Grantee Research Project Results
2003 Progress Report: Hybridization Between an Invasive Exotic and a Declining Native Amphibian: Molecular Characterization, Ecological Dynamics, and Genetic Remediation
EPA Grant Number: R828896Title: Hybridization Between an Invasive Exotic and a Declining Native Amphibian: Molecular Characterization, Ecological Dynamics, and Genetic Remediation
Investigators: Shaffer, Howard B. , Koenig, Walter D. , Voss, S. Randal , Fitzpatrick, Benjamin
Institution: University of California - Davis , University of Kentucky , University of California - Berkeley
Current Institution: University of California - Davis , University of California - Berkeley , University of Kentucky
EPA Project Officer: Packard, Benjamin H
Project Period: August 20, 2001 through August 19, 2004 (Extended to August 31, 2005)
Project Period Covered by this Report: August 20, 2002 through August 19, 2003
Project Amount: $433,708
RFA: Exploratory Research to Anticipate Future Environmental Issues (2000) RFA Text | Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , Water , Aquatic Ecosystems
Objective:
The overall objective of this research project is to understand the evolutionary and ecological consequences of hybridization between an introduced tiger salamander (Ambystoma tigrinum) and its declining native relative, the California tiger salamander (A. californiense). The specific objectives of this research project are to:- develop a set of mapped genetic markers for describing multilocus genotypes of individuals with mixed ancestry;
- use these markers to describe the geographic distribution of nonnative alleles and assess concordance/discordance in patterns of introgression among genes;
- describe life history and demographic differences among genotypes;
- and investigate the influence of habitat variation on the dynamics of admixture.
We expect our work to influence the definition of management goals for the California tiger salamander, the identification of management strategies with respect to those goals, and to contribute to a more general understanding of the differences between invasive and declining species.
Progress Summary:
We used the growing Tiger Salamander Genome Project (http://salamander.uky.edu/ Exit ) to develop 11 molecular markers in the nuclear genome that we can identify as homozygous native, homozygous nonnative, or heterozygous for each individual salamander. Together with mitochondrial DNA, these provide information on eight physically independent genomic linkage groups. In a recently submitted publication, we describe the variation in population genetic patterns in these eight linkage groups among 12 salamander populations. The populations include four natural vernal pools, four seasonal cattle ponds, and four perennial ponds. Perennial ponds tended to have higher frequencies of nonnative alleles than either type of seasonal pond. Certain nonnative traits such as facultative paedomorphosis and flexible breeding phenology could be advantageous in perennial ponds. Natural selection of these traits could create a hitchhiking effect, increasing the frequency of nonnative genetic markers in perennial ponds. Asymmetrical linkage disequilibria suggest that nonnative alleles are more likely to invade native genetic backgrounds. 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.
Material from this work has been a key component of ongoing efforts to recognize threats to the California tiger salamander, particularly the threat of genetic biopollution from invasive species hybridization.
Future Activities:
To develop a deeper understanding of the locus- and environment-dependent patterns mentioned above, we presently are collecting samples for a detailed cohort analysis. We are live-trapping adult salamanders in representative ponds. By analyzing toe clips from these animals, we intend to describe any shifts in the genetic composition of the breeding population over the breeding season and the age distribution of breeding animals (via skeletochronology). We are collecting samples of freshly laid eggs to investigate whether assortative mating or differential reproductive success causes the genotype distribution in the progeny to differ from that of the adult population. Genotype distributions in egg samples also will provide a baseline for testing the influence of natural selection on the genotype distribution in larvae. To test one potential explanation for environment-dependent fitness variation, we have initiated a study of escape performance variation in a sample of 100 hybrid larvae.
Our conversations with long-time residents of the Salinas Valley indicate that introductions of nonnative tiger salamanders happened in several places at varying times during the 1950s. In addition, animals from established hybrid populations have been moved within Central California as late as the 1970s. We are collecting samples to develop a better description of the present distribution of nonnative alleles. By comparing with a smaller set of samples taken in 1990-1991, we will use these data to test for changes in allele frequencies over time. We also will be establishing important baseline information for continued monitoring of spatio-temporal changes. Our completed work indicates that spatio-temporal patterns will vary significantly among different regions of the genome. For example, one newly developed marker tends to exhibit high nonnative allele frequencies, even in samples that appeared to be pure native-based on 2-3 other markers. In addition, our prior results suggest that perennial ponds, where nonnative genotypes have some fitness advantage, may play an important role in determining the rate and pattern of spatial spread of nonnative alleles.
Journal Articles on this Report : 3 Displayed | Download in RIS Format
Other project views: | All 13 publications | 5 publications in selected types | All 5 journal articles |
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Fitzpatrick BM, Benard MF, Fordyce JA. Morphology and escape performance of tiger salamander larvae (Ambystoma tigrinum mavortium). Journal of Experimental Zoology Part A: Comparative Experimental Biology 2003;297(2):147-159. |
R828896 (2003) |
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Fitzpatrick BM, Shaffer HB. Environment-dependent admixture dynamics in a tiger salamander hybrid zone. Evolution 2004;58(6):1282-1293. |
R828896 (2003) R828896 (2004) |
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Riley SPD, Shaffer HB, Voss SR, Fitzpatrick BM. Hybridization between a rare, native tiger salamander (Ambystoma californiense) and its introduced congener. Ecological Applications 2003;13(5):1263-1275. |
R828896 (2003) |
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Supplemental Keywords:
ecological effects, sensitive populations, genetic polymorphisms, aquatic ecosystems, restoration, conservation, ecology, genetics, surveys, California, CA, geographic area, health, biology, environmental exposure and risk, ecological indicators, ecological risk assessment, ecology and ecosystems, amphibian, animal models, biodiversity, biopollution, demographic analyses, ecological dynamics, endangered species, environmental hazard exposures, exotic genotypes, exotic species, extinction risk, futures research, genetic predisposition, genetic remediation, hybridization, interbreeding, invasive species,, RFA, Scientific Discipline, Health, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Genetics, Ecosystem/Assessment/Indicators, exploratory research environmental biology, State, Environmental Microbiology, Ecological Effects - Environmental Exposure & Risk, Susceptibility/Sensitive Population/Genetic Susceptibility, Monitoring/Modeling, Ecological Risk Assessment, genetic susceptability, Biology, Futures, Exp. Research/future, Ecological Indicators, extinction risk, ecological effects, biodiversity, endangered species, biopollution, molecular characterization, genetic predisposition, conservation, amphibian, animal models, exotic genotypes, genetic remediation, invasive species, ecological dynamics, demographic analyses, California (CA), hybridization, futures research, interbreeding, exotic speciesProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.