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My research focuses on three main topics, click below to find out more.
Can we slow the evolution of drug resistance?
Drug resistant pathogens, also known as 'superbugs', threaten the success of medical procedures that we have come to take for granted. New drugs are difficult and expensive to develop. While we await the development of new drugs, can we use the principles of evolutionary ecology slow the evolution of drug resistance?
Drug resistance, like any trait, arises in an ecological context - in an environment where drugs are present, drug resistance gives microbes a competitive advantage over their susceptible relatives (which, after all, killed by drugs!). Yet in the absence of drugs, drug resistance is often associated with costs and resistant microbes lose in competition with their susceptible competitors. I found that the we can manipulate ecological interactions between parasites to prevent emergence of superbugs. I identified a nutrient that drug resistant parasites require more of than their susceptible competitors and demonstrated that it mediates competition between drug -susceptible & -resistant parasites. I then showed limiting that nutrient can prevent the emergence of drug resistance. Importantly, resource limitation does not kill resistant parasites outright, rather it makes them lose in competition with susceptible competitors. This work demonstrates that a sublethal intervention can thwart drug resistance, opening up new, much-needed avenues for drug discovery. Thus, we showed that evolutionary ecology could help to slow down the evolution of drug resistance & might even get the drying-up drug development pipeline flowing again.
Key papers: Wale et al. Proc R Soc. 2017; Wale et al. PNAS 2017
Collaborators & coauthors: The Read Group (Penn State), Troy Day (Queen's University Canada).
Drug Resistance
Anchor 2
How does the host response control an infection? How does this host response shape the course of an infection & parasite trait evlution?
Most of us imagine the immune response as an army of cells, or a predator, that hunts & kills parasites. Yet, killing an enemy population is not the only way to limit its growth; restricting access to resources can also be effective. Elucidating the defense strategies the host employs to fight off infection is essential for understanding the evolution of parasite counter-defenses. It will also help to understand 'who' (parasite vs. host). causes disease & thus 'who' to target treatment at.
Combining novel mathematical modeling approaches & experiments, we quantified the strategies the host uses to combat malaria infections. In the early stage of infection the host kills parasites but it also targets the red blood cells, in which malaria parasites live & reproduce. Specifically, the host employs a 'siege' & 'scorched earth' strategy: cutting off the supply of red blood cells (RBCs) and destroying them outright (C & D, left). In so doing, the host causing anemia, the major symptom of malaria infection. On the plus side, RBCs are so scarce that parasite reproduction reduces by almost 25% (in left B, brown area). In the second half of the infection, we found the host employs a hitherto unrecognized RBC-directed defense strategy, which we dub `juvenilization'. As the host pumps RBCs back into the bloodstream, enabling it to recover from anemia, it simultaneously increases the removal rate of RBCs (pink & blue lines respectively in A, left) . By thus increasing the turnover of cells (C, left) it prevents further parasite reproduction.
Future work will focus on i) using novel data collection methods to collect high-resolution, time series data on different in-host cell populations to better understand the dynamical interplay between host & parasite cells. This will help us to develop predictive models of infection dynamics and understand the evolutionary implications of the host defense strategies for parasite life history evolution. Ultimately, through this combination of empirical and theoretical work we hope to ask do we need new ecological theory to describe within-host infection dynamics? and, if so, to develop that theory.
Key papers: Wale et al. (2019) PNAS
Collaborators & coauthors: Aaron King (UMich), The Read Group (Penn State).
Spiro
Team Spiro
as of 2018.
Collecting Daphnia, the host of Spiro. in the field.
Color variation in Daphnia at the terminal stage of
Spirobacillus infection
What are the causes & consequences of color variation in a virulent parasite?
Spirobacillus cienkoswkii ("Spiro") is a lethal bacterial pathogen of Daphnia, a herbivorous crustacean that plays an important role in lake food webs. Despite being first described in the late 1800s, and turning its hosts a striking red color, this bacteria had gone unstudied in the laboratory...until now.
Having worked out how to grow Spiro in the laboratory & described color variation among infected hosts in the lab & field, I am developing the Daphnia-Spiro system as a model system with which to investigate how ecological forces outside of the host (e.g. predators, light) interact with in-host stresses (e.g. immunity) to shape parasite traits, using color as the trait of interest. In addition to elucidating the basic biology of the pathogen - what does Spiro's life cycle look like? How does it transmit between hosts? -I am investigating:
i. the cause & evolutionary role of the distinctive colorful symptom of infection. What molecules cause the infected host to change color? Is the host or parasite responsible for this 'blushing' & what (if any) adaptive purpose does it serve?
ii. the impact of Spiro's symptoms on predator-prey interactions & hence parasite ecology & evolution. (How) does Spiro infection alter the perception of Daphnia hosts by predators & therefore their susceptibility to predation? What is the downstream impact of altered predator-prey interactions on parasite transmission & trait evolution?
Key papers: Wale et al. (2019) Ecology
Collaborators & coauthors: Team Spiro - a team of fantastic undergraduate researchers who work with me (I am looking to establish this team at MSU). Sherman lab (UMich), Becky Fuller (U. Illinois), Sonke Johnsen (Duke U.).
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