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Bradley H Shaffer - One of the best experts on this subject based on the ideXlab platform.
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allele specific expression and gene regulation help explain transgressive thermal tolerance in non native hybrids of the endangered california Tiger Salamander ambystoma californiense
Molecular Ecology, 2021Co-Authors: Robert D Cooper, Bradley H ShafferAbstract:Hybridization between native and non-native species is an ongoing global conservation threat. Hybrids that exhibit traits and tolerances that surpass parental values are of particular concern, given their potential to outperform native species. Effective management of hybrid populations requires an understanding of both physiological performance and the underlying mechanisms that drive transgressive hybrid traits. Here, we explore several aspects of the hybridization between the endangered California Tiger Salamander (Ambystoma californiense; CTS) and the introduced barred Tiger Salamander (Ambystoma mavortium; BTS). We assayed critical thermal maximum (CTMax) to compare the ability of CTS, BTS and F1 hybrids to tolerate acute thermal stress, and found that hybrids exhibit a wide range of CTMax values, with 33% (4/12) able to tolerate temperatures greater than either parent. We then quantified the genomic response, measured at the RNA transcript level, of each Salamander, to explore the mechanisms underlying thermal tolerance strategies. We found that CTS and BTS have strikingly different values and tissue-specific patterns of overall gene expression, with hybrids expressing intermediate values. F1 hybrids display abundant and variable degrees of allele-specific expression (ASE), likely arising from extensive compensatory evolution in gene regulatory mechanisms between CTS and BTS. We found evidence that the proportion of genes with allelic imbalance in individual hybrids correlates with their CTMax, suggesting a link between ASE and expanded thermal tolerance that may contribute to the success of hybrid Salamanders in California. Future climate change may further complicate management of CTS if hybrid Salamanders are better equipped to deal with rising temperatures.
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allele specific expression and gene regulation explain transgressive thermal tolerance in non native hybrids of the endangered california Tiger Salamander ambystoma californiense
bioRxiv, 2019Co-Authors: Robert D Cooper, Bradley H ShafferAbstract:Hybridization between native and non-native species is an ongoing global conservation threat. Hybrids that exhibit traits and tolerances that surpass parental values are of particular concern, given their ability to outcompete the native parent. It is crucial to understand the mechanisms that drive these transgressive hybrid traits to diagnose and develop strategies to manage hybrid populations. Here, we explore several aspects of the hybridization between the endangered California Tiger Salamander (Ambystoma californiense; CTS) and the introduced barred Tiger Salamander (Ambystoma mavortium; BTS). We assayed critical thermal maximum (CTMax) to compare the ability of CTS, BTS and hybrids to tolerate acute thermal stress, and found that hybrids exhibit a wide range of CTMax values, with 40% (6/15) able to tolerate temperatures greater than either parent. We quantified the genomic response of each individual to discover and compare thermal abatement strategies. We found that CTS and BTS have strikingly different numbers and tissue-specific patterns of overall gene expression, with hybrids expressing intermediate values. We evaluated transgressive and variable phenotypes by uncovering regulatory mechanisms that give rise to these unique traits. F1 hybrids display abundant and variable degrees of allele specific expression (ASE), likely arising from extensive compensatory evolution in gene regulatory mechanisms of the parental lineages. We found that the proportion of genes with allelic imbalance in individual hybrids correlates with their CTMax, suggesting that BTS biased expression confers improved thermal tolerance. We discuss the implications of these findings with respect to ongoing management of CTS in the face of future climate change.
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Appendix B. Principal components analysis of introduced allele frequencies at eight DNA markers among 28 Tiger Salamander breeding ponds.
2016Co-Authors: Benjamin M. Fitzpatrick, Bradley H ShafferAbstract:Principal components analysis of introduced allele frequencies at eight DNA markers among 28 Tiger Salamander breeding ponds
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Appendix A. A table showing Tiger Salamander breeding pond sites assayed for introduced alleles at three or eight molecular markers.
