The snap, crackle and pop of the marshes are sounds well known to residents of the South Carolina Lowcountry. But where do the sounds come from and what do they mean?
The answer to the first half of the question is simple. The sounds are made by snapping shrimp (not quite the same as the plump curls of succulence that line your shrimp cocktail: These are wee crustaceans, each as small as the tip of your little finger).
The second part of the question – what do the sounds mean – is a bit trickier. That’s where biologist Melissa Hughes, a specialist in animal communication, comes in.
“I never thought I’d go back to shrimp,” says Hughes, who wrote her Ph.D. dissertation on the subject and later moved on to studying birdsong. “But when I accepted a position at the College of Charleston in 2001, the temptation was too much to pass up. The marshes around here are chock-full of them.”
Hughes is fascinated by the signals animals use to convey information. After all, these signals directly impact their abilities to find food, avoid physical harm and achieve reproductive success.
“Animals have to make all kinds of decisions in social situations,” she says. “Should I fight you? Should I mate with you? Are you my offspring? Should I be protecting you?”
What she has found is that most of the time, animals are conveying reliable information. This begs the question of why animals are honest when they are competing for finite resources.
“Honesty is often maintained by some kind of physical limit,” she notes. A much bigger claw makes a much bigger snap, for example, and that kind of information is useful in a fight-or-flight situation. “An animal that is dishonest – for example, if the signal does not convey truthful information about its physical size – might end up in a lot of trouble when a fight actually does occur.”
In other words, you have to be able to walk the walk if you’re going to talk the talk.
The questions that can be asked about honesty and deception, signaler and receiver, physical and chemical signals and the relationship between form and function are virtually endless. And Hughes has enlisted the help of two SURF (Summer Undergraduate Research with Faculty) grant students, Kathleen Hollowell and Rachel Vickery, to help answer them.
Hollowell, a senior marine biology major, will be expanding upon the research into honesty, deception and visual signals. Vickery, a biology major with an interest in medical school, is studying the ways in which snapping shrimp use their antennae to facilitate communication.
“There are social interactions in which they will fling out their antennae,” Hughes notes. “There are also times when they will not.” It’s no small thing to fling your antennae forward in the presence of a potentially hostile intruder wielding a big snapping claw, so the potential benefit of the action should outweigh the risk. She has found that the decision – to fling or not to fling – depends upon the sex of the shrimp and their individual statuses, as resident or intruder, in the burrow.
Time spent collecting shrimp in the field and staging interactions between them in the laboratory is just the beginning of the process. There’s data to be sorted through and decisions to be made about the what, the how and the why. Hughes uses game theory, an application of mathematics, to explore the interactions between signalers and receivers that she observes.
“The best outcome for each of them may be very different,” she notes. “So, again, why are animals honest? There seems to be a selective pressure on signalers to convey useful information.”
With snapping shrimp in particular, the process is made even more interesting by the fact that other shrimp likely do not experience the snap as sound but rather as something like a pressure wave. The snapping of the claw (both the size and the shape of the claw matter) forms a small bubble that collapses with a concussive pop, known as cavitation, and this is what the receiver perceives.
Though her current research has her knee-deep in the marsh, where her main subjects of interest happily burrow and snap the days away, Hughes still looks to the skies quite frequently. “I have a field site up in Pennsylvania, near Lake Erie, that I visit each year to study sparrows,” she says.
When asked why the subject of animal communication fascinates her, Hughes offers her own honest, straightforward answer: “I just think that it’s really cool.”
For Hughes, it’s all about better understanding the natural world. When she’s not in the classroom, the field or the lab, she can usually be found hiking or kayaking. This makes living in the Lowcountry another big plus for her.
“The ACE Basin and the Francis Marion National Forest are some of my favorite places,” she says. “I like to be outside whenever I can.”
In those peaceful moments of relaxation, while wandering in the woods or dipping an oar in the water, she listens quietly as nature tells its story.
– Jason Zwiker ’97
Photos by Ben Williams