Can something the size of a grain of rice play a pivotal role in the biodiversity of our freshwater environment? According to junior Kait Esson, the answer is yes. Exploring the springs and caves of the Shenandoah Valley area in Virginia, Esson investigated Gammarus minus, a small freshwater crustacean that plays a bigger role in our ecosystem than meets the eye.
G. minus is a basic-level organism in the environment that takes up and shreds leaves, removes the nutrients, and then provides them to other organisms nearby. Because of its most basic function, G. minus plays a key role in the interactions of other organisms and ultimately in the environment’s biodiversity. Esson’s research on the crustacean consisted of two projects, both in the lab of biology professor Dan Fong, a cave ecologist and Gammarus specialist. The first project investigated its size variation in surface populations, and the second examined its blindness in cave populations.
In the springs and caves of the Shenandoah Valley, Esson took many random samples of the organisms using a D-frame dip net and looked into size variation in sexual selection. “When the Gammarus are mating, the males carry the females in what we call amplexing pairs,” she explained. Esson picked out these amplexing, or entangled, pairs and preserved them in ethyl alcohol.
“What we found was that bigger males tend to select bigger females.” Why that is so, she does not yet know but says they plan to conduct more research next season to determine why.
Esson also found that size variation in G. minus is influenced by the presence of sculpins, small fish that feed on Gammarus in the springs. Collecting random samples of the crustaceans in springs with sculpins and in springs without sculpins, she compared the two groups.
Interestingly, springs with sculpins had smaller Gammarus but more biodiversity, while springs without sculpins had bigger Gammarus but less biodiversity. “Although they are important, having too much would mean leaving less room for biodiversity,” Esson explained. “Like in many organism interactions, there needs to be a balance.”
Currently, Esson is investigating blindness in Gammarus populations in caves. Because there is no light in caves, these organisms do not need to use their sight. “What I am doing is crossing the cave populations together to see what would come out in order to map the gene that the blindness is occurring,” she said. Esson will then look into the presence of the opsin pigment in the crossed offspring to detect the presence of sight. She is still awaiting the results.
Esson’s projects were funded by the Biology Department’s Grebe Award, an award that promotes research experience for undergraduates, and by the Cave Conservancy Undergraduate Fellowship Grant. After earning her bachelor’s degree, she plans to attend graduate school for a master’s and PhD in integrative biology.
Of all the courses for her biology major and environmental studies minor, ecology is the subject she likes most “because it puts all science practices together and allows me to see how everything works mathematically . . . Even [if] it means looking at the small things to get the bigger picture.”