Progress 07/01/02 to 06/30/07
Outputs
OUTPUTS: Overview of project: Introductions and invasions of exotic species into new ranges cause environmental, aesthetic, and economic damage, and are an emerging problem of global import. Knowing the areas of origin of invasive weeds can be useful in understanding the traits that make them invasive, and also in targeting highly specific and damaging biological control agents. Additionally, knowing levels of genetic diversity in invasive weeds can help in predicting the evolution of resistance to herbicides, and understanding whether and how they will further expand their invasive range. Hybridization can increase genetic diversity and is thought to stimulate invasion. It may also interfere with biological control, as hybrids might not be attacked as much as parent species. Another consideration with invasive weeds is whether novel chemical compounds (allelochemicals) might interfere with the growth of native plants, further facilitating invasion and potentially disrupting
restoration. We studied the invasions of two species of knapweed (Centaurea) that reduce rangeland quality in Colorado and across the western states. We conducted population genetic surveys to narrow down the areas of origin of these invasive weeds and evaluate their genetic diversity. Additionally, as these species are known to hybridize, we surveyed hybrids in the introduced U.S. range and in the native European range. We evaluated the frequency of hybridization using both morphological and molecular measures and the effects of hybridization on interactions with biological control agents. An on-going greenhouse experiment is in place to determine the fitness effects of hybridization. These two species are thought to be allelopathic, and we studied in particular the compound suggested to be responsible for the invasion of diffuse knapweed. Outputs: A key output of this final year was the dissemination of a newsletter to all the county weed agents and state and federal land managers
who assisted us in finding research sites for our survey of hybridization. This newletter led to graduate student Amy Blair presenting on the topic at the Colorado Weed Management Association meeting in December. In previous years, PI Hufbauer spoke to that same management group on these invasive weeds, and has disseminated results regarding allelopathy at the Ecological Society of America, and at several invited departmental seminars (University of Maryland, University of Idaho, Washington State University). Further dissemination to scientists is in the form of peer-reviewed publications. Thus far, 10 publications have come from this program, six on these species, and three review articles prompted by this research. Five of these have been listed on previous annual reports, and five are listed below. An additional publication is in press, another is in revision and a third is in review. Four more manuscripts focused on hybridization are being drafted and should be submitted by June
2008. If all of these pending publications are successful, 17 scientific publications will be associated with this research program.
PARTICIPANTS: Ruth Hufbauer (PI, population genetics, allelopathy, hybridization, biological control); Scott Nissen, Colorado State University (allelopathy); Amy Blair, Colorado State University (hybridization, biological control, allelopathy); Robin Marrs, Colorado State University (population genetics, allelopathy); Stephen Meyer, Colorado State University (undergraduate; hybridization, biological control); Rene Sforza, USDA ARS Montpellier, France (native range surveys, population genetics); Urs Schaffner, CABI Europe-Switzerland (native range surveys, hybridization); Patrick Haefliger, CABI Europe-Switzerland (native range surveys, hybridization). The two main partner organizations were CABI Europe-Switzerland and the USDA ARS facility in Montpellier, France. Scientists at these organizations provided many samples from the native range, and local expertise in overseas collection trips.
TARGET AUDIENCES: We have two main target audiences: land managers and scientists. Land managers in the western united states include individuals from federal, state, and county organizations. The scientists targeted come from three main groups: applied ecologists studying invasive weeds, evolutionary biologists studying hybridization and population genetics, and plant ecologists studying allelopathy
PROJECT MODIFICATIONS: Two factors delayed the completion of this research and led to a change in the personnel actively involved in the research. Co-PI Shanna Carney, who was to conduct the molecular work to document hybridization, did not receive tenure and was not able to contribute to the project. Thus, that component of the research was delayed. We have finally completed data collection, and have a manuscript nearly ready for submission. Co-PI Jorge Vivanco strongly disagreed with our rigorous approach to research on allelopathy. While his lab did not use negative controls or positive controls and reported exceedingly high production of potential and toxicity of allelopathic agents, our lab in collaboration with Dr. Scott Nissen, was not able to replicate either their methodology or their findings. Furthermore, contamination of samples of the putative alleochemical catechin with the potent herbicide 2,4-D and the well-known anti-microbial 8-hydroxyquinoline led us to question
the previous reported results from the Vivando lab on toxicity and antimicrobical effects of catechin. These findings led to former graduate student Robin Marrs withdrawing a publication from review and to other delays in our research and subsequent publications. The disagreement led to Dr. Vivanco voluntarily declining to be involved further in this project and forbidding his lab members from speaking with Hufbauer or Hufbauer lab members. Producing high quality science has been worth the inevitable delays caused by this unfortunate situation.
