The role of hybridization during ecological divergence of southwestern white pine (Pinus strobiformis) and limber pine (P. flexilis) |
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| Authors: | Mitra Menon Justin C Bagley Christopher J Friedline Amy V Whipple Anna W Schoettle Alejandro Leal‐Sàenz Christian Wehenkel Francisco Molina‐Freaner Lluvia Flores‐Rentería M Socorro Gonzalez‐Elizondo Richard A Sniezko Samuel A Cushman Kristen M Waring Andrew J Eckert |
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| Affiliation: | 1. Integrative Life Sciences, Virginia Commonwealth University, Richmond, VA, USA;2. Department of Biology, Virginia Commonwealth University, Richmond, VA, USA;3. Departamento de Zoologia, Universidade de Brasília, Brasília, DF, Brazil;4. Department of Biological Sciences and Merriam Powel Center for Environmental Research, Northern Arizona University, Flagstaff, AZ, USA;5. Rocky Mountain Research Station, USDA Forest Service, Ft. Collins, CO, USA;6. Programa Institucional de Doctorado en Ciencias Agropecuarias y Forestales, Universidad Juárez del Estado de Durango, Durango, Mexico;7. Instituto de Silvicultura e Industria de la Madera, Universidad Juarez del Estado de Durango, Durango, Mexico;8. Institutos de Geologia y Ecologia, Universidad Nacional Autónoma de Mexico, Estación Regional del Noroeste, Hermosillo, Sonora, Mexico;9. Department of Biology, San Diego State University, San Diego, CA, USA;10. Instituto Politecnico Nacional, CIIDIR, Durango, Durango, Mexico;11. Dorena Genetic Resource Center, USDA Forest Service, Cottage Grove, OR, USA;12. Rocky Mountain Research Station, USDA Forest Service, Flagstaff, AZ, USA;13. School of Forestry, Northern Arizona University, Flagstaff, AZ, USA |
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| Abstract: | Interactions between extrinsic factors, such as disruptive selection and intrinsic factors, such as genetic incompatibilities among loci, often contribute to the maintenance of species boundaries. The relative roles of these factors in the establishment of reproductive isolation can be examined using species pairs characterized by gene flow throughout their divergence history. We investigated the process of speciation and the maintenance of species boundaries between Pinus strobiformis and Pinus flexilis. Utilizing ecological niche modelling, demographic modelling and genomic cline analyses, we illustrated a divergence history with continuous gene flow. Our results supported an abundance of advanced generation hybrids and a lack of loci exhibiting steep transition in allele frequency across the hybrid zone. Additionally, we found evidence for climate‐associated variation in the hybrid index and niche divergence between parental species and the hybrid zone. These results are consistent with extrinsic factors, such as climate, being an important isolating mechanism. A build‐up of intrinsic incompatibilities and of coadapted gene complexes is also apparent, although these appear to be in the earliest stages of development. This supports previous work in coniferous species demonstrating the importance of extrinsic factors in facilitating speciation. Overall, our findings lend support to the hypothesis that varying strength and direction of selection pressures across the long lifespans of conifers, in combination with their other life history traits, delays the evolution of strong intrinsic incompatibilities. |
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| Keywords: | conifers ecological speciation extrinsic barriers hybrid zone introgression population genomics |
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