Why are some populations and species more susceptible to novel stressors than others?
My research is driven by a passion for the conservation of herpetofauna (amphibians and reptiles), fondly referred to as "herps." Other than being fascinating organisms to study, herps play critical roles in ecosystem function and are particularly vulnerable to population declines. Most of my research has centered around the hypothesis that the interactions of multiple stressors are to blame for these declines. The stressors I have focused on in my research include recent habitat fragmentation, emerging infectious disease, and climate change.
Physalaemus signifer, a tiny leaf litter frog found only in Brazil's Atlantic Forest. This species is especially sensitive to habitat fragmentation.
Emerging infectious wildlife disease contributes to biodiversity loss.
In my postdoctoral research, I am working to deepen understanding of what drives susceptibility vs. resistance/tolerance to amphibian chytridiomycosis, one of the most destructive contemporary wildlife diseases.
In my postdoctoral research, I am working to deepen understanding of what drives susceptibility vs. resistance/tolerance to amphibian chytridiomycosis, one of the most destructive contemporary wildlife diseases.
Researching the drivers of susceptibility vs. resistance to protect frogs from a deadly fungus
My first encounter with foothill yellow-legged frogs (Rana boylii)! Visiting field sites (California's Central Coast,
March 2020)
Two decades of scientific research on the amphibian-killing fungus Batrachochytrium dendrobatidis (Bd) have shed light on Bd’s distribution, biology, and how it causes the disease amphibian chytridiomycosis. However, we still don’t have a complete understanding of what makes some amphibians so susceptible to Bd (they get really sick and die) while other amphibians seem to be resistant or tolerant (they don’t get as sick and they survive).
In the western United States, Bd has been implicated in declines of a number of ranid frogs, including the endangered foothill yellow-legged frog Rana boylii in California, and the lowland leopard frog, Rana yavapaiensis in Arizona. For threatened and endangered species like these, captive breeding to produce “rescue colonies” (e.g., in zoos) is currently the main conservation/rescue measure, with the hope that captive individuals can eventually be reintroduced into the wild. However, when Bd is the biggest threat to these species, this strategy might not work: even where susceptible host species have gone completely extinct, Bd persists in the wild on other amphibians that are still out there (“reservoir hosts"). Reintroduction of captive individuals back into the wild therefore comes with the risk of future Bd outbreaks, unless we can ensure that the animals we release are Bd resistant or tolerant.
In addition, with limited resources and funding, it is difficult to actively monitor and conserve all wild populations. Gaining a better understanding of potential Bd susceptibility or resistance would allow for more effective amphibian conservation and management, e.g., protection strategies could be focused on the most susceptible wild populations. Fortunately, previous research and preliminary Bd studies suggest that there are some naturally resistant or tolerant populations of both R. boylii and R. yavapaiensis.
In my postdoctoral research I am assessing the mechanisms driving intraspecific variation in Bd susceptibility using a combination of approaches, including synthetic and collaborative spatiotemporal analyses of Bd incidence in R. boylii, and museomics in R. yavapaiensis. I have been learning a lot with my team of postdoctoral mentors, Laura Patterson of California Dept of Fish and Wildlife, Kelly Zamudio of UT Austin, and Rob Fleischer of the Smithsonian Center for Conservation Genomics; and wonderful collaborators including Dr. Ryan Peek, Dr. Sarah Kupferberg, Dr. Andrea Adams, renowned R. boylii experts, Dr. Michael Campana, ancient DNA specialist, and Dr. Anna Savage, whose extensive research on R. yavapaiensis has not only shaped our understanding of this species but also of amphibian immunity against Bd more broadly. Stay tuned for updates on these projects!
In the western United States, Bd has been implicated in declines of a number of ranid frogs, including the endangered foothill yellow-legged frog Rana boylii in California, and the lowland leopard frog, Rana yavapaiensis in Arizona. For threatened and endangered species like these, captive breeding to produce “rescue colonies” (e.g., in zoos) is currently the main conservation/rescue measure, with the hope that captive individuals can eventually be reintroduced into the wild. However, when Bd is the biggest threat to these species, this strategy might not work: even where susceptible host species have gone completely extinct, Bd persists in the wild on other amphibians that are still out there (“reservoir hosts"). Reintroduction of captive individuals back into the wild therefore comes with the risk of future Bd outbreaks, unless we can ensure that the animals we release are Bd resistant or tolerant.
In addition, with limited resources and funding, it is difficult to actively monitor and conserve all wild populations. Gaining a better understanding of potential Bd susceptibility or resistance would allow for more effective amphibian conservation and management, e.g., protection strategies could be focused on the most susceptible wild populations. Fortunately, previous research and preliminary Bd studies suggest that there are some naturally resistant or tolerant populations of both R. boylii and R. yavapaiensis.
In my postdoctoral research I am assessing the mechanisms driving intraspecific variation in Bd susceptibility using a combination of approaches, including synthetic and collaborative spatiotemporal analyses of Bd incidence in R. boylii, and museomics in R. yavapaiensis. I have been learning a lot with my team of postdoctoral mentors, Laura Patterson of California Dept of Fish and Wildlife, Kelly Zamudio of UT Austin, and Rob Fleischer of the Smithsonian Center for Conservation Genomics; and wonderful collaborators including Dr. Ryan Peek, Dr. Sarah Kupferberg, Dr. Andrea Adams, renowned R. boylii experts, Dr. Michael Campana, ancient DNA specialist, and Dr. Anna Savage, whose extensive research on R. yavapaiensis has not only shaped our understanding of this species but also of amphibian immunity against Bd more broadly. Stay tuned for updates on these projects!
