A recent theory which says that the dominant animal in a pack bears the proverbial cross might lead to more systematic studies of relationships between animal behaviour and hormones
THE animal kingdom is inhabited by
some species which exist in groups or
packs, and these groups are led and
dominated upon by individual male or
female members. It had been believed
for long that animals which are subjugated are the most stressed and suffer
from various problems like miscarriages
and failure to reproduce. New research,
however, shows that it is the other way
round - the animal which dominates is
the actual sufferer.
Behaviourial biologists Scott and
Nancy Creel of Rockefeller University,
New York, along with Steven L
Monfort, an endocrinologist at the
Smithsonian Institution's Conservation
Research Centre, Washington, us,
report that dominant females in 14 packs
of dwarf mongooses had the highest
levels of the stress-related hormone,
cortisol. Similar studies on female
baboons and male and female wild dogs
indicate that dominance comes at a high
price. In baboons, it leads to higher rates
of miscarriages, while in dogs and
mongooses persistent stress shortens
the lifespan of the alpha/dominant
animals (Science, Vol 271, No 5247).
The Creels' study is the first of its
kind where hormonal levels have been
studied in several free-ranging
rather than captive species. The older
theory about subordinates with higher
chronic stress levels arises from studies
conducted on captive colonies of
rodents and primates in the '50s and
'60s, They found that the subordinates
had higher cortisol levels and suffered
from ill health and reproductive failure.
Higher stress levels in subordinates
support the theory of dominance where
survival of the fittest was the main
feature; the Creels embarked on their
study believing this. "We thought that
stress could be a factor in suppressing
the subordinates' reproduction," says
Nancy Creel.
The researchers collected samples of
urine and faeces of mongooses and dogs
to establish the basal stress hormone
levels for each species and to obsme
any disparity among individuals.
Contrary to expectations, they found
higher glucocorticoid (a corticoid that
affects glucose metabolism) levels in
alpha males and females
- probably as a result
of their aggressive
behaviour.
It is still unclear how
this phenomenon affects,
the animals' health.
According to behaviourial ecologist Sam
Wasser of the University
of Washington, alpha
female baboons do have
higher rates of miscarriages, but Wasser has
not analysed stress hormone levels. Biologists
have not been able to
find a similar response in
mongooses and dogs.
"They must be paying
)port e the price in another way,
perhaps a shorter lifespan," says Scott Creel.
The methodology adopted in the
study has come under fire. According to
critics, the hormonal levels derived
from urine and faeces can never be
the same as that extracted directly
from the animals' blood. The accuracy
in the time of collection and the level
of steroids in the animals' urine have
also been questioned. Notwithstanding its criticism, the study has
made biologists realise the potential
variety of relationships that can exist
between animal behaviour and hormones. "We are realising that hormonal
levels are more and more situation
dependent," says Jeanne Altmann, a
behaviourial ecologist at the University
of Chicago in US.
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