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Current Biology
Dispatches
7. Baker, A.J., Haddrath, O., McPherson, J.D.,
and Cloutier, A. (2014). Genomic support for
a moa-tinamou clade and adaptive
morphological convergence in flightless
ratites. Mol. Biol. Evol. 31, 1686–1696.
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M.S., and Cooper, A. (2014). Ancient DNA
reveals elephant birds and kiwi are sister taxa
and clarifies ratite bird evolution. Science 344,
898–900.
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clocks. Curr. Biol. 26, R399–R402.
10. Jarvis, E.D., Mirarab, S., Aberer, A.J., Li, B.,
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D.J., Townsend, J.P., Moriarty Lemmon, E.,
and Lemmon, A.R. (2015). A comprehensive
phylogeny of birds (Aves) using targeted nextgeneration DNA sequencing. Nature 526,
569–573.
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phylogenetic model for investigating
correlated evolution of substitution rates and
continuous phenotypic characters. Mol. Biol.
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in the Northern Hemisphere suggest a new
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14. Nesbitt, S.J., and Clarke, J.A. (2016). The
anatomy and taxonomy of the exquisitely
preserved Green River Formation (Early
Eocene) lithornithids (Aves) and the
Relationships of Lithornithidae. Bull. Am. Mus.
Nat. Hist. 406, 1–91.
Insect Evolution: The Origin of Wings
Andrew Ross
Department of Natural Sciences, National Museum of Scotland, Chambers Street, Edinburgh EH1 1JF, UK
Correspondence: a.ross@nms.ac.uk
http://dx.doi.org/10.1016/j.cub.2016.12.014
The debate on the evolution of wings in insects has reached a new level. The study of primitive fossil insect
nymphs has revealed that wings developed from a combination of the dorsal part of the thorax and the body
wall.
How animals acquired the ability to fly is a
question of major interest to evolutionary
biologists. Flight enables an animal to
disperse across physical barriers, such as
seas, live in comparatively safe places
away from ground-dwelling predators, to
access food sources that others cannot
reach and to find a mate. Vertebrates
evolved the ability for powered flight
independently in several lineages, such as
pterosaurs, birds and bats. However, the
insects got there first and it is widely
believed that they evolved wings and the
ability to fly only once. A recent paper in
Current Biology by Prokop et al. [1] has
taken the long discussion of the origin of
wings and flight in insects to the next level.
The debate on the subject goes back to
the 19th century when there were two
main positions on the origin of insect
wings, namely whether they developed as
entirely new structures or from preexisting structures. As the latter gained
acceptance, the discussion moved on
to which structures, either tracheal gills
(like those of mayfly nymphs) or paranota
(lateral extensions of the nota, the dorsal
part of thoracic body segments). The
latter idea received support when
Lithomantis carbonarius, one of the first
articulated Carboniferous fossil insects,
was discovered (Figure 1A) [2]. This
species belongs to the extinct order
Palaeodictyoptera, which is widely
regarded as the most primitive group of
winged insects. Its oldest known fossil
representative (the oldest known
winged insect), is the 325 million year
old Delitzschala bitterfeldensis [3].
Palaeodictyoptera had their heyday in
the Carboniferous and rapidly diversified
into over 30 families though had become
extinct by the end of the Permian (252
million years ago) [4]. They had a pointed
beak for piercing and it is believed they
fed on fluids from the seeds and stems of
giant clubmosses and tree ferns, as holes
of the right size have been found in fossils
[5]. Palaeodictyoptera possessed two
pairs of outstretched wings and veined
paranotal lobes on the prothorax as can
been seen on L. carbonarius. Thus the
paranotal theory gained acceptance [6],
though the tracheal gill theory did not
go away and was championed by others
later [7].
In the first half of the 20th century, there
were two main theories for the origin of
flight in insects, the ‘flying squirrel’ and
‘flying fish’ theories depending on whether
the author believed flight originated on
land (by launching off giant clubmosses)
or from the surface of the sea. Both
hypothesised that the extended paranotal
lobes enabled the insect to glide, then
to steer and finally to flap [8]. The ‘flying
squirrel’ model became the generally
accepted norm, particularly supported by
the discovery of the then oldest known
fossil ‘insect’, the 407 million year old
springtail Rhyniella praecursor preserved
in Rhynie Chert. The chert was deposited
by hot volcanic springs and preserved the
earliest known terrestrial ecosystem [9].