2016Co-Authors: Benjamin M. Fitzpatrick, Bradley H ShafferAbstract:A table showing Tiger Salamander breeding pond sites assayed for introduced alleles at three or eight molecular markers
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delayed life history effects multilevel selection and evolutionary trade offs in the california Tiger Salamander
Ecology, 2014Co-Authors: Christopher A Searcy, Peter C Trenham, Levi N Gray, Bradley H ShafferAbstract:Delayed life history effects (DLHEs) occur when fitness in one life stage affects fitness in subsequent life stages. Given their biphasic life cycle, pond-breeding amphibians provide a natural system for studying DLHEs, although these effects are not restricted to species with biphasic life histories. In this study, we used multiple mark-recapture techniques enabled by a large trapping array to monitor components of fitness and resulting DLHEs in a population of the endangered California Tiger Salamander (Ambystoma californiense). We found that DLHEs are prominent across all life stage transitions and that there is variation in whether selection acts primarily at the individual or cohort level. We also demonstrated that there is more than an order of magnitude variation in mean cohort fitness, providing tremendous variation for DLHEs to act upon. We documented an evolutionary trade-off between mass at emergence and date of emergence, which may play a role in maintaining the variation in mass (fitness) at emergence. A literature review revealed that such high levels of intercohort variation occur in many other pond-breeding amphibians, and that appropriately documenting the magnitude of intercohort variation requires long-term studies (roughly two population turnovers). Given the profound effect that DLHEs can have on population dynamics, quantifying intercohort variation in mean fitness and the level(s) at which selection acts will be very important for developing accurate models of population dynamics. In general, when developing models of population dynamics, more attention should be paid to variation in mean fitness and not just variation in total numbers.
Joshua J Smith - One of the best experts on this subject based on the ideXlab platform.
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amphibian sex determination segregation and linkage analysis using members of the Tiger Salamander species complex ambystoma mexicanum and a t tigrinum
Heredity, 2009Co-Authors: Joshua J Smith, Stephen R VossAbstract:Amphibian sex determination: segregation and linkage analysis using members of the Tiger Salamander species complex ( Ambystoma mexicanum and A. t. tigrinum )
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a comprehensive expressed sequence tag linkage map for Tiger Salamander and mexican axolotl enabling gene mapping and comparative genomics in ambystoma
Genetics, 2005Co-Authors: Joshua J Smith, David Kevin Kump, John A Walker, David M Parichy, Stephen R VossAbstract:Expressed sequence tag (EST) markers were developed for Ambystoma tigrinum tigrinum (Eastern Tiger Salamander) and for A. mexicanum (Mexican axolotl) to generate the first comprehensive linkage map for these model amphibians. We identified 14 large linkage groups (125.5–836.7 cM) that presumably correspond to the 14 haploid chromosomes in the Ambystoma genome. The extent of genome coverage for these linkage groups is apparently high because the total map size (5251 cM) falls within the range of theoretical estimates and is consistent with independent empirical estimates. Unlike most vertebrate species, linkage map size in Ambystoma is not strongly correlated with chromosome arm number. Presumably, the large physical genome size (∼30 Gbp) is a major determinant of map size in Ambystoma. To demonstrate the utility of this resource, we mapped the position of two historically significant A. mexicanum mutants, white and melanoid, and also met, a quantitative trait locus (QTL) that contributes to variation in metamorphic timing. This new collection of EST-based PCR markers will better enable the Ambystoma system by facilitating development of new molecular probes, and the linkage map will allow comparative studies of this important vertebrate group.
Andrew Storfer - One of the best experts on this subject based on the ideXlab platform.
