Current Research Projects
Understanding and developing tools to combat the unprecedented loss of turtle habitat and its fragmentation, the illegal pet trade, and the devastating amphibian disease crisis are some of the current major research themes of the Chatfield Lab.
Wood Turtle Ecology and Management
Turtles are the most endangered vertebrate group on earth with more than 60% of species already extinct or threatened with extinction. The Wood Turtle (Glyptemys insculpta) is experiencing widespread declines throughout its range in the eastern United States and Canada, and is listed as Endangered on the IUCN's Red List. The Wood Turtle is unusual in its habitat requirements as it has distinct aquatic and terrestrial seasonal stages. Individuals largely reside in upland foraging habitat during the summer months but return to medium to large streams to overwinter. Research has also documented sensitivity of the species to relatively minor human disturbance, such as opening inhabited areas to human recreation. Habitat fragmentation and loss – such as through agriculture, road construction, and development – is thought to be the major driver of Wood Turtle declines, although collection for the pet trade is likely an important cause as well.
Research conducted through the Maine Wood Turtle Project is enhancing our understanding of Wood Turtle ecology while directly addressing important species management considerations. Current studies focus on the following areas: (1) habitat selection, home ranges, and movement patterns; (2) population demography, morphometrics, and behaviors. (3) nesting success and recruitment; (4) environmental DNA (eDNA), forensics, and combating the illegal turtle trade; and (5) the use of scent detection dogs in conservation research. Click here for more information on the Maine Wood Turtle Project.
Uncovering the Causes of Amphibian Declines
At the global level, amphibians are the most endangered of all vertebrate classes, with over a third of species threatened with extinction. Drivers of the amphibian extinction crisis are numerous – including climate change, habitat loss and fragmentation, and pollution, which are undoubtedly acting synergistically. Perhaps the single, most acute threat to amphibian populations is the spread of introduced pathogens. The amphibian chytrid fungus (Batrachochytrium dendrobatidis, Bd) and ranavirus are two pathogens that have been linked to global declines. Bd, for example, is among the deadliest pathogens the world has ever witnessed, being responsible for over 200 amphibian extinctions worldwide. Similarly, ranavirus is an emergent pathogen causing some of the largest vertebrate die-offs ever recorded.
Our research to date has extended the geographic and taxonomic distribution of Bd, expanding how this deadly pathogen may be impacting protected populations and formerly undocumented hosts. Our work has also clearly identified sublethal fitness consequences to infected frogs, namely by implicating Bd’s ability to influence jumping ability, reproduction, and survival. Understanding the impacts of Bd in the absence of mass die-offs remains an understudied area of research that greatly expands our understanding host-pathogen dynamics is this system, and may reveal ongoing threats to populations once thought to be in post-epidemic recovery.
Our current aim is to identify which drivers are influencing the health of Green Frogs (Lithobates clamitans) in Maine. We are especially interested in synergistic effects that Bd and ranavirus may have when combined with other stressors such as poor water quality and intraspecific competition. We have documented both Bd and ranavirus at most of our study populations, and have identified some key intrinsic and extrinsic differences among them. The ultimate goal of this project is to form a holistic picture of Green Frog health, which will contribute to our understanding of threats facing amphibian populations worldwide.
Other Research Projects
Previous research has focused on population-level ecology, evolution, and conservation of a variety of organisms, with an emphasis on amphibians and reptiles. Some of the larger, longer-term research projects are highlighted below.
Maine Big Night: Amphibian Migration Monitoring
Road mortality is thought to be a major cause of decline in many amphibian populations. This is especially true for migratory salamanders and frogs as they move from their upland overwintering grounds to breeding wetlands in early spring. Vernal pool-breeding species – such as Spotted Salamanders (Ambystoma maculatum), Blue-spotted Salamanders (Ambystoma laterale), and Wood Frogs (Lithobates sylvaticus) – are especially vulnerable during these times. As a community science project, Maine Big Night was created to address these declines through citizen involvement in scientific data collection, while promoting amphibian conservation. To learn more about Maine Big Night, including how to get involved, visit the website here.
Restoring the American Chestnut
The American chestnut (Castanea dentata) is a forest tree species that occurs throughout much of the eastern United States. With the introduction of the pathogenic fungus Cryphonectria parasitica that causes blight, the American chestnut was declared functionally extinct across its range in 1950 by the USDA. Sparse historical data suggests chestnuts were once a foundational species in many forests, comprising 50% of the forest canopy in some areas. Studies also suggest that, upon its demise, co-occurring plant and animal communities shifted drastically in response. It is likely, for example, that several insect species went extinct as a result of declining chestnut populations and that nutrient cycling and other ecosystem processes were severely altered.
Research projects in the lab align with the mission of The American Chestnut Foundation, that is, to introduce blight-resistant chestnut trees throughout the species’ former range. Using a backcross breeding approach common in the agricultural industry, along with modern genetic technologies, reintroduction may begin in the foreseeable future. To this end, we have integrated large-scale greenhouse plantings and field work to identify practical guidelines and best practices for returning the species to its native distribution.
Salamander Hybridization and Speciation
The salamander family Plethodontidae has been called the ideal system in which to study the evolutionary process of speciation. For no group within Plethodontidae is this more true than the Plethodon glutinosus group. Despite the long history of ecological and taxonomic studies, dating back well over a hundred years, it is only with the application of molecular tools in recent decades that we have begun to understand the complex underlying ecological and evolutionary processes giving rise to the considerable diversity in the group.
Our research in this system – which has primarily focused on natural hybridization occurring among the Red-cheeked Salamander (P. jordani), Southern Appalachian Salamander (P. teyahalee) and Southern Gray-cheeked Salamander (P. metcalfi) – aims to elucidate species boundaries using a suite of molecular and morphological markers. We have taken this work to the next level by incorporating GIS-based analyses to understand the role that past climate has had in influencing species distributions and the extent of hybridization. Furthermore, additional modeling of future climate scenarios has yielded insights into how hybrid zones and, as a consequence, species boundaries may shift under the specter of modern climate change.