Research on Invasive Species
One of the main thrusts of our research is to unravel and understand why some introduced species become invasive, how they behave once they have invaded, and to develop effective management strategies for them. Links to each of our current projects in this area are seen below.
Part of the CTAHR vision is to actively help Hawaii diversify its economy, to ensure a sustainable environment, and to strengthen its communities. Our Molecular Ecology lab contributes to achieving this vision through enhancing environmental sustainability – helping to prevent invasive species from destroying natural and agricultural potential in the Islands. Increased environmental sustainability is basic to diversifying the economy and maintaining healthy communities. At the same time, we contribute to a better understanding of basic aspects of evolution and ecology, which can contribute significantly to the international scientific community. In summary – our lab looks into some of the very basic things that make invasive species succeed, and we try to contribute to making the world a better place through finding ways to use this information to reduce their impacts.
Population Genetics and Development of Sustainable Management Tactics of Papaya Ringspot Virus
The Papaya ring spot virus (PRSV) is a threat to the Hawaii papaya industry. Although the virus can be controlled by producing genetically engineered varieties that are resistant to PRSV, there are major issues concerning the use of GE papaya for export and risks that new viral strains might overcome the current resistance. PRSV is obligately spread among papaya plants through aphids. Nevertheless, there is little information on the aphid's biology, mode of reproduction, diversification, movement and ability to colonize papaya orchards. This lack of knowledge impairs our ability to develop effective and specific strategies for management of PRSV.
Biological Invasion of Pentalonia nigronervosa in Hawaiian Banana Plantings
The banana aphid: Pentalonia nigronervosa (Coquerel) afflicts significant damages to the Hawaiian banana industry by transmitting banana bunchy top virus (BBTV). The viral disease currently affects banana crops across most of the major Hawaiian Islands: Hawaii, Maui, Molokai, Oahu, and Kauai.
This project address a number of questions on the biology of the banana aphid by analyzing the diversification of aphid populations from banana plantings and alternative host plants in major Hawaiian Islands where BBTV afflicts banana production. Significantly, we are working on identifying the diversity of aphid clonal lineages that comprise banana aphid populations in Hawaii, and whether or to what extent sub-clonal lineages have been generated by asexual reproduction. Furthermore we would like to elucidate patterns of aphid invasion across the major Hawaiian Islands producing banana, and what aphid genotype(-s) colonize banana plantings compared to those colonizing alternative plant species. Our final goal is to provide a clear and detailed understanding of the way banana aphid has spread in Hawaii and the way insects move between cultivated banana fields and wild and ornamental plants. This information is fundamental for understanding the epidemiology of BBTV, and in turn to develop specific control strategies.
Ecological and Genetic Changes in a Biological Control Agent Following Introduction into New Environment
It is of great concern that after the introduction of these new beneficial organisms, an unfavorable shift (genetic or behavioral) may occur that might result in negative impacts on species in the new environment.To accomplish this, the host shift of the beneficial parasitoid wasp Diachasmimorpha tryoni from its primary host, the devastating agricultural pest Ceratitis capitata (fruit fly), onto another beneficial organism Eutreta xanthocaeta, a fly that was introduced to Hawai'i to control lantana, a serious invasive weed. Adam is using microsatellite DNA to assess to what extent the wasps on different hosts have evolved into distinct populations. He is also comparing the Hawai'i wasps to samples from their native Australia to determine how much they have changed genetically in the past 100 years since being introduced to Hawaii. Using this new association as a model system we plan to incorporate our analysis into a risk assessment that will be better able to predict the success of a biological control agent and reduce the risks associated with it. This project also addresses some very basic aspects of evolution, and stands to make a significant contribution soon.
Development of Unique Molecular Markers for Rapid Identification of Potentially Invasive Weeds in Hawaii
The ideal way to control invasive species is to prevent them from being introduced into Hawaii in the first place. Quarantine personnel are in place to inspect imported plants; however it is difficult to differentiate invasive weeds from closely related and morphologically similar desirable species. For this reason, another aspect of the lab's research on invasive species addresses development of unique molecular markers for rapid identification of potentially invasive weeds. Graduate student, Martha Gauthier is concentrating on the development of these molecular markers. The objective is to develop a screening tool that can be easily used by the Hawaii Department of Agriculture quarantine staff at Hawaii's ports, allowing them to accurately identify and intercept species that pose a potential threat.
Although CTAHR has a proven record of rapid response to invasive species outbreaks, we urgently need to broaden resident expertise in invasive species, and develop cross-disciplinary research teams to solve the problems caused by emergent invasive species. The development of molecular markers will provide a significant contribution to the capacity of CTAHR to address invasive species in collaboration with regulatory authorities. Development of this capacity will allow CTAHR researchers to identify potential problem species quickly, accurately, and cost-effectively.
Dispersal and Population Genetics of Invasive Weeds: Management Implications
Dr. Johannes Le Roux completed his PhD dissertation on various invasive weed species, he used molecular biology as a tool to investigate invasiveness of these species, by quantifying their genetic diversity and channels of dispersal. One of these species, the highly aggressive fountain grass that is notorious as one of Hawaii’s worst invaders, was the subject in a major population genetics study. This work revealed a new but hitherto overlooked mechanism promoting invasiveness. From his results, Dr. Le Roux proved that fountain grass collected from various locations around the world share a single genotype (exactly the same DNA makeup) and that this species’ ability to tolerate various environmental conditions (known as phenotypic plasticity) contributes to its success in disturbed habitats in Hawaii, California and Africa. To our knowledge this is the first time this phenomenon has been observed over such a large geographical scale. This has implications for the ornamental industry that often creates clones for nursery plants – we assume they are safe because they have low genetic diversity, but is this true considering the fountain grass phenomenon?
In collaborative work with the Hawaii Department of Agriculture Dr. Le Roux was able to identify the source population of another invasive species, fireweed (Senecio madagascariensis), and this information will be used in an ongoing biological control project to locate effective control organisms. Fireweed is of major concern to the beef ranching industry since it is toxic to livestock. He assessed patterns of dispersal for this weed in the Hawaiian Islands making use of various DNA markers.
Dr. Le Roux has also conducted genetic research on Miconia calvescens throughout the Pacific (Hawaii, Moorea, New Caledonia, Raiatea, Tahiti and Nuku Hiva). Miconia is especially problematic in Tahiti where it has taken over 65% of all vegetation and the climate similarities between Tahiti and Hawaii makes a genetic analysis a very important tool to establish the likelihood that Hawaii’s Miconia problem can reach the same devastating levels as in Tahiti. Similar genetic makeup should be alarming to management authorities. The importance of genetic diversity in invasion success for this species is another aspect we examined.
