The Role of Hybridization in Biological Invasions: a Study with Centaurea maculosa and C. diffusa.

EPA Grant Number: F6F10356
Title: The Role of Hybridization in Biological Invasions: a Study with Centaurea maculosa and C. diffusa.
Investigators: Blair, Amy C
Institution: Colorado State University
EPA Project Officer: Hahn, Intaek
Project Period: September 1, 2006 through September 1, 2009
Project Amount: $104,250
RFA: STAR Graduate Fellowships (2006) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Ecological Indicators/Assessment/Restoration , Fellowship - Terrestrial Systems Ecology


Invasive species represent the second greatest threat to world biodiversity and cost the United States alone over $100 billion annually. A species invasion is a complex phenomenon with multiple interacting ecological and evolutionary forces. One force, hybridization, has recently received attention in the literature, but few have examined experimentally its consequences for invasion. Hybridization may stimulate invasiveness through the creation of transgressive phenotypes, i.e. extreme phenotypes that exceed those of parental lines, opening up the opportunity for selection on novel traits. Indeed, there are at least 28 examples of successful invaders that have undergone hybridization, which suggests that this evolutionary change may be important. Additionally, hybridization may alter the effectiveness of biological control agents, which can influence management decisions. With this EPA STAR grant, I will experimentally evaluate the role of interspecific hybridization in invasion, focusing on two highly problematic plant species, Centaurea maculosa and C. diffusa.

The objective of this research is to examine the impact of hybridization on the invasion of two noxious weeds. Specifically, I will survey phenotypic and molecular variation in C. maculosa and C. diffusa populations by quantifying the degree of hybridization in the western United States relative to the native range, examine if hybrids suffer more, less or equally from enemy attack, and assess if morphological measures reflect overall genetic introgression. Additionally, I will compare performance among hybrid and parental classes to experimentally evaluate whether hybridization facilitates invasion.


This past summer (2005) I surveyed 47 C. maculosa and C. diffusa populations for hybridization frequency in natural populations and took extensive morphological measures on a subset of random plants. Putative hybrids were found frequently, especially in the populations with parental diffuse-like plants. To explore whether the genotype reflects the phenotype, I will use the samples from 2005 and additional sampling supported by this fellowship in genetic analyses (microsatellites and AFLPs). Additionally, I will conduct a greenhouse common garden with experimentally created backcross 1 individuals and pure C. maculosa and C. diffusa. It will be a full factorial experiment with competition (high, low) and water (high, low). Because the two parental species inhabit differing environments, this experiment will allow me to examine if hybrids have traits that might allow them to be more successful in the extreme of dry and disturbed to wet and competitive. Finally, this research will compare the susceptibility of hybrids and their parent species to an introduced specialist biological control agent.

Expected Results:

This proposed research has the potential to make important contributions to both basic and applied science. Studying the performance and distribution of hybrids relative to parental species will add to a growing body of literature investigating the role of hybridization in adaptation and speciation. Furthermore, this research has the potential to reveal an important mechanism underlying the success of two of the most problematic rangeland weeds in the west, which can influence management approaches. For example, if hybrids are found to have higher performance or transgressive variation, then hybrid populations can be targeted for aggressive control.

Supplemental Keywords:

Interspecific hybridization, invasion, Centaurea maculosa, Centaurea diffusa, biocontrol, common garden, transgressive variation,, RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Monitoring/Modeling, Habitat, Environmental Monitoring, habitat dynamics, biodiversity, invasive plant species, biological invasion, ecological consequences

Progress and Final Reports:

  • 2007
  • 2008
  • Final