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geography is more important than life history in the recent diversification of the Tiger Salamander complex
bioRxiv, 2020Co-Authors: Kathryn M Everson, Levi N Gray, Angela Jones, Nicolette M Lawrence, Mary E Foley, Kelly L Sovacool, Justin D Kratovil, Scott Hotaling, Paul M Hime, Andrew StorferAbstract:The North American Tiger Salamander species complex, including its flagship species the axolotl, has long been a source of biological fascination. The complex exhibits a wide range of variation in developmental life history strategies, including populations and individuals that undergo metamorphosis and those able to forego metamorphosis and retain a larval, aquatic lifestyle (i.e., paedomorphosis). Such disparate life history strategies are assumed to cause populations to become reproductively isolated, but the degree to which they have actually shaped population- and species-level boundaries is poorly understood. Using a large multi-locus dataset from hundreds of samples across North America, we identified genetic clusters with clear signs of admixture across the geographic range of the Tiger Salamander complex. Population clusters often contain a mixture of paedomorphic and metamorphic taxa, and we conclude that geography has played a large role in driving lineage divergence relative to obligate paedomorphosis in this system. This conclusion is bolstered by model-based analyses demonstrating gene flow between metamorphic and paedomorphic populations. Even the axolotl, a paedomorphic species with an isolated native range, apparently has a history of gene flow with its neighboring populations. This fine-scale genetic perspective on life-history variation establishes a framework for understanding how plasticity, local adaptation, and gene flow contribute to lineage divergence. The axolotl is currently used as the vertebrate model system in regenerative biology, and our findings chart a course for more informed use of these and other Tiger Salamander species in experimental and field research, including conservation priorities.
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Combined Effects of Virus, Pesticide, and Predator Cue on the Larval Tiger Salamander (Ambystoma tigrinum)
EcoHealth, 2011Co-Authors: Jacob L. Kerby, Alison J. Hart, Andrew StorferAbstract:Emerging diseases and environmental contamination are two of the leading hypotheses for global amphibian declines. Yet few studies have examined the influence of contaminants on disease susceptibility, and even fewer have incorporated the role of natural stressors such as predation. We performed a factorial study investigating the interaction of the insecticide carbaryl, dragonfly predator cue, and the emerging pathogen Ambystoma tigrinum virus (ATV) on fitness correlates and disease susceptibility in Tiger Salamander larvae. Four week old larvae were exposed for 22 days in a 2 (0, 500 μg/l carbaryl) × 2 (control, predator cue water) × 2 (0, 1 × 10^4 pfu ATV) factorial designed laboratory study. Results show significant impacts to survival of larvae for both virus and predator cue treatments, as well as an interactive effect between the two, in which predator cue strongly exacerbated disease-driven mortality. There was a clear pattern of reduced survival with the addition of stressors, with those where all three stressors were present exhibiting the worst effects (a decrease in survival from 93 to 60%). On those that survived, we also detected several sub-lethal impacts in mass, SVL, and development. Predator cue and pesticide treatments significantly reduced both SVL and mass. Virus and predator treatments significantly slowed development. Stressors also exhibited opposing effects on activity. Predator cue caused a significant reduction in activity, whereas virus caused a significant increase in activity over time. These results highlight the importance of examining combined natural and introduced stressors to understand potential impacts on amphibian species. Such stressors may contribute to the emergence of ATV in particular regions, raising concerns about the influence of pesticides on disease emergence in general.
