听Disco clams (Ctenoides ales) are unusually colorful bivalves: They have bright-red appendages and a strip of tissue that flashes like a strobe light.
听A new study suggests听this flashy appearance could be a strategy for scaring away potential enemies such as the听peacock mantis shrimp (Odontodactylus scyllarus).
听Mantis shrimp are equally听colorful predators on coral reefs and pack an incredibly powerful punch.
Banner image: A peacock mantis shrimp and a disco clam (not to scale). Credits: Lindsey Dougherty
When Lindsey Dougherty was an undergraduate student at 抖阴旅行射 Boulder in 2011, she got the chance to visit North Sulawesi, Indonesia, on a research trip. There, in the clear tropical waters off the coast, she encountered an animal that would change the course of her career.
It was the disco clam (Ctenoides ales). And it caught Dougherty鈥檚 eye for good reason: Even in a coral reef, these tropical bivalves are explosions of color. They have bright-red appendages that dangle out of their shells and thin strips of tissue that pulse with sparkly light like a disco ball鈥攈ence their name.
In that moment, she found her research calling.
鈥淗ow do they flash?鈥欌�� Dougherty remembered thinking as she dove through the reef with scuba gear.
As a graduate student at the University of California, Berkeley, the young scientist solved that first puzzle: the clams, she discovered, .
Now back in Colorado as an instructor in the Department of Ecology and Evolutionary Biology (EBIO), Dougherty is pursuing an even trickier mystery: Why are these bivalves so colorful in the first place?
The answer could reveal new clues to how the interaction between species drives the evolution of ocean animals over millions of years.
It鈥檚 a pursuit that has expanded to include several high school students and introduced Dougherty to an animal that may be even more groovy-looking than the disco clam鈥攁 fierce predator on the same coral reefs called the peacock mantis shrimp (Odontodactylus scyllarus). And in a , she and her colleagues report that they may be finally getting close to solving that puzzle.听
鈥淚t鈥檚 a long time to spend on one organism,鈥� Dougherty said. 鈥淏ut I think it also shows how many questions there are about one seemingly simple clam.鈥�
Clams vs. mantis shrimp
To grasp Dougherty鈥檚 obsession with this shelled organism, it helps to understand the weirdness of the disco clam.
Jingchun Li is a curator of invertebrates at the 抖阴旅行射 Museum of Natural History and听advised Dougherty during her postdoctoral studies at 抖阴旅行射 Boulder. Li has spent her career exploring the diversity of the world鈥檚 bivalves鈥攁 class of aquatic mollusks that include animals like clams, scallops and mussels.
鈥淣ormally, if you think about clams like the ones in clam chowder鈥攖hey鈥檙e little white things,鈥� said Li, also an assistant EBIO professor. 鈥淏ut these clams are so colorful. One hypothesis we had is this might be some sort of warning signal to predators saying, 鈥楧on鈥檛 eat me.鈥欌��
In other words, disco clams might taste really bad, and they advertise that to the world using their bright colors. Kind of like a coral reef version of poison dart frogs in the Amazon.听
To test that idea, Li and Dougherty recruited several peacock mantis shrimp鈥攚hich, despite their names, aren鈥檛 actually shrimp鈥攁nd kept them in tanks on the 抖阴旅行射 Boulder campus.听
Like disco clams, these animals are pretty wild to look at. They come in a rainbow of colors, from blues and greens to neon orange and yellow. But don鈥檛 let their appearance fool you. Known for their powerful punches, mantis shrimp can extend their front claws at speeds of nearly 75 miles per hour鈥攆ast enough to generate an underwater shock wave that can shatter aquarium glass on impact.
The researchers, in other words, set up an ecological contest between the colorful mantis shrimp and flashing clams.听
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They offered their mantis shrimp a choice between two types of disco clam tissue. The mantis shrimp could either eat bright-red meat from the clams鈥� exterior or normal, white meat from their inner muscles.听
The mantis shrimp didn鈥檛 even hesitate. They went for the white meat.听
鈥淚t turns out they really hate the red tissue,鈥� Li said.听
That, along with chemical analyses of the two types of meat, certainly seemed to suggest that the team鈥檚 poison dart frog hypothesis had been spot on.
But another wrinkle emerged: When the group offered the mantis shrimp white meat that was dyed to look red, the invertebrates still chowed down.
As Dougherty put it, 鈥淲hether or not the red color is a warning needs more research.鈥澨�
Vinegar vs. Sriracha
It鈥檚 work that鈥檚 happening now in Li鈥檚 lab. She鈥檚 hoping to discover whether the same mantis shrimp can learn to fear the color red鈥攁 key step in determining whether that shade may act as a warning signal.听
Aiding Li in that effort are two seniors from Monarch High School in Louisville, Colorado, who are helping out in her lab through the Science Research Seminar program in the Boulder Valley School District. They鈥檙e tackling a pretty basic question: What kinds of food taste gross to a mantis shrimp?
Get to know mantis shrimp
- More than 400 species of mantis shrimp (stromatopods) scuttle around the world鈥檚 oceans, mostly in reefs in the Indo-Pacific.听
- Not all of them punch. Some mantis shrimp are 鈥渟pearers鈥� that use their claws to stab their prey.
- One study found that a peacock mantis shrimp's punch can be as fast as 75 miles per hour.
- Their eyes are also powerful, containing 16 types of cones for detecting color. Humans have just three.
- Some species of mantis shrimp mate in monogamous pairs.听
The students, Grateful Beckers and Elysse DeBarros, have spent their semester trying out different flavor combinations, which they add to chunks of supermarket shrimp meat. Once they find a suitably yucky taste, they鈥檒l mix it with meat dyed red to see if mantis shrimp will become wary of that hue over time.听听
Early results suggest that mantis shrimp can鈥檛 stand the taste of vinegar but, like many people, don鈥檛 seem to mind Sriracha sauce.
鈥淭hey鈥檙e so unique,鈥� Beckers said. 鈥淭hey鈥檙e a large, interesting shrimp with a lot of interesting adaptations.鈥�
Dougherty herself may still have a way听to go before she resolves the听mystery that first caught her attention on the Indonesian reef all those years ago. But it鈥檚 been a fascinating road of discovery for this Colorado native who first learned to scuba dive in the Pueblo Reservoir.
鈥淚 love the mountains, and I love diving. I don鈥檛 think they should ever be mutually exclusive,鈥� Dougherty said. 鈥淓veryone is connected to the ocean whether they realize it or not.鈥�
Other coauthors on the new research included Alexandria Niebergall of UC Berkeley, Corey Broeckling of Colorado State University and Kevin Schauer of the University of Wisconsin-Madison.
