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Retention of low-fitness genotypes over six decades of admixture between native and introduced tiger salamanders

BACKGROUND: Introductions of non-native tiger salamanders into the range of California tiger salamanders have provided a rare opportunity to study the early stages of secondary contact and hybridization. We produced first- and second-generation hybrid salamanders in the lab and measured viability am...

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Autores principales: Johnson, Jarrett R, Fitzpatrick, Benjamin M, Shaffer, H Bradley
Formato: Texto
Lenguaje:English
Publicado: BioMed Central 2010
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2889957/
https://www.ncbi.nlm.nih.gov/pubmed/20482794
http://dx.doi.org/10.1186/1471-2148-10-147
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author Johnson, Jarrett R
Fitzpatrick, Benjamin M
Shaffer, H Bradley
author_facet Johnson, Jarrett R
Fitzpatrick, Benjamin M
Shaffer, H Bradley
author_sort Johnson, Jarrett R
collection PubMed
description BACKGROUND: Introductions of non-native tiger salamanders into the range of California tiger salamanders have provided a rare opportunity to study the early stages of secondary contact and hybridization. We produced first- and second-generation hybrid salamanders in the lab and measured viability among these early-generation hybrid crosses to determine the strength of the initial barrier to gene exchange. We also created contemporary-generation hybrids in the lab and evaluated the extent to which selection has affected fitness over approximately 20 generations of admixture. Additionally, we examined the inheritance of quantitative phenotypic variation to better understand how evolution has progressed since secondary contact. RESULTS: We found significant variation in the fitness of hybrids, with non-native backcrosses experiencing the highest survival and F2 hybrids the lowest. Contemporary-generation hybrids had similar survival to that of F2 families, contrary to our expectation that 20 generations of selection in the wild would eliminate unfit genotypes and increase survival. Hybrid survival clearly exhibited effects of epistasis, whereas size and growth showed mostly additive genetic variance, and time to metamorphosis showed substantial dominance. CONCLUSIONS: Based on first- and second- generation cross types, our results suggest that the initial barrier to gene flow between these two species was relatively weak, and subsequent evolution has been generally slow. The persistence of low-viability recombinant hybrid genotypes in some contemporary populations illustrates that while hybridization can provide a potent source of genetic variation upon which natural selection can act, the sorting of fit from unfit gene combinations might be inefficient in highly admixed populations. Spatio-temporal fluctuation in selection or complex genetics has perhaps stalled adaptive evolution in this system despite selection for admixed genotypes within generations.
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spelling pubmed-28899572010-06-23 Retention of low-fitness genotypes over six decades of admixture between native and introduced tiger salamanders Johnson, Jarrett R Fitzpatrick, Benjamin M Shaffer, H Bradley BMC Evol Biol Research article BACKGROUND: Introductions of non-native tiger salamanders into the range of California tiger salamanders have provided a rare opportunity to study the early stages of secondary contact and hybridization. We produced first- and second-generation hybrid salamanders in the lab and measured viability among these early-generation hybrid crosses to determine the strength of the initial barrier to gene exchange. We also created contemporary-generation hybrids in the lab and evaluated the extent to which selection has affected fitness over approximately 20 generations of admixture. Additionally, we examined the inheritance of quantitative phenotypic variation to better understand how evolution has progressed since secondary contact. RESULTS: We found significant variation in the fitness of hybrids, with non-native backcrosses experiencing the highest survival and F2 hybrids the lowest. Contemporary-generation hybrids had similar survival to that of F2 families, contrary to our expectation that 20 generations of selection in the wild would eliminate unfit genotypes and increase survival. Hybrid survival clearly exhibited effects of epistasis, whereas size and growth showed mostly additive genetic variance, and time to metamorphosis showed substantial dominance. CONCLUSIONS: Based on first- and second- generation cross types, our results suggest that the initial barrier to gene flow between these two species was relatively weak, and subsequent evolution has been generally slow. The persistence of low-viability recombinant hybrid genotypes in some contemporary populations illustrates that while hybridization can provide a potent source of genetic variation upon which natural selection can act, the sorting of fit from unfit gene combinations might be inefficient in highly admixed populations. Spatio-temporal fluctuation in selection or complex genetics has perhaps stalled adaptive evolution in this system despite selection for admixed genotypes within generations. BioMed Central 2010-05-18 /pmc/articles/PMC2889957/ /pubmed/20482794 http://dx.doi.org/10.1186/1471-2148-10-147 Text en Copyright ©2010 Johnson et al; licensee BioMed Central Ltd. http://creativecommons.org/licenses/by/2.0 This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
spellingShingle Research article
Johnson, Jarrett R
Fitzpatrick, Benjamin M
Shaffer, H Bradley
Retention of low-fitness genotypes over six decades of admixture between native and introduced tiger salamanders
title Retention of low-fitness genotypes over six decades of admixture between native and introduced tiger salamanders
title_full Retention of low-fitness genotypes over six decades of admixture between native and introduced tiger salamanders
title_fullStr Retention of low-fitness genotypes over six decades of admixture between native and introduced tiger salamanders
title_full_unstemmed Retention of low-fitness genotypes over six decades of admixture between native and introduced tiger salamanders
title_short Retention of low-fitness genotypes over six decades of admixture between native and introduced tiger salamanders
title_sort retention of low-fitness genotypes over six decades of admixture between native and introduced tiger salamanders
topic Research article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2889957/
https://www.ncbi.nlm.nih.gov/pubmed/20482794
http://dx.doi.org/10.1186/1471-2148-10-147
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