild populations may cause there to be a genetic loss within the population, therefore the captive population could possibly represent a small sample of wild populations, and finally 3. that the artificial selections of individuals have not been seen, which would reduce the possibility of divergences that can be found in allelic frequencies from human intervention. This study showed that there was an importance in keeping rhea farms as way of captive breeding and to then release the offspring into the wild populations in order to increase population size.
Rantanen et al, (2010) looked at the development of anti-predator behaviour and whether or not this behaviour is altered when the individual is subject to captive conditions. This could mean that reintroduced captive bred individuals may not have the same vigilance to predators as the native population and therefore more likely to be vulnerable to predators. Behaviour deficiencies such as this could be a main factor into why some reintroductions have low success rates. Rantanen et al looked at wild and captive bred grey partridges. The captive bred released individuals were observed and the vigilance was looked into both as a group and on an individual scale. They found that overall the released individuals were less vigilant both individually and as part of a group compared to wild individuals. This makes the reintroduced population more at risk of predation and that the wild population will remain small.
In conclusion there is plenty of evidence showing that captive breeding has some major disadvantages into the reintroduction of individuals that have been bred in captivity and the chance that these individuals could possibly have a shorter life span than native wild individuals e.g. the anti-predator behaviour (Rantanen et al, 2010). There are also many studies that show that there is a need for individuals to be bred in captivity and then released into the wild in order to increase the levels of wild populations of a species (Roldán et al, 2011). Overall it is too soon to see if captive breeding reintroduction has a positive long term effect on threatened / endangered species populations, with the Arabian oryx being seen as one of the most successful reintroductions from captivity (Kleiman et al, 1994).
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Growth curve for sheep introduced into Tasmania in 1800. It shows the fluctuations in the number of sheep from around 1.5 million to 1.9 million over a period of 60 years, with a proposed carry capacity level
The reintroduction of a species into a release site will fail if the habitat cannot provide the correct support for the species, irrespective of the strategies put forward to initiate the growth a new population (Armstrong, 2008). Resultantly there are some important questions which need answering in regards to population persistence. The first being; what sorts of conditions are needed in a habitat for the reintroduced population to have a positive, persistent trend in growth? In order for this to occur, the carrying capacity of the release site should be monitored and understood before releasing a new species into it. This is because the number of organisms must be below the carrying capacity in order for a positive growth to be observed; otherwise the released population will not be sustained by the environment.
The carrying capacity of a habitat is the largest population that can be sustained by the limiting resource (in most cases, this is abundance of food). In the best situation, a population will limit the use of the resources, in relation to the amount of resource available, thereby slowing down the rate of growth. However when a new population is introduced into a habitat they will inevitably decrease the carrying capacity (an intrinsic limit to growth) of the area, therefore the carrying capacity of the area needs to be monitored before the new species can be reintroduced. Without this they could have a profound and adverse effect, not only on their own survival but also on the survival of the current inhabitants. As stated by Newth (1985) "if the resource is expendable, as with food, carrying capacity is reached when rate of resource replenishment equals rate of depletion by the population". Most populations in nature have a habit of fluctuating above and below the carrying capacity, for example, when sheep were introduced into Tasmania their numbers "change logistically with small oscillations around an average population size of about 1.7 million" (Newth, 1985) (Figure 1). Although this is not an example of a reintroduced species, the sheep are still new to the habitat. Figure 1 shows that the proposed carrying capacity for the area is around 1.7 million (Krebs, 2001)
The growth of a reintroduced population can also be affected by extrinsic factors; biotic (predation, inter-specific competition and parasitism) and abiotic factors like floods, forest fires and storms. Abiotic factors are density - independent, meaning they do not regulate population growth in the same way as biotic factors. This is because the effects is only as great in relation to the number of individuals in the population; for example, a forest fire may wipe out an entire population with numbers exceeding the thousand, or a flood may effect a group of 100, abiotic factors deplete populations regardless of their number (Newth, 1985). Therefore when choosing a habitat to release a new species into, the abiotic factors which have affected the area in previous years, needs to be researched. This was evident in a study undertaken by Barreto et al (1998). After releasing 12 populations of Water Vole (Arvicola amphibious) into a tributary offset, one of the populations was ultimately killed due to severe flooding at the catchment area of the river. It was later shown that the area was prone to flooding and better measures should have been taken by the team when choosing areas to release the Water Voles (Barreto, 1998).