Springtails (Collembola) are wingless and
have six legs (hexapods, like all insects)
and today they, along with some other
apterygotes (diplurans and proturans), are
regarded as the sister group to the Insecta
because they have internal rather than
external mouthparts. Springtails have a
unique structure, the furcula (spring) that
they use to propel themselves into the
air to escape hazardous situations. The
furcula can be seen on Rhyniella [10]
(Figure 1B). So even though springtails
were the first to experience the wind
Current Biology 27, R103–R122, February 6, 2017 ª 2016 Elsevier Ltd. R113
Current Biology
Dispatches
A
Prothoracic
lobes
C
B
Furcula
Figure 1. Early hexapods, showing adaptations for flight or propulsion into the air.
(A) Lithomantis carbonarius, a palaeodictyopteran from the Upper Carboniferous of Scotland. Scale
bar 10 mm. Photograph by Phil Crabb. Copyright Natural History Museum, London. (B) Abdomen of
Rhyniella praecursor, a springtail from the Lower Devonian of Scotland. Scale bar 0.1 mm. Photograph
by Peter York. Copyright Natural History Museum, London. (C) Idoptilus peachii, an early instar
palaeodictyopteran nymph from the Upper Carboniferous of Scotland. Scale bar 5 mm. Photograph by
Bill Crighton. Copyright National Museums Scotland, Edinburgh.
R114 Current Biology 27, R103–R122, February 6, 2017
rushing through their antennae, they had
no control on where (or which way up) they
would land. At the time they were
collectively included with all the other
apterygotes and Rhyniella supported the
theory that pterygotes evolved from
apterygotes on land [11]. A true insect,
Rhyniognatha hirsti, was subsequently
recognised from the Rhynie Chert and
although it’s jaws were mayfly-like, there
was no evidence as to whether it had any
vestiges of wings [12].
In the 1970s and 80s there was a
rennaisance of discussion papers on
the origin of flight in winged insects
(pterygotes; e.g. [13,14]). One important
suggestion to come from these was
that the greater surface area provided
by the paranotal lobes could have
been used for thermoregulation, i.e. the
quicker an insect warmed up by basking,
the more active it would become, and it
was argued that this was a driver for the
lobes to become extended in the first
place.
The discussion moved on to exactly
what part of the body did the protowings
develop from, paranota or pleura (lateral
extensions of the body wall), or even
from a combination of the two [15]. Now
the new paper by Prokop et al. [1]
appears to have solved this issue from
the close study of the nymphs of
Palaeodictyoptera. The nymphs, although
rare as fossils, possessed two pairs of
wing pads on the thorax as well as a pair
of prothoracic lobes, which they retained
to adulthood (Figure 1C). Different sized
instars (growth stages between moults)
demonstrate the development of the rich
wing venation that can be seen in the
adults but it has not yet been possible to
match nymphs and adults of the same
species. Close examination of the wing
pads of nymphs by Prokop et al. [1]
provided support for the idea that they
were not fixed but articulated, and that the
amount of articulation increased as the
nymph grew (the prothoracic lobes could
also articulate but to a lesser degree).
Prokop et al. [1] also conclude that
insect wings and the hinge articulation
developed from a combination of the nota
and the lateral body wall, so they can’t be
called ‘paranotal’ lobes any more. If the
nymphs could articulate their wing pads,
could they fly? The authors concluded no,
but they could have been used for gliding
to some extent.
Current Biology
Dispatches
Thus Palaeodictyoptera nymphs
support the theory that the ancestral
pterygote had three pairs of veined
thoracic lobes, enabling it to warm up and
become more active faster. Extended
lobes with some articulation enabled
the insect to glide, perhaps to escape
predators and to aid dispersal. The
final step was for the articulation and
musculature to develop to allow two
pairs of wings to be actively flapped.
This major development allowed insects
to colonise the world.
REFERENCES
1. Prokop, J., Pecharová, M., Nel, A.,
ska, E.,
Hörnschemeyer, T., Krzemin
ski, W., and Engel, M.S. (2017).
Krzemin
Paleozoic nymphal wing pads support dual
model of insect wing origins. Curr. Biol. 27,
263–269.
2. Ross, A.J. (2010). A review of the
Carboniferous fossil insects from Scotland.
Scot. J. Geol. 46, 157–168.
3. Brauckmann, C., and Schneider, J. (1996). Ein
unter-karbonisches Insekt aus dem Raum
Bitterfeld/Delitzsch (Pterygota, Arnsbergium,
Deutschland). Neu. Jahr. Geol. Pal., Monat.
1996, 17–30.
