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Skriven 2004-09-20 21:55:00 av Michael Ragland (1:278/230)
Ärende: Aggression in fish, lobst
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Teaching and Learning Resources (July 2004)
 
Stress Management for Dummies

>From bullies in the fish tank to lizards with black eyes, animals
exhibit a startling range of behavioural and physiological responses to
help them cope with stressful situations. The fact that stress is
currently a hot topic in behavioural research was highlighted by the
range of contributions on stress at this year's Annual Main Meeting in
Edinburgh, of which a selection is presented here. Perhaps humans can
pick up some top tips on stress management from the animal kingdom1,2,3?

Stress relief for bullies

Humans do it, primates do it - now fish have been found to do it too.
New research on displaced aggression indicates that the central
signalling systems controlling behavioural and endocrine stress
responses may be highly evolutionarily conserved.

At last! An excuse for those of us who take our work-related stress out
on our family. In humans and other primates, violent behaviour by
victims of aggression is often directed towards an individual that was
not the original source of provocation. Psychologists refer to this
phenomenon as displaced aggression. Now researchers have discovered that
dominant rainbow trout do the same thing: they reduce their stress
levels by venting their frustration on socially subordinate animals.
Writing in Hormones and Behavior, Dr. Øyvind Øverli and colleagues
(University of Oslo) suggest that this method of stress reduction may be
an evolutionarily conserved strategy, which may increase our
understanding of violent aggressive behaviour in humans4.

"Rainbow trout are highly territorial animals" says Dr. Øverli "When a
dominant fish harasses a subordinate, stress levels drop off quickly in
the dominant animal but remain high in the subordinate. One possible
explanation for this is that beating up a subordinate relieves stress."
To study the behavioural and endocrine effects of social stress, Dr.
Øverli paired test fish with larger (dominant) and smaller
(subordinate) fish. Test fish are first paired with a smaller,
subordinate fish that they can beat up, then paired with a bigger fish
that beat up the test fish, and finally put back with the subordinate
fish (win - lose - win). A second group of test fish are paired with a
subordinate, isolated, and then paired with the subordinate again (win -
isolation - win), while a third group are subjected to a
win-lose-isolation paradigm. "Test fish that suffer social defeat are
far more aggressive when they are re-introduced to their subordinate
partner" explains Dr. Øverli "In contrast, fish that are isolated
between encounters with a subordinate show decreased levels of
aggression when re-introduced to their smaller partner."

Neuroendocrine analysis revealed that the presence of a socially
subordinate fish inhibits the stress response of the test fish. The
researchers assessed the levels of serotonin, a neurotransmitter that is
involved in stress-related responses, and the level of the stress
hormone cortisol in each fish. 

Interestingly, the test fish that were not re-introduced to their small
partner exhibited elevated forebrain serotonin and plasma cortisol
levels compared with test fish that had access to their partner after
losing a fight. Like humans and other primates, these territorial fish
appear to use displaced aggression as a stress coping mechanism.

Fish have personalities too

Dominant fish cause problems in aquaculture by eating more than their
fair share of food and harassing subordinate animals, resulting in poor
growth and high stress levels in subordinate fish. Scientists around
Europe are examining the behaviour of farmed fish to identify new ways
to improve the social environment and efficiency of aquaculture and
fisheries.

Scientists have confirmed what you may always have suspected of your pet
goldfish: fish have 'personalities'. Selective breeding of rainbow trout
by Dr. Tom Pottinger (Centre for Ecology and Hydrology) has resulted in
two lines with two distinctive stress coping styles or 'personality
types'. So-called 'proactive' fish are more aggressive, are generally
more active and are usually dominant over fish with a 'reactive' coping
style, which tend to be passive and less active than 'proactive' fish.
Dr. Svante Winberg (University of Uppsala) and his colleagues are
interested in the relationship between stress responses and aggressive
behaviour in these fish.