Impacts
Our results show that both diffuse and spotted knapweed have high genetic diversity in the U.S. and it seems likely that they were introduced several times. Pinpointing areas of origin for diffuse knapweed is difficult: the native range of the species exhibited remarkably little population structuring, which might be due to the long history of agriculture and wars in that region. Interestingly, population structuring is higher within the U.S. than within Europe, showing a leap-frog pattern of dispersal, with long-distance dispersal events facilitated by humans and equipment appearing highly likely. Spotted knapweed in the native range does have the expected genetic structuring by location. Plants in the U.S. appear to be related to those from Bulgaria, but with much genetic admixture from other locations, leading to higher diversity within U.S. populations than there exists within populations in the native range. The potential for this weed to evolve appears quite
high. These results support results from other species, and contribute to the growing recognition among scientists studying invasions that invasive species are rarely genetically depauperate, and have great potential to evolve new ecological roles not realized within their native ranges. With respect to hybridization, our results indicate that hybrids were likely introduced with diffuse knapweed, and that on-going hybridization is not happening. Biological control agents do not appear to distinguish between hybrids and diffuse knapweed, and control both equally well. These results suggest that hybrids do not pose an additional threat within this system. Managers have been relieved to hear this, and the information has lead to a change in action. Now rather than focusing control measures on hybrid plants, they can manage new patches of the weeds to prevent further spread. The scientific impact of our work on hybridization relates to evaluating its role in biological invasions. While
hybridization has been suggested to facilitate invasion, often the only data available are rates of hybridization, and little has been reported on the actual impacts of hybridization. Our data run counter to the hypothesis that hybridization stimulates invasion: we show that hybrids do not appear to pose an additional threat in this system, leading to a change in knowledge for the scientific community. It has been suggested that allelopathy is the main driver of the invasion of these two weeds. In our research on allelopathy of spotted knapweed, we found that the putative alleochemical, catechin is released in extremely small amounts and is unlikely to build up in the soils to toxic levels due to rain wetting the soil and causing rapid break-down of the compound. The scientific relevance of our research is that it calls into question a popular explanation for invasions (the novel weapons hypothesis) and specifically contradicts other reports in the published literature. Our research
highlights the critical importance of including and reporting data on positive and negative controls, which should lead to a change in scientific practice in research on allelopathy.
Publications
- Hufbauer, RA and R Sforza. 2007. Multiple introductions of two invasive Centaurea taxa into North America. Diversity and Distributions. On-line-early publication October 2007. DOI: 10.1111/j.1472-4642.2007.00424.x
- Marrs, RA, R Sforza, RA Hufbauer. 2007. When invasion increases population genetic structure: A study with Centaurea diffusa. Biological Invasions. On-line-early publication August 2007. DOI: 10.1007/s10530-007-9153-6
- Marrs, RA, RA Hufbauer, SM Bogdanowicz, R Sforza. 2006. Nine polymorphic microsatellite markers in Centaurea stoebe L. [subspecies C. s. stoebe and C. s. micranthos (S. G. Gmelin ex Gugler) Hayek] and C. diffusa Lam (Asteraceae). Molecular Ecology Notes. 6:897-899.
- Hufbauer, RA, GK Roderick. 2005. Microevolution in biological control: Mechanisms, patterns, and processes. Biological Control. 35:227-239.
- Hufbauer, RA. 2004. Population and ecological genetics of invasions: can we link neutral loci to ecology and management? Weed Technology. 18:1522-1527.
