The Magnetic Map In Sea Turtles

T h e M a g n e t i c M a p i n S e a life sciences

Sam Shutt

Dr. Catherine Lohmann, an animal behavior biologist at UNC-Chapel Hill, is fascinated with how sea turtles find their way home. Sea turtles travel hundreds, and even thousands of miles across the ocean. Yet they somehow manage to return to the precise location where they hatched. This could be attributed to sea turtles’ special sense known as the magnetic map. 1 Sea turtles appear to utilize the Earth’s magnetic field to recognize specific geography. Indeed, the turtles can distinguish between different coastlines and find the exact area where they were born. Dr. Lohmann and her lab uncovered evidence that supports the theory that sea turtles geomagnetically imprint on the magnetic field of where they were born. 2 Imprinting may allow sea turtles to recognize the magnetic field of their home. Dr. Lohmann’s research has contributed to scientific knowledge of long-distance marine animal migration and will have tangible applications in the near future. Dr. Lohmann began researching sea turtles in 1989. Over the years, she and her husband, Kenneth Lohmann, have created a lab that is at the forefront

of sea turtle and marine animal navigation research. Much of their collaboration occurs in Florida, where they study how loggerhead sea turtles detect magnetic fields. In one important experiment, they collected young turtles along the coast and attached harnesses to them with computerized tracking systemts. 3 They applied different magnetic fields to the newly hatched turtles in an outdoor water arena by using a surrounding metal coil. Then, they recorded turtle movement orientation using the tracking system. Dr. Lohmann found that turtles exposed to northern magnetic fields oriented themselves south and those exposed to southern magnetic fields oriented themselves north. The experiment clearly showed that sea turtle navigation is affected by the Earth’s magnetic field and that turtles seemed to use some kind of magnetic map (Figure 1). Sea turtles appear to use the map by responding to both the inclination angle

Dr. Catherine Lohmann

and intensity of the Earth’s magnetic field. The intensity of the Earth’s magnetic field is strongest at the poles. Inclination field lines, however, are somewhat more difficult to understand. The lines crisscross and are affected by the intensity of the Earth’s magnetic field, marking different geographic locations with distinct magnetic fields for sea turtles to recognize and remember.

Figure 1: Dr. Lohmann’s Detection System. Source courtesy of Lohmann et al.

After Dr. Lohmann and her lab acquired evidence for a magnetic map in sea turtles, they became interested in exploring the relationship between the genes of sea turtles and the Earth’s magnetic field. The Lohmann lab studied sea turtles along the coast of Florida and examined their genetic makeup. They found that turtles living at similar latitudes were genetically similar; 4 even turtles at the same latitude but separated from each other by large distances bore genetic resemblance. In contrast, sea turtles that were near each other but at different latitudes were not as genetically similar. The evidence strongly suggests that there is an interaction between magnetic fields and the genes of sea turtles. Perhaps, turtles that are genetically similar live at similar latitudes because of the magnetic fields or perhaps the magnetic fields have affected their genes somehow. There is no definitive answer of how sea turtle genes are affected by the Earth’s magnetic field yet, but the Lohmann lab’s research provides a promising start for future research on this topic. When asked to explain the reason behind her primary focus on sea turtles for so many years, Dr. Lohmann simply responded, “I was captivated.” 5 Sea turtles are special animals that perform fascinating feats. Sadly, almost all species of seas turtles are classified as endangered, but Dr. Lohmann’s research may one day help in the conservation of sea turtles. Turtles may be made to geomagnetically imprint on specific magnetic fields so that they may return to safe locations later in life instead of populated and polluted coastlines. Nonetheless, there may be unforeseen consequences if sea turtles imprint on different magnetic fields. There are many avenues for research which the Lohmann Lab plans to pursue in the future. The physiological processes of sea turtle magnetic detection and navigation remains a mystery. Dr. Lohmann plans to do neurobiological work on fish that also detect magnetic fields, in an effort to further explain the magnetic map. Furthermore, she hopes to learn whether or not marine animal navigation, influenced by magnetic detection, is a widespread phenomenon. Dr. Lohmann is optimistic about the future for marine animal navigation research and where it could lead: “I feel we are learning something that can be very applied and can expand our understanding.” 5 Dr. Lohmann’s research has radically expanded scientific knowledge on sea turtle navigation and the magnetic map. Her important work will continue to do so, and one day the mysterious process of how sea turtles return home may be fully understood.

References

1. Lohmann, K. J.; Lohmann, C. M. F. There and back again: Natal homing by magnetic navigation in sea turtles and salmon. J Exp Biol. 2019, 222, 184077-184087. 2. Lohmann, K. J.; Putman, N. F.; Lohmann, C. M. F. Geomagnetic imprinting: A unifying hypothesis of longdistance natal homing in salmon and sea turtles. 2008, 105, 19096-19101. 3. Lohmann, K. J.; Lohmann, C. M. F.; Ehrhart, L. M.; Bagley, D. A.; Swing, T. Geomagnetic map used in sea-turtle navigation. Nature. 2004, 428, 909-910.. doi:10.1038/428909a 4. Lohmann, K. J.; Lohmann, C. M.; Brothers, J. R.; Putman, N. F. Natal Homing and Imprinting in Sea Turtles. Biology of Sea Turtles 2013, 3, 59-77. 5. Interview with Catherine Lohmann, Ph.D. 02/07/2020