Invasive Rodents and Biodiversity Conservation

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The Problem

Our 2013-14 IGERT student cohort assessed the potential and appropriateness of using transgenic methods to manage mouse populations on islands, where invasive mice are a threat to biodiversity. Species that are not native to their current ecosystems, but rather were introduced, can become invasive species and major pests. Many of these introductions are human-mediated, resulting from global trade, travel, attempted biocontrol, and even recreation. Mice and rats enjoy much success as invasive species, and these invasive rodents can significantly reduce native species’ diversity. This is no more evident than on oceanic islands lacking native rodents or natural predators, where invasive species can become destructive predators and cause extinction of endangered species.

Although oceanic islands account for less than 5% of the earth’s land area, they are home to 20% of bird, reptile and plant species. More dramatically, 69%, 90%, and 95% of recorded extinctions of mammals, reptiles, and birds, respectively, occur on islands. Currently, attempts to eradicate invasive rodents often involve the use of expensive pesticides that can have severe, adverse impacts on native animal species. Might transgenesis provide an alternative, and, if so, what are the ecological, social, and ethical implications of such an approach? Although our focus is on application of transgenic approaches to biodiversity conservation, many rodent species are also pests with negative impacts on crop production and human health. Our 2013-14 cohort also explored broader topics related to rodents as a major cause of post-harvest loss in agriculture and as reservoirs for disease vectors such as hantaviruses (hemorrhagic fever and hantavirus pulmonary syndrome) and Borrelia (Lyme disease).


Genetics

Among all invasive animals that negatively impact biodiversity, health, and agriculture, one reason to focus on mice and rats is that there already exists highly sophisticated tools for manipulating and engineering their genomes. These tools have been developed over the last three decades of laboratory research and should be readily transferable to wild mice and rats. Effective methods for transgenesis, gene replacement, and gene silencing are all available, and members of our team have extensive experience with these technologies. Furthermore, our team has expertise in elucidating genetic structures of populations that can be exploited to better understand the genetic makeup, distribution, and colonization histories of invasive rodent species.To complement these genetic approaches, our team also has expertise in understanding of genes involved in gametogenesis, embryo development, and sex determination that can be combined with innovative genetic approaches to eliminate or alter target rodent species with little or no impact on closely related species. Additionally, knowledge gained from laboratory investigations has revealed the existence of naturally occurring genetic elements that can also be utilized for genetic pest management such as selfish genetic elements for super-Mendelian inheritance to ‘genetically’ drive engineered genes into populations. The spread of these genetic elements in natural populations is critical to the success of this approach, and thus an integral step in this process is exploring the population genetic conditions under which such an engineered allele can reach high frequencies in natural populations; our team also has significant expertise with this type of modeling.

Some members of our IGERT cohort have worked on developing genetic technologies targeted at suppression or eradication of invasive mice. As part of developing technologies for targeting rodent species, some students students have worked toward performing controlled release trials of non-engineered mice to study gene flow through populations. Other students studied the population genetics of invasive and native species and how engineered mice might best integrate into and alter existing populations.


Ecology

To assess the feasibility of any genetic method for eradicating a rodent population, it is critical to understand the factors controlling its population dynamics. An ill-conceived control measure could actually increase the pest population. Rodent species, even invasive ones, are integral parts of many ecosystems. As part of natural food webs, they consume and control populations of other species including weedy plants and insect pests. As prey themselves, they may also support populations of native predators like raptors. Competition is common among rodent species, and it is possible that in some habitats elimination of one pest would simply result in increased numbers of another pest. These facts point to the need for a careful and nuanced application of genetic techniques, if they are to be used at all.For example, it will be critical to conduct early field tests for rodent population suppression or eradication in areas that are ecologically isolated. Isolated oceanic islands fit this mandate. As part of our IGERT, students investigated the community, and ecosystem consequences of removing invasive rodent species from island ecosystems. We examined the population dynamics of both the engineered and resident mice to better understand the feasibility of specific genetic approaches for achieving eradication. We also investigated the behavioral ecology of engineered relative to native mice, which will be a critical factor for efficient introduction of engineered mice. Finally, we are studying the ecological consequences of alternative strategies, including those that involve engineering, pesticides, and other approaches.