On the other hand, biotic factors act density - dependently. With predators and parasites they "respond to changes in density of their prey and host populations, respectively, to maintain populations at fairly constant sizes". The sizes in which they remain are more often than not below the carrying capacity, as extrinsic factors regulate populations without limitations from resources. Therefore, when locating a habitat to release a population into, the surrounding area must be studied in order to find the best place. This would be one with a minimum number of natural predators (Newth, 1985).
The amount of competition from other surrounding populations also needs to be addressed; when two or more species are competing for the same limited resource, one species will out-compete the other, excluding the species from the habitat. This is a form of competitive exclusion and needs to be addressed if a species is going to be reintroduced into a habitat.
As stated by the IUCN reintroduction guidelines, the original cause of decline also needs to be identified and eradicated before a species can be reintroduced into the habitat (IUCN, 1998). This is vital due to the fact that if these causes aren't addressed then the population number will ultimately decline again, resulting in extinction of the population in the area. The conditions in which a population will grow in a certain area are not easy to understand, especially when the sites being used for reintroduction need to be assessed prior to release, and when there is seldom information about the species already present at the site. Biologists studying invasion also incur similar problems when trying to predict which habitats are more likely to be invaded by foreign species (Hartley, 2006), therefore, similar "habitat modelling methods can be applied to projecting fates of reintroduction" (Armstrong, 2008). Once released the data for survival, reproduction and dispersal rates can be modelled to estimate the rate of population growth. As shown by Hall et al, (1997) the quality of the habitat should have reference to the 'ability of the environment to provide conditions appropriate for individual and population persistence'. Not only this, but the survival and reproduction rates of the species should indefinitely be linked to the habitat quality and should not consider the featuring vegetation, thereby referring to all aspects of the environment 'including food, predators and parasite' (Hall, 1997). Therefore, the biological requirements of the species in question should be focused on more than the assessable features like vegetation, and to "measure habitat quality using post-release data on survival and reproduction" (Thatcher, 2006).
Habitat conditions can also be altered over time and space using 'adaptive management techniques' to discover the correct requirements needed for a positive population growth. A good example of this form of management technique is the failed reintroduction of New Zealand hihi, or Stitchbird (Notiomystis cincta) to areas of regenerating forest. The reason for the failure was thought to be the insufficient food supply on the island. Scientists then produced a series of experiments using food supplementation in order to discover the effects of 'presence, quality and distribution' of food on the growth rate of the reintroduced population. This 'adaptive management technique' could be very useful for future reintroduction sites, adding to the criteria needed for a successful reintroduction (Armstrong, 2007).
The overall success for a reintroduction programme is ultimately decided upon by the choice of habitat in which the captive bred species, or relocated species is being released into. Scientists need to ask themselves questions, like, what type of intrinsic/extrinsic factors will affect the species? What was the original cause of decline, and how do you eliminate the problem? In order to address these issues, not only does the history of habitat choice not be overlooked (this is evident from the successful introduction of sheep into Tasmania, resulting in a steady growth and decline around the carrying capacity (Figure 1)), but also adaptive management techniques must be applied if the reintroduction is to be successful.
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Potentially, there are several genetic issues that can arise as a consequence of captive breeding which can then impact upon the subsequent reintroduction of the species to the wild. These issues include; an inbreeding depression, hybridisation (more commonly known as outbreeding depression), potential adaptation to the captive environment, and even a potential for the accumulation of new deleterious alleles. Each of these factors is an issue because in one way or another, they will impede the organism's successful reintroduction to the wild, by hampering their ability to survive.
