Region-specific magnetic fields structure sea turtle populations

Philopatry and long distance migrations are common in the animal kingdom, of which sea turtles are flagship examples. Recent studies have suggested sea turtles use the Earths magnetic field to navigate across ocean basins to return to their natal area, yet the mechanisms underlying this process remain unknown. If true though, the genetic structure at nesting sites should positively correlate with differences in location-specific magnetic vectors within nesting regions. Here, we confirm this working hypothesis but only in certain regions of the world and for all sea turtle species nesting in those regions. Reversely, where no correlations were found between genetic differentiation and geomagnetic vectors, this was the case for all nesting sea turtle species. Our approach hence reveals parallel but not universal use of geomagnetic cues in sea turtles. We describe magneto-sensing regions as characterized by sharp clines of total and vertical field intensity vectors offering the navigation cues that increase philopatric accuracy and promote genetic structuring among sea turtle populations.