Society

Biodiversity conservation has garnered broad popular appeal in the United States and elsewhere. Nonetheless, the use of transgenic techniques as a method of conservation raises a series of cross-cutting questions that we explore throughout the IGERT program: What ethical concerns do these techniques raise for individuals, communities, organizations, and societies, across varied cultural and political contexts? What are the roles of technical experts, corporations, nongovernmental agencies, and advocacy groups as these technologies are considered, potentially developed and deployed, and evaluated? How can governmental policy and regulatory processes operate effectively in this new arena? How can affected parties best participate in inclusive and democratic communication to guide policy and regulation?In the case of biodiversity conservation, some issues merit particular attention. For example, conservation practices, such as protected areas, originally aimed at maintaining an ecological landscape devoid of human intervention. While this premise has received considerable re-consideration, the use of transgenics raises the issue anew. What exactly is the role of human intervention in shaping ecological outcomes? Conservation programming already has a long track record of community-based initiatives. These tend to be administered by staff trained in the social and biological sciences, forestry and fisheries, as well as agricultural extension. Transgenesis has the potential to alter this professional landscape to include laboratory scientists. How might the use of transgenesis change the field of conservation, including the training and career paths of conservation practitioners?


An Interdisciplinary Approach

The technical challenges and social concerns raised by projects aimed at release of engineering mice and rats to protect island biodiversity require a strong interdisciplinary effort. Although we are dedicated to exploring the potential for genetic engineering methods to alleviate this biodiversity crisis, it is not a foregone conclusion that these approaches are appropriate. The ethical and policy concerns presented by using genetic engineering in this system will challenge our students and faculty to dig deep into uncharted areas of social science and humanities research. We are not expecting to find broadly acceptable answers to the questions that are raised, but we believe that by bringing together perspectives of diverse individuals and diverse disciplines, we will all gain a richer understanding of these issues. We expect that our work will help inform policy makers and concerned citizens. Our team at NC State University is working closely with the non-profit organization, Island Conservation, as well as with other non-profit and government agencies that consider the use of transgenic technologies for the eradication of invasive species.


Collaborators

Students in the 2013 cohort focusing on Invasive Species and Biodiversity may affiliate with any IGERT faculty member. Here are a list of faculty that have specific interest in this topic.

  • Matthew Booker, History
  • Hannah Burrack, Entomology
  • Jim Gilliam, Biology
  • John Godwin, Biology
  • Kevin Gross, Biomath
  • Nick Haddad, Biology
  • Nora Haenn, Anthropology
  • William Kinsella, Communication
  • Alun Lloyd, Biomath
  • Lisa McGraw, Biology
  • Michael Roe, Entomology
  • Michael Schulman, Family and Consumer Sciences
  • Nadia Singh, Genetics
  • David Threadgill, Genetics

Our major effort in collaboration is with the non-profit environmental group Island Conservation. Island Conservation has focused major efforts at eradicating invasive mice from islands using conventional methods. To eradicate mice from a single island can take nine years of planning, approvals, and actions. The actions mainly rely on dropping from helicopters, baits laced with anti-coagulatants. The cost of eradicating mice from a single island has been up to $26 million dollars. These funds typically come from governments and philanthropists. Because of the nature of current eradication efforts that depend on dispersal of large quantities of rodent poisons, lawsuits are common.


Cohort Project

island-miceOur 2013 Student Cohort developed and maintains a website dedicated to exploring the intersection of invasive species, biodiversity, island conservation, and genetic engineering. In particular they examine the potential uses of genetically modified organisms (GMOs) as a tool for the field of conservation.

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