Keeping track of the literature
isn’t easy, so Outside JEB is a
monthly feature that reports the
most exciting developments in
experimental biology. Short
articles that have been selected
and written by a team of active
research scientists highlight the
papers that JEB readers can’t
afford to miss.
SOCIAL ORGANISATION
788
Outside JEB
FEEDING THE BROOD
Social insects such as honey bees live in
complex societies, and it is a fascination to
many scientists how bees co-ordinate their
behaviour according to the needs of the
colony. Worker bees must perform a
number of tasks in order to keep the hive
functioning correctly. Younger bees tend
the larvae and the hive and, from the age
of three weeks, can abandon their hive
tasks and switch to foraging for pollen and
nectar. The performance of these two types
of task within the colony relies on the bees
altering their behaviour as the colony’s
needs change. Brood pheromone is
secreted by the larvae and stimulates
younger bees to switch from hive tasks to
foraging to feed the youngsters. On the
other hand, the presence of older bees,
which do most of the foraging, inhibits the
onset of foraging in younger bees. The
sensitivity of the bees to either brood
pheromone or older bees alters according
to the needs of the colony, but can also be
manipulated experimentally.
bees. Then the colonies were sealed for 3
days. Upon opening the hives again, all the
transplant bees were removed and the time
of onset of foraging as well as the number
of foragers was noted. They found that
octopamine makes the younger bees less
responsive to the inhibitory effect of the
older bees that usually prevents the
youngsters from foraging. After treatment
with octopamine, more younger bees
foraged even when the older bees should
have inhibited them!
Then the team tested how octopamine
affects the number of bees foraging in a
colony when they are exposed to brood
pheromone. This time they used triple
cohort colonies in which the worker bees
belong to one of three different age groups.
Dishes containing brood pheromone, which
activates foraging, were placed in the comb
of two colonies, and one of these colonies
also received octopamine. It was
discovered that the bees were more likely
to forage when octopamine is available in
their food because it makes the bees more
sensitive to brood pheromone.
This study shows that octopamine plays an
important role in the complex organisation
of bee behaviour, reducing the foraging
workload when there are already enough
bees on the job while ensuring that enough
pollen and nectar are collected when there
are hungry mouths to feed.
10.1242/jeb.00148
Barron, A. B., Schulz, D. J. and
Robinson, G. E. (2002). Octopamine
modulates responsiveness to foraging
related stimuli in honey bees (Apis
mellifera). J. Comp. Physiol. A 188, 603610.
Octopamine is a neurochemical that can
modulate the activity of neurons and alter
the behaviour of an insect. Andrew Barron
and his colleagues at the University of
Illinois used two types of bee colony that
have controlled population structures to
investigate how octopamine affects the
responsiveness of honeybees to the
presence of older bees in the hive and
brood pheromone released by larvae.
First, the team tested how octopamine
alters the effect that older bees have on the
foraging activity of younger bees. They
took single cohort colonies, which
consisted of a queen and young worker
bees that are all the same age. Two
colonies were treated with octopamine
mixed with sucrose that was provided as a
food source, and one of the colonies
received a transplant of 100 older forager
THE JOURNAL OF EXPERIMENTAL BIOLOGY 206 (5)
Laura Blackburn
University of Cambridge
[email protected]
Outside JEB
COMMUNICATION
desaturase produced the O. furnacalis
blend rather than the O. nubilalis blend. If
O. furnacalis arose from a species with a
pheromone consisting of Z and E11-14
acetates, then evolution of the new
pheromone blend is likely to have
proceeded by duplication, mutation and a
change in expression of desaturase genes.
LIKE THAT NEW PERFUME
YOU'RE WEARING!
Most studies of signal evolution have
concentrated on auditory and visual
signals. In some cases, studies have shown
that receivers are able to respond to a
wider range of signals than are commonly
produced by conspecifics. A new study by
Wendell Roelofs and colleagues
demonstrates that a similar phenomenon
can occur in chemical signaling between
moths.
Most insects rely on their sense of smell
for sexual communication. Female moths
emit a species-specific pheromone, either a
single chemical or a blend of structurally
related chemical compounds. The
pheromone is produced by desaturase
enzymes from unsaturated fatty acid
precursors in an abdominal pheromone
gland. Male antennae are finely tuned to
the female pheromone. Males are able to
identify their species-specific components
and ratios and can follow small quantities
of airborne pheromone to a calling female.
