Palo Verde is our last field station, and marks the end of our course in Costa Rica. As always, the days are packed - within a week we had finished two faculty-led projects and begun our final independent projects.
My friend and I worked on a fun little aquatic plant called Neptunia natans. It is seismonastic (the leaflets fold into themselves when touched or blown on) as well as nyctinastic (the leaflets close at night). This movement occurs remarkably quickly and is thought to be a response against predation. We decided very quickly that we would like to work on this behaviour.
In order to formulate a question we spent a few hours snooping around the marsh. We noticed that the walkway extending into the marsh seemed to create a constantly shaded habitat for the Neptunia. This meant that there were two different light habitats for the plants: one shaded (under the boardwalk) the rest were lit (exposed to the sun). Organisms adapt to their constantly changing habitats using plastic adaptations that allow them to maximize resource gathering. This phenomenon is known as phenotypic plasticity. We decided to ask whether our plants had plastic adaptations and whether these affected their willingness to take risks in terms of seismonastic behaviour.
We then set to work. Our first task was to collect plants from the marsh, which involved wading through thick vegetation and dodging the throngs of ants that crawled over the stems of the water lilies, Once we collected shade and sun plants we whisked them off to the lab, where we measured how much they closed and how long they took to open when tapped with a pencil. We also timed their nyctinastic behaviour to see whether sun plants and shade plants showed any differences in circadian rhythm.
Four days later, we had a dataset to analyze. The results of our small experiment surprised me: the two types of plants showed clear differences in circadian rhythm and response to threat despite growing less than two meters apart from each other in the same stream. The boardwalk had created plants that looked and behaved completely differently to their neighbors in the marsh.
Throughout the course we have encountered many examples of the dizzying complexity of biotic and abiotic interactions. To me, the behavioural complexity of a simple water plant highlighted this characteristic of tropical forests.