Senosry systems II: Perception of magnetic fields

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Senosry systems II Perception of magnetic fields
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Amazing animal migrations
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Can animals sense magnetic fields? The degree to
which animals can sense magnetic fields
unclear European Robins (Erithacus
rubecula) Tend to migrate in a particular
direction Preferred flight direction is
maintained in a closed room with no optical
references implies that vision is not
necessary If test cage is moved to all-steel
chamber (a shield against magnetic fields), bird
no longer finds natural migratory
direction Artificially generated magnetic fields
can influence the direction choice
of robins Other organisms shown to be affected
by magnetic fields Marine mollusks, Salmon,
Salamanders, Turtles, Hornets, Honeybees
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Puzzle The geomagnetic field is weak (ca. 0.5
Gauss). Three possible ways that animals can
detect magnetic fields Mechanical Reception
Same as a compass needle requires the presence
of ferromagnets (small magnetic particles in
body) Electric Induction Any kind of movement
in an induced electric field Allows animals to
follow magnetic lines However, electro-sensitive
organs not found in all animals who can use
magnetoreception Chemical Reception Chemical
reactions inside body can be influenced by
magnetic fields poorly understood
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Honeybees carry discrete bodies of
ferromagnetic material that could be affected by
earths magnetic field Certain cells in their
abdomen contain iron granules 0.6
micrometers in diameter These cells
(trophocytes) are innervated by axons from the
ventral nerve Cord Mechanism poorly understood
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Newts Can migrate up to five km to and from
their natal ponds (and this is after being in a
forest for five years) How? Photoreceptors
(light sensitive regions in the brain)
facilitated migration Sensory vision with a
brightness pattern imposed (due to magnetic
field) Example (Quote from researchers) "If
the newt is pointing north, the newts'
photoreceptors would align north-south and would
show an excitation response, whereas if the newt
points itself to the east it would still show an
increased pattern but now the pattern will have
rotated 90 degrees because the newt has now
rotated,"
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Sea turtles migrate for thousands of kilometers
to the same beach on which they were born The
migratory routes of turtles have unique
combinations of magnetic field intensity and
field line inclination Hatchling loggerhead
turtles can distinguish between different field
intensities and magnetic inclination angles along
routes Turtles thus possess the ability to
determine their global position using a
bi-coordinate map
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Vision and sorting of information
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Vision and Lateral inhibition Lateral
inhibition The horseshoe crab (Limulus)
has compound eye in which individual receptor
units can be stimulated by a fine beam of
light However, the signals in the axon do not
completely represent the stimulus The pattern
also depends on the amount of light falling on
other receptor units Why? Because each visual
receptor is connected to its neighbors
and Inhibits their activity lateral inhibition
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Potential advantage of lateral inhibition? Enhanc
ed edge effects Consider 12 units that are
stimulated by uniform light of two intensities
(bright and dim) Because units 2-5 are
bordered by other units getting
bright Illumination, they are subject to lateral
inhibition Units 6 and unit 7 are not Thus,
their discharge frequency is higher better
picture of edge
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Information processing Ex. The eye of a
frog Rods and cones are distributed uniformly
such that the structure of the retina is similar
from place to place Within the frog eye, there
are neurons called ganglion cells. The axons of
these ganglions make up the optic nerve There
are about 500,000 ganglion cells, but there are
about 1 million receptor cells (rods and cones)
in the retina Thus, there cannot be a 11
correspondence between the incoming and outgoing
messages Fibers in the optic nerve are divided
into five different classes on the basis of the
responses of the ganglion cells
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On fibers Respond to the onset of
illumination Off fibers Respond to only the
termination of a light stimulus ON-off fibers
Respond to either onset or offset of a light
stimulus or its termination Edge receptors
Respond to the presence of a sharp edge in the
visual field Bug detectors Respond only to
small, dark, moving objects But NOT to large dark
moving objects or to stationary objects In fact,
switching a light on and off will not affect
these final fibers The retina of the frog
contains a matrix of many kinds of specialized
fibers, each of which is beneficial for a
different purpose
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Recent article in Time magazine The Science of
Romance
Could romance be driven by our senses?
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The idea of love as a biological phenomenon to
promote mating and nurturing of children
May go all the way back to early human culture
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Animal senses-A guide to humans?
Hamsters and pheromones-dictates sexual behavior
OK, I thought that we dropped this!
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Within human females, college roommates tend to
develop synchronized Menstrual cycles
(pheremones?) If you apply sweat from a donor to
a subjects lip, the subjects Menstrual cycle
started an average of 9 days away from
donor About 4 months later the difference was
only an average of 3 days No change in the
control group
Driver Hormones
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Pheromones may be linked to MHC genes Strongly
influence the immune system and tissue
rejection Idea MHC matching -Conceive a child
with a person whose MHC is too similar to yours,
and risk increases that the womb will expel the
fetus Find a partner with sufficiently different
MHC, and you're likelier to carry a baby to term.
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MHC information may be contained within pheremones
-Lab mice can smell too-similar MHC in the
urine of other mice -Will avoid mating with
those individuals Human females smelled
T shirts worn by anonymous males and then pick
those that were most appealing They chose the
ones worn by men with a safely different MHC
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Confounding factor birth control pill Women who
are on the Pill-which simulates pregnancy-tend
to choose wrong in the T-shirt test When they
discontinue the daily hormone dose, the
protective smell mechanism kicks back in
Pheromones may be a natural mechanism of
partner selection-pregnancy may interfere with
this
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Preference also relates to faces Just before,
during and after period - when women are least
likely to become pregnant - more attracted to
more feminine male faces If woman is on the
pill, no preference is shown through cycle
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How do researchers study facial symmetry?
Digital manipulation!
                      
                      
                      
                      
                      
Symmetric Female Face
Original Female Face
Asymmetric Female Face
Symmetric Male Face
Original Male Face
Asymmetric Male Face
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Facial attractiveness researchers also create
composite faces
                      
Composite of 60 Faces
Composite of 15 Most Attractive Faces
Hyper-Attractive Composite
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Researchers can also make more male and
female faces
                      
Femininised Female Face
Masculinised Female Face
Femininised Male Face
Masculinised Male Face
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Saliva also contains MHC genes Kissing may be a
taste test for future compatibility
Testosterone is also present in male saliva-can
be passed onto The female
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Men may use pheromones too
Body odor
Evaluation of the subject as sexy
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What IS attractive? Deep voice in males
(auditory signal) Research on the Hadza
tribesmen found that the richer and lower a man's
voice, the more children he had Sample group of
149 volunteers listened to recordings of men's
and women's voices Ranked them from "very
unattractive" to "very attractive." Voices that
scored high on attractiveness also had physical
features considered sexually appealing
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Ideas of beauty change among cultures and across
time Waist-hip ratio in women Scientists have
claimed that a certain waist-hip ratio is
preferable Across cultures Europe Women with
0.7 WHR (waist circumference that is 70 of hip
circumference) are rated more attractive Marilyn
Monroe, Sophia Loren and the Venus de Milo
ratios 0.7 Preferences range from 0.6 in
China to 0.8 or 0.9 in South America Or Africa
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Things to consider In many culture, men always
have beards-but this has fallen out of favor in
modern culture The male beard a sexually
dimorphic trait
Common in some cultures, but increasingly more
rare in ours
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Consider all the machinations that men take to
get a hairless attractive body
Ouch!
There may not be one universal best qualities
at any one time If true - then what are
pheromones signalling?