What Do Squid Hear?
The ocean is a noisy place. Although we don't hear much when we stick our heads underwater, the right instruments can reveal a symphony of sound. The noisemakers range from the low-frequency bass tones of a fish mating ritual to the roar of a motorboat. The study of how underwater animals hear is a growing topic in marine science, especially with regards to naval sonar and whales. This summer at the MBL, zoologist T. Aran Mooney will be the first scientist to look at cephalopod hearing, using the squid, Loligo pealeii, as a model. To learn how sensitive the translucent animals are to noise, he is monitoring squid brain waves as they respond to various sounds, specifically the echolocation clicks of its main predators: the sperm whale, beaked whale, and dolphin. In addition to the brain wave experiments, he also plans to condition squid to avoid certain sounds.
"Sound is one of the most important cues for marine animals. Light doesn't travel well through the ocean. Sound does much better," says Mooney, who is a Grass Fellow at the MBL and beginning postdoctoral research at Woods Hole Oceanographic Institution this fall. He predicts that squid probably hear very low-frequency sounds, which means they pick up on fish tones and boat traffic. A better understanding of what these animals hear could reveal how human-induced noise affects cephalopods and how their auditory system evolved separately from that of fish.
Sharing the Grass Lab with Mooney are two other fellows investigating animal behavior. Keram Pfeiffer of the University of Marburg in Germany is training bees to respond to polarized light and Gwyneth M. Card of Caltech is recording how flies decide to initiate flight. They are among nine people to receive 2008 fellowships from the Grass Foundation to conduct summer research in neurobiology at the MBL.
The squid -- the translucent animal in the net -- is surrounded by a soundproof booth while T. Aran Mooney measures its brain waves.
(Photo Credit: Joseph Caputo)
Lost an Appendage? Grow Another
Cut off one finger from a salamander and one will grow back. Cut off two and two will grow back. It sounds logical, but how the salamander always regenerates the right number of fingers is still a biological mystery.
The salamander isn't the only animal with this regenerative ability. Take the sea squirt, Ciona intestinalis, a cylindrical marine creature about the size of a small cucumber that regularly loses its siphons, or feeding tubes, to hungry predators. At the base of each siphon are eight photoreceptors, cells used to detect light. Whenever the sea squirt experiences a violent loss at the siphon base, the number of photoreceptors that grow back is always eight.
Understanding the molecular pathway responsible for this phenomenon is a research objective for MBL investigator William R. Jeffery, a former director of the MBL Embryology course and professor of biology at the University of Maryland. "The question I'm interested in is not only what mechanisms are involved in regeneration, but how exact [photoreceptor] patterns are formed," Jeffery says.
Following up on previous research, in which he experimentally induced variations in the number of photoreceptors that regenerate by manipulating the siphon's diameter, this summer Jeffery will test the role of the Notch signaling pathway, a highly conserved molecular cascade that determines how an embryo forms. If Jeffery is on the right track, not only will he develop a model of regeneration in sea squirts, but in salamanders as well. Basic research on animal regeneration is a foundation for a major goal in medicine: Learning how to guide human stem cells to regenerate new tissues or organs.
Two of the sea squirt's eight photoreceptors, dyed red, which are found at the base of its siphons.
(Photo Credit: Dr. William Jeffery)
Cellular Symmetry
Cells are intrinsically artistic. When the right signals tell a cell to divide, it usually splits down the middle, resulting in two identical daughter cells. (Stem cells are the exception to the rule.) This natural symmetry is visible on the macroscopic scale as well. All living creatures, be they mushrooms or humans, are visibly symmetric, a product of our cells' preference for equilibrium.
Scientists at the MBL's Whitman Center for Visiting Research are curious to know what cues tell a cell to divide at the center. Fred Chang, professor of microbiology at Columbia University, his postdoctoral student Nicolas Minc, and David Burgess, professor of biology at Boston College, are placing sea urchin eggs in snug, microscopic chambers shaped like triangles, squares, rectangles, stars, and ice cream cones to see whether the cell will still split 50-50. A cell's shape, which is naturally circular, is known to play an important role in where it divides. "We're trying to figure out the plane of division when cells are placed in oddly shaped chambers," Dr. Chang says. "Is it in the same place or way off the middle?"
Cell division is an ancient process. All multicellular organisms have similar proteins for the task, so any information gathered from the sea urchin research is relevant to human biology as well. Chang and Burgess hope to apply their findings to the established theories of cell division or possibly come up with a model of their own.
Source: Marine Biological Laboratory
The sea urchin egg divides in a star-shaped compartment.
(Photo Credit: Fred Chang)