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Progress 01/01/06 to 12/31/06
Outputs
Introductions and invasions of exotic species into new ranges cause environmental, aesthetic, and economic damage, and are an emerging problem of global import. We are studying the invasions of two species of knapweed (Centaurea) that reduce rangeland quality in Colorado and across the western states. One key concern with these species is that the potential for allelopathy (negative interactions between plants mediated by plant chemistry) may make areas invaded by these plants particularly difficult to restore. Production of allelochemicals has been shown in some cases to be higher when plants are attacked by biological control agents, making one of the key means of managing these noxious weeds suspect. We surveyed soils for the putative allelochemical, catechin, from spotted knapweed (C. stoebe micranthos, previously known as C. maculosa). In most soil samples, we found only trace levels of catechin in the soil, far below amounts that would be toxic to other plants.
The highest amount of catechin we found was 1.3 ppm, which was also far below toxic levels. This higher amount of catechin was found in the driest soil sample. Knowing that catechin is unstable in water unless it is acidic (pH < 5), we tested the hypothesis that moistening the soil would break the catechin down. Indeed, when soils were spiked with catechin (as positive controls) and then moistened, the catechin was not recoverable. We therefore hypothesize that rain fall prevents the build-up of catechin in natural soils.
Impacts
Our results strongly suggests that avoiding biological control as a management approach for spotted knapweed is not necessary. Even if biological control agents do increase production of catechin, the catechin is unlikely ever to build up in the soils to toxic levels due to rain wetting the soi. Having the most affordable long-term management option available again for management of spotted knapweed is critical to the economy of invaded areas. The scientific relevance of our research is that it calls into question a popular explanation for invasions (the novel weapons hypothesis) and specifically contradicts other reports in the published literature. Our research highlights the critical importance of including and reporting data on positive and negative controls. Because other studies lack such controls, evaluating the validity of their data and possible reasons for our differing findings is difficult.
Publications
- Blair AC, SJ Nissen, GR Brunk, RA Hufbauer. 2006. Lack of evidence for an ecological role of the putative allelochemical (+/-)-catechin in spotted knapweed invasion success. Journal of Chemical Ecology. 32:2327-2331.
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Progress 01/01/05 to 12/31/05
Outputs
We are exploring the origins of diffuse and spotted knapweed, allelopathy of spotted knapweed and the consequences of hybridization for biological control. Allelochemistry: A phytotoxic compound from C. maculosa had been characterized prior to the initiation of this proposal. A key hypothesis to explain biological invasions is that invasive species have evolved during the introduction and invasion process in ways that facilitate the invasion. To test this hypothesis with respect to allelochemicals, PhD student Amy Blair started working with catechin. However, rather than being able to address our hypothesis, we found that the reported methods can not be used to measure catechin. Further, catechin breaks down rapidly in both water (< 8 hours) and soil (<24 hours). Thus, catechin is not likely to explain the invasion of spotted knapweed, and we suggest that it is not likely to inhibit revegetation efforts. Many published experiments on allelopathy use activated carbon
to absorb the allelopathic chemicals thereby enabling scientists to disentangle competition for resources from allelopathy. However, few of these studies examine the effects of activated carbon directly. We have found that through changing the soil water balance and nutrient dynamics, activated carbon alone can increase plant growth (Lau et al. in review). This suggests that in some cases, studies claiming an allelopathic affect may simply have been measuring a carbon effect. Phylogeography and population genetics: We are collecting microsatellite data from populations from the native and introduced range to determine their relationships (Marrs et al. in review). Chloroplast DNA sequence data suggesting that a cryptic invasion has occurred: it appears that we have both C. maculosa and C. vallesiaca, a closely related species, in North America, in addition to C. diffusa. Another finding from this work is that the most common haplotype found in both C. maculosa and C. diffusa is common
to the two species, supporting reports of hybridization. Hybridization: We surveyed 49 natural populations of C. diffusa and C. maculosa for hybrids, and found them in most populations of C. diffusa, and a few populations of C. maculosa. We are developing AFLP markers to distinguish hybrids genetically. Through experimental crosses, we are creating F1 hybrids. These will be used to generate backcross individuals for use in testing the resistance of hybrids to biological control agents.
Impacts
The research this year has produced some exciting results. The finding that the putative allelochemical catechin disappears quickly from soils should make restoration efforts simpler. Finding what appears to be a distinct species may have a dramatic economic impact if it spreads. Areas where the distinct samples came from are being targeted for eradication in hopes of preventing such an invasion. Scientifically, the methodology developed for working with the putative allelochemicals, and the finding that carbon alone can facilitate plant growth should facilitate future work on allelopathy. The work on hybridization eventually will lead to concrete recommendations for the management of hybrids in the field.
