POPULATION LEVEL AND BEHAVIORAL INVESTIGATIONS OF GEOMAGNETIC IMPRINTING AND NATAL HOMING IN SEA TURTLES Public Deposited

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Last Modified
  • March 22, 2019
Creator
  • Brothers, Roger
    • Affiliation: College of Arts and Sciences, Department of Biology
Abstract
  • Diverse animals migrate long distances before returning as adults to reproduce in the same location where they began life. This phenomenon, called natal homing, is exemplified by sea turtles. Turtles travel immense distances through seemingly featureless open ocean and sometimes cross entire ocean basins before laying eggs on the same stretch of coastline where they themselves hatched. Although natal homing is widespread among sea turtles, how it is accomplished has remained a long-standing mystery of animal behavior. One idea, called the geomagnetic imprinting hypothesis notes that Earth’s magnetic field varies across the globe; as a result different geographic areas are characterized by different magnetic fields. Therefore, animals that derive navigational information from Earth’s field might learn the magnetic signature that marks their natal area when they are young and use this information to return as adults. This hypothesis carries with it two central tenets: Firstly, it proposes that adult animals use magnetic navigation to guide reproductive migrations to the natal area. Secondly, it suggests that young animals learn the local magnetic field of the natal location prior to leaving. The research presented hereafter provides evidence that sea turtles use Earth’s magnetic field to accomplish natal homing. Results from a behavioral experiment indicate that adults use magnetic navigation to guide their nesting migrations and return to the natal beach. Additional findings examine the ecological implications of geomagnetic imprinting; as predicted by the hypothesis, population level analyses revealed that natural changes in Earth’s field result in detectable shifts in where sea turtles choose to nest. Moreover, spatial variation in Earth’s field is strongly related to genetic differentiation between nesting beaches suggesting that magnetic navigation can play a role in shaping population genetic structure. Finally, evidence indicates that sea turtle embryos orient non-randomly inside the egg and might use Earth’s magnetic field to do so. Taken together these findings represent four independent lines of evidence that are consistent with geomagnetic imprinting and suggest that turtles use Earth’s magnetic field to accomplish natal homing. The results provide insight into an enigmatic phenomenon in animal behavior and are likely applicable to diverse migratory animals.
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Advisor
  • Sockman, Keith
  • Johnsen, Sönke
  • Bruno, John
  • Wiley, R. Haven
  • Lohmann, Kenneth
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2018
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