When organisms are bred in a captive environment there are typically only a small number of them, and because of this reduced population size - mating between family members becomes alot more likely; this is of course known as inbreeding. This inbreeding is thought to drastically reduce the population's overall fitness, and significantly affect the viability of these small populations (Frankham, 1995., Saccheri, 1998., Hedrick, 2000., Spielman, 2004). The danger of inbreeding lies in the fact that it reduces heterozygosity by bringing together alleles that are copies of the same ancestral allele (in other words; alleles that are Identical by Descent) when related individuals mate and produce offspring. Therefore the chances of their offspring being homozygous, increases within only a few generations of inbreeding. This creates an inbreeding depression; 'inbreeding depression' is basically the reduced fitness of the offspring that the related individuals produce, relative to the fitness of the offspring produced by non related individuals (Leberg, 2008). An example of only a few generations of inbreeding causing a reduction in fitness can be seen in the study by Araki et al (2007) where only 2 generations of captive breeding caused an observed decline in reproductive fitness among captive reared populations of steelhead trout by as much as 40%, compared to these fish found in their natural environment (Araki, 2007).
The reason why there is a reduction in fitness among these genotypically homozygous offspring produced by inbreeding between related individuals in the captive environment, is simply because the amount of potentially deleterious recessive alleles they inherit will increase with each generation of inbreeding. Fox et al (2008) demonstrated this with their study regarding inbreeding effects on the genetic load; where they captively bred small numbers of Stator limbatus (a seed-feeding beetle). It was claimed that after only three generations of inbreeding, the beetle showed inbreeding depression at multiple stages of development, and the probability that an egg matured into an adult was reduced by 50%. They were able to conclude that Inbreeding depression affected the fitness (survival) of the beetle larvae mainly as a result of the accumulation of recessive deleterious alleles of a large effect (Fox, 2008). Basically, a genotype where recessive alleles become dominant is only created when the recessive alleles are present in both parent's genomes; and the more related (genetically similar) the parents are, the greater the probability of their offspring having homozygous deleterious alleles (Hedrick, 1994). In the wild, these deleterious or even lethal homozygous combinations of alleles would be purged by selection (the organism would not be able to survive due to its detrimental phenotype expressing the mutated genes, and would die), in a captive environment however, the organisms are a lot less likely to be exposed to the same environmental factors which would otherwise cause purging to occur (Leberg, 2008), meaning that this issue would affect the successful reintroduction of these particular captive bred animals into the wild, by severely reducing their fitness (ability to survive and successfully reproduce in the wild).
Potential adaptation to the captive environment is another issue directly linked to the inbreeding issue caused by captive breeding. Because there is little or no natural purging (selection) occurring in the artificial captive environment (Leberg, 2008), the previously mentioned reduction in heterozygosity inherent with captive breeding is allowed to continue, and as a result the organisms can become too far adapted to their captive environment for any reintroduction into the wild to have any success. For example, Latter and Mulley (1995) investigated into the effects of inbreeding depression on the adaptation of Drosophilia melanogaster to a captive environment. They discovered that after several generations in captivity a wild-derived population was had only 75% of the overall fitness out a wild population. They also conducted similar parallel experiments, only they used competitive captive environments (creating intra specific competition, which leads to selection), and the result was a population that was similar in fitness to the wild type, in some cases it even exceeded it. Therefore they showed that normal, non competitive captive breeding environments, promote adaptation to these artificial conditions and compromise fitness (Latter, 1995).