Pheromones have been identified in five
species of Ostrinia moths. Four use a blend
of Z and E11-14 acetates, but the Asian
corn borer, O. furnacalis, uses a blend of Z
and E12-14 acetates. Roelofs et al. argue
that both female production of and male
response to the pheromone have changed
in O. furnacalis, relative to the European
corn borer, O. nubilalis.
The authors found genes in both Ostrinia
species for the ∆11 desaturase, which
produces the O. nubilalis pheromone, and
the ∆14 desaturase, which produces the O.
furnacalis pheromone. While the ∆14
desaturase is non-functional in O. nubilalis,
the ∆11 desaturase is non-functional in O.
furnacalis. The biochemical pathways for
pheromone production indicate that
switching from ∆11 desaturase to ∆14
But what about the males? Female moth
pheromone production and male response
are not genetically linked, so without a
male around who liked what he smelled,
the female ancestors of O. furnacalis that
produced the new pheromone blend would
have quickly died out. In wind-tunnel
experiments, Roelofs and his team found
that a large proportion (4%) of male O.
nubilalis were attracted to both their
species-typical pheromone blend and that
of O. furnacalis. This suggests that when
the O. furnacalis pheromone blend
appeared, males could have responded to
the new female pheromone, allowing
speciation to occur while preserving the
sender–receiver coupling essential for
chemical signaling.
The research of Roelofs et al. presents one
of the first examples of mechanisms by
which evolution of a pheromone
communication system and subsequent
speciation may occur. This research raises
practical issues for the practice of mating
disruption, a pest control technique in
which large amounts of insect pheromone
are dispensed in agricultural environments,
resulting in reduced larval damage to crops
by disrupting adult sexual communication.
Many pesticides have lost their
effectiveness due to evolution of resistance
in target insect species. Although resistance
to mating disruption has never been
observed, the findings of Roelofs et al.
suggest mechanisms whereby it could
occur.
10.1242/jeb.00149
Roelofs, W. L., Liu, W., Hao, G., Jiao, H.,
Rooney, A. P. and Linn, C. E., Jr (2002).
Evolution of moth sex pheromones via ancestral
genes. Proc. Natl. Acad. Sci. USA 99, 1362113626.
Frédérique de Lame
Michigan State University
[email protected]
Heather Eisthen
Michigan State University
[email protected]
UNCOUPLING PROTEINS
789
EXERCISE FOR
MITOCHONDRIA
An important source of metabolic
inefficiency is a futile cycle of protons
across the mitochondrial inner membrane,
a process called proton leak. In brown fat,
proton leak is catalysed by a protein called
uncoupling protein 1 (UCP1), and two
homologues of this protein have been
discovered called UCP2 and UCP3. UCP2
is expressed in most tissues, while UCP3 is
expressed mostly in skeletal muscle. Many
studies have reported rapid and drastic
increases in the level of UCP3 mRNA in
skeletal muscle after a single bout of
exercise, whilst others demonstrated
decreases in UCP3 mRNA during longterm training. It was assumed that these
changes had functional significance and
that an increase in the level of UCP3
expression could protect muscle cells
against elevated substrate supply following
exercise by uncoupling substrate oxidation
from ATP production, whereas a decrease
during long-term training could augment
metabolic efficiency. These data suggest
changes in the composition of
mitochondria in response to exercise such
that they display markedly different UCP3
levels, relative to other mitochondrial
proteins. Since exercise leads to an
increase in the content of mitochondria in
muscle fibers, and the expression of UCPs
is most probably regulated in a manner
similar to that of other mitochondrial
proteins, Jones and collaborators
hypothesized that UCP3 protein level in
skeletal muscle increases during training as
part of the increase in the content of
mitochondria and that each mitochondrion
preserves similar levels of UCP3 proteins.
Additionally, they tested whether
mitochondria rich type I muscle fibers have
higher levels of UCP3 expression than type
IIa or IIb fibers that have a lower
mitochondrial content.
THE JOURNAL OF EXPERIMENTAL BIOLOGY 206 (5)
Outside JEB
To test their main hypothesis, the authors
used rats accustomed to swimming. The
exercise protocol consisted of two 3 hour
swimming sessions separated by a resting
period. The first group of rats performed
the protocol for one day, the second for
three days and the last group for ten days.
