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
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