<
https://gizmodo.com/monarch-butterflies-are-losing-their-navigational-abilities-you-can-guess-why-2000642640>
"Each fall, millions of eastern North American monarch butterflies migrate up
to 3,000 miles south to the mountains of central Mexico, then return to their
northern range in the spring. These winged insects rely on a complex navigation
system to go to and from their overwintering sites, and new research suggests
climate change may be messing with it.
Monarch butterflies have two distinct biological “compasses.” The primary one
infers direction based on their circadian rhythm and the position of the Sun,
but on overcast days, they switch to a backup compass that infers direction
from Earth’s magnetic field. Scientists already knew seasonal temperatures play
a critical role in calibrating these navigational biomechanisms during the fall
migration, but they weren’t sure if the same rules apply to the spring
migration. A new study published Wednesday, August 13, in the journal
PLOS
One confirmed that they do, suggesting that rising winter temperatures in
Mexico could prevent monarchs from returning to their northern range.
“The question was, if they use the Sun compass or the magnetic compass to go
southwards, do they use the same kind of compass mechanisms to fly back north?
And we weren’t sure what triggered that,” co-author Patrick Guerra, an
independent neuroecology researcher based in North Carolina, told
Gizmodo. He
participated in this research while working as an assistant professor at the
University of Cincinnati.
When temperatures drop in the fall, this shift calibrates both of the
butterflies’ biological compasses to point south, guiding them toward their
overwintering sites in Mexico. “Once they get there, they’re basically
overwintering in a fridge,” Guerra explained. His previous research showed that
this long period of exposure to cool temperatures recalibrates the Sun compass
to point north so that it can guide monarchs back to their summer range in the
spring. In this new study, he and his colleagues investigated whether this is
also true for the magnetic compass.
To that end, the researchers conducted a series of righting response trials
with migratory and non-migratory monarchs. During these trials, the butterflies
were exposed to artificial magnetic fields that mimic geographic conditions
south of their overwintering sites, then positioned so they were upside down.
Upon righting themselves, non-migrating monarchs faced magnetic north, whereas
migrating monarchs faced magnetic south. This indicated that monarchs exhibit
something akin to migratory restlessness—a compulsion to go toward the
direction their migratory instincts are telling them to follow even if they
can’t actually fly there.
With this established, Guerra and his colleagues chilled the monarchs to trick
their bodies into thinking they had gone through an overwintering period. When
they performed the righting response trials again, the migrating monarchs
pointed toward magnetic north. The non-migrating monarchs, however, still
pointed toward magnetic south.
“That told us that, just like the Sun compass, the magnetic compass is
recalibrated by the cold conditions that are consistent with being in Mexico
while they’re overwintering,” Guerra explained. “So that kind of hammers home
that their whole ability to navigate is really tuned to the environmental
conditions that they’re experiencing.”"
Via Joyce Donahue.
Cheers,
*** Xanni ***
--
mailto:xanni@xanadu.net Andrew Pam
http://xanadu.com.au/ Chief Scientist, Xanadu
https://glasswings.com.au/ Partner, Glass Wings
https://sericyb.com.au/ Manager, Serious Cybernetics
