First published in the MLA Newsletter, May, 2012
If you have ever seen a colored lobster, you likely remember it. Any color or pattern other than the typical muddy green is rare, yet many combinations of primary colors are possible. Probably one of the most remarkable patterns is the half-and-half lobster shell – each side of the lobster’s shell is a different color, separated by a straight line.
“Lobsters have bilateral symmetry, meaning each side is a mirror image of the other,” explained Bob Steneck, professor at University of Maine’s School of Marine Sciences. “You have to have a sense of development to understand how these colors emerge.”
Male lobsters deposit sperm packets in a female lobster which has recently molted. The female can then store these packets for months before fertilizing them. Once the eggs are fertilized they begin to develop into zygotes. “Zygotes divide in the middle. It is at this time that mutations in color genes can occur in the side that just split,” Steneck said. The process is complex. “You start with a single-cell egg and end up with multi-cell larvae,” he said.
Lobsters with abnormal color, often called color morphs, found in the wild are usually the result of genetic mutations. However, lab-raised color morph lobsters are often the result of an altered diet. Michael Tlusty, director of research at the New England Aquarium, said they alter the color of young lobsters in the lab by eliminating astaxanthin, the pigment found in lobsters. Astaxanthin is an orange-red color in its natural state. When lobsters are fed a diet without astaxanthin, they become colorless.
“When white lobsters are changed back to a diet containing astaxanthin, their color changes depending on how fast they deposit pigment in their shell,” said Tlusty. “If the lobster turns blue, the astaxanthin is bound to proteins in the shell. If astaxanthin stays in the skin, the lobster turns red.” He added that when astaxanthin moves to the outer layer of the shell, the lobster becomes yellow or gold.
“The color of wild lobsters is not uniform. There are different amounts of pigment in the shell,” added Tlusty. “But this is where our knowledge drops off quickly. The typical color of lobsters is mottled, but we are not sure why that happens.” Scientists are not really sure how astaxanthin, which is a large molecule, gets from a lobster’s skin into its shell. “It’s like if you wore a jacket, that would be your shell,” he said. Under that jacket are layers that the pigment has to move through. “But it’s too big to diffuse through the membrane like other molecules do. There is a theory that proteins bind to astaxanthin to help move it through the membrane. But that would just make the molecule bigger, so it doesn’t really make sense,” Tlusty said.
Steneck compared the natural color of lobsters to paintings such as Jackson Pollock’s abstract art. “If you have a white canvas and blue, red, yellow, and green paint in jars, and you take your paint brush and spatter the canvas with all the colors, you end up with a muddy brown color. That’s what happens to a lobster shell,” he explained.
No matter what layer of color you see in a live lobster, you always end up with a red lobster when it is cooked. “All the chromataphores (pigment containing cells) are heat fragile and break down when they are cooked,” explained Steneck. “When this happens, you are left with the primary color in the lobster shell, an orangey-red from a carotinoide.” The carotinoide found in lobsters is also responsible for the orange color of carrots and is an antioxidant.
“We know that the carotinoide is an antioxidant and lobsters with diets lacking astaxanthin also lack the antioxidant,” said Tlusty. “But are white lobsters more likely to be stressed?” He said he would guess so, but as of now, there are no stress tests for lobsters. However, a white lobster in the wild stands out against the ocean floor, making it easier for predators to spot, which would certainly seem to lead to a stressful situation. The typical, muddy color of a lobster is a camouflage defense mechanism. But Steneck believes it’s not as important as it used to be. “Most of the big fish predators have been removed, so there is no need to blend in like there was many years ago. The ocean is a different place than it was years ago,” he said.
Color morphs remain rare however. “Blue lobsters occur about one in one million,” Steneck said. “The chance of two blue lobsters mating in the wild is one chance in a million times a million.” But, he said, if you put the word out that you want blue lobsters, lobstermen will find them. “We did a lobster survey along the coast and handled over ten thousand lobsters. We didn’t seen any color variants and it took ages to do. A modern lobster boat will get a colored lobster in just a few days because they handle so many lobsters.”Category: Science