John Sparks, one of the co-curators behind the new exhibition Life at the Limits, was born to be an ichthyologist. He loved fish since boyhood, nurturing cichlids in a home aquarium, and was certified as a scuba diver when he was just 16. As curator-in-charge in the Museum’s Department of Ichthyology, Dr. Sparks has studied freshwater fishes in Madagascar, blind cavefishes, and, more recently, a variety of bioluminescent and biofluorescent fishes around the world.
They're Electric!
Sparks says he’s fascinated by electric fishes, especially South American gymnotiformes (knifefishes) and African mormyrids (elephantfishes).
In the deep, dark, turbid rivers where these species live, vision is of little use. To compensate for their poor sight, these groups have independently evolved similar systems of communication via electric signals. Gymnotiformes use electrical signals to get the attention of potential mates, while mormyrids send the signals while they hunt as a pack.
“Even as a kid I was amazed by electric fishes,” says Sparks. “But when I learned that some groups have evolved unique, species-specific systems of communication based entirely on electric wave and pulse signals, I was blown away.”
Amazing Glow
An accidental discovery on a 2011 trip to the Cayman Islands led Sparks to his recent focus on biofluorescent fishes. One photo of a coral reef showed a bright green eel none of the team had seen while in the water. It turned out to be a false moray eel (family Chlopsidae) that exhibited biofluorescence—the capacity to absorb light and then emit it in a different color.
The phenomenon was then virtually unknown in fishes, but Sparks and his team have gone on to discover that molecules in many fishes absorb ambient blue light—left over after most of the remaining visible light spectrum has been absorbed in shallow water—and re-emit it in neon green, red, and orange hues.
“Well-camouflaged fishes you would never notice otherwise under white light exhibit extremely brilliant and vivid fluorescent patterns,” says Sparks.
As for a favorite species from the exhibition? “There are so many to choose from, but I would have to say the treehopper,” says Sparks, calling out a harmless, plant-eating insect (Cyphonia clavata) with a structure on its back that resembles the venomous turtle ant (Cephalotes atratus).
Best in Show
The treehopper is among the many different species that mimic ants, which can be venomous, have a painful sting, or taste acrid—any of which might scare off a predator. This species has never been observed using the “ant” as protection, so its purpose in this case is conjecture, says Sparks.
Visitors can get a look at the uncanny resemblance between treehopper and turtle ant in the model currently on display as part Life at the Limits.
A version of this article originally appeared in our member magazine, Rotunda.