Simultaneous inbreeding and outbreeding depression in reintroduced Arabian oryx
T C Marshall and J A Spalton; August 2000
Animal Conservation
Abstract
In most species the offspring of closely related parents have reduced fitness compared with the offspring of unrelated parents, a phenomenon known as inbreeding depression. However if parents are very distantly related, their offspring may also have reduced fitness. This pattern, outbreeding depression, has been most commonly observed in plants and only rarely in animals. Here we examine the consequences of inbreeding and outbreeding on juvenile survival of reintroduced Arabian oryx (Oryx leucoryx) in Oman, a population with a small number of founders drawn from a number of sources. Using microsatellite-based measures of inbreeding and outbreeding, there was no apparent relationship between inbreeding or outbreeding and survival when inbreeding and outbreeding were tested in separate statistical models. However when inbreeding and outbreeding were tested in the same statistical model, we found simultaneous inbreeding depression and outbreeding depression acting on juvenile survival. Outbreeding depression may be more common in vertebrates than previously supposed, and conservation strategies that seek to maximize the genetic diversity of managed populations may risk mixing lineages that are sufficiently differentiated to cause outbreeding depression among descendants.
Posts mit dem Label Conservation Biology werden angezeigt. Alle Posts anzeigen
Posts mit dem Label Conservation Biology werden angezeigt. Alle Posts anzeigen
Dienstag, 5. November 2013
Modeling Factors Affecting the Severity of Outbreeding Depression
Modeling Factors Affecting the Severity of Outbreeding Depression
Suzanne Edmands and Charles C Tmmerman; June 2003
Conservation Biology
Abstract
Hybridization between populations may cause either increased fitness ( “hybrid vigor” ) or decreased fitness ( “outbreeding depression” ). Translocation between populations may therefore in some cases be a successful means of combating genetic erosion and preserving evolutionary potential, whereas in other cases it may make the situation worse by inducing outbreeding depression. Because genetic distance alone is a poor predictor of the success or failure of hybridization, we developed a computer model ( ELAB ) to explore other factors affecting the consequences of hybridization. Our model simulates diploid, unisexual populations following Mendelian rules, and in this study we used it to test the effect of a variety of parameters on both the magnitude and duration of outbreeding depression. We focused our simulations on the effects of ( 1 ) divergence between populations, ( 2 ) the genetic basis of outbreeding depression ( disruption of local adaptation vs. intrinsic coadaptation ), ( 3 ) population parameters such as mutation rate and recombination rate, and ( 4 ) alternative management schemes ( 50:50 mixture vs. one migrant per generation ). The magnitude of outbreeding depression increased linearly with genetic distance, whereas the duration of outbreeding depression showed a more complex curvilinear relationship. With genetic distance held constant, magnitude increased with larger population size, lower mutation rate, cross-fertilization, and higher recombination rate, whereas duration increased with larger population size and partial self-fertilization. Fitness problems caused by disruption of local adaptation were stronger but more transient than those caused by a disruption of intrinsic coadaptation. Finally, simulations showed that, depending on the genetic basis of outcrossing problems, recurrent transfer of only one migrant per generation into a population of 100 individuals could cause as much or more damage as a one-time 50:50 mixture.
Suzanne Edmands and Charles C Tmmerman; June 2003
Conservation Biology
Abstract
Hybridization between populations may cause either increased fitness ( “hybrid vigor” ) or decreased fitness ( “outbreeding depression” ). Translocation between populations may therefore in some cases be a successful means of combating genetic erosion and preserving evolutionary potential, whereas in other cases it may make the situation worse by inducing outbreeding depression. Because genetic distance alone is a poor predictor of the success or failure of hybridization, we developed a computer model ( ELAB ) to explore other factors affecting the consequences of hybridization. Our model simulates diploid, unisexual populations following Mendelian rules, and in this study we used it to test the effect of a variety of parameters on both the magnitude and duration of outbreeding depression. We focused our simulations on the effects of ( 1 ) divergence between populations, ( 2 ) the genetic basis of outbreeding depression ( disruption of local adaptation vs. intrinsic coadaptation ), ( 3 ) population parameters such as mutation rate and recombination rate, and ( 4 ) alternative management schemes ( 50:50 mixture vs. one migrant per generation ). The magnitude of outbreeding depression increased linearly with genetic distance, whereas the duration of outbreeding depression showed a more complex curvilinear relationship. With genetic distance held constant, magnitude increased with larger population size, lower mutation rate, cross-fertilization, and higher recombination rate, whereas duration increased with larger population size and partial self-fertilization. Fitness problems caused by disruption of local adaptation were stronger but more transient than those caused by a disruption of intrinsic coadaptation. Finally, simulations showed that, depending on the genetic basis of outcrossing problems, recurrent transfer of only one migrant per generation into a population of 100 individuals could cause as much or more damage as a one-time 50:50 mixture.
