Losing Track of Time
Time flies on the Eighth Continent. The summer rains have long given way to the dry chill of a highland autumn here in Madagascar, and the days grow short as night falls abruptly at this southern latitude. Back home, the snow is replaced by a riot of life and color, and as ever, I find myself caught and confused among my many disparate worlds.
“Whoa, time passes!” says my co-worker, Malagasy PhD student Christian Ranaivoson, as he scoops up the rambunctious five-year-old son of our favorite Marovitsika cook. This boy, Andry Kely, was not much more than a baby in a blanket when we first started this work, over two years ago now. Compared to many, I am still a Madagascar neophyte, but daily, the amount of time I have spent here—and the memories amassed—feel less and less insignificant.
“In Madagascar, the days pass like months, and the months pass like days,” a friend of mine told me last week. And I can think of no truer way to describe it—always, in Madagascar, I feel as though I have been here forever simultaneously with hardly at all.
Big Meeting for Small Mammals
I’ve been all over since I wrote to you last: in Marovitsika, Ambakoana, Ankarana, Mantasoa; the east, the north, the middle; chasing fruit bats, tracking pathogens, and watching as my dataset grows into something tangible and sensible, a story knitting itself together at the seams.
I write fresh from a week in the highland resort town of Mantasoa, home to Peace Corps’ Training Center, as well as an idyllic-looking lake chock-full of weekend canoers and Schistosoma mansoni, a disease-causing parasitic worm. In Mantasoa, I attended the 12th African Small Mammal Symposium (ASMS), a one-week conference featuring biologists from all of the world discussing research relating to the natural history, phylogeny, and species interactions of African—including Malagasy—bats, shrews, and rodents. This year, maverick Madagascar biologist, Steve Goodman, and his NGO, Vahatra, hosted the remarkable conference.
It was Christian’s first science symposium ever and my first international meeting, and the whole experience was simply delectable. I found myself chattering away—in English, French, and Malagasy—happily explaining to passing colleagues what on Earth my poster full of math has to do with my fuzzy fruit bat friends. Steeped as I am now in the epidemiological arena, I found it refreshing to immerse myself once again among ecologists—people, who, as science journalist David Quammen, once wrote, “are interested in the shape of the world.”
A Natural Laboratory for Evolution
Acclaimed South African bat biologist, Corrie Schoeman, gave an inspiring plenary presentation at ASMS, in which he touched on the concept of macroecology—the theory by which scientists seek to apply general principles to understand the distribution of species and their interactions. At Princeton, we do this most often with mathematical modeling—we search for general parameters in an equation that can repeatedly map onto data from multiple ecosystems across a longitudinal trajectory. We are interested, yes, in fruit bats in Madagascar, but we are interested, too, in what they can tell us about critical community size thresholds for pathogen persistence, host-virus coevolution, and so much more.
Madagascar is arguably the perfect evolutionary laboratory for exploring macroecological principles. Floating alone in the Indian Ocean for the past 85 million years, Madagascar has witnessed four major mammalian colonization events—of tenrecs, lemurs, carnivores, and rodents—each of which led to the radiation of these clades into multiple species (sometimes hundreds!) within each clade.
Corrie touched on the extent to which these radiations could be predicted from resource availability—both in time and place. Typically, in ecology, high resource environments enable competition and specialization and beget many varieties living sympatrically (or side-by-side) in what ostensibly appears to be the same environment—though they use that environment in different ways. By contrast, low resource environments often necessitate that species remain generalists, able to exploit multiple habitats and adapt plastically (through behavioral rather than genetic means) to changes in their surroundings.
Thinking Like a Pathogen
A few months ago, my Princeton classmate, Jen Guyton, and I co-authored a short prospectus highlighting connections between general rules in macroecology and those governing pathogen dynamics, specifically in reference to African bats. Throughout the conference, these themes weighed heavily on my mind, as I sat talking science among colleagues long into the star-studded night.
“Isn’t it true,” asked Christian, “that the perfect pathogen will evolve to not harm its host?”
“Sometimes,” I answered, “but not always.” Like any organism, the perfect pathogen evolves to maximize its own reproduction—in other words, infect the greatest number of subsequent hosts possible. Sometimes this means specialization, which can necessitate keeping the host alive and well, but for many pathogens, transmission to a second host necessitates harming the original host in some way—be it a virus which causes a host to sneeze out its progeny or a worm which incites diarrhea in a host to sheds its eggs or anthrax, a bacterium which must kill its host to transmit via spores released in oozing blood.
Thus, in those cases where causing harm to the host is a quintessential part of pathogen reproduction, the pathogen will evolve to continue this harm unless some alternative transmission mechanism presents itself. For our bats with their many coevolved pathogens—mostly viruses—it appears that they have mediated this tradeoff in virulence and transmission to achieve a kind of balance; many bat viruses transmit between bats but appear not need to harm the host in doing so. But, sometimes, these viruses spill over to other species, and the balance is torn asunder.
Scaling Up From the Microbe
“It is advisable,” wrote John Steinbeck in The Log from the Sea of Cortez, “to look from the tide pool to the stars and then back to the tide pool again.”
And, in Madagascar, I find myself doing just that. I hold up a test tube full of virus particles and wonder why they spell doom for some species and not others. But then I glance out the window at the Milky Way and I know that these questions run deeper than that. “Ecology has a synonym which is ALL,” said Steinbeck, and if we think hard enough, these tiny microbes can tell us something about the shape of the universe.