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Viability and invasive potential of hybrids between yellow toadflax (Linaria vulgaris) and dalmatian toadflax (Linaria dalmatica)




Turner, Marie F. S., author
Ward, Sarah, advisor
Richards, Christopher, committee member
Steingraeber, David, committee member
Beck, George, committee member
Sing, Sharlene, committee member

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Although outcomes of hybridization are highly variable, it is now considered to play an important role in evolution, speciation, and invasion. Hybridization has recently been confirmed between populations of yellow (or common) toadflax (Linaria vulgaris) and Dalmatian toadflax (Linaria dalmatica) in the Rocky Mountain region of the United States. The presence of hybrid toadflax populations on public lands is of concern, as both parents are aggressive invaders already listed as noxious weeds in multiple western states. A common garden experiment was designed to measure differences in quantitative (shoot length, biomass, flowering stems, seed capsule production) phenological (time of emergence, first flowering and seed maturity) and ecophysiological (photosynthesis, transpiration and water use efficiency (WUE)) traits for yellow and Dalmatian toadflax, F1 and BC1 hybrids, as well as natural field-collected hybrids from two sites. Genotypes were cloned to produce true replicates and the entire common garden was also replicated at two locations (Colorado and Montana); physiological data were collected only in Colorado. All genotypes grew larger and were more reproductively active in Colorado than in Montana, and hybrids outperformed parent taxa across vegetative and reproductive traits indicating heterosis. Hybrids also emerged earlier, but did not flower or set seed sooner than parent taxa, and all genotypes set seed more quickly in Montana than in Colorado indicating a strong environmental influence on this trait. There were indications that for some traits, yellow toadflax alleles conferred a relative advantage in Montana and Dalmatian toadflax alleles conferred a similar advantage in Colorado. Natural hybrids collected from Montana had higher rates of overall germination than any other class, suggesting selection for transgressive germination; they also emerged earlier in the Montana common garden suggesting possible local adaptation. Aside from these indications of GxE , general patterns of genotypic class performance remained relatively consistent across sites. Ecophysiological patterns were intermediate: yellow toadflax had the highest rates of photosynthesis and WUE; Dalmatian toadflax had the lowest rates of these two metrics and hybrid rates were distributed between them. Plants with higher rates of photosynthesis and transpiration reached phenological stages earlier than those with lower rates. For natural hybrids, the direction of the correlation between ecophysiological traits and quantitative and phenological traits changed depending on when the physiological data was collected. Overall, results indicate most toadflax hybrids may have increased fitness relative to their parents as well as multiple phenotypic attributes which may enable them to expand and invade. However, which of these specific genotypes become invasive will also depend on the direction of crossing and location at which hybridization occurs. Given the observed heterosis, transgressive trait expression, a lack of other apparent phenotypic shortcomings and the potential impacts of hybridization on current mechanisms of control, known hybridization sites, as well as other locations where yellow and Dalmatian toadflax are co-invading should be prioritized for management.


2012 Fall.
Includes bibliographical references.

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