When you get sick, you become an entire world to the organisms infecting you. Parasites don’t just cause disease: they cooperate with each other, compete for resources and mates, and even form societies. My work explores how these agents of misery interact with each other as they try to survive inside one of the harshest environments on Earth: you!
About Dan
My work tests mathematical models of parasite behavior with empirical data from both laboratory experiments and field observations. I’m fascinated by what parasites do, both inside their host (within-host dynamics and immune system interactions) and out in nature (disease ecology).
As a parasitologist, I also work to identify and monitor emerging public health threats. I am currently involved in work to assess the threat to United States public health of emerging, invasive foodborne parasites.
One of the joys of working with organisms that most people never directly encounter is that I sometimes find things no one has ever seen before! Discovering and describing new species of parasites is an ongoing endeavor.
Research
Parasitic decomposers
Lots of organisms, from myiatic flies to chytrid fungi to cholera bacteria, are parasites in one phase of their life cycle and decomposers in another. But we have empirical and theoretical evidence that trade-offs exist between these two strategies: being a good parasite makes you a worse decomposer and vice versa. What keeps some organisms in the “middle ground” between these two extremes? And how much variety exists in the ways that such organisms exist… how many unique life history strategies do parasitic decomposers employ?
To answer these questions, I built mathematical models describing the various ways these deadly decomposers get by in life and the circumstances permitting them to exist as a jack-of-all-trades, rather than specializing on parasitism or decomposition. I have also “discovered” a group of long-known (but poorly studied) parasites of aquatic crustaceans (such as the rather infested Daphnia above) to tackle this question. Organisms in this group alternate between parasitism and decomposition throughout their life cycle, with some species being “better” at one part of the cycle than others. Using this natural variability in life history strategies within a phylogenetically constrained experimental group lets me begin to answer mechanistic questions of how and why organisms employ this fascinating lifestyle.
Public health & food safety
At least seven species of trematode – a type of parasitic flatworm – have invaded the Americas with their host snail, Melanoides tuberculata. Three of these worms are capable of infecting humans! I documented this invasion in Southern California and am collaborating with the Hechinger Lab at the University of California, San Diego and the National Institutes of Health to assess the public health threat posed by these new parasites. Two of these worms infect people through raw or pickled fish, including species commonly caught in lakes throughout the southwestern U.S.A.
Parasite cooperation
When we talk about social organization, we typically think of insects: worker bees, soldier ants, queens and drones. However, several kinds of parasites also have social structure! Trematode flatworms in their snail host are the latest parasite found to have caste structure. Small, aggressive worms protect the host – and thus themselves – from infection by competing parasites. My work involves developing a general mathematical theory for how these parasite societies function, both inside their host and within ecosystems. I also documented the first-known example of a truly sterile soldier caste in flatworms, as featured in PNAS and Science: in this species, soldier worms are incapable of reproducing and exist only to defend their host snail from being invaded by competing parasites.
Describing new species
Much of life remains undiscovered. This is especially true of parasites and microscopic organisms! Part of my work involves discovering and describing new species and genera of parasites. This involves both morphological characterization and genetic sequencing. My area of specialization is the group of microscopic single-celled eukaryotes called ciliates, having described a new genus and species of crab-infecting ciliate from the North American Pacific coast. I am currently involved in describing new species of parasitic worms, such as trematodes and mermithid nematodes.
