Beauty is in the brain size of the beholder


OUTSIDE JEB

Beauty is in the brain size
of the beholder

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There are many fish in the sea, but
having a large school to choose from
doesn’t make mate choice decisions any
easier. In fact, selecting a mate requires
members of the choosing sex to process,
integrate and recall a great deal of
information related to mate quality
across many potential mates. As this
choice is directly related to fitness,
it stands to reason that the cognitive
ability of the choosing sex is under
considerable selective pressure.
Therefore, Alberto Corral-López, a PhD
student in Niclas Kolm’s laboratory at
Stockholm University, Sweden, along
with several colleagues, decided to test
the hypothesis that smarter individuals
choose better mates. They knew from
previous work in the Kolm lab that
female guppies with big brains have
a higher cognitive ability than female
guppies with small brains, so they staged
a dating game to test whether or not the
big-brained guppies made better mate
choice decisions.

To begin the matchmaking experiments,
Corral-López presented individual big-
or small-brained female guppies with
two males to choose from. One male
was brightly coloured with a large tail,
as these traits are known to represent a
high-quality mate in guppies. The other
male was dull-coloured and nondescript
– a less optimal choice by far. Corral-
López tracked how much time a female
spent with each male and found that
while small-brained females spent just
as much time with the ugly male as the
attractive male, the big-brained females

preferred to swim with the beautiful
beau. While this result supports a
connection between female brain size
and mate choice decisions, Corral-
López wanted to rule out that the
preferences he observed weren’t caused
by inherent differences in the female
visual system.

So, for his next experiment, Corral-
López tested the ability of females to
distinguish and perceive colour. He
tracked how well each female oriented
herself during an optomotor response
test, which involved moving alternating
bands of colour (red and green to match
the males) along the wall of the fish tank
while recording her movements. He also
varied the intensity of each colour band
to create high- and low-contrast colour
stimuli, similar to the attractive and dull
male fish. Corral-López found that all
females, irrespective of brain size, were
better at following high-contrast colour
bands compared with low-contrast
bands, meaning that brain size does
not influence colour perception.
Furthermore, small- and big-brained
females had similar gene expression
profiles in their retinas for the opsins
that are essential proteins for vision
and colour perception. Therefore, he
concluded that the big- and small-brained
female guppies were equally capable of
distinguishing colourful males from dull
males. This means that small- and big-
brained females gathered the same visual
information from the two males that were
presented to them; however, the females
with large brains were better at using this
information to choose the superior mate.
Or, put another way, big-brained guppies
are smart enough to judge a fish by its
colours.

10.1242/jeb.147470

Corral-López, A., Bloch, N. I., Kotrschal, A., van
der Bijl, W., Buechel, S. D., Mank, J. E. and
Kolm, N. (2017). Female brain size affects the
assessment of male attractiveness during mate
choice. Sci. Adv. 3, e1601990.

Sarah Alderman
University of Guelph
alderman@uoguelph.ca

The bee microbiota as a
barrier against disease

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Poop is all the rage these days. It isn’t
some new weird trend championed by
hipster youth, but rather the enthusiasm
of scientists who study our microbiomes,
the bacteria that live on and within us.
These bacteria, which are often best
characterized by studying our poop
(hence the rage), provide endless benefits
to our health and well-being. They
influence metabolism, development,
immunity, behavior and much else. But
when these beneficial microbes are
eliminated by antibiotics, which are
crucial life-savers against bacterial
pathogens, things can go horribly awry.
Most notably, treatment can cause
dysbiosis, a microbial imbalance in our
guts that increases our susceptibility to
opportunistic bacteria like Clostridium
difficile. But dysbiosis isn’t just a human
phenomenon. As elegantly shown in a
new paper in PLoS Biology by Kasie
Raymann and her colleagues from the
University of Texas, what’s true for
humans is also true for bees.

Bees are in global decline and one of the
reasons for their troubles is a disease
called American foulbrood, caused by the
bacterial pathogen Paenibacillus larvae.
Bee keepers can treat foulbrood by
feeding bees or spraying hives with
the broad-spectrum antibiotic
oxytetracycline, which is effective against
P. larvae. However, Raymann and her
team wondered whether these drugs could
also have off-target effects on the normal
microbiota of bees and, if so, would the
resulting dysbiosis harm bees just like it
does humans?

Outside JEB is a monthly feature that reports the most exciting developments in experimental biology. 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.

