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Structural mouthpart interaction evolved
already in the earliest lineages of insects
Research
Alexander Blanke1, Peter T. Rühr2, Rajmund Mokso3, Pablo Villanueva3,
Fabian Wilde4, Marco Stampanoni3,5, Kentaro Uesugi6, Ryuichiro Machida1
and Bernhard Misof2
1
Cite this article: Blanke A, Rühr PT, Mokso R,
Villanueva P, Wilde F, Stampanoni M, Uesugi
K, Machida R, Misof B. 2015 Structural
mouthpart interaction evolved already in the
earliest lineages of insects. Proc. R. Soc. B 282:
20151033.
http://dx.doi.org/10.1098/rspb.2015.1033
Received: 1 May 2015
Accepted: 26 June 2015
Subject Areas:
evolution, taxonomy and systematics
Keywords:
entognathy, functional morphology, Diplura,
Collembola, microCT
Author for correspondence:
Alexander Blanke
e-mail: [email protected]
Sugadaira Montane Research Center, University of Tsukuba, Sugadaira Kogen, Ueda, Nagano 386-2204, Japan
Zentrum für Molekulare Biodiversitätsforschung, Zoologisches Forschungsmuseum Alexander Koenig,
Bonn 53113, Germany
3
Swiss Light Source, Paul Scherrer Institute, Villigen, Switzerland
4
Helmholtz-Zentrum Geesthacht, Zentrum für Material- und Küstenforschung GmbH, Geesthacht 21502,
Germany
5
Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
6
Japan Synchrotron Radiation Research Institute/SPring-8, Sayo, Hyogo 679-5198, Japan
2
In butterflies, bees, flies and true bugs specific mouthparts are in close contact
or even fused to enable piercing, sucking or sponging of particular food
sources. The common phenomenon behind these mouthpart types is a complex composed of several consecutive mouthparts which structurally interact
during food uptake. The single mouthparts are thus only functional in conjunction with other adjacent mouthparts, which is fundamentally different
to biting–chewing. It is, however, unclear when structural mouthpart interaction (SMI) evolved since this principle obviously occurred multiple times
independently in several extant and extinct winged insect groups. Here, we
report a new type of SMI in two of the earliest wingless hexapod lineages—
Diplura and Collembola. We found that the mandible and maxilla interact
with each other via an articulatory stud at the dorsal side of the maxillary
stipes, and they are furthermore supported by structures of the hypopharynx
and head capsule. These interactions are crucial stabilizing elements during
food uptake. The presence of SMI in these ancestrally wingless insects, and
its absence in those crustacean groups probably ancestral to insects, indicates
that SMI is a groundplan apomorphy of insects. Our results thus contradict the
currently established view of insect mouthpart evolution that biting–chewing
mouthparts without any form of SMI are the ancestral configuration. Furthermore, SMIs occur in the earliest insects in a high anatomical variety. SMIs in
stemgroup representatives of insects may have triggered efficient exploitation and fast adaptation to new terrestrial food sources much earlier than
previously supposed.
1. Background
Electronic supplementary material is available
at http://dx.doi.org/10.1098/rspb.2015.1033 or
via http://rspb.royalsocietypublishing.org.
Hexapoda (insects in the broad sense) have evolved an astonishing diversity of
mouthparts tailored to use different resources of food [1,2]. For example, dragonflies and crickets use biting–chewing motions of their mandibles to chop food
particles, true bugs evolved piercing–sucking mouthparts to suck fluids from
plants, flies evolved sponging mouthparts, and moths and butterflies evolved
the unique, maxillary-derived proboscis to siphon mostly nectar of flowers
[1,2]. Although mouthparts functionally interact in nearly all insects to process
food, many winged insects evolved a structural interaction [2], sometimes even
leading to mouthpart fusion, resulting in the formation of new mouthpart
types such as the proboscis of many lineages. Corresponding morphological
changes are radical, and morphologically very different to each other; a comparable diversity and complexity of mouthparts is not present in any other arthropod
group. It is unclear when this major trend in insect evolution—structural
mouthpart interaction (SMI)—evolved for the first time.
& 2015 The Author(s) Published by the Royal Society. All rights reserved.
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Samples were critical-point dried (model E4850, BioRad) to
avoid shrinking artefacts of the internal anatomy and mounted
on beamline-specific specimen holders. High-resolution SRmCT (HR SR-mCT) was performed at the Deutsches Elektronen
Synchrotron (DESY; beamlines DORIS III/BW2 and PETRA
III/IBL P05, operated by the Helmholtz-Zentrum Geesthacht,
Hamburg, Germany) with a stable beam energy of 8 keV and
high-density resolution in absorption contrast mode [12,15].
