Source: INDIANA UNIVERSITY submitted to
INTROGRESSION AND THE EVOLUTION OF WEEDY SUNFLOWERS
 
PROJECT DIRECTOR: Rieseberg, L. H. Clay, K.
 
PERFORMING ORGANIZATION
BIOLOGY
INDIANA UNIVERSITY
BLOOMINGTON,IN 47405
 
NON TECHNICAL SUMMARY: Effective weed management requires an understanding of the general mechanisms underlying plant invasiveness. The proposed research will investigate gene flow through sexual hybridization and backcrossing (i.e., introgression) as a mechanism contributing to increased invasiveness in weedy sunflowers. The common weed sunflower (Helianthus annuus) is postulated to have colonized Texas by acquiring genes from the cucumber-leaf sunflower (H. debilis), which is native to Texas. To evaluate this hypothesis, and to identify traits facilitating colonization, three experiments are proposed. First, hybrids between the two species will be planned at three localities in southeastern Texas, where they will experience natural selection for two generations. Seeds for genetic analyses will be collected after two growing seasons, and frequencies of genes from H. debilis will be monitored to determine whether certain genes enhance the fitness of H. annuus when introduced to Texas. Second, hybrid individuals will also be greenhouse-grown, and genes contributing to the morphological and physiological traits that differentiate the two species will be mapped. Third, frequencies of H. debilis genes will be assayed in natural populations of Texan H. annuus (ssp. texanus) to determine if genes enhancing fitness in experimental populations correspond to those found in natural populations of ssp. texanus. The proposed experiments will help to answer a longstanding question about the role of introgression in the origin of invasive taxa, and will also allow us to identify the particular trait(s)/genes
 
OBJECTIVES: Investigate the role of introgression as a mechanism contributing to increased invasiveness in a weedy sunflower, Helianthus annuus. Determine whether certain traits from a native, adapted species are required for H. annuus to colonize southern Texas. Identify quantitative trait loci (QTL) that control these traits. Assay natural populations of H. annuus from Texas for these QTL.
 
APPROACH: Hybrids between H. annuus and H. debilis, a species native to Texas, will be planted at three localities in southern Texas, and correlations between trait differences and fitness will be sought. Hybrid individuals will also be greenhouse-grown and quantitative trait loci (QTL) that control these differences will be genetically mapped using microsatellite markers. Frequencies of molecular markers that flank critical QTL will be then be assayed in natural populations of H. annuus from southern Texas.
 
CRIS NUMBER: 0188921 SUBFILE: CRIS
PROJECT NUMBER: INDR-2001-00706 SPONSOR AGENCY: CSREES
PROJECT TYPE: NRI COMPETITIVE GRANT PROJECT STATUS: TERMINATED MULTI-STATE PROJECT NUMBER: (N/A)
START DATE: Jul 1, 2001 TERMINATION DATE: Jun 30, 2005

GRANT PROGRAM: BIOLOGY OF WEEDY AND INVASIVE PLANTS
GRANT PROGRAM AREA: Plant Systems

CLASSIFICATION
Knowledge Area (KA)Subject (S)Science (F)Objective (G)Percent
213230011404.2100%

CLASSIFICATION HEADINGS
KA213 - Weeds Affecting Plants
S2300 - Weeds
F1140 - Weed science
G4.2 - Reduce Number and Severity of Pest and Disease Outbreaks


RESEARCH EFFORT CATEGORIES
BASIC 80%
APPLIED 20%
DEVELOPMENTAL (N/A)%

KEYWORDS: hybridization; introgression; fitness; colonization; helianthus annuus; weed control; invasive species; gene transfer; plant genetics; microsatellites; sunflowers; quantitative genetics; traits; gene loci; evolution; weeds; regional research; gene analysis; population genetics; hybrids; helianthus; native plants; genetic mapping; genetic markers

PROGRESS: Jul 1, 2001 TO Jun 30, 2005
We investigated gene flow through sexual hybridization and backcrossing (i.e., introgression) as a mechanism contributing to increased invasiveness in sunflowers. The common weed sunflower (Helianthus annuus) is postulated to have colonized Texas by acquiring genes from H. debilis, which is native to Texas. To evaluate this hypothesis, and to identify traits facilitating colonization, 5 experiments were conducted between July 2001 and June 2005. (1) Between Nov 2001 and July, 2002, a greenhouse experiment was conducted to evaluate the effects of soil and water stress on the wild introgressed taxon (ssp texanus) and pure taxa (ssp annuus & H. debilis). Under drought conditions, ssp texanus had greater fitness relative to ssp annuus. In addition, this experiment revealed a previously unknown flowering time difference among all taxa, which may be associated with drought avoidance in the wild. (2) A pilot selection experiment was conducted in Austin, TX between April and Aug. 2002. Results from this field experiment were consistent with those from the greenhouse indicating that there is a selective advantage for ssp texanus in the wild. Semi-permanent experimental field plots were established in Feb. 2003 at 2 localities in Texas where they will experience natural selection for 5 generations. These plots consist of experimental hybrids between the two pure species and an additional plot of pure ssp annuus individuals to control for local adaptation. (3) The goal of the third experiment was to identify traits influencing the invasibility of hybrid sunflowers. Over a single field season (2003), over 50 traits were measured. Fitness estimates for each plant were completed in Aug. 2005. Phenotypic selection analyses have indicated strong natural selection acting on numerous traits in the direction of H. debilis. These patterns are consistent with the hypothesis that the hybrids have been able to colonize Texas by incorporating genetic material from H. debilis. (4) Genetic material was collected from both experimental hybrid populations and a linkage map was constructed using 201 microsatellite markers. Over the next year, QTL contributing to the traits that differentiate the two species will be mapped in order to ascertain loci associated with enhanced fitness in the field. (5) Natural ssp texanus populations were surveyed for H. debilis specific molecular markers associated with morphological QTL. Three markers (out of 44) appear to be under positive selection in the wild populations. Once QTL from the experimental populations have been mapped, frequencies of these loci will also be assayed to determine if genes enhancing fitness in experimental populations correspond to those found in natural populations of ssp texanus. Finally, seeds for genetic analyses will be collected after 5 growing seasons (Fall 2008), and frequencies of genes from H. debilis will be monitored to determine whether certain genes enhance the fitness of H. annuus when introduced to Texas. These experiments will help to answer a longstanding question about the role of introgression in the origin of invasive taxa, and will also allow us to identify the particular trait(s)/genes.

IMPACT: 2001-07-01 TO 2005-06-30 Understanding general mechanisms of plant invasiveness is needed for a better predictive theory and more effective management of plant populations. The proposed research will investigate introgressive hybridization as a mechanism leading to increased geographical range and ecological amplitude of weedy sunflowers. The proposed experiments will help to answer a longstanding question about the role of introgression in the origin of invasive taxa, and will also allow us to identify the particular trait(s)/QTL that enable invasions by weedy sunflowers.

PUBLICATION INFORMATION: 2001-07-01 TO 2005-06-30
No publications reported this period

PROJECT CONTACT INFORMATION
NAME: RIESEBERG, L. H.
PHONE: 812-855-7614
FAX: 812-855-6705