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© 2017. Published by The Company of Biologists Ltd | Journal of Experimental Biology (2017) 220, 2299-2302

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http://dx.doi.org/10.1126/sciadv.1601990
http://dx.doi.org/10.1126/sciadv.1601990
http://dx.doi.org/10.1126/sciadv.1601990
http://dx.doi.org/10.1126/sciadv.1601990
http://dx.doi.org/10.1126/sciadv.1601990
mailto:alderman@uoguelph.ca


To test this, the team fed bees with
oxytetracycline and compared their
microbiomes with those of bees fed the
same diet without the drug. As expected,
antibiotic treatment had a dramatic effect
on the core bacterial species of the bee
microbiome. Bacterial abundance in
oxytetracycline-treated bee guts declined
nearly 5-fold as did overall bacterial
diversity. However, it wasn’t only core
bacteria that declined; so too did bee
health. Roughly two-thirds of the treated
bees died; around twice the mortality
of control bees. But why did the treated
bees die?

The cause, it turns out, is highly
reminiscent of the factors leading to
opportunistic C. difficile infections in
humans: dysbiosis. So, oxytetracycline
caused the ‘good’ bacteria of the bee
microbiome to decline and in so doing
created a vacuum that allowed other
species to thrive, including a well-known
insect pathogen called Serratia. And
when the team fed antibiotic-treated
larvae with Serratia, these bees died too,
providing unambiguous evidence that
antibiotic-induced dysbiosis increased
bee susceptibility to off-target
opportunistic pathogens. More
importantly, the results confirmed
that the core microbiome is a barrier to
disease under normal conditions.

Sometimes in medicine, the treatment is
worse than the disease itself. This is
unlikely to be the case here, as the benefits
of foulbrood eradication almost certainly
exceed the costs of Serratia-induced
mortality. However, this study nicely
demonstrates the unanticipated dangers
of perturbing the microbiome. In addition,
it perhaps suggests a solution to bee
dysbiosis. One of the most promising
treatments for C. difficile infections is
to repopulate the human gut with a
so-called fecal transplant. This provides
an apparent barrier to C. difficile
disease and works markedly better than
antibiotics. Although I don’t envy the bee
proctologist administering microbiome
enemas to larval bees, perhaps this type of
fecal replacement (‘bee-cal’ transplants)
is just what the hive ordered? Such an
approach would avoid the dysbiosis that
increases the risks of Serratia and other
pathogens, while maintaining the
treatment benefits against foulbrood.
Novel solutions are needed to arrest
global bee declines. Microbiome

manipulation seems a worthwhile place
to look.

10.1242/jeb.147447

Raymann, K., Shaffer, Z. and Moran, N. A. (2017).
Antibiotic exposure perturbsthe gut microbiota and
elevates mortality in honeybees. PLoS Biology.

Daniel E. Rozen
University of Leiden

d.e.rozen@biology.leidenuniv.nl

MantisBot successfully
mimics prey tracking

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The praying mantis is a notorious insect,
known for its calm, motionless stance
while waiting for prey to draw near,
followed by a swift and powerful strike.
Mantises track moving prey using rapid
turning head movements to keep their
target in the foveal region of the eyes,
where the highest resolution images are
produced. Though much is known about
insect motion and control, exactly how
mantises use visual information to
produce these sharp head turns remains
unclear. What makes this insect especially
interesting is that numerous studies have
found that once a turn is initiated, it
cannot be stopped – meaning that the
mantis must predict the future position of
its prey. So, what information does the
brain send to the nerve clusters controlling
locomotion in order to produce these
precise movements?

This is the question that an
interdisciplinary team of researchers
attempted to answer with their
mantis-inspired robot, MantisBot. Based
on previous studies of praying mantis
head movements and insect locomotion in
the literature, the team – led by Nicholas
Szczecinski from Case Western Reserve
University in Ohio, USA – hypothesised
that commands to the nerve centres that
control locomotion are relatively simple.
To test this, they designed a simple
nervous network with commands inspired
from those biological results, and

incorporated it into MantisBot, a 13.3:1
scale robot model of a praying mantis.
Based on information provided by the
‘eyes’ – five solar cells arranged around
the front of the head – a bioinspired brain-
like controller gave simple instructions
to the unit controlling the robot’s
movements: either move or stand still,
and which direction to orient the body.

To test how well the proposed network
directed the robot, the team shone a
1600 lumen LED at it to simulate prey; the
difference in voltage of the solar cells told
the robot which direction the prey was in.
If the prey moved outside a 20 deg cone
from the centre of its vision, the controller
told the robot to move its head, and if it
moved even further (30 deg outside), the
robot also used its body and legs too, just
like real praying mantises do. But could
it track prey accurately?

MantisBot’s control network was a
success, allowing the robot to track prey
to within 30 deg of its centre of vision,
even when moving its legs and body.
Switching direction mid-step was
no problem either, and the robot
successfully used its legs to help rotate its
body while standing still. The robot’s
high accuracy in tracking prey
demonstrates that simple commands –
which direction, and whether or not to
move – are capable of producing tracking
behaviour comparable to that of the
praying mantis, and provides plausible
evidence that the information sent to the
animal’s own locomotion control centre
could be just as simple.