The team collected muscle samples after
each group’s last training session and
measured the muscles’ UCP3 transcript
and protein levels. The transcript level of
UCP3 increased very rapidly after a single
bout of exercise, while UCP3 protein level
displayed a significant increase only after
several hours. The level of UCP3 protein
increased steadily over 10 days of
swimming. Importantly, the increase in
UCP3 protein level paralleled that of other
mitochondrial proteins, indicating that
exercise leads to a rise in the number of
mitochondria in the muscle, rather than to
a modification in the UCP3 protein content
of pre-existing mitochondria.
In a separate experiment using sedentary
rats, the protein level of UCP3 was
compared with that of other mitochondrial
proteins in type I, IIa and IIb muscle fibers.
The content of UCP3 was higher in type I
fibers than in type IIa and IIb fibers, and
this pattern is similar to that of other
mitochondrial proteins. So the UCP3
protein content of each fiber type parallels
their number of mitochondria.
Overall, the results presented in this paper
support the original hypothesis of the
authors and suggest that modification in the
expression level of UCPs under certain
conditions could reflect changes in the
content of mitochondria in cells, possibly
due to alteration in cellular energy status.
10.1242/jeb.00152
Jones, T. E., Baar, K., Ojuka, E., Chen, M.
and Holloszy, J. O. (2003). Exercise induces an
increase in muscle UCP3 as a component of the
increase in mitochondrial biogenesis. Am. J.
Physiol Endocrinol. Metab. 284, E96-E101.
Julie St-Pierre
Dana-Farber Cancer Institute and
Harvard Medical School
[email protected]
AEROBIC CAPACITY
790
EVOLVING COUCHPOTATOES AND
ENDURANCE ATHLETES
I have never come close to finishing an
endurance race anywhere near the time of
the winners. However, I take some solace
in the notion that the ability to sustain a
high level of aerobic activity probably has
a strong genetic basis, and therefore
regardless of how hard or long I train,
there will always be others that simply
have a higher intrinsic capacity for
exercise. Wouldn’t it be great to understand
the functional basis for such differences in
aerobic capacity? Rather than blaming
one’s genes, wouldn’t it be more satisfying
to pinpoint where in the oxygen transport
system (from the lungs through the blood
to the tissue) the differences between
“natural” endurance athletes and the rest of
us are manifested? Although physiologists
have been exploring what limits aerobic
capacity for decades, recent experiments
published by Henderson and others
approach these questions in a novel and
intriguing way.
Henderson and colleagues have used
artificial selection to develop lines of rats
with different inherent exercise capacities.
Their selective regimen worked as follows.
Animals from a large founder population
were trained for one week to run on an
inclined treadmill. The following week
these rats underwent five days of testing to
see how far they would run during a
progressive test to exhaustion. The 13 rats
with the longest runs were considered
high-capacity runners (HCR); the 13 with
the shortest runs were low-capacity runners
(LCR). HCR and LCR rats were randomly
bred, and their offspring underwent similar
testing and categorization based on
treadmill endurance. Again, the 13
high/low extremes were selected and bred
randomly. Following seven generations of
this selective breeding, HCR and LCR
animals differed substantially in their
running capacity: an average HCR rat ran
close to 1600 meters before exhaustion,
while average LCR rats ran just over 220
meters before quitting.
When the team measured the rats’ maximal
oxygen consumption rate, they found it
was significantly greater in HCR than LCR
animals. Various physiological tests were
then performed on these animals to explore
potential differences in oxygen transport at
various points in the oxygen transport
system such as lung ventilation, lung
oxygen diffusion capacity, cardiac output
and oxygen diffusion from the blood into
tissues. However, no differences in lung
ventilation or lung-blood diffusing capacity
were found. The team found higher levels
of cardiac output in HCR rats, but these
were offset by relative decreases in blood
hemoglobin and arterial oxygen
concentration in these same animals.
Hence, differences in maximal oxygen
consumption rate were not mediated by
differences in convection in the lungs or
circulatory system, or by differences in
diffusion between the alveoli and lung
capillaries. Rather, differences in oxygen
diffusion/extraction at the level of the
tissues seem to underlie differences in
maximal oxygen consumption rate between
HCR and LCR individuals.
Thus, divergent selection on endurance
capacity led to rats that differ greatly in
their maximal rates of oxygen uptake.
Moreover, these differences in oxygen
consumption are determined largely by
differences in oxygen transport at the
tissues rather than at other sites in the
oxygen transport system. An obvious next
step is to use these evolved lines to explore
in more detail the structural and/or
physiological mechanisms underlying these
differences in tissue oxygen transport.