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Combined Effects of Atrazine and Chlorpyrifos on Susceptibility of the Tiger Salamander to Ambystoma tigrinum Virus
EcoHealth, 2009Co-Authors: Jacob L. Kerby, Andrew StorferAbstract:Several hypotheses have been examined as potential causes of global amphibian declines, including emerging infectious diseases and environmental contaminants. Although these factors are typically studied separately, animals are generally exposed to both stressors simultaneously. We examined the effects of the herbicide atrazine and the insecticide chlorpyrifos on the susceptibility of Tiger Salamander larvae, Ambystoma tigrinum, to a viral pathogen, Ambystoma tigrinum virus (ATV). Environmentally relevant concentrations of atrazine (0, 20, 200 μg/L) and chlorpyrifos (0, 2, 20, 200 μg/L) were used along with ATV in a fully factorial experimental design whereby individually housed, 4-week-old larvae were exposed for 2 weeks. Atrazine alone was not lethal to larvae, and chlorpyrifos alone was lethal only at the highest concentration. When combined with ATV, chlorpyrifos increased susceptibility to viral infection and resulted in increased larval mortality. A significant interactive effect between atrazine and ATV was detected. Atrazine treatments slightly decreased survival in virus-exposed treatments, yet slightly increased survival in the virus-free treatments. These findings corroborate earlier research on the impacts of atrazine, in particular, on disease susceptibility, but exhibit greater effects (i.e., reduced survival) when younger larvae were examined. This study is the first of its kind to demonstrate decreases in amphibian survival with the combination of pesticide and a viral disease. Further examination of these multiple stressors can provide key insights into potential significance of environmental cofactors, such as pesticides, in disease dynamics.
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atrazine increases ranavirus susceptibility in the Tiger Salamander ambystoma tigrinum
Ecological Applications, 2006Co-Authors: Diane Denise Forson, Andrew StorferAbstract:Pathogenic diseases and environmental contaminants are two of the leading hypotheses for global amphibian declines, yet few studies have examined the influence of contaminants on disease susceptibility. In this study, we examined effects of ecologically relevant doses of atrazine (0, 1.6, 16, and 160 lg/L), sodium nitrate (0, 6.8, 68 mg/L), and their interactions on susceptibility of four laboratory-bred Tiger Salamander families to Ambystoma tigrinum virus (ATV), a pathogen implicated in global amphibian die-offs. Salamanders were from Arizona populations where a coevolutionary history with ATV is supported, and thus cofactors rather than recent introduction may contribute to disease epizootics. Use of atrazine and nitrogenous fertilizers are ubiquitous; therefore, the impact of these cofactors on disease susceptibility is an important consideration. Atrazine and sodium nitrate significantly decreased peripheral leukocyte levels, suggesting an impact of these contaminants on the immune system. As expected from this result, atrazine significantly increased susceptibility of larvae to ATV infection. In contrast, nitrate had a marginally significant main effect and significantly decreased infection rate at the highest level. However, neither atrazine nor sodium nitrate had significant effects on viral copy number per individual. These results suggest that ecologically relevant concentrations of atrazine and nitrates have immunosuppressive effects, and atrazine may contribute to ATV epizootics, raising concerns about the influence of contaminants on diseases in general.
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Evidence for Introgression in the Endangered Sonora Tiger Salamander, Ambystoma tigrinum stebbinsi (Lowe)
Copeia, 2004Co-Authors: Andrew Storfer, Stephen G. Mech, Matthew W. Reudink, Robert E. Ziemba, Jaime Warren, James P CollinsAbstract:Abstract Introduction of nonnative species and consequent genetic introgression of native taxa is a primary conservation concern, particularly for endangered species. Our ongoing molecular study of the endangered Sonora Tiger Salamander, Ambystoma tigrinum stebbinsi (Lowe), has uncovered evidence of introgression by the Barred Tiger Salamander, Ambystoma tigrinum mavortium. We conducted both mitochondrial DNA sequencing and analyses of nine microsatellite loci to (1) evaluate the distinctiveness of A. t. stebbinsi from the two other Tiger Salamander subspecies in Arizona; and (2) test for introgression in A. t. stebbinsi. Two mitochondrial haplotypes were found. One was undescribed for Tiger Salamanders, and the other was identical to that found in nearby A. t. mavortium. Microsatellite analyses, including assignment tests, diagnostic alleles, and high genetic distances, supported distinctness of A. t. stebbinsi. Thirty-nine animals that were putatively A. t. stebbinsi had mtDNA haplotypes identical to th...
Benjamin M. Fitzpatrick - One of the best experts on this subject based on the ideXlab platform.
