Fitness Effects and Genetic Architecture of Plant-Herbivore Interactions in Sunflower Crop-Wild Hybrids

Authors: DECHAINE, JENNIFER - University Of Georgia; BURGER, JUTTA - University Of Georgia; CHAPMAN, MARK - University Of Georgia; Seiler, Gerald; BRUNICK, ROBERT - Oregon State University; KNAPP, STEVE - University Of Georgia; BURKE, JOHN - University Of Georgia

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/28/2009
Publication Date: 12/1/2009
Citation: Dechaine, J.M., Burger, J.C., Chapman, M.A., Seiler, G.J., Brunick, R., Knapp, S.J., Burke, J.M. 2009. Fitness Effects and Genetic Architecture of Plant-Herbivore Interactions in Sunflower Crop-Wild Hybrids. New Phytologist. 184:828-841.

Interpretive Summary: Since the dawn of agriculture, wild plant populations have experienced gene flow from their cultivated relatives. It was not until recently, however, that concerns regarding the economic, ecological, and evolutionary consequences of crop-to-wild gene flow began to mount. The dominant parameter governing the spread of crop alleles into wild populations is the selective advantage of the allele. Whereas increased fitness does not necessarily translate into increased invasiveness, fitness remains the best predictor of allelic establishment and spread. Crop-to-wild gene flow is of concern if cultivar alleles persist in wild populations and lead to range expansion or enhanced weediness in wild species. The pervasiveness of cultivar alleles is primarily determined by their selective advantage and the selective advantage of linked loci. Selection on cultivar alleles and cultivar-like traits in natural environments has been shown to vary with herbivore presence. This study investigated the effects of naturally-occurring herbivory on patterns of phenotypic selection and the genetic architecture of plant-herbivore interactions in a recombinant inbred line population of sunflower crop-wild hybrids in two non-crop sites. Phenotypic selection analyses suggested that cultivar alleles conferring increased size were generally favored, but at one site cultivar-like flowering time was favored only if three types of herbivory were included in the selection model. Quantitative trait loci (QTL) mapping identified three chromosomal regions in which the cultivar allele conferred a selective advantage for two or more co-localized traits. QTL for several measures of insect herbivory were detected, and although the cultivar allele increased herbivory damage at the majority of these QTL, they rarely co-localized with advantageous cultivar alleles for morphological traits. These results suggest that a subset of cultivar traits/alleles are advantageous in natural environments, but that herbivory may mitigate the selective advantage of some cultivar alleles.

Technical Abstract: Crop-to-wild gene flow is of concern if cultivar alleles persist in wild populations and lead to range expansion or enhanced weediness in wild species. The pervasiveness of cultivar alleles is primarily determined by their selective advantage and the selective advantage of linked loci. The fitness of crop-wild hybrids is often dependent on environmental factors, such as the presence/absence of herbivory, but less is understood about how aspects of the environment affect individual cultivar alleles. This study investigated the effects of naturally-occurring herbivory on patterns of phenotypic selection and the genetic architecture of plant-herbivore interactions in a recombinant inbred line population of sunflower crop-wild hybrids in two non-crop sites. Phenotypic selection analyses suggested that cultivar alleles conferring increased size were generally favored, but at one site cultivar-like flowering time was favored only if three types of herbivory were included in the selection model. Quantitative trait loci (QTL) mapping identified three chromosomal regions in which the cultivar allele conferred a selective advantage for two or more co-localized traits. QTL for several measures of insect herbivory were detected, and although the cultivar allele increased herbivory damage at the majority of these QTL, they rarely co-localized with advantageous cultivar alleles for morphological traits. These results suggest that a subset of cultivar traits/alleles are advantageous in natural environments, but that herbivory may mitigate the selective advantage of some cultivar alleles.