Coming up with a research question might have been the most difficult aspect of the independent project assignment for everyone. Many people chose to start in the field, finding interesting study systems such as dragonflies and ant lions. The challenge of this approach, they found, was that many of their questions of interest were “patterns, not biological hypotheses”. My approach was different, but also full of challenges. I started by reading papers, quickly came up with a relatively unexplored question that I was excited about, and then spent the next several days struggling to find an appropriate study system in Palo Verde.
I hoped to study preferences of different species of pollinators that visit the same species of flower. I knew that pollinator-mediated selection on floral traits was well documented among flower species. Hummingbird-pollinated flowers tend to be red and elongated; bee-pollinated flowers are blue or purple; bat-pollinated flowers are large and white. It’s not difficult to imagine how this works: pollinators tend to go to flowers that are easily visible within the color spectrum of the pollinator, or ones with a size and shape that facilitates nectar access for the pollinator.
What I wondered about was variation within a flower species. I knew that some flower species are pollinated by multiple types of pollinators, and that even within a species, individual flowers can vary slightly in size, shape, and hue. I wondered whether pollinators that pollinate the same flower species might tend to visit different types of flowers, thus imposing non-random mating on the flower species. I’m very interested in mating system evolution, but previously, I had only mentally categorized mating system variation based on whether or not mating occurs: sexual reproduction, parthenogenesis, self-fertilization, haplodiploidy. I was interested in genome structures and evolutionary trajectory of populations, but I hadn’t been thinking about the ecological context that these mating systems occur in. And for flowering plants, one of the most important ecological drivers of mating patterns is pollinator behavior.
I went out in to the field to look for a generalist flower species, and settled on Malvaviscus arboreus, a small shrub visited by bees, butterflies, and hummingbirds. But when I came back from the field and started reading papers about my study system, it turned out that the bees and butterflies did not pollinate the plant—they just drank the nectar. And Malvaviscus arboreus was also self-compatible, as it turned out, so any study of pollinator behavior would not accurately capture the reproductive events that were occurring.
But while I was conducting field observations on the flower visitors that I thought were polinators, I noticed a few ants crawling in and out of the flowers. Could ants be pollinators? It didn’t seem likely that they traveled enough between flowers to transfer pollen. But luckily, I wrote down my observations in my field notebook. By the time I found out that Malvaviscus arboreus wasn’t the right study system for a project on preference differences between multiple pollinators—and I had spent too much time on this study system to start over again with another—I was already wondering what the ants were doing.
I read about ants as nectar robbers and began to develop a new question: does nectar theft deter hummingbirds from visiting, since their nectar reward has been depleted? I had been interested in coevolutionary interactions—such as between mutualists, or hosts and pathogens—as a link between ecology and evolutionary biology. But it was new to me to consider how multiple ecological interactions could affect one another. In the case of nectar robbers, the antagonistic relationship between nectar robbers and the plant could affect the mutualistic relationship between the plant and its pollinator. As I read papers about complex species interactions, I learned that the ants that protect Vachellia (Acacia) trees from herbivory can scare pollinators away from the flowers. That was a case of one mutualism affecting another. I couldn’t understand the relationship between the plants and the hummingbirds without zooming out and considering the broader ecological context.
I learned a few important lessons from this independent project. I had been interested in mating system evolution for a while, but I had only been thinking about mechanisms by which genomic material is inherited from the parent or parents. I hadn’t considered how ecological factors—such as assortative mating, sexual selection, and pollinator behavior—can influence which genomes recombine and contribute to future generations. I also learned that when I study an organism or an ecological interaction in the field, there is likely more to the picture than I initially realize. Any given species may have many mutualistic, antagonistic, or competitive interactions, and these interactions can influence one another. As I discussed in my blog post for Las Cruces, I am learning the importance of trying to figure out what might be going on in an ecosystem that I do not see.
Lastly, I learned that it was okay to start out a research project by asking the wrong question—in this case, whether different species of pollinators have different floral trait preferences in a single flower species—because conducting exploratory fieldwork for the wrong question eventually led me to the right one.
Reena DeBray, Duke University