Meet Stengl-Wyer Scholar: Jeffrey Coleman

January 22, 2024 • by Nicole Elmer
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Jeff collecting stomach, skin, and leaflitter samples from a population of an inconspicuous poison-frog—Silverstoneia flotator—at a field site near Pipeline Road in Gamboa, Panama in August of 2022. PC: Luke Larter

What got you interested in studying tropical ecosystems?

When was 12, I read an article about Field Museum field biologist Steve Goodman, whose travels to the tropics enabled him to discover new species, implement conservation measures, and mentor scientists from developing countries. I fantasized about doing the same. But it was an independent research program in Costa Rica during my junior year of college that confirmed a love for the Neotropics. Here, I studied the dietary ecology of a large fruit-eating bird species (the black guan). I discovered that guans’ digestion of fruits caused seeds to break and pulp to come off, which, contrary to expectation, did not enhance seed germination capacity post-defecation. However, there was high inter-locality variation in the plant species the guans consume, potentially enabling the plants to expand their ranges. The research was initially trying, because it relied on fecal samples that took me weeks to start successfully locating. I also initially wanted to do a comparative study using another large bird species (gray-headed chachalacas), but these birds hid well, and I could not collect their feces. The project materialized despite the hurdles, however, and even earned me a research prize.

Can you explain a bit how you use the various scientific tools in your research?

Sure. In David Cannatella’s lab, I am carrying out my Stengl-Wyer research incorporating both lab and field work to ask why a poison-frog genus from Ecuador (Epipedobates) is so variable in chemical defense levels. Epipedobates, like other poison frogs (family Dendrobatidae), does not make its own toxins, instead sequestering the compounds from a diet of arthropods (mostly ants and mites). Conspicuously colored Epipedobates species are well-defended, having high skin-toxin amounts, whereas dull-colored ones have low amounts. The question is if this variation is genetic (sequestration ability), behavioral (feeding preferences), or environmental (arthropods present). To test the contribution of genetics, I feed conspicuous and dull-colored species the same amount of a toxin, and use chemical techniques to determine if the amount the two species types sequester into their skin differs. I also use genomic tools to ask whether the conspicuous species overexpress sequestration-related genes. I study if toxin ingestion is physiologically easier for conspicuous species since they have evolved to sequester more toxins, using behavioral assays to compare energy levels and whole-organism performance between the species types. In other words, my students and I jump the frogs around a swimming pool until the animals tire themselves out. Another tool is morphological identification and chemical analysis of arthropods; collaborators and I sample bugs from frog stomachs and jungle leaflitter to determine if conspicuous species choose to eat (behavior) or have available (environment) more toxic arthropods.

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