10.1242/jeb.00150
Henderson, K. K., Wagner, H., Favret,
F., Britton, S. L., Koch, L. G., Wagner, P.
D. and Gonzalez, N. C. (2002).
Determinants of maximal O2 uptake in rats
selectively bred for endurance running
capacity. J. Appl. Physiol. 93, 1265-1274.
THE JOURNAL OF EXPERIMENTAL BIOLOGY 206 (5)
Gary B. Gillis
Mount Holyoke College
[email protected]
Outside JEB
791
ION TRANSPORT
chloride/bicarbonate exchange. Evans’ lab
recently collected evidence suggesting that
pendrin is responsible for
chloride/bicarbonate exchange in V-ATPase
cells of the mammalian kidney.
PENDRIN PROTEIN
PRESENT IN EURYHALINE
ELASMOBRANCH!
Pendrin is a recently discovered protein in
mammals that has the ability to transport
chloride ions in exchange for a variety of
different molecules including bicarbonate.
Chloride/bicarbonate exchange is important
in euryhaline organisms and it insures
chloride uptake when the animal is in
freshwater. David Evans’ team presents
new evidence that pendrin is present in the
Atlantic stingray (Dasyatis sabina) gill
tissue, which is believed to be the site of
chloride/bicarbonate exchange in the
elasmobranch.
Bicarbonate and protons are produced in
the cell by the enzyme carbonic anhydrase.
The active elimination of protons from
within the cell by V-ATPases leaves
bicarbonate to build-up, creating a
favorable bicarbonate gradient for
In elasmobranchs (sharks, skates and rays),
the gills are the primary site of acid/baserelated ion transport. Up until now, the
identity or cellular location of a
chloride/bicarbonate exchanger in the
elasmobranch gill was not known, even
though evidence suggests that net
bicarbonate secretion occurs across the gill
epithelium. However, there are cells in the
elasmobranch gill teeming with V-ATPases,
which are similar to the bicarbonatesecreting cells in the mammalian kidney
where pendrin is found. Thus, there were
three main objectives of the present study.
Firstly, the authors sought to determine if
pendrin-like transporters were present in
elasmobranch gill cells. Secondly, if the
presence of this transporter was dependent
on whether the stingray was adapted to
freshwater or seawater. And thirdly,
whether these transporters are associated
with cells that are rich in V-ATPases,
similar to the bicarbonate-secreting cells of
the mammalian kidney.
By using semiquantitative immunoblotting,
a pendrin or pendrin-like exchanger was
located in the gills of both freshwater and
marine Atlantic stingrays. The relative
abundance of pendrin immunoreactivity
was highest in the gills of freshwater
stingrays. Immunohistochemical findings
demonstrated that the location of these
pendrin-like transporters on the gill
filament was also influenced by
environmental salinity, as freshwater
stingrays appeared to have more discrete
pendrin immunoreactivity on the apical
membrane of the cell, which separates the
external environment from the cell’s
interior. As Piermarini and co-workers
point out, greater protein expression and
apical membrane association of a pendrinlike exchanger in freshwater stingray gills
makes sense, as there is a crucial need for
enhanced chloride uptake from freshwater
in order to counteract the large diffusional
loss of chloride into the environment.
Double-labeling experiments clearly
demonstrated that pendrin
immunoreactivity was found in V-ATPaserich cells, similar to the mammalian
kidney. Therefore, these elasmobranch gill
cells could potentially be the site of
pendrin-mediated chloride/bicarbonate,
similar to chloride/bicarbonate exchange in
the mammalian kidney. However, the
function of pendrin in the stingray gill is
yet to be determined.
This study presents the first evidence of a
pendrin-like transporter in an iontransporting tissue from any lower
vertebrate and has furthered the
development of the Atlantic stingray gill
epithelium ion transport model.
10.1242/jeb.00151
Piermarini, P. M., Verlander, J. W.,
Royaux, I. E. and Evans, D. H. (2002).
Pendrin immunoreactivity in the gill
epithelium of a euryhaline elasmobranch.
Am. J. Physiol. 283, R983-R992.
© 2003 The Company of Biologists Limited
THE JOURNAL OF EXPERIMENTAL BIOLOGY 206 (5)
M. Danielle McDonald
University of Miami
[email protected]