The field of view (FOV) was adjusted to each sample in order
to maximize resolution. HR SR-mCT at the Swiss Light
Source of the Paul-Scherrer Institut (PSI; Villigen, Switzerland;
beamline TOMCAT [13]) was done using a stable beam energy
of 10 keV in absorption-contrast mode and with an energy of
20 keV in phase-contrast mode. We used the 20 objective in
order to realize a FOV of 0.83 0.70 mm with a resulting
pixel size of 0.325 mm2. HR SR-mCT at the Super Photon
ring-8 GeV (SPring-8; Hyogo, Japan) was done at the beamline
BL47XU [14] using a stable beam energy of 8 keV in
3. Results and discussion
The mouthparts of Collembola and Diplura are hidden
within the head, which is defined as an entognathous condition. Only the tips of the mouthparts protrude from the
oral opening, which is generated by the fused head capsule
and labium [4]. Collembolan and dipluran mouthparts
show a specific type of SMI, based on an articulatory point
between the mandible and the maxilla. This contact point
has the same structural basis and is present in all studied
taxa, although Collembola show a wide variety of mandible
forms [5].
2
Proc. R. Soc. B 282: 20151033
2. Experimental procedures
absorption-contrast mode. The tomography system consists
of full-field X-ray microscope with Fresnel zone plate optics
[16]. The FOV and effective pixel size are 0.11 mm2 and
0.0826 mm2, respectively.
The dipluran Campodea sp. and the collembolan
Pogonognathellus flavescens were scanned at DESY as well as at
PSI. All following species were investigated at PSI: Neanura
muscorum, Thaumanura sp., Megaphorura arctica, Lepidocyrtus
lignorum, Orchesella sp., Dicyrtoma sp., Triacanthella rosea,
Neotropiella carli, Brachystomellides neuquensis, Podura aquatica,
Sminthurinus niger, Isotoma sp., Desoria sp. (all Collembola),
Campodea augens, Metriocampa sp., Lepidocampa weberi,
Occasjapyx japonicus, Occasjapyx akiyamae, Catajapyx aquilionaris,
Atlasjapyx cf atlas (all Diplura). The proturan Acerentomon sp.
and the collembolan Megalothorax sp. were investigated at
SPring-8. Collembola show a wide variety of mandible and
maxilla forms [5], which is the reason for our coverage of all
major groups within Collembola (see electronic supplementary
material S2 for taxon coverage). However, we restrict our results
to the biting–chewing mouthpart type for Collembola, as
groups with this mouthpart type were repeatedly recovered
as more ancestral with respect to collembolan phylogenetic
relationships [17–19].
Subsequent segmentation of the reconstructed image
stacks was accomplished with RECONSTRUCT [20] and ITKSNAP [21]. We used manual segmentation as well as semiautomatic segmentation algorithms based on grey-value
differences (‘Wildfire’ tool in RECONSTRUCT), or the ‘region
competition’ algorithm for fully automatic three-dimensional
segmentation (in ITK). Rendering of the resulting mesh
objects was done with BLENDER (blender.org). Objects were
imported as wrl-files (RECONSTRUCT) or stl-files (ITK) into
BLENDER. The surface meshes were smoothed using the
smoothing modifier of BLENDER. Vertex reduction of the
meshes was done with the ‘remove doubles’ algorithm set
to 0.03. No further processing was done, other than light
and camera adjustment in order to minimize structure alteration. Figures were produced with SCRIBUS; all programs used
are distributed under the general public license. Threedimensional models of the relevant mandible, maxilla and
head structures of A. cf. atlas (electronic supplementary
material S3) and P. flavescens (electronic supplementary
material S4) can be viewed with the open-source program
MESHLAB. Other three-dimensional model viewing programs
should also work, but were not tested by us. TIFF image
stacks of the SR-mCT scans of Atlasjapyx and P. flavescens
are provided as reduced film sequences in electronic supplementary material, movies S1a,b, and in full size (16 GB)
upon request.
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The general principle of SMI apparently evolved multiple
times independently in several extant winged insect groups,
and in other extinct groups such as Palaeodictyopterida.
Current hypotheses assume the rolling –biting mouthpart
type without any form of SMI as ancestral. This condition
consists of mandibles attached with one or two joints to the
head, as the potential groundplan in insects [3,4]. However,
these hypotheses fall short in explaining the early evolution
of insect mouthparts, as they neglect the mouthpart configuration and phylogenetic relationships of the earliest insects,
the ancestrally wingless Protura, Collembola and Diplura.