Bioinspired robotic models are not just
great precursors to more advanced robots;
studies like this demonstrate that they can
also supply meaningful feedback, helping
us to understand the underlying biology to
answer questions that current biological
experiments cannot address. Continuing
such interdisciplinary work is therefore
essential for both fields to progress,
and could potentially provide answers
to many biological conundrums.

10.1242/jeb.147462

Szczecinski, N. S., Getsy, A. P., Martin, J. P.,
Ritzmann, R. E. and Quinn, R. D. (2017).
MantisBot is a robotic model of visually guided
motion in the praying mantis. Arthropod
Struct. Dev.

Michelle A. Reeve
michelle.a.reeve@gmail.com

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http://dx.doi.org/10.1371/journal.pbio.2001861
http://dx.doi.org/10.1371/journal.pbio.2001861
http://dx.doi.org/10.1371/journal.pbio.2001861
mailto:d.e.rozen@biology.leidenuniv.nl
http://dx.doi.org/10.1016/j.asd.2017.03.001
http://dx.doi.org/10.1016/j.asd.2017.03.001
http://dx.doi.org/10.1016/j.asd.2017.03.001
http://dx.doi.org/10.1016/j.asd.2017.03.001
http://dx.doi.org/10.1016/j.asd.2017.03.001
mailto:michelle.a.reeve@gmail.com


Juvenile marsupials need
the sun to warm up

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Staying warm whatever the weather is
energetically costly and many mammals
resort to torpor and abandon their stable
body temperature during challenging
periods in order to save energy. While
entering torpor is energetically cheap,
coming out is expensive as the body has to
warm up, although the costs can be
mitigated by basking in the sun. Even
though the cost of emerging from torpor
may be even more extreme for juveniles –
because they are smaller than adults and
have a high surface area to volume ratio –
they use it frequently, which raises the
question: do juveniles attempt to reduce
their rewarming costs by basking in
the sun?

An Australian team led by Chris Wacker
from the University of New England
was interested in whether juvenile
marsupials – which are the size of a
jellybean at birth and spend their first
months of life snuggled in their mother’s
warm pouch – might use the sun to
aid rewarming from torpor. Dunnarts
(Sminthopsis crassicaudata), small
nocturnal marsupials that live in desert
areas, are known to use torpor throughout
the year and often bask in the early
morning sun. The team looked at juvenile
dunnarts between the ages of 40 and
160 days – the age at which they leave
the mother’s pouch and switch from
depending on her warmth to maintaining
their own body temperature. They
measured the dunnarts’ ability to
maintain a stable body temperature,
whether and when juveniles used torpor
and whether they would use an artificial
heat source to reduce the costs of heat
production as they aroused from a bout
of torpor.

Interestingly, the team found that the
juveniles are already capable of entering
torpor even before they can regulate their
body temperature fully and they were
able to achieve this by basking. When

the juveniles emerged from the pouch
at around 60 days, they were able to
maintain a more or less stable body
temperature for a few hours, although
they entered torpor during the later part
of the night. However, they were unable
to restore a warm body temperature
after torpor unless they had the
opportunity to crawl under the warmth
of a heat lamp.

To find out whether the juveniles were
just losing too much heat, causing them to
cool down involuntarily, or had entered
a genuine state of torpor, the team
compared the juvenile dunnarts’ heat loss
rate with the heat loss of dead animals that
had been warmed to the same initial body
temperature. This comparison showed
that the live dunnarts cooled faster
than the dead animals, indicating that
they controlled the decrease in body
temperature and entered torpor. And
when the team monitored the juveniles’
use of torpor, they found that animals
were still entering torpor during the night
at around 90 days of age when they were
already able to maintain a stable warm
body temperature during the course of the
entire night, although the older youngsters
were able to rewarm and emerge from
torpor with greater ease. Nonetheless,
dunnarts of all ages still basked under
a heat source whenever they had the
chance.

Wacker and colleagues conclude that
juvenile dunnarts are able to enter torpor
even before they are capable of producing
sufficient heat to maintain a stable
temperature, and they need to bask in the
sun to resume a warm body temperature
after torpor. This observation also raises
the possibility that basking may be a
crucial step in the development of
heterothermy – where an animal does not
always maintain a single stable body
temperature – in small animals that live in
warm habitats. Importantly, the team has
revealed that basking is not an option for
juvenile marsupials wishing to capitalize
on energy savings during torpor; it is
essential.

10.1242/jeb.147454

Wacker, C. B., McAllan, B. M., Körtner, G. and
Geiser, F. (2017). The role of basking in the
development of endothermy and torpor in a
marsupial. J. Comp. Physiol. B.