Habitat fragmentation, the division and reduction of once-contiguous habitats,
is likely to drive increased wildlife susceptibility to other stressors.
I have explored this hypothesis in two systems, described below.
is likely to drive increased wildlife susceptibility to other stressors.
I have explored this hypothesis in two systems, described below.
Habitat fragmentation and disease susceptibility in tropical amphibians
Dr. Felipe Toledo, our main collaborator from Brazil. Here Felipe is accompanying my advisor Tim and me on a trip to a little explored land-bridge island off the coast of São Paulo state.
One likely explanation for variation in disease susceptibility within host species is variation in genetic diversity. Genotype could determine resistance to emerging infectious disease, especially at immunogenetic loci, genetic regions involved in the immune response. Genetic differences and/or population fragmentation (via reductions in dispersal) could also contribute to variation in the host-associated microbiome, the host's resident community of microscopic organisms (including bacteria, fungi, and other tiny eukaryotic beasties).
To examine these potential mechanisms of variation in disease susceptibility, I sampled frogs in the Atlantic Forest of Brazil in three areas that exemplify different challenges to amphibian genetic diversity and dispersal: (1) a system of small land-bridge islands, inhabited by highly inbred amphibian populations that have been isolated on the islands for 12,000-20,000 years (a model for the long-term impacts of contemporary fragmentation); (2) a system of ~100 year old habitat fragments, embedded within intensive cattle pasture that likely forms a strong barrier to dispersal for forest specialists; and (3) preserved areas that contain patches of "natural" forest and patches of cultivated agroforest (cabruca cacao) which is hypothesized to serve as less of a barrier to dispersal. In these systems, I evaluated whether fragmented frog populations exhibit effects on pathogen infection rates, genetics and immunogenetics, and microbiome diversity relative to continuous baseline host populations.
This work involved extensive collaboration with Dr. Felipe Toledo and lab members at the University of Campinas in São Paulo, Brazil.
Check out our papers from this work in Frontiers in Ecology and Evolution, Ecology and Evolution, and Immunogenetics. Please don't hesitate to reach out to me for pdfs of these publications.
To examine these potential mechanisms of variation in disease susceptibility, I sampled frogs in the Atlantic Forest of Brazil in three areas that exemplify different challenges to amphibian genetic diversity and dispersal: (1) a system of small land-bridge islands, inhabited by highly inbred amphibian populations that have been isolated on the islands for 12,000-20,000 years (a model for the long-term impacts of contemporary fragmentation); (2) a system of ~100 year old habitat fragments, embedded within intensive cattle pasture that likely forms a strong barrier to dispersal for forest specialists; and (3) preserved areas that contain patches of "natural" forest and patches of cultivated agroforest (cabruca cacao) which is hypothesized to serve as less of a barrier to dispersal. In these systems, I evaluated whether fragmented frog populations exhibit effects on pathogen infection rates, genetics and immunogenetics, and microbiome diversity relative to continuous baseline host populations.
This work involved extensive collaboration with Dr. Felipe Toledo and lab members at the University of Campinas in São Paulo, Brazil.
Check out our papers from this work in Frontiers in Ecology and Evolution, Ecology and Evolution, and Immunogenetics. Please don't hesitate to reach out to me for pdfs of these publications.
Habitat fragmentation, genetic diversity, and thermal biology in Mediterranean lizards
Here I am conducting vegetation quadrats on Naxos, the largest island in the Cyclades. Photo by Binbin Li (2011)
The Mediterranean is a global hotspot of lizard diversity, but also stands to become significantly hotter and drier with progressed climate change. For my master's thesis in the Foufopoulos Lab (University of Michigan School of Natural Resources and Environment), I evaluated the sensitivity of Greek land-bridge island lizards to future climate change. We hypothesized that small, genetically impoverished land-bridge island populations would be more susceptible to climate change through a loss in variability of thermal tolerances and performance.
However, contrary to expectations, smaller populations did not exhibit reduced variability in field body temperature, preferred/optimal temperature, and critical thermal maxima and minima. However, water loss rates appeared to vary by population, with lizards coming from hotter, drier sites able to maintain lower rates of water loss than those from cooler, wetter sites. And these differences seem to be heritable! Taken together, these findings suggest that local adaptation could make some populations (particularly those adapted to cool, wet habitats) more sensitive to warming and drying conditions.
This work was only possible through collaboration with Dr. Barry Sinervo and his lab and Dr. Panayiotis Pafilis and Dr. Efstratios Valakos and their labs at the University of Athens. Read more in our paper published in Oikos!
However, contrary to expectations, smaller populations did not exhibit reduced variability in field body temperature, preferred/optimal temperature, and critical thermal maxima and minima. However, water loss rates appeared to vary by population, with lizards coming from hotter, drier sites able to maintain lower rates of water loss than those from cooler, wetter sites. And these differences seem to be heritable! Taken together, these findings suggest that local adaptation could make some populations (particularly those adapted to cool, wet habitats) more sensitive to warming and drying conditions.
This work was only possible through collaboration with Dr. Barry Sinervo and his lab and Dr. Panayiotis Pafilis and Dr. Efstratios Valakos and their labs at the University of Athens. Read more in our paper published in Oikos!