These minute soil and leaf litter inhabitants are important
decomposers of rotten organic material [5], also frequently feeding on the cell content of fungal hyphae [6], plant roots [2,7]
and, in rare cases, on soft-bodied soil arthropods [7]. They
possess mouthparts (mandibles and maxillae) which are
almost entirely hidden within the head capsule (entognathy)
so that the head forms an external (functional) mouth opening
(henceforth ‘oral opening’) in addition to the anatomical mouth
opening. Piercing, and to a minor extent biting–chewing
motions, through this narrow oral opening allows the insect
to penetrate plant cell walls or soft animal tissue and suck out
the contained liquids [4]. Small blended food particles also
are milled between the mandibles in many Collembola, while
some species of Diplura prey on other soil organisms with
their knife-like mandibles after hauling them towards the oral
opening with their maxillae [4]. A growing body of morphological [8–10] and transcriptome-based studies [11] supports
a sistergroup relationship of the entognathous Diplura with
ectognathous insects (Cercophora hypothesis), while Protura þ
Collembola (¼Ellipura) are the sistergroup to Cercophora.
Owing to their entognathy and their small size, mouthpart morphology and movements during food uptake have
been a long-standing enigma in Collembola and Diplura. In
this study, we used three complementary synchrotron
microCT (SR-mCT) imaging set-ups [12–14] to investigate
the mouthpart anatomy of Collembola and Diplura at high
magnifications while entirely preserving the spatial mouthpart arrangement. The mouthpart morphology of these
ancestral insects displays an unusual type of SMI, based on
homologous structures of the mandibles and maxillae.
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(a)
(e)
hc
3
hc
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dorsal
an
posterior
e
anterior
ventral
(b)
Proc. R. Soc. B 282: 20151033
an
STST
(f)
APHC
(c)
APHY
APHC
APHC
STST
THCL
APHY
HF
(g)
SRmd
APHC
(d)
STST
SR
APHY
SR
STST
100 mm
500 mm
mandible
maxilla
mandible interactions with the endoskeleton or head capsule
Figure 1. Overview of dipluran and collembolan mouthpart organization illustrated with three-dimensional reconstructions of SR-mCT data. (a) Dorsolateral view to
indicate the location of the mandible – maxilla hypopharynx complex in the dipluran head. (b) Same as (a), with head capsule removed. Note the stipital stud (STST)
embracing the posterior part of the mandible, and the apodemes (APHC þ APHY) embracing the anterior inner part of the mandible. (c) Same as (b) in mediolateral view, showing the APHY and APHC structures embracing the mandible. (d ) Mediolateral view of the posterior parts of mandible and maxilla, showing the
strengthening ridges of the stipes. (e) Dorsolateral overview of the mouthpart location within the collembolan head. (f ) Same as in (e), with head capsule removed.
Note the stipital stud (STST) contacting the mandible to prevent posterior sheering out of the mandible. The thickening of the clypeus (THCL) prevents lateral
sheering out of the mandibles, while the apodemes (APHC þ APHY) embrace the anterior inner part of the mandibles, as in Diplura. (g) Mediolateral view
of the posterior parts of mandible and maxilla illustrating the contact of STST with the mandible, the location of the strengthening ridges (SR) and the arrangement
of APHC and APHY which are the same as in Diplura. Additional abbreviations: an, antenna; e, eye; hc, head capsule; HF, hypopharyngeal fulturae; SR, strengthening
ridge; SRmd, strengthening ridge of mandible (electronic supplementary material, movie S1a,b; figure S1).
(a) Anatomy of the structural mouthpart interaction
in Diplura
In Diplura, the contact point is formed by an articulatory stud
of the maxillary stipes (STST; figure 1a,b,d). This stud is a short,
upraised prominence, and is supported by two internal stipital
strengthening ridges (SR, figure 1d). The dorsal ridge originates at the base of the stud and extends along the inner
stipital wall to fuse with the ventral stipital ridge. The tip of
the stud is in contact with a slight concavity at the posterior
outer wall of the mandible. At the contact point, a further
strengthening ridge is present inside the mandible continuing
from the dorsal to the ventral mandibular rim (SRmd;
figure 1d).
Two other formerly described contact points [4] are present
in Diplura, which interact with the mandible during food
uptake. One is composed of a spine-like anterior part of the
hypopharynx (APHY; figure 1c), which is in contact with the
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The newly found SMI in Collembola also is composed of a
stipital stud (STST) that originates at the median anterior
(dorsal) wall of the stipes (figure 1e–g). As in Diplura, this
stud is supported by two strengthening ridges, one spanning from the base of the stud to the opposite side of the
maxillary stipes where it fuses with the second strengthening
ridge (SR; figure 1g). The stipital stud articulates with the
posterior mandibular wall during mouthpart movement
(electronic supplementary material, movie S1b).
