Wednesday, June 28, 2006

The Bees at Paramo

The first two days here at Cuerici were spent in the Paramo, the Costa Rican equivalent of our alpine regions: the highest elevation, all above treeline. There we were led by Kathleen Kay, a guest instructor on this part of our course, in a “faculty field project.” Kathleen led us to a field wherein at least 5 plant species shared a single pollinator, bombus epiphiatus, a species of bumble bee. Our challenge was to explain how these flowering plants effectively maintained population isolation: how they avoided degeneration into hybrids. We broke into groups interested in pursuing different approaches to the question; my group focused on the combination of flower and bee morphology to see if there was a prezygotic (before fertalization) mechanism at work that was based on the shape or size of the bee and the various flowers. The idea was that bees would choose flowers that “matched” their body size and shape and thus avoid cross pollination between flower species.

Here’s how we did it: braving the cold and rain of the Paramor, we caught bees pollinating each of the four flower species in butterfly nets and iced them for ten minutes or so (which effectively immobilizes them without really hurting them), allowing us to subsequently measure the area of their thorax. We then took some basic metrics on each of the four flowers. I will interject here that a chief challenge of OTS course field work is short time frame. In the matter of a few days, we must develop a research question, design our approach, execute, analyze and present. We’ll repeat this furious process many times at each site, hopefully gaining some amount of proficiency. Intermixed in this fury are non-stop lectures and field walks. The time constraint for projects is thus completely unrealistic with respect to actual (publishable) field research so what we’ll often end up with is a result that says this: our results were inconclusive.

So it was especially surprising that our bee/flower morphology matching exercise ended up with a statistically significant result. There was a clear difference in the size of the bees that were visiting 2 groups of similarly sized flowers. That said, there were a number of problems with our study including a small sample size: only 10 samples of each of the four bee pollinators. Also, our results showed differences across 2 groups of 2 species each but we couldn’t explain why the 2 species within groups weren’t cross pollinating. Another team was looking at the actual pollen on flowers under a microscope and showed that cross pollination was actually occurring between at least two species. Our overall conclusion was thus inconclusive: some yet unstudied mechanism is retaining species integrity, perhaps at the molecular level within styles or even post-zygotic (after fertilization). That’s it, write it up and on to the next project!

Sidebar: Meet some of my classmates. At the top of the post, that's Tawny who studies invasive species ecology at UC Davis. We're sharing an interest in improving our nature photography skills while on the course. My "Bee Team" follows including Javier who studies social bees in Bogota, Columbia and can lead a lovely salsa, the amazingly bright Annika, a plant specialist and Tawny again in the back.