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Appendix B. Principal components analysis of introduced allele frequencies at eight DNA markers among 28 Tiger Salamander breeding ponds.
2016Co-Authors: Benjamin M. Fitzpatrick, Bradley H ShafferAbstract:Principal components analysis of introduced allele frequencies at eight DNA markers among 28 Tiger Salamander breeding ponds
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Appendix A. A table showing Tiger Salamander breeding pond sites assayed for introduced alleles at three or eight molecular markers.
2016Co-Authors: Benjamin M. Fitzpatrick, Bradley H ShafferAbstract:A table showing Tiger Salamander breeding pond sites assayed for introduced alleles at three or eight molecular markers
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invasive hybrid Tiger Salamander genotypes impact native amphibians
Proceedings of the National Academy of Sciences of the United States of America, 2009Co-Authors: Maureen E Ryan, Jarrett R Johnson, Benjamin M. FitzpatrickAbstract:Although the ecological consequences of species invasions are well studied, the ecological impacts of genetic introgression through hybridization are less understood. This is particularly true of the impacts of hybridization on “third party” community members not genetically involved in hybridization. We also know little about how direct interactions between hybrid and parental individuals influence fitness. Here, we examined the ecological effects of hybridization between the native, threatened California Tiger Salamander (Ambystoma californiense) and the introduced Barred Tiger Salamander (Ambystoma tigrinum mavortium). Native x introduced hybrids are widespread in California, where they are top predators in seasonal ponds. We examined the impacts of early generation hybrids (first 2 generations of parental crosses) and contemporary hybrids derived from ponds where hybrids have been under selection in the wild for 20 generations. We found that most classes of hybrid Tiger Salamander larvae dramatically reduced survival of 2 native community members, the Pacific Chorus Frog (Pseudacris regilla) and the California Newt (Taricha torosa). We also found that native A. californiense larvae were negatively impacted by the presence of hybrid larvae: Native survival and size at metamorphosis were reduced and time to metamorphosis was extended. We also observed a large influence of Mendelian dominance on size, metamorphic timing and predation rate of hybrid Tiger Salamanders. These results suggest that both genetic and ecological factors are likely to influence the dynamics of admixture, and that Tiger Salamander hybridization might constitute a threat to additional pond-breeding species of concern in the region.
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environment dependent admixture dynamics in a Tiger Salamander hybrid zone
Evolution, 2004Co-Authors: Benjamin M. Fitzpatrick, Bradley H ShafferAbstract:After an estimated five million years of independent evolution, the barred Tiger Salamander (Ambystoma tigrinum mavortium) was introduced by bait dealers into the native range of the California Tiger Salamander (A. californiense). Hybridization and backcrossing have been occurring in central California for 50-60 years, or an estimated 15-30 generations. We studied genetic and ecological factors influencing admixture of these two divergent gene pools by analyzing frequencies of hybrid genotypes in three kinds of breeding habitats: natural vernal pools, ephemeral man-made cattle ponds, and perennial man-made ponds. Perennial ponds tended to have higher frequencies of nonnative alleles than either type of seasonal pond, even in cases where perennial and seasonal ponds are within a few hundred meters. Thus, the hybrid zone has a mosaic structure that depends on pond hydrology or ecology. The presence of some broadly acting constraints on admixture is suggested by linkage disequilibria between physically unlinked molecular markers within ponds. In addition, we found several marker-specific deviations from Hardy- Weinberg equilibrium. One marker showed a consistent deficit of heterozygotes across pond types. Another showed heterozygote deficits only in vernal pools. A third was more likely to have heterozygote excess in ephemeral cattle ponds. These patterns indicate that admixture is influenced by complex genotype-by-environment interactions.
