Abstract Detail

Genetics Section

Williams, Tanisha [1], Isabel, Nathalie [2], Gros-Louis, Marie-Claude [2], Fisher, Kirsten [3], Thompson, Stacey Lee [4].

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.

Broader Impacts:

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 - Umeå University, Umeå Plant Science Centre

Keywords:
Populus
SNP assay
SNV assay
hybridization
introgression
Populus trichocarpa
Populus fremontii
Populus nigra.

Presentation Type: Oral Paper:Papers for Sections
Session: 5
Location: Delaware D/Hyatt
Date: Monday, July 9th, 2012
Time: 9:00 AM
Number: 5003
Abstract ID:883