Hybridization rapidly reduces fitness of a native trout in the wild
Hybridization rapidly reduces fitness of a native trout in the wild
Clint C Muhlfeld et al.; 2009
http://rsbl.royalsocietypublishing.org/content/5/3/328.full
Abstract
Human-mediated hybridization is a leading cause of biodiversity loss worldwide. How hybridization affects fitness and what level of hybridization is permissible pose difficult conservation questions with little empirical information to guide policy and management decisions. This is particularly true for salmonids, where widespread introgression among non-native and native taxa has often created hybrid swarms over extensive geographical areas resulting in genomic extinction. Here, we used parentage analysis with multilocus microsatellite markers to measure how varying levels of genetic introgression with non-native rainbow trout (Oncorhynchus mykiss) affect reproductive success (number of offspring per adult) of native westslope cutthroat trout (Oncorhynchus clarkii lewisi) in the wild. Small amounts of hybridization markedly reduced fitness of male and female trout, with reproductive success sharply declining by approximately 50 per cent, with only 20 per cent admixture. Despite apparent fitness costs, our data suggest that hybridization may spread due to relatively high reproductive success of first-generation hybrids and high reproductive success of a few males with high levels of admixture. This outbreeding depression suggests that even low levels of admixture may have negative effects on fitness in the wild and that policies protecting hybridized populations may need reconsideration.
Clint C Muhlfeld et al.; 2009
http://rsbl.royalsocietypublishing.org/content/5/3/328.full
Abstract
Human-mediated hybridization is a leading cause of biodiversity loss worldwide. How hybridization affects fitness and what level of hybridization is permissible pose difficult conservation questions with little empirical information to guide policy and management decisions. This is particularly true for salmonids, where widespread introgression among non-native and native taxa has often created hybrid swarms over extensive geographical areas resulting in genomic extinction. Here, we used parentage analysis with multilocus microsatellite markers to measure how varying levels of genetic introgression with non-native rainbow trout (Oncorhynchus mykiss) affect reproductive success (number of offspring per adult) of native westslope cutthroat trout (Oncorhynchus clarkii lewisi) in the wild. Small amounts of hybridization markedly reduced fitness of male and female trout, with reproductive success sharply declining by approximately 50 per cent, with only 20 per cent admixture. Despite apparent fitness costs, our data suggest that hybridization may spread due to relatively high reproductive success of first-generation hybrids and high reproductive success of a few males with high levels of admixture. This outbreeding depression suggests that even low levels of admixture may have negative effects on fitness in the wild and that policies protecting hybridized populations may need reconsideration.
Between a rock and a hard place: evaluating the relative risks of inbreeding and outbreeding for conservation and management
Between a rock and a hard place: evaluating the relative risks of inbreeding and outbreeding for conservation and management
Suzanne Edmands; 2007
http://onlinelibrary.wiley.com/doi/10.1111/j.1365-294X.2006.03148.x/full
Abstract
As populations become increasingly fragmented, managers are often faced with the dilemma that intentional hybridization might save a population from inbreeding depression but it might also induce outbreeding depression. While empirical evidence for inbreeding depression is vastly greater than that for outbreeding depression, the available data suggest that risks of outbreeding, particularly in the second generation, are on par with the risks of inbreeding. Predicting the relative risks in any particular situation is complicated by variation among taxa, characters being measured, level of divergence between hybridizing populations, mating history, environmental conditions and the potential for inbreeding and outbreeding effects to be occurring simultaneously. Further work on consequences of interpopulation hybridization is sorely needed with particular emphasis on the taxonomic scope, the duration of fitness problems and the joint effects of inbreeding and outbreeding. Meanwhile, managers can minimize the risks of both inbreeding and outbreeding by using intentional hybridization only for populations clearly suffering from inbreeding depression, maximizing the genetic and adaptive similarity between populations, and testing the effects of hybridization for at least two generations whenever possible.
["Hybridization between divergent populations or species can result in increased fitness in some cases, but it is generally expected to result in reduced fitness."]
Suzanne Edmands; 2007
http://onlinelibrary.wiley.com/doi/10.1111/j.1365-294X.2006.03148.x/full
Abstract
As populations become increasingly fragmented, managers are often faced with the dilemma that intentional hybridization might save a population from inbreeding depression but it might also induce outbreeding depression. While empirical evidence for inbreeding depression is vastly greater than that for outbreeding depression, the available data suggest that risks of outbreeding, particularly in the second generation, are on par with the risks of inbreeding. Predicting the relative risks in any particular situation is complicated by variation among taxa, characters being measured, level of divergence between hybridizing populations, mating history, environmental conditions and the potential for inbreeding and outbreeding effects to be occurring simultaneously. Further work on consequences of interpopulation hybridization is sorely needed with particular emphasis on the taxonomic scope, the duration of fitness problems and the joint effects of inbreeding and outbreeding. Meanwhile, managers can minimize the risks of both inbreeding and outbreeding by using intentional hybridization only for populations clearly suffering from inbreeding depression, maximizing the genetic and adaptive similarity between populations, and testing the effects of hybridization for at least two generations whenever possible.
["Hybridization between divergent populations or species can result in increased fitness in some cases, but it is generally expected to result in reduced fitness."]
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