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      Hybridization and extinction


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          Hybridization may drive rare taxa to extinction through genetic swamping, where the rare form is replaced by hybrids, or by demographic swamping, where population growth rates are reduced due to the wasteful production of maladaptive hybrids. Conversely, hybridization may rescue the viability of small, inbred populations. Understanding the factors that contribute to destructive versus constructive outcomes of hybridization is key to managing conservation concerns. Here, we survey the literature for studies of hybridization and extinction to identify the ecological, evolutionary, and genetic factors that critically affect extinction risk through hybridization. We find that while extinction risk is highly situation dependent, genetic swamping is much more frequent than demographic swamping. In addition, human involvement is associated with increased risk and high reproductive isolation with reduced risk. Although climate change is predicted to increase the risk of hybridization‐induced extinction, we find little empirical support for this prediction. Similarly, theoretical and experimental studies imply that genetic rescue through hybridization may be equally or more probable than demographic swamping, but our literature survey failed to support this claim. We conclude that halting the introduction of hybridization‐prone exotics and restoring mature and diverse habitats that are resistant to hybrid establishment should be management priorities.

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          Hybridization and speciation.

          Hybridization has many and varied impacts on the process of speciation. Hybridization may slow or reverse differentiation by allowing gene flow and recombination. It may accelerate speciation via adaptive introgression or cause near-instantaneous speciation by allopolyploidization. It may have multiple effects at different stages and in different spatial contexts within a single speciation event. We offer a perspective on the context and evolutionary significance of hybridization during speciation, highlighting issues of current interest and debate. In secondary contact zones, it is uncertain if barriers to gene flow will be strengthened or broken down due to recombination and gene flow. Theory and empirical evidence suggest the latter is more likely, except within and around strongly selected genomic regions. Hybridization may contribute to speciation through the formation of new hybrid taxa, whereas introgression of a few loci may promote adaptive divergence and so facilitate speciation. Gene regulatory networks, epigenetic effects and the evolution of selfish genetic material in the genome suggest that the Dobzhansky-Muller model of hybrid incompatibilities requires a broader interpretation. Finally, although the incidence of reinforcement remains uncertain, this and other interactions in areas of sympatry may have knock-on effects on speciation both within and outside regions of hybridization. © 2013 The Authors. Journal of Evolutionary Biology © 2013 European Society For Evolutionary Biology.
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            Does global change increase the success of biological invaders?

            Biological invasions are gaining attention as a major threat to biodiversity and an important element of global change. Recent research indicates that other components of global change, such as increases in nitrogen deposition and atmospheric CO2 concentration, favor groups of species that share certain physiological or life history traits. New evidence suggests that many invasive species share traits that will allow them to capitalize on the various elements of global change. Increases in the prevalence of some of these biological invaders would alter basic ecosystem properties in ways that feed back to affect many components of global change.
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              Between a rock and a hard place: evaluating the relative risks of inbreeding and outbreeding for conservation and management.

              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.

                Author and article information

                Evol Appl
                Evol Appl
                Evolutionary Applications
                John Wiley and Sons Inc. (Hoboken )
                22 February 2016
                August 2016
                : 9
                : 7 , Gene Flow and Applied Evolutionary Biology ( doiID: 10.1111/eva.2016.9.issue-7 )
                : 892-908
                [ 1 ] Department of Botany and Biodiversity Research CentreUniversity of British Columbia Vancouver BCCanada
                [ 2 ] Department of Bioagricultural Sciences and Pest ManagementColorado State University Ft Collins COUSA
                [ 3 ] Department of BiologyIndiana University Bloomington INUSA
                Author notes
                [*] [* ] Correspondence

                Loren H. Rieseberg, Botany Department, University of British Columbia, 3529‐6270 University Blvd, Vancouver, BC, Canada, V6T 1Z4..

                Tel.: +1 604 8274540;

                fax: +1 604 8226089;

                e‐mail: lriesebe@ 123456mail.ubc.ca

                © 2016 The Authors. Evolutionary Applications published by John Wiley & Sons Ltd

                This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                : 01 December 2015
                : 28 January 2016
                Page count
                Pages: 17
                Funded by: Human Frontiers in Science Postdoctoral Fellowship
                Funded by: NSERC Graduate Fellowship
                Funded by: US National Science Foundation Graduate Fellowship
                Funded by: Swiss National Science Foundation Postdoctoral Fellowship
                Funded by: Natural Sciences and Engineering Research Council of Canada (NSERC)
                Reviews and Syntheses
                Reviews and Syntheses
                Custom metadata
                August 2016
                Converter:WILEY_ML3GV2_TO_NLMPMC version:4.9.1 mode:remove_FC converted:16.07.2016

                Evolutionary Biology
                conservation,demographic swamping,gene flow,genetic swamping,hybrid fitness,introgression,invasive species,outbreeding depression


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