Publications
- Blair, AC, BG Hanson, GR Brunk, RA Marrs, P Westra, SJ Nissen, RA Hufbauer. 2005. New techniques and findings in the study of a candidate allelochemical implicated in invasion success. Ecology Letters. 8: 1039-1047.
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Progress 01/01/04 to 12/31/04
Outputs
We are exploring the origins of diffuse and spotted knapweed, and allelopathy of the two cytotypes (diploid and tetraploid) of the two species and their hybrids. Cytology: We have found only diploid diffuse knapweed in North America, but both diploid and tetraploid spotted knapweed. It was previously thought that only tetraploids of this species were present. Allelochemistry: A phytotoxic compound from C. maculosa had been characterized prior to the initiation of this proposal. This proposal supported work to determine the identity of phytotoxic chemical(s) from C. diffusa. The chemical 8-hydroxyquinoline was found in root exudates, and can be phytotoxic in sterile culture. A key hypothesis to explain biological invasions is that invasive species have evolved during the introduction and invasion process in ways that facilitate the invasion. To test this hypothesis with respect to allelochemicals, PhD student Amy Blair assayed exudates in a set of plants from the
native and introduced ranges. We find a trend towards greater allelochemical production from North American individuals, which suggests that an evolutionary shift in production may have occurred (Blair, Callaway & Hufbauer, in prep.). Blair also has developed more efficient methods for measuring allelochemical production in soil and media. Catechin can disappear from soil within 24 hours, suggesting it may not prevent revegetation efforts. Phylogeography and population genetics: We are collecting microsatellite data from populations from the native and introduced range to determine their relationships. Chloroplast DNA sequence data suggesting that a cryptic invasion has occurred: it appears that we have both C. maculosa and C. vallesiaca, a closely related species, in North America, in addition to C. diffusa. Another finding from this work is that the most common haplotype found in both C. maculosa and C. diffusa is common to the two species, supporting reports of hybridization.
Impacts
Our findings should have economic, environmental and scientific impacts. The finding that the putative allelochemical catechin disappears quickly from soils should make restoration efforts simpler. Finding what appears to be a distinct species may have a dramatic economic impact if it spreads. Areas where the distinct samples came from are being targeted for eradication in hopes of preventing such an invasion. Scientifically, the methodology developed for working with the putative allelochemicals, and the finding that carbon alone can facilitate plant growth should facilitate future scientific study of allelopathy.
Publications
- Hufbauer, RA, Marrs,RA , Jackson,AK, Sforza,R, Bais,HP, Vivanco, JM and Carney, SE . 2004. Population structure, ploidy levels and allelopathy of spotted and diffuse knapweed Pp. 121-126 in North America and Eurasia. Proceedings of the XI International Symposium on Biological Control of Weeds, JM Cullen, DT Briese, DJ Kriticos, WM Lonsdale, L Morin, JK Scott eds. CSIRO Entomology, Canberra, Australia.
- McClay, AS, Crisp,MD, Evans,HC, Heard,T., Hufbauer,RA, Qin, T-K and Shaw, R. 2004. Centres of origin: do they exist, can we identify them, does it matter? Pp. 619-620 in Proceedings of the XI International Symposium on Biological Control of Weeds, Cullen, JM, Briese, DT, Kriticos,DJ, Lonsdale,WM, Morin,L, Scott, JK eds. CSIRO Entomology, Canberra, Australia.
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Progress 01/01/03 to 12/31/03
Outputs
We are exploring the origins of diffuse and spotted knapweed, and allelopathy of the two cytotypes (diploid and tetraploid) of the two species and their hybrids. Cytology: We have found only diploid diffuse knapweed in North America, but both diploid and tetraploid spotted knapweed. It was previously thought that only tetraploids of this species were present. Allelochemistry: The plants each produce separate allelochemicals, and are toxic to each other. When they hybridyze do we get super-invaders that produce both toxins? Or are they autotoxic, or produce neither chemical and have low fitness? In an assay of a hybrid swarm, we found that the offspring of phenotypic hybrids produced little of either chemical, suggesting that most hybrids will have low fitness. Phylogeography and population genetics: We are collecting microsatellite data from populations from the native and introduced range to determine their relationships. We also have cpDNA sequence data suggesting
that at least two introductions of spotted knapweed have occurred: one from populations similar to those in the south of France, and one from further east in Europe. The U.S. populations related to the French populations seem to be restricted to California.
