Hybridization And The Evolution Of Invasiveness In California Wild Radish (Raphanus Sativus)

EPA Grant Number: F5F11535
Title: Hybridization And The Evolution Of Invasiveness In California Wild Radish (Raphanus Sativus)
Investigators: Ridley, Caroline
Institution: University of California - Riverside
EPA Project Officer: Jones, Brandon
Project Period: September 1, 2005 through June 1, 2008
Project Amount: $107,564
RFA: STAR Graduate Fellowships (2005) RFA Text |  Recipients Lists
Research Category: Academic Fellowships


Description Hybridization between species and subspecies has been linked to the creation of invasive lineages in several systems. One such system is radish ( Raphanus) in California. In the mid-1800’s, two Raphanus species, namely cultivated radish ( Raphanus sativus) and jointed charlock ( Raphanus raphanistrum), were introduced to California. Since their arrival, they have freely hybridized into a coalescent complex that has invaded almost the entire geographic range of the state, spanning habitats as diverse as inland deserts and coastal dunes. While hybrid-derived radish has certainly been successful in California, it is not clear that hybridization itself is the mechanism that is directly responsible. Another non-mutually exclusive possibility is that, given California wild radish is notoriously genetically diverse and displays distinct phenotypes in different environments, rapid adaptive evolution may have played a role in the lineage’s ability to expand its range. This project will test both hybridization and rapid local adaptation as potentially complementary explanations for the evolution of invasiveness in California wild radish.

To determine whether hybridization, rapid local adaptation or both are responsible for the evolution of invasiveness in hybrid-derived California wild radish.

This project seeks to understand the mechanisms by which an introduced species may evolve invasiveness in its new habitat. Two potential mechanisms relevant to the proposed study system, California wild radish (Raphanus sativus), are hybridization and rapid local adaptation. Molecular data will be collected and field experiments will be conducted to distinguish between these two non-mutually exclusive possibilities, leading to a better basic understanding of invasive species dynamics and to new management considerations.


This project has three parts. First, I will genetically characterize the relationships between populations of hybrid-derived California wild radish and between California wild radish and both of its progenitor parents, cultivated radish (Raphanus sativus) and jointed charlock (R. raphanistrum). Second, I will measure the relative fitnesses of California wild radish, cultivated radish and jointed charlock in common garden experiments in multiple field locations and over multiple years to determine whether or not past hybridization has contributed to the relative reproductive success of California wild radish. Third, I will conduct a reciprocal transplant experiment of California wild radish populations within the state to test for local adaptation.

Expected Results:

If hybridization has played a role in the evolution of invasiveness in California wild radish, I expect it to display higher fitness than both progenitor parents across environments and across years. Anecdotal evidence suggests that this will, indeed, be the case. However, if hybridization cannot be implicated in the evolution of invasiveness in California wild radish, rapid local adaptation may be alternative mechanism which has contributed to the plant’s ability to expand its range within the state. Either outcome has important implications for both the basic understanding of the dynamics of invasive species and for their successful management.

Supplemental Keywords:

evolution of invasiveness, hybridization, adaptive evolution, Raphanus,, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Habitat, Environmental Monitoring, Ecology and Ecosystems, habitat dynamics, habitat species co-occurrence, habitat selection, landscape context, community composition, diversity of species, community genetic diversity, genetic consequences, invasive plant species, plant diversity, hybrid derived radish, ecological consequences, invasive species