This allele fixing in captivity is especially detrimental in the case of new harmful allele mutations immerging and becoming fixed, in which case the fitness of that particular group of captive bred organisms would be crippled (Meffert 2005). Mutations in the genetic material of organisms occur in every population (wild or captive): point mutations, deletions, frame shifts, insertions, and inversions of the nucleotide sequences, have the potential to occur randomly any dividing meiotic cell of any living organism, therefore they are hardly exclusive to captive bred organisms. However as mentioned, their effects can be more detrimental to populations of organisms in a captive bred environment. The lack of natural selection pressures present in that environment will in some cases allow these disadvantageous mutations to be inherited and expressed in the phenotype of the next generation, without the organism being purged. This along with the small size of the captive population, means that because genetic drift acts more profoundly on small populations, these mutated alleles will become fixed rather than purged, and within a shorter number of generations than would be expected in the wild (Araki 2007). A good example would be, when Bush et al, in 1976 discovered that captive breeding of Screwworm Flies (Cochliomyia hominivorax) caused a rather un-common ÃŽÂ±-glycerol phosphate allele with lowered enzyme activity, to appear in the genotypes of offspring. The prevalence of this allele increased with each generation of breeding in captivity. Although it's effects were negligible while in the captivity, it reduced fitness and any likelihood of wild reintroduction because it severely impaired their ability to fly (Bush 1976).
One way of avoiding these fixations of alleles within these small captive bred populations is to breed them with other populations (most often wild populations) of the same species (Charlesworth, 2009). This can introduce new alleles into the small population (gene flow). However because these two populations of organisms have been separated, and different phenotypes and mutations will now exist providing both with alleles advantageous to their respective environment, the result of breeding individuals from the two can be a hybrid offspring. For example, when breeding organisms from the wild with a captive bred population, the wild organisms will have advantageous alleles that are being selected for, where as the captive bred organism most likely will not, and the result of a pairing between the two in most cases, is a progeny that possesses traits advantageous to neither the captive or wild environments - a hybrid of the two (Charlesworth, 2009). An example of this can be seen in Dolgin et al, 2007 study, where they crossed examined captive populations of a species of roundworm known as Caenorhabditis elegans. What they found was that hybridisation occurred in the first generation of this cross, and they suggested that this was caused by a disruptive interaction of two beneficial traits from each population hybridising to form one useless trait (Dolgin, 2007). This can create a loss of fitness within the captive bred population because the act of cross breeding these two separated populations can introduce non-additive genetic effects. Basically by replacing neutral genetic material in the next generation with either; more neutral genetic material, or with the new hybrid or even mutated alleles, this further impurifies the gene pool (Meffert, 2005). This issue is also going to affect the success of the captive bred organism's reintroduction into the wild.
In conclusion, there are many genetic issues that can arise as a result of captive breeding, many of them stemming from Inbreeding, which is caused by the simple fact that most of the captive bred populations are too small. Too small to be able to resist the effects of genetic drift and it's fixation of mutations that most often offer no benefit to the organism's fitness and successful reintroduction into the wild. Therefore careful consideration needs to be applied when designing captive environments, and steps need to be taken in order to reduce the impacts it will have upon the genetics of the species involved.
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With many organisms being endangered and facing extinction, it is important that actions be taken to prevent the problem from persisting. One such action; reintroduction is used as a way of tackling the issue of possible extinction with some success, however reintroduction still comes with its own problems, such as the issues with expense, captive breeding, genetics, and habitat.
As reintroduction programmes come with such high costs and with little funding provided, some ask; is it really worth it? This is why it is important that ever reintroduction is cost efficient otherwise the future of reintroduction programmes could be bleak. There is also plenty of evidence showing that captive breeding has some major disadvantages into the reintroduction of individuals that have been bred in captivity as well as many studies that show that there is a need for individuals to be bred in captivity and then released into the wild in order to increase the levels of wild populations of a species (Roldán et al, 2011). Overall it is too soon to see if captive breeding reintroduction has a positive long term effect on threatened / endangered species populations. Before a captivity bred species can be released back into the wild, it is very important for biologists to choose a suitable habitat. They need to take into consideration the intrinsic factors (like the carrying capacity of the given area), extrinsic factors like the biotic and abiotic issues of an area. There are also some useful methods in which biologists can use to help map out a positive population growth. Not only with this, but the IUCN guidelines for reintroduction need to followed.
Finally, there are many genetic issues that can arise as a result of captive breeding, many of them stemming from Inbreeding, which is caused by the simple fact that most of the captive bred populations are too small. Too small to be able to resist the effects of genetic drift and it's fixation of mutations that most often offer no benefit to the organism's fitness and successful reintroduction into the wild.
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