Impacts
It appears that the diffuse-spotted hybrids, unlike with some other systems, may not pose an additional threat to our rangelands. However, selection for production of both allelochemicals may be strong, and if individuals with that phenotype do come out of hybridization, then they are likely to increase in frequency. Colleagues with the USDA ARS are actively searching for additional biological control agents for these noxious weeds. The information we provide regarding the areas of provenance of the introductions will aid them in targeting their prospecting. Our results to date also suggest that the populations in California that have distinct genotypes of spotted knapweed should be eradicated if possible, to reduce the chances that they will outcross with other invasive populations.
Publications
- Hufbauer, RA, RA Marrs, AK Jackson, R Sforza, HP Bais, JM Vivanco and SE Carney. 2004 Population structure, ploidy levels and allelopathy of spotted and diffuse knapweed in North America and Eurasia. Proceedings of the XI International Symposium on Biological Control of Weeds, JM Cullen, Editor. Commonwealth Scientific and Industrial Research Organization (CSIRO), Melbourne, Australia.
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Progress 01/01/02 to 12/31/02
Outputs
Most weedy plants in natural ecosystems, rangelands, and parks are exotic invaders. Invasive weeds reduce forage for wild animals and livestock, can increase fuels and therefore frequency and intensity of burns, and alter ecosystem function (e.g. nutrient cycling). To manage invasive plants effectively, whether through herbicides, biological control, or altering competitive regimes, we must understand the fundamental processes involved in their colonization to and spread in novel environments. The knapweeds (Centaurea spp.) are particularly troublesome invasive plants in North America because of their negative chemical effects (allelopathy) on other plants. In addition, multiple species have invaded North America, and among those species are pairs that are known to hybridize. We are studying two of these species: diffuse and spotted knapweed (Centaurea diffusa and C. maculosa). We are using genetic tools to explore their population structure within both their native
and introduced ranges, and determine the populations of origin of both species. We are studying the frequency and importance of hybridization in the invasion of these species to North America. In addition we are exploring the ecological effects of ploidy levels (diploid vs. tetraploid) on their invasiveness, in particular, their ability to have allelopathic effects on each other and native vegetation. Our ultimate aim is to improve their control through biological, chemical, and cultural methods. Our research is of relevance to state and national land managers and ranchers faced with controlling these noxious weeds. This year we have focused on 1) gathering samples for ecological and genetic study from the native and introduced ranges, 2) determining ploidy levels of introduced populations, 3) assessing the population genetic structure of native and introduced populations. We have found that the introduced populations contain a surprising mixture of diploid and tetraploid individuals.
We are in the process of determining their relative competitiveness and allelopathic potential. There is significant population structure in both plants within North American populations, which bodes well for being able to determine their populations of origin from their native ranges.
Impacts
The magnitude of the problem posed by diffuse and spotted knapweed is vast. For example, in the state of Colorado alone, these plants infest over 146,000 acres. With a cost of control at approximately $40 per acre, managing these plants with traditional methods is simply not feasible. The expected impacts of this research are: (1) Economic. The information we gain about the ability of different species of grasses used for restoration to withstand the allelochemicals exuded by the plants should streamline and speed restoration efforts. In addition, improving our fundamental understanding of the biology of these plants will improve our ability to implement effective biological control. (2) Scientific. We will provide our international colleagues who are actively searching for more effective biological control agents with a focal area to collect prospective agents, and (3) Environmental. By fostering biological control and restoration efforts, we will facilitate the
control of these noxious invasive environmental weeds.
Publications
- Marrs, RA, RA Hufbauer, SE Carney, R Sforza. 2002. Genetic structuring and ploidy level in populations of spotted and diffuse knapweed. Proceedings, International Organization for Biological Control Symposium: The Role of Genetics and Evolution in Biological Control.
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