Rhynie, Scotland. In Terrestrial Conservation
€tten: Windows into the Evolution of
Lagersta
Life on Land, N.C. Fraser and H.-D. Sues
(eds). (Edinburgh: Dunedin Academic Press
Ltd).
4. Nicholson, D.B., Mayhew, P.J., and Ross, A.J.
(2015). Changes to the fossil record of insects
through fifteen years of discovery. PLoS One
10, 1–61.
10. Whalley, P., and Jarzembowski, E.A. (1981).
A new assessment of Rhyniella, the earliest
known insect, from the Devonian of Rhynie,
Scotland. Nature 291, 317.
5. Labandeira, C.D., and Phillips, T.L. (1996).
Insect fluid-feeding on Upper Pennsylvanian
tree ferns (Palaeodictyoptera, Marattiales) and
the early history of the piercing-and-sucking
functional feeding group. Ann. Ent. Soc. Am.
89, 157–183.
11. Scourfield, D.J. (1940). The oldest known fossil
insect. Nature 145, 799–801.
6. Crampton, G. (1916). The phylogenetic origin
and the nature of the wings of insects
according to the paranotal theory. J. New York
Ent. Soc. 24, 1–38.
13. Kingsolver, J.G., and Koehl, M.A.R. (1985).
Aerodynamics, thermoregulation, and the
evolution of insect wings: differential scaling
and evolutionary change. Evol. 39, 488–504.
7. Wootton, R.J. (1986). The origin of insect flight:
where are we now? Antenna 10, 82–86.
14. Kukalová-Peck, J. (1987). New Carboniferous
Diplura, Monura, and Thysanura, the hexapod
ground plan, and the role of thoracic side lobes
in the origin of wings (Insecta). Can. J. Zool. 65,
2327–2345.
8. Forbes, W.T.M. (1943). The origin of wings and
venational types in insects. Am. Mid. Nat. 29,
381–405.
9. Trewin, N.H., and Kerp, H. (in press). The
Rhynie and Windyfield cherts, Early Devonian,
12. Engel, M.S., and Grimaldi, D.A. (2004). New
light shed on the oldest insect. Nature 427,
627–630.
15. Grimaldi, D., and Engel, M.S. (2005). Evolution
of the Insects (Cambridge: Cambridge
University Press).
Motor Control: Winging It with a Few Good Muscles
Troy R. Shirangi
Department of Biology, Villanova University, Villanova, PA 19085, USA
Correspondence: troy.shirangi@villanova.edu
http://dx.doi.org/10.1016/j.cub.2016.12.027
A recent study reveals how flies achieve their remarkable aerodynamic agility with only a small number
of wing muscles.
Few flying animals are as agile as flies.
Centuries of frustrated fly swatters can
attest to that. In a split second, a fly can
change direction at will or react to
turbulence to stay on course. Amazingly,
this agility is achieved along three axes of
rotation [1]. While terrestrial animals only
rotate about the vertical axis and turn
left or right, flies can also rotate nose-up
or nose-down and roll from side to
side. To manoeuver rapidly and
stably along these three axes requires
a highly sophisticated flight control
system. Anatomists have long
recognized, however, that flies control
their flight with a strikingly small number
of wing muscles: the fruit fly Drosophila,
for instance, uses only a dozen
wing muscles to control
flight, each supplied by a single
motoneuron. How such a sparse
motor system can allow flies to fly
with such finesse has eluded
neuroethologists for decades.
That is, until now. In this issue of Current
Biology, Lindsay et al. [2] report the secret
to a fly’s remarkable aerial agility. They
discovered that the wing musculature of
Drosophila, while consisting of only a few
muscles, is functionally organized in a far
more ‘stratified’ and logical fashion
than we previously appreciated.
To crack the mystery of fly flight,
neuroethologists have sought to
understand how each wing muscle
contributes to flight stability and steering.
Traditionally, this problem has been
approached using electrophysiology: a fly
is tethered to the tip of a tiny rod, and an
electrode is inserted into an individual
muscle to record the muscle’s firing pattern
during flight. By correlating patterns of
muscle activity with changes in wing
kinematics during flight, scientists can infer
the role of that muscle in flight control.
These types of experiments have
provided great insights into how wing
muscles control flight, particularly during
rapid turns [3]. Most muscles examined
were found to be inactive during straight
flight, but transiently activated when the fly
steered. Moreover, the activity of each
wing muscle was associated with specific
changes in the motion of the wing located
Current Biology 27, R103–R122, February 6, 2017 ª 2016 Elsevier Ltd. R115
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