Capstone Title

Magnetoreception in Marine Organisms with Emphasis on Bacteria, Fish, Sea Turtles, and Cetaceans

Defense Date

5-2007

Document Type

Capstone

Degree Name

M.S. Marine Biology

First Advisor

Patricia Blackwelder

Second Advisor

Edward Keith

Abstract

Many animals utilize annual migratory pathways in feeding and reproductive strategies. These journeys can cover thousands of kilometers over open-ocean with the animals returning to the same location. Celestial cues, bathymetry, and coastal topography could assist in these navigations but are not consistently available. The geomagnetic field of the Earth is a continuously available feature, providing both positional and directional information, which can be used for navigation during migratory travels. Two different types of magnetoreception have been proposed including electromagnetic induction and magnetite-based magnetoreception. Electrical induction can only be used in a saltwater medium by organisms capable of electroreception, while magnetite-based magnetoreception can only be used by organisms which contain single-domain magnetite. Magnetite has been detected and extracted in many organisms, both terrestrial and aquatic. Bacteria, sea turtles, fish, and cetaceans have all been found to contain single-domain magnetite. In the latter three, single-domain magnetite has been isolated in consistent locations within the cranium. The presence of magnetite alone has resulted in speculation as to whether it is used in magnetoreception. However, researchers believe that in order for geomagnetic field information to be transduced into directional information by organisms, there must be a magnetoreceptor cell transmitting information into signals to the brain. Further investigations have found that the location of magnetite in several teleost species could behave as a candidate receptor cell. The close association with various cranial nerves could allow for reception and transference of positional information to the brain. Consistent anatomical location of the magnetite has been identified between different species within each group. Laboratory and field research involving geomagnetic field detection in various aquatic organisms has provided evidence in support of geomagnetic field detection. However, not all field research has been able to support geomagnetic field detection by particular organisms, such as sea turtles, cetaceans, and teleosts. Recent field investigations into the use of the geomagnetic field by adult sea turtles during migration through geomagnetic field disruption and displacement techniques are the first to provide evidence in support of geomagnetic field use by adult sea turtles. Prior to this research, laboratory and field investigations have shown that hatchlings and juvenile sea turtles are able to detect and use the geomagnetic field in navigation, but adult sea turtles did not. As technological advances are made in magnetite detection methodology, along with improvements in laboratory and field investigatory techniques, more evidence accrues in support of the use of the geomagnetic field in navigation by animals.

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