Magnetoreception Flashcards
why does the earth have a magnetic field?
has a magnetic core, making the earth a magnetic dipole. some characteristics of the magnetic field are unique to location, so animals can use this for orientation.
it changes by 10s of km per year. inclination and field intensity lines create a bi coordinate grid. 1000nT is distance between lines of isointensity.
How do sand pipers use magnetoreception?
they have well defined pop specific migratory corridors. populations which have distinct breeding areas and share breeding grounds may take distinct routes. unknown how decide route.
loggerhead turtles
Go from brazil to Ascension island. lines of inclination and amplitude create a grid surrounding ascension islandand may form a bi-coordinate position-finding system northwest-southeast.
Bacteria
Blakemore 1975.
found magnetite crystals in bacteria. observed downwards movement of bacteria when magnet placed at bottom of a tank. possibly unrelated.
since, magnetite has been found in many species.
describe an experiment on loggerhead turtles
in lab, attached to sling so they can swim freely in a pool. changed magnetic field from 1 to 2. at 1, turtles oriented NE. 2 - westerly course.
what shows multimodality in turtles orientation?
tracked turtles with GPS along 100s km route. results not direct support of magnetoreception at that scale, but generally turtles seem to know their location. when displaced, could have used olfactory cues to help find island, if downstream/downwind of it.
What evidence is there that pigeons use magnetoreception?
{ambient field is much larger than the local variations, typically 1000 nT, depends on geographical location, and more importantly, the behavioural thresholds for changes in magnetic field intensity of 25-50 nT. }
Wu and Dickman 2012 - inner ear part called Lagena - cells encode info on magnetic field’s direction, intensity and polarity. also, iron deposits in the beak thought to be part of a sensory mechanism.
monitored brain activity of homing pigeons in a dark room whilst changing magnetic field. Vestibular neurons fired differentially to changing field and were tuned with particular bandwidth of earth.
Describe experiment of spiny lobsters
Lohmann 1995
tested for sensitivity to local field.
used coils operated underwater.
covered eyes to prevent visual stimuli and interference by presence of observer. in field conditions
found reversal of magnetic N by 180 degrees causes reversal of migration. reversal of Z = no change.
How do cows and deer use magnetically mediated orientaion?
Begall 2008.
studied Cattle, Roe deer and red deer.
Calculated mean vector of animals N-S alignment body position at one locality. found Red deer most consistent.
how was it seen that trout are magnetosensitive?
found magnetite in the olfactory cells
magnetic chain hypothesis is a suggestion.
what is a different mechanism suggested for turtles magnetoreception ability?
Natan and Virtman 2017.
Magnetotactic bacteria align along lines of inclination.
sensor for MTB known but no reason for this is clear, whereas in many metazoan organisms, a need for magnetoreception is clear but mechanism unknown. perhaps symbiosis.
bacteria sense via chain of magnetite crystals, forming a magnetosome.
communication to turtle maybe via accumulation at specific points in glands,allowing cell/cell communication.
Maybe MTB secrete substance which excited nerves directly.
Maybe via visual system, as bacteria secreted across cornea.
