September, 1996
Hormone/behavior relationships
Becker, J.B., Breedlove, S.M. & Crews, D. (eds) (1992) Behavioral Endocrinology.
Nelson, R.J. (1995) An
Introduction to Behavioral Endocrinology.
The effect of hormones on behavior
and the effect of the social environment on hormones are at the heart of
sociophysiology.
Seeing
these books well reviewed in the May issue of Animal Behaviour, I ordered them
from the library and was surprised how soon they came. Not much of a queue of readers for behavioral endocrinology!
I have
not read them all through, but will recommend some bits. The Becker volume contains an excellent
chapter by David Crews. He describes the
analysis of mating behavior in parthenogenetic
forms of whiptail lizard - in which the receipt of male behaviour is necessary
for ovulation to proceed successfully. Some females adopt the male role and mount
their sisters, including the transfer of bite from neck to pelvic region to
form what the author calls a "doughnut". The neural basis for male behaviour is
present in these unisexual females, but what switches it on, since they
completely lack androgens? I will not spoil anyone's excitement by revealing
the answer.
Crews
also describes how the phenomenon of "dissociated
reproduction" has helped to
disentangle cause and effect in
hormone/behaviour relationships. In some animals the sperm and eggs are
synthesised many months before embryogenesis begins.
In some, such as the garter snake, the male retains the sperm over the winter,
in others the female keeps the sperm in storage, in yet others fertilisation
occurs in the autumn but the zygote is held in suspension over the winter and embryogenesis does not resume until the spring. In the red-sided garter snake, sex hormones
are used for gamete synthesis and play no part in the control of sexual
behaviour. In arid
The
Becker book also contains an excellent chapter on "stress" by Robert Sapolsky. He points
out that stress not only prevents more energy and resources flowing into the
immune system, but that the immune system is actively inhibited, even to the
extent of lymphocytes undergoing lysis. This is likely to have evolved to prevent
stress-induced autoimmunity, which seems plausible since stresses are likely to
be associated with tissue damage, and the experiencing
by the immune system of self products that in normal circumstances it does not
encounter.
The
single-authored Nelson book contains a most readable
chapter on "aggression
and social behaviour" among much else. For instance, many rodents are
aggressive during the breeding season but form social groups which huddle
together during the winter (they could be said to switch to the hedonic mode in
winter). But some male prairie voles
remain agonic all the year round, and presumably find females to mate with when
the winter is less severe.
In
Harris sparrows the level of testosterone during the autumn moult determines
social status throughout the winter, including priority of access to food. It does this both by making the birds more
aggressive in their behavior for the next few months,
and by ensuring that they have a high ratio of dark to pale feathers on the
crown and throat, a social signal of dominance which is respected by the
subordinate pale sparrows. Is this another
instance of Mike Waller's comparator gene in operation?
It is
becoming clear that there is a vast amount of within-species individual
variation in both agonistic and reproductive behaviour. In some species, some of this variation is
due to variation in sex hormone levels; but in male house mice, there is
evidence that androgens conceal individual variation in aggressiveness, which
is revealed by castration and concealed again by the administration of
androgens.