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hybridization between a rare native Tiger Salamander ambystoma californiense and its introduced congener
Ecological Applications, 2003Co-Authors: Seth P D Riley, Bradley H Shaffer, Randal S Voss, Benjamin M. FitzpatrickAbstract:Exotic species threaten native biodiversity through predation, competition, and habitat alteration, but also by hybridizing with native species. A lack of reproductive isolation between exotic and native species can lead to genetic swamping, loss of native genetic diversity, and, in rare or endangered species, extirpation or extinction. We examined hybridization between a declining native Salamander, the California Tiger Salamander, Am- bystoma californiense, and an introduced congener, A. tigrinum. Ambystoma californiense is restricted to central California where A. tigrinum has been deliberately introduced as fish bait. In the Salinas Valley, we sampled Salamanders from four artificial ponds and two natural vernal pools. Based on mitochondrial DNA and two nuclear loci, we found that hybrids were present in all six ponds, and that these hybrids were viable and fertile. No potentially pure A. californiense were present in three of the six ponds, and only one pond had more than 8% possibly pure native animals. Despite a relatively ancient split and wide genetic divergence between these taxa, they are interbreeding and threatening the genetic purity of the native species. Our data also suggest that the extent of the genetic mixing depends on the breeding habitat. There is little evidence of barriers to gene exchange in the four artificial breeding ponds. However in the two vernal pools, we found significantly fewer larvae with hybrid genotypes and significantly more with pure parental genotypes than expected. Linkage disequilibria revealed positive associations between native alleles and genotypes, and neg- ative associations between native and introduced alleles and genotypes in these two ponds. Despite rampant hybridization, these data provide evidence of some constraints on hy- bridization in the native breeding habitats. Our results suggest that habitat characteristics of native species should be exploited in management strategies to limit hybridization with exotics.
Jarrett R Johnson - One of the best experts on this subject based on the ideXlab platform.
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The origin of Tiger Salamander (Ambystoma tigrinum) populations in California, Oregon, and Nevada: introductions or relicts?
Conservation Genetics, 2011Co-Authors: Jarrett R Johnson, Robert C. Thomson, Steven J. Micheletti, H. Bradley ShafferAbstract:Whether intentionally or accidentally introduced, exotic species have the capacity to dramatically disrupt native communities. In central California, Tiger Salamanders ( Ambystoma tigrinum ) have been introduced as a by-product of the sport fishing bait industry. Some of these introductions are relatively well known and have resulted in the formation of hybrids with the imperiled native California Tiger Salamander ( A. californiense ). Other populations of A. tigrinum , particularly in the northern and eastern parts of the state, remain poorly characterized and are present in regions where relictual amphibian populations of other species have persisted, suggesting that these might be relictual, native A. tigrinum . We used genetic sequence data to determine the provenance of all known extralimital A. tigrinum populations in California and adjacent Oregon and Nevada through comparison with reference samples from the native range of A. tigrinum . Our results suggest that A. tigrinum have been introduced in Northern California, Southern California and the Sierra Nevada, originating from multiple sources across the Great Plains of the US. Furthermore, two populations near the California-Oregon border are most closely related to A. tigrinum populations from Washington and Oregon and may represent native Tiger Salamander lineages.
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effective population size is strongly correlated with breeding pond size in the endangered california Tiger Salamander ambystoma californiense
Conservation Genetics, 2011Co-Authors: Jarrett R Johnson, Ian J Wang, Benjamin Johnson, Bradley H ShafferAbstract:Maintaining genetic diversity and population viability in endangered and threatened species is a primary concern of conservation biology. Genetic diversity depends on population connectivity and effective population size (Ne), both of which are often compromised in endangered taxa. While the importance of population connectivity and gene flow has been well studied, investigating effective population sizes in natural systems has received far less attention. However, Ne plays a prominent role in the maintenance of genetic diversity, the prevention of inbreeding depression, and in determining the probability of population persistence. In this study, we examined the relationship between breeding pond characteristics and Ne in the endangered California Tiger Salamander, Ambystoma californiense. We sampled 203 individuals from 10 breeding ponds on a local landscape, and used 11 polymorphic microsatellite loci to quantify genetic structure, gene flow, and effective population sizes. We also measured the areas of each pond using satellite imagery and classified ponds as either hydrologically-modified perennial ponds or naturally occurring vernal pools, the latter of which constitute the natural breeding habitat for A. californiense. We found no correlation between pond area and heterozygosity or allelic diversity, but we identified a strong positive relationship between breeding pond area and Ne, particularly for vernal pools. Our results provide some of the first empirical evidence that variation in breeding habitat can be associated with differences in Ne and suggest that a more complete understanding of the environmental features that influence Ne is an important component of conservation genetics and management.
