Hybrid vigor between native and introduced salamanders raises new challenges for conservation. Proc Natl Acad Sci USA

Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN 37996, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 11/2007; 104(40):15793-8. DOI: 10.1073/pnas.0704791104
Source: PubMed


Hybridization between differentiated lineages can have many different consequences depending on fitness variation among hybrid offspring. When introduced organisms hybridize with natives, the ensuing evolutionary dynamics may substantially complicate conservation decisions. Understanding the fitness consequences of hybridization is an important first step in predicting its evolutionary outcome and conservation impact. Here, we measured natural selection caused by differential viability of hybrid larvae in wild populations where native California Tiger Salamanders (Ambystoma californiense) and introduced Barred Tiger Salamanders (Ambystoma tigrinum mavortium) have been hybridizing for 50-60 years. We found strong evidence of hybrid vigor; mixed-ancestry genotypes had higher survival rates than genotypes containing mostly native or mostly introduced alleles. Hybrid vigor may be caused by heterozygote advantage (overdominance) or recombinant hybrid vigor (due to epistasis or complementation). These genetic mechanisms are not mutually exclusive, and we find statistical support for both overdominant and recombinant contributions to hybrid vigor in larval tiger salamanders. Because recombinant homozygous genotypes can breed true, a single highly fit genotype with a mosaic of native and introduced alleles may eventually replace the historically pure California Tiger Salamander (listed as Threatened under the U.S. Endangered Species Act). The management implications of this outcome are complex: Genetically pure populations may not persist into the future, but average fitness and population viability of admixed California Tiger Salamanders may be enhanced. The ecological consequences for other native species are unknown.

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Available from: Benjamin Minault Fitzpatrick, Sep 29, 2015
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    • "Follow-up studies are needed to test the stability of the hybrid zone. Nevertheless, even a stable hybrid zone would provide a window for genetic pollution via introgressive hybridization (Fitzpatrick and Shaffer, 2007). "
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    ABSTRACT: Genetic pollution of a native species through hybridization with an invasive species poses an insidious conservation threat. To expose genetic pollution, molecular methods employing multilocus data are required. We present a case study of genetic pollution via hybridization of a native crested newt species, Triturus cristatus, by the invasive Triturus carnifex on the Veluwe in the Netherlands. We sequenced 50 nuclear markers by next generation sequencing and one mitochondrial marker by Sanger sequencing for four populations from the native range of both parent species and eleven ponds on the Veluwe. We use three population genetic approaches (HIest, BAPS and Structure) to determine the genetic composition of the Veluwe newts based on all nuclear markers, a subset of 18 diagnostic markers and the complementary 32 non-diagnostic markers, with and without parental populations. BAPS underestimates genetic pollution, whereas Structure is comparatively accurate compared to HIest, although Structure’s relative advantage decreases with the diagnosticity of the markers. Data simulation confirms these findings. Genetic composition of the Veluwe ponds ranges from completely native, via different degrees of genetic admixture, to completely invasive. The observed hybrid zone appears to be bimodal, suggesting negative selection against hybrids. A genetic footprint of the native species is present in invasive populations, evidencing that the invasive locally replaced the native species. Genetic pollution is currently confined to a small area, but the possibility of further expansion cannot be excluded. Removal of genetic pollution will not be easy. We emphasize the need for legal guidance to manage genetic pollution.
    Biological Conservation 04/2015; 184:145-153. · 3.76 Impact Factor
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    • "If F1 offspring have relatively high fitness and cannot backcross with parental types, then the outcome might be a new species of hybrid origin (e.g., Rhymer et al., 1994). If F1 offspring have higher fitness than parental types and can backcross with parental types and other hybrids, the result can be a 'hybrid swarm', which is characterized by a relatively wide hybrid zone (e.g., Fitzpatrick and Shaffer, 2007; Latch et al., 2011), and can possibly result in the replacement of parental types by introgressed individuals. "
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    ABSTRACT: Interspecific hybridization and introgression are of conservation concern because they can lead to lower fitness, and in some cases, extinction of the parental population or species. Alternatively, hybridization can lead to increased fitness (i.e., heterosis) via generation of new genetic combinations and increased adaptive potential. There have been isolated observations of the Canada lynx (Lynx canadensis) hybridizing with the closely-related bobcat (Lynx rufus), but no comprehensive study has been undertaken of lynx–bobcat hybridization across their geographic ranges. The lynx distribution in North America has contracted by 40% from its historical range, and hybridization with bobcats is a potential, uncertain threat to lynx conservation. We conducted a continental-scale assessment of the prevalence of hybridization and genetic introgression between lynx (n = 1776, Canada and Alaska, USA) and bobcat (n = 1075, Canada and conterminous USA). Using control region sequences and clustering of microsatellite data, we found that the prevalence of genetic introgression was relatively low (7 of 2851 individuals (0.24%)). We found evidence of backcrossing to both lynx and bobcat parental types, suggesting that hybrids can be fertile. If the abundance of Canada lynx at the southern extent of its distribution is low relative to bobcat, hybridization and backcrossing with bobcat over several generations could result in the loss of lynx in areas of sympatry. If climate warming results in the bobcat distribution shifting northward towards the southern extent of the lynx distribution, the likelihood of interspecific hybridization could increase.
    Biological Conservation 10/2014; 178:107-115. DOI:10.1016/j.biocon.2014.07.016 · 3.76 Impact Factor
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    • "Nonetheless, monitoring the genetic makeup of introduced populations using neutral markers, such as microsatellite loci, still remains an informative mean of exploring the underlying genetics of invasiveness (Alda et al. 2013; Frisch et al. 2013; Ghabooli et al. 2013; McMahon et al. 2013; Perdereau et al. 2013; Simpson et al. 2013). The effects of introduced populations on the genetic makeup of their native counterparts can range from increased vigor to complete loss of fitness in the introduced– native hybrids (Huxel 1999; Fitzpatrick and Shaffer 2007). Additionally, hybridization may stimulate invasiveness in the introduced populations (Ellstrand and Schierenbeck 2000). "
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    ABSTRACT: Successful invasive species can overcome or circumvent the potential genetic loss caused by an introduction bottleneck through a rapid population expansion and admixture from multiple introductions. We explore the genetic makeup and the timing of a species introduction to Santa Cruz Island in the Galápagos archipelago. We investigate the presence of processes that can maintain genetic diversity in populations of the broad-nosed weevil Galapaganus howdenae howdenae. Analyses of combined genotypes for 8 microsatellite loci showed evidence of past population size reductions through moment and likelihood-based estimators. No evidence of admixture through multiple introductions was found, but substantial current population sizes (N0 298, 95% credible limits 50-2300), genetic diversity comparable with long-established endemics (Mean number of alleles = 3.875), and lack of genetic structure across the introduced range (FST = 0.01359) could suggest that foundations are in place for populations to rapidly recover any loss of genetic variability. The time estimates for the introduction into Santa Cruz support an accidental transfer during the colonization period (1832-1959) predating the spurt in human population growth. Our evaluation of the genetic status of G. h. howdenae suggests potential for population growth in addition to our field observations of a concurrent expansion in range and feeding preferences towards protected areas and endemic host plants. © 2014 © The American Genetic Association 2014. All rights reserved. For permissions, please e-mail: [email protected] /* */
    The Journal of heredity 01/2014; 105(3). DOI:10.1093/jhered/est096 · 2.09 Impact Factor
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