A decade of tropical entanglement

If you stay in science long enough, you’ll probably find that there’s a project in your life that seems like it just won’t go away. Something you care about, but you leave to simmer on the back burner for a while because it’s never quite your #1 priority. And sometimes, in the blink of an eye, “a while” becomes years. This is a story about one of those projects, nearly orphaned, and how we finally found it a home in Ecology and Evolution. By Lauren Carley.

It started in Costa Rica in 2011. I was a junior in college, and I’d left my friends and classmates in the U.S. to learn ecology hands-on with the Organization for Tropical Studies. My lifelong love affair with plants was already beginning back home, but so far had taken place mostly at the lab bench. I was ready for more — to be in situ, to be enveloped. I suspected I could get that in Costa Rica, and so I went. I didn’t suspect that I’d spend the next ten years of my life entangled, to various degrees, with the plants, people, and ideas that I came to know there.

Near Palo Verde Biological Station in northwest Costa Rica, non-agricultural species like swollen-thorn acacias (Vachellia collinsii; left) grow along irrigation canals that move water and agricultural runoff through rice fields (right).

As a part of the OTS course, students conceive and execute independent projects at a few field stations during the semester. One of those projects — a brief, four-day endeavor — became the first data gathered for this paper: a bioassay testing to see whether leaf extract from plants sampled upstream and downstream of irrigated rice fields differed in how palatable they were to consumers. Many species of plants produce chemicals in their leaves that are distasteful or toxic to herbivores, because losing biomass to consumption can be evolutionarily disadvantageous. However, it takes energy and nutrients to produce chemical defenses, resources that could otherwise be put towards growth or reproduction. Ultimately, whether and how much defense a plant should invest in is thought to arise from balancing the benefit of protection with the cost of defense production. The exact quantities of those costs and benefits are expected to vary depending on context, such as how many herbivores are present, and how much they eat. Applying this principle to an agroecosystem, we hypothesized that the benefits of plant defenses might decrease in sites exposed to agricultural runoff, since the amount of herbivory they face could be systematically decreased by insecticides. We wondered, could human modification of the chemical environment shift the cost-benefit balance of plant defenses on a small geographic scale around agricultural fields?

We made extracts made from plant leaves collected upstream and downstream of agriculture. By presenting droplets of the different extracts to ants and monitoring their foraging responses, we tested whether leaves from one location or another might be tastier — or, conversely, more repellant — to herbivores.

I’d done my fair share of small independent projects back home, but this one felt different. I was excited about the question I’d conceived, and even though we had just a few days to execute our projects, it seemed like we could collect relevant data to test it. Indeed, our bioassay suggested that plants downstream of agriculture might have lower chemical defenses than their upstream counterparts. When I presented these results, Susan Letcher, one of the course leaders, seemed as excited about them as I was. She suggested that we try to publish the findings after the OTS semester wrapped up. This was the first time a scientific mentor had suggested that to me, and I was equal parts ecstatic and terrified. I was also 21 years old and completely clueless about what that process entailed.

Nevertheless, I spent the summer of 2011 writing up my first manuscript draft. It was met with swift rejection; our reviewers critiqued our work for being small in scope, and descriptive rather than manipulative. The story might have ended there, but once again Susan was thinking a step ahead: what if, rather than abandoning the project, we tried to improve it with our reviewers’ criticisms in mind? I took her advice and applied for a small pilot grant through OTS; a year and a half later, I was on a plane back to Costa Rica. I spent another month in the field collecting data to complement the bioassays from the course project, expanding my sampling to a second location, and characterizing other types of plant defenses (physical defenses, like thorns, and biotic defenses, like aggressive mutualist ants). I wanted to see if the initial pattern of reduced investment downstream of agriculture was consistent across different defense types, and across different agricultural sites.

Swollen-thorn acacias (Vachellia collinsii), one of the species we studied, have multiple modes of plant defense. In addition to chemical defenses, these plants produce thorns as physical defenses and house colonies of aggressive ant “bodyguards” as biotic defenses. Here, ants can be seen feeding at specialized nectar glands on the leaves, which the plants produce to maintain the protective mutualism.

Armed with new data, we wrote up a revised manuscript draft, only to be met with rejection yet again. We had no funding to collect more data, and I was beginning my PhD studying alpine wildflowers that lived far from the tropics. Susan changed jobs and had new students and new projects to advise. Despite our initial excitement, it began to feel like maybe this project wasn’t going anywhere after all; in time, we both just had to focus on other things.

Years passed. By the time I was finishing up my PhD, I had a better understanding of how peer review and publishing worked. My writing improved, too. When taking stock of projects outside of my dissertation chapters that I wanted to finish up, the OTS project I started as an undergrad came to mind. Even after all the time that had passed and the challenges we’d faced before, I still thought this project had potential. I emailed Susan telling her I wanted to try rewriting the paper and submitting it to a different journal. She was, as usual, supportive. Perhaps I wasn’t the only one who felt like we had unfinished business.

Now it is the spring of 2021, exactly 10 years after we collected our first data around the rice fields near Palo Verde Station, and we are delighted to have found a home for this project in Ecology and Evolution. Susan and I have both long moved on in our careers, and this paper is unlikely to be the most important one that either of us produces. Nevertheless, we hope that our findings will inspire others to search for similar patterns in other agroecosystems, and to pursue some manipulative follow-up experiments that we were unable to do ourselves due to the meandering of time, priorities, and career trajectories that ensued for both of us since 2011. We are especially grateful to have found a journal that shares our conviction that descriptive studies can be valuable contributions to the scientific literature.

By reflecting on this process, we also hope to provide some inspiration to others who have struggled to publish side projects. At times, it can feel embarrassing or shameful to have backlogged data; many times, I wondered to myself, “If I had just done X at Y time, would I have succeeded in publishing this already?” Ultimately, though, I am proud that we saw this through to completion, even if it took a lot longer than either of us anticipated. In many ways, the trajectory of this project has paralleled the trajectory of my early scientific career, and even the “unsuccessful” steps along the way were valuable learning experiences; over the years, this project brought me my first manuscript draft, my first journal rejection, my first small grant proposal, and my first fully independent, solo fieldwork. These were all critical milestones in my scientific development.

Ultimately, the experience underlying it all — opening my eyes as a student to the enchanting complexity and variation of the natural world — was a turning point in my life. In the tropics, it is impossible to ignore biodiversity, because its richness is palpable, buzzing and clamoring around you in the dappled sunlight. It is awesome, and it will envelop you, just like I hoped it would. But, once you are tuned in, you realize that such complexity is everywhere, even in the less obvious places. The process of seeking, finding, and trying to understand natural variation has become the central driving force in my scientific life. It is no coincidence that the core concepts from this project — the causes and consequences of intraspecific variation in plant traits — have now become the focus of my research as an evolutionary ecologist. This project was my first exploration of these themes, and I am happy to finally share it with you. Read the full article here.

R-L: The authors (Lauren Carley and Susan Letcher) with Rukhshana Tuli and Owen McAleer at a banquet dinner concluding the Tropical Ecology OTS semester course in spring 2011.

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