Julia Nowack
University of Veterinary Medicine Vienna

julia.nowack@vetmeduni.ac.at

Unearthing HIFs in a
hardy marsh fish

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When it comes to surviving hypoxia, or
low oxygen, animals get by with a little
help from their factors – hypoxia-
inducible factors (HIFs), that is. HIFs are
useful molecules that, when activated by
hypoxia, help form switches to crank gene
expression up or down as needed, thereby
regulating cellular processes that help
animals cope with the stress. Because of
the low capacity of water for dissolved
oxygen, fish are especially likely to
encounter this stress, particularly in
shallow, productive environments like
estuaries and salt marshes; therefore,
estuarine fish, particularly the hypoxia-
hardy mummichog (Fundulus
heteroclitus), are useful models for
studying HIFs. In general, HIF molecules
are made of two subunits: the β-subunit,
which is always expressed and available,
and one of multiple varieties of the α-
subunit. One variety, HIF2αa, has already
been described in the mummichog, but
Ian Townley and his colleagues at the
University of New Orleans, USA, as well
as researchers from Xavier University of
New Orleans, USA, and Woods Hole
Oceanographic Institution, USA, sought
to discover what other forms of HIFα exist
in this fish.

To hunt for HIFαs, Townley and the other
researchers used a small piece of a HIF1α
gene from rainbow trout and a piece
of what they suspected to be a HIF3α
gene from the mummichog to probe
mummichog liver DNA for matching
sequences. This enabled them to
determine the full mummichog HIFα
sequences and compare them with HIFα
genes in other vertebrates. They also
investigated in which of the fish’s
organs the different forms of HIFα were
expressed. Finally, they used cultured
cells in vitro to translate the HIFα coding
sequences into proteins and looked at how
well the proteins performed their jobs,
such as binding to areas of DNA called
hypoxia response elements (HREs) in

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http://dx.doi.org/10.1007/s00360-017-1060-2
http://dx.doi.org/10.1007/s00360-017-1060-2
http://dx.doi.org/10.1007/s00360-017-1060-2
http://dx.doi.org/10.1007/s00360-017-1060-2
mailto:julia.nowack@vetmeduni.ac.at


order to influence gene expression. In this
case, the researchers analyzed expression
of a specially engineered reporter gene
containing mummichog HREs that
produces light when activated; this made it
easy to detect and quantify HIFα-induced
activation by measuring light production.

The team discovered DNA sequences
for HIF1α and HIF3α genes in the
mummichog that were similar to those
of other fish and encoded proteins that
functioned as HIFαs should, confirming
that mummichog HIFαs operate under the
same basic framework as those in other
species. They also found a shorter version
of HIF2α, HIF2αb, whose sequence
suggests it is unable to detect hypoxia or
activate genes; alternatively, it may be
involved in regulating other HIFαs,

similar to one variety of HIF3α found in
mammals. The group further noticed that
the three full-length forms of HIFα were
distributed among tissues in patterns
similar to those in other fish. Surprisingly,
however, HIFα expression was very low
in the brain and heart compared with
reported values for other fish species, with
unclear implications for HIFα-mediated
processes. Furthermore, there were
several areas where the sequence was
variable in the newly identified HIFα
genes as well as the previously identified
HIF2αa gene, which could allow for
variation in hypoxia responses among
individuals or populations.

Many questions remain about exactly
how the expression patterns and
sequence variations might translate

into protein abundance and function,
as well as which HIFα characteristics
might influence the mummichog’s
hardiness. Nevertheless, this
characterization of mummichog HIFα
genes lays important groundwork for
further research into why these water
warriors are so good at surviving
in low-oxygen environments.

10.1242/jeb.147488

Townley, I. K., Karchner, S. I., Skripnikova, E.,
Wiese, T. E., Hahn, M. E. and Rees, B. B. (2017).
Sequence and functional characterization
of hypoxia-inducible factors, HIF1α, HIF2αa,
and HIF3α, from the estuarine fish, Fundulus
heteroclitus. Am. J. Physiol. Regul. Integr. Comp.
Physiol. 312, R412-R425.

Molly H. B. Amador
University of Miami

m.broome@umiami.edu

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http://dx.doi.org/10.1152/ajpregu.00402.2016
http://dx.doi.org/10.1152/ajpregu.00402.2016
http://dx.doi.org/10.1152/ajpregu.00402.2016
http://dx.doi.org/10.1152/ajpregu.00402.2016
http://dx.doi.org/10.1152/ajpregu.00402.2016
http://dx.doi.org/10.1152/ajpregu.00402.2016
http://dx.doi.org/10.1152/ajpregu.00402.2016
mailto:m.broome@umiami.edu