Plastic Responses to shade: the Milkweed story
In our ecosystems plants face numerous challenges to sustain themselves, one being acquiring enough sunlight for survival. Adaptation is therefore key in plants to survive in suboptimal conditions. By observing specific compositions of light and how they affect a plant we can better understand the dynamics and adaptations plants undergo to obtain optimal fitness within a habitat. This summer we compared macroevolutionary and plastic responses to shade in closely related pairs of shade-tolerant and sun-loving milkweeds (genus Asclepias) with field and greenhouse experiments. Specifically, we monitored growth and other morphological changes across shading treatments intended to mimic the deep shade typical of forest sub-canopies and the neighbor-shade typical of densely vegetated fields. In the field, we grew individuals of all four milkweed species in three forest plots and three adjacent plots outside the forest edge; the latter plots consisted of both unmanipulated control plots and neighbor-removal plots in which we clipped all neighboring vegetation to ground level. In the greenhouse similar effects were achieved with three light manipulation treatments: a black filter that reduced ambient light by ~50%, a green filter that reduced ambient light by ~50% and reduced the ratio of red:far red wavelengths (to mimic the presence of neighbors), and a clear filter that did not alter light levels or wavelengths as a procedural control. In both the field and greenhouse experiments, we found that sun-loving species tended to be taller and have longer internode distances when grown in shaded conditions, consistent with previous observations of shade-avoidance responses in plants. In contrast, the shade-tolerant species showed more muted responses to varying light conditions, and in one instance grew taller in full sun compared to shade. Shade-tolerant species also exhibited increased branching, earlier flowering, and greater anthocyanin (a sun-protecting phytochemical) production in full sun habitats. Our results shed light on the differences between plastic and macroevolutionary responses to a common plant stress (shade), and future work in the lab will strive to understand how these same species modulate their defense investment in response to the same environmental heterogeneity.
My experience at the Boyce Thompson Institute gave me further insight into a plethora of skills I can implement into my career as a scientist. Understanding how research is done day in and day out of the lab had allowed me to solidify what I want to do in my own career. Offering an array of workshops and panels to attend, I was able to learn about how to apply to graduate schools as well as how to further make myself a competitive applicant when I apply. Another advantage of interning for Boyce Thompson Institute was connecting and creating a larger pool of young and old scientists alike. In the end I ultimately learned the type of research I would like to be doing in my own career and the internship has helped me navigate myself better as a young scientist.