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genotype and temperature affect locomotor performance in a Tiger Salamander hybrid swarm
Functional Ecology, 2010Co-Authors: Jarrett R Johnson, Benjamin B Johnson, Bradley H ShafferAbstract:Summary 1. Anthropogenic environmental changes have the capacity to disrupt natural population dynamics. For amphibians with complex life cycles, it is important to understand how environmental perturbations interact with variation in larval period duration to affect the timing of dispersal and the abiotic conditions under which terrestrial movements occur. 2. Widespread hybridization between California Tiger Salamanders and introduced Tiger Salamanders has created a situation in which length of larval development and metamorphic timing varies because of extrinsic variation in abiotic factors such as temperature, and also as a result of individual-specific variation in genomic admixture. 3. We examined how line-cross type (e.g. F1, F2, backcrosses, etc.), morphology and temperature interact to affect the performance of emigrating immature Salamanders. We performed endurance trials on a mechanized treadmill to simulate dispersal following metamorphosis. Our study provides insights into the interaction of environmental change and genomic composition on locomotor performance and the spread of the hybrid swarm. 4. We found that temperature had a significant positive impact on endurance, potentially making it an important factor driving dispersal distances in the wild. Line-cross type also affected performance, with F1 hybrids demonstrating the greatest movement capacity. However, we did not observe an interaction between line-cross type and temperature. 5. These results demonstrate that an increase in ambient temperature may enhance the dispersal ability of hybrid individuals and accelerate the spread of the hybrid swarm. An increase in the rate of introgression of non-native Tiger Salamander alleles into formerly pure native habitats places enhanced importance on the proper management of populations near the boundary of the hybrid swarm and emphasizes the need for management actions that prevent the intentional or accidental translocation of non-native species.
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invasive hybrid Tiger Salamander genotypes impact native amphibians
Proceedings of the National Academy of Sciences of the United States of America, 2009Co-Authors: Maureen E Ryan, Jarrett R Johnson, Benjamin M. FitzpatrickAbstract:Although the ecological consequences of species invasions are well studied, the ecological impacts of genetic introgression through hybridization are less understood. This is particularly true of the impacts of hybridization on “third party” community members not genetically involved in hybridization. We also know little about how direct interactions between hybrid and parental individuals influence fitness. Here, we examined the ecological effects of hybridization between the native, threatened California Tiger Salamander (Ambystoma californiense) and the introduced Barred Tiger Salamander (Ambystoma tigrinum mavortium). Native x introduced hybrids are widespread in California, where they are top predators in seasonal ponds. We examined the impacts of early generation hybrids (first 2 generations of parental crosses) and contemporary hybrids derived from ponds where hybrids have been under selection in the wild for 20 generations. We found that most classes of hybrid Tiger Salamander larvae dramatically reduced survival of 2 native community members, the Pacific Chorus Frog (Pseudacris regilla) and the California Newt (Taricha torosa). We also found that native A. californiense larvae were negatively impacted by the presence of hybrid larvae: Native survival and size at metamorphosis were reduced and time to metamorphosis was extended. We also observed a large influence of Mendelian dominance on size, metamorphic timing and predation rate of hybrid Tiger Salamanders. These results suggest that both genetic and ecological factors are likely to influence the dynamics of admixture, and that Tiger Salamander hybridization might constitute a threat to additional pond-breeding species of concern in the region.