Williams, Tanisha , Isabel, Nathalie , Gros-Louis, Marie-Claude , Fisher, Kirsten , Thompson, Stacey Lee .
Discovering the next-generation of hybrids: Evidence from high-throughput SNV assays that three Populus species lack significant reproductive barriers.
By revisiting classic hybrid zones we can clarify long-term consequences of hybridization. In 1977, morphological analyses identified first generation (F1) hybrids between two native Californian species, Populus fremontii and P.trichocarpa, and one European exotic, P. nigra, commonly planted as an ornamental, and inferred an F1 block. To determine whether hybrid composition has changed over the past 30 years, eight of the nine hybrid zones, plus one newly discovered population, were sampled and genotyped using a 27 single nucleotide variant (SNV) assay, and these results were compared with leaf morphology. The diagnostic SNVs included 22 species-specific biparental nuclear markers and five chloroplast markers to identify maternal lineages. Hybrid classes were assigned using a molecular hybrid index. In addition, five leaves from each individual (n=2400) were digitally scanned to determine the accuracy of leaf morphology for hybrid identification. A series of 27 measurements were analyzed with LAMINA, a semi-automated program. Genotyping results from 468 trees showed an overall frequency of 44.6% of pure species (26.0% P. fremontii,18.1% P. trichocarpa, 0.4% P. nigra) and 52.9% hybrids/introgressants. F1 hybrids were detected in every population, while advanced-generation hybrids (F2s, backcrosses, or more complex combinations) were seen at four of the nine sites, with an overall frequency of 7.9%. In the majority of the cases (79.9%), P.fremontii was the maternal parent. Hybridization between the native species was more common (65.3% of hybrids), with a tendency to backcross towards P. fremontii. No F1 P. trichocarpa x P. nigra was found, suggesting the presence of prezygotic or postzygotic reproductive barriers. However, one trihybrid was found ((P. fremontii x P.trichocarpa) x P. nigra) at a site that lacked P. nigra 30 years ago. Preliminary analyses of leaf morphology (n=12 samples) indicate that eight characters, such as leaf area, width and length, are significantly different between the native parental species and hence useful for identification. A shift in the genotypic composition of these hybrid zones has occurred through time with increased admixture from exotics, while our detection of advanced-generation hybrids implies that there are few reproductive barriers among the species. This rampant hybridization suggests the need for long-term perspective when assessing potential impacts of gene flow on natural resources.
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1 - 83 E Orange Grove Blvd, Apt 3, Pasadena, CA, 91103, USA
2 - Canadian Forest Service
3 - California State University, Los Angeles, Biological Sciences, 5151 State University Blvd., Los Angeles, CA, 90014, USA
4 - UmeŚ University, UmeŚ Plant Science Centre
Presentation Type: Oral Paper:Papers for Sections
Location: Delaware D/Hyatt
Date: Monday, July 9th, 2012
Time: 9:00 AM