"A stress tolerant strain of fish is highly desirable for aquaculture"
says Dr. Winberg "However, the problem is that stress tolerant fish are
often also the most aggressive." Dr. Winberg's group is part of an EU
funded collaborative project involving scientists around Europe (The
STRESSGENES project, coordinated by Dr. Patrick Prunet, INRA, France)5,
which aims to identify candidate genes in fish associated with
resistance to stressful conditions. Scientists hope that a better
understanding of the biological mechanisms behind stress tolerance may
inform new selection strategies and lead to practical benefits for
aquaculture.

Once bitten, twice shy

Lobsters use cues in urine to distinguish between individuals. What's
more, they can remember who they lost a fight to, giving them the
opportunity to flee to fight another day.
Fish may only have a 3-second memory, but lobsters certainly don't.
Professor Jelle Atema6's group at the Boston University Marine Program
has discovered that when two lobsters fight, the loser remembers the
winner and determines the intensity of a later fight when the two meet
again.

Male lobsters can distinguish between individual opponents using the
smell of their urine. To investigate how the lobsters use this
information, Molly Steinbach7 sets up a 'boxing match' between two male
lobsters, after which the 'nose' of either the loser or winner is
disabled so they can no longer recognise their opponent. Perhaps
surprisingly, Ms. Steinbach found that it is the loser who determines
the intensity of subsequent fights, not the winner. During the fight,
the researchers record a number of aggressive behaviours, from fleeing
at one end of the scale to 'ripping and shredding' at the other.

Professor Atema's group found that when the loser's nose was disabled,
the behaviour of both animals in the second fight was no different from
their behaviour in the first fight. However, when the winner's nose was
disabled but the loser's nose was intact, the second fight was shorter
and less aggressive. "As soon as the loser catches a whiff of the
winner, they back off. By recognising the winner of a previous fight and
fleeing more quickly in their second fight, the losers receive less
aggression from the winner" says Ms. Steinbach. The researchers hope to
determine which cue in the urine enables individual recognition in the
lobsters, and to establish the genetic basis for this cue.

Who knew he was the alpha male?

Anolis lizards show their fighting fitness through a colour signal on
their face. New research indicates that dominant males are the ones that
recover from stress and develop these colour signals fastest.

How do you know if a stranger will be nice or nasty? Professor Cliff
Summers8' group at the University of South Dakota has found that you can
predict the social status of male Anolis lizards before they fight.
Wayne Korzan has discovered that how fast you recover from stress, to
participate in feeding and courtship, foreshadows dominant social rank.
Fast lizards are dominant lizards.

As in humans, when anoles are stressed their adrenaline levels shoot up.
As well as causing the 'fight or flight' response, adrenaline results in
black eyespots developing behind the lizards' eyes. In a fight, the male
who develops these eyespots fastest is dominant and usually wins. When
the researchers painted artificial black signals onto a male lizard,
they found that other lizards became subordinate to the animal with fake
eyespots.

The researchers are studying the effects of neurotransmitters that are
involved in stress-related responses, such as dopamine and serotonin, to
understand how these influence social behaviour. "Animals with high
levels of dopamine in the regions of the brain that are involved in
motivation and locomotion tend to win their fights" say Korzan and
Summers; "Animals that initiate the stress response faster and recover
from stress faster tend to win". Conversely, animals with high levels of
dopamine in the region of the brain associated with fear are usually
subordinate and lose fights.

Anolis lizards may prove to be a useful model system for studying
stress, aggression and depression in humans. The group hopes that a
better understanding of the brain neurochemistry of these lizards may
help the development of future treatments for stress and depression in
humans.

Yfke van Bergen
University of Cambridge

References
1. http://www.ivf.com/stress.html
2. http://www.rci.rutgers.edu/~lwh/drugs/
3. http://salmon.psy.plym.ac.uk/year1/stressho.htm
4. Øverli et al. Behavioral and neuroendocrine correlates of displaced
aggression in trout. Hormones and Behavior. Vol. 45, pp. 324-329. 
5. http://www.irisa.fr/stressgenes/
6. http://www.bu.edu/biology/Faculty_Staff/atema.html
7. http://people.bu.edu/mollyann/
8. http://www.usd.edu/~cliff/
  
 
 
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