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

BMC Evolutionary Biology

Research Article

Benjamin M Fitzpatrick¹  Jarrett R Johnson²  H Bradley Shaffer² 

[1] Department of Ecology and Evolutionary Biology, University of Tennessee, 37996, Knoxville, TN, USA;Department of Evolution and Ecology & Center for Population Biology, University of California, 95616, Davis, CA, USA;

关键词: Hybrid Zone;    Secondary Contact;    Admix Population;    Tiger Salamander;    Hybrid Swarm;   

DOI  :  10.1186/1471-2148-10-147

 received in 2009-09-21, accepted in 2010-05-18,  发布年份 2010

来源: Springer

【 摘 要 】

BackgroundIntroductions 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.ResultsWe 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.ConclusionsBased 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.

【 授权许可】

CC BY   
© Johnson et al; licensee BioMed Central Ltd. 2010