Natures wonders: more on magnetic migration (Introduction)

by David Turell , Monday, September 05, 2022, 18:19 (808 days ago) @ David Turell

Sharks use the field:

https://www.sciencenews.org/article/omicron-booster-shot-vaccine-covid-coronavirus-pfiz...

"The navigational mechanism used to facilitate these movements is unresolved

"We show that sharks use the Earth’s magnetic field for homeward orientation

"This ability is useful for navigation and possibly maintaining population structure

"Migration is common in marine animals, and use of the map-like information of Earth’s magnetic field appears to play an important role. While sharks are iconic migrants and well known for their sensitivity to electromagnetic fields, whether this ability is used for navigation is unresolved. We conducted magnetic displacement experiments on wild-caught bonnetheads (Sphyrna tiburo) and show that magnetic map cues can elicit homeward orientation. We further show that use of a magnetic map to derive positional information may help explain aspects of the genetic structure of bonnethead populations in the northwest Atlantic. These results offer a compelling explanation for the puzzle of how migratory routes and population structure are maintained in marine environments, where few physical barriers limit movements of vagile species.

"Sharks, skates, and rays, from the subclass Elasmobranchii, are among the most ecologically important groups of marine fishes. Many species of elasmobranchs are highly mobile and their habitats can span thousands of kilometers, with some migratory species exhibiting site fidelity, in which individuals return to specific locations.29,30 Researchers have long known that elasmobranchs are sensitive to electromagnetic fields, and the possibility that sharks use their electrosensory organs in some capacity to glean information from Earth’s magnetic field (hereby referred to as the geomagnetic field [GMF]) for navigational purposes has been widely discussed. The GMF provides animals with both map and compass information. The map allows animals to garner spatial information relative to their location,7 while the compass allows animals to maintain a directed heading,32 and together, these facilitate successful migrations toward targeted locations. Elasmobranchs appear capable of discriminating between different components of the GMF14 and have also been trained to respond to geomagnetic polarity and intensity. Tracking studies of wild sharks have revealed striking associations between swimming trajectory and local magnetic maxima and minima extending from seamounts to feeding grounds;35 however, whether sharks use geomagnetic cues for navigation remains unresolved.

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"These results suggest that sharks can differentiate geographic locations using map information from the GMF. Bonnetheads appeared to perceive the southern magnetic field as different from the field at the capture site and responded to the magnetic displacement with homeward orientation. It is tempting to speculate that the northern field did not elicit different orientation from the field at the capture site because the sharks had no experience with such strong magnetic fields and that their magnetic map is “learned.” Sharks in the Gulf of Mexico could learn that fields weaker than those at the capture site indicate more southward locations but would never experience stronger fields than the capture site and thus may not know how to respond to such conditions. However, the lack of response to the northern treatment is also consistent with findings in animals with innate magnetic maps; hatchling loggerhead sea turtles (Caretta caretta) failed to orient in magnetic fields far outside of their normal migratory route, but were strongly oriented within the typical population range.37 While our experiment suggests that magnetic fields that are more familiar (either from individual experience or evolutionary history) elicit more robust orientation responses, further study is required to conclude how bonnetheads derive and extrapolate magnetic map information.

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"The use of magnetic maps appears to be a widely shared trait in species that occupy a variety of habitats, possess divergent life history strategies, and move over a wide range of spatial scales.39,43,44 Our work adds to the growing body of literature that the map-like use of the GMF is an evolutionary underpinning for how animals across a variety of taxa successfully derive spatial information from diverse habitats."

Comment: Animals used a magnetic compass mechanism long before we did!!!