The movement of the mandible is further stabilized by
three other contact points. One articulation point is composed
of a thickening of the lateral parts of the clypeus (THCL) close
to the base of the labrum (figure 1f ), which interacts with the
mandibles at the anterior transition zone between mola and
incisivi (electronic supplementary material, movie S1b). The
other two contact points are an anterior part of the hypopharynx (APHY) interacting with the mandible at the inner wall
dorsal of the mola [4,22,23] and a spine-like apodeme of
the head capsule (APHC) in contact with the anterior
(dorsal) mandibular wall, as in Diplura (figure 1f,g; electronic
supplementary material, movie S1b).
Mandible movement in Collembola is characterized
by rotation around the dorsoventral axis in addition to
protraction/abduction and retraction/adduction (electronic
supplementary material, movie S1b). The rotation is executed
during and after protraction in order to shear off food particles
or to mill these fragments between the mandibular molar areas
[4,22]. As Koch [4] and Manton [24] previously pointed out,
collembolan mandibles are distally supported during this
movement by the THCL, and the APHC and APHY, which
hold the mandibles like fingers a pencil. However, it was
unclear how proximal (or posterior) support of the mandibles
could be achieved with this configuration and how the mandibular main body is prevented from moving posterad.
The STST of the maxillae fulfils both of these functions by
stabilizing mandible movement in the transversal plane.
During biting, mandibles and maxillae move synchronously
(electronic supplementary material, movie S1b; [5]) with the
(c) The evolution of structural mouthpart interactions
in insects
In current hypotheses, it is postulated that the rolling–biting
mouthpart type without any form of SMI, but composed of
mandibles attached with one or two joints to the head, is the
ancestral condition in insects (groundplan) [3,4]. However,
these hypotheses inadequately explain the evolution of insect
mouthparts as they fail to account for the mouthpart configuration and phylogenetic relationships of the earliest insects, the
ancestrally wingless Protura, Collembola and Diplura.
Although the stipital studs of the maxillae in Collembola
and Diplura support slightly different functions during
mouthpart movement, we consider them homologous. In
both groups, these articulatory studs are located on the
dorsal side of the stipes and are supported by a conspicuous
configuration of two strengthening ridges at the inner side of
the stipes that show the same arrangement. These ridges
reinforce the stipital stud to counter loads imposed on it and
the maxilla during mandibular movement, as is the case for
other ridges in the insect head [25–28]. The two modes of
mandible–maxilla interaction in Collembola and Diplura are
thus examples of a structural mouthpart interaction in
ancestrally wingless insects.
We further propose that the APHC and APHY interactions
with the mandibles are also homologous in Collembola and
Diplura [4]. In both lineages, the apodeme of the head capsule
originates at the same location lateral to the labral base and
above the oral opening, and continues inwards alongside the
dorsal base of the incisival area of the mandibles. Likewise,
the ventral part of the hypopharyngeal fulturae extends
along the ventral base of the incisival area and is connected
to the APHC in both Collembola and Diplura. The location,
structural basis, origin, contact with the mandibles and spatial
arrangement to other structures are the same in Collembola
and Diplura.
The homology of the SMIs in Collembola and Diplura has
important implications for our understanding of insect
mouthpart evolution (figure 2). Currently available morphological [9,33] and molecular evidence [11] strongly suggests
that Collembola and Diplura do not form a monophyletic
group. Instead Diplura are the sistergroup to ectognathous
insects (bristletails, silverfish and winged insects) and Collembola the sistergroup to Protura (Ellipura hypothesis;
figure 2). Additionally, SMIs of any type are not known to
occur in crustaceans [34,35]. Thus, the presence of a homologous SMI in Collembola and Diplura implies the presence of
this basic principle in stemgroup representatives of the entire
Hexapoda.
Although the SMI in Collembola and Diplura is based on
homologous structures, the general principle is morphologically variable among early insects (figure 2). Recently,
another SMI type was discovered in the ectognathous
Archaeognatha [31], but its structural basis is different: the
maxillary palpus instead of the stipes interacts via a protuberance with the anterior side of the mandible and prevents
an anterior sheering out of the mandible during movement.
The SMI in entognathous Protura is formed by the so-called
fulcro-tentorium [36] as well as the anterior portion of the
stipital body, both of which act as a ‘sheath’ guiding the
4
Proc. R. Soc. B 282: 20151033
(b) Anatomy of the structural mouthpart interaction
in Collembola
effect that the maxillae are stabilizing the entire movement
sequence of the mandibles.
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ventral base of the incisival area of the mandible. The other contact point is formed by a spine-like apodeme of the head
capsule (APHC; figure 1b,c), which is in contact with the
dorsal base of the incisival area right opposite the APHY.
The APHC and APHY are connected to each other at the
inner mandibular rim, thus forming an arch enclosing the
mandible (figure 1c). The mandible of Diplura is moved by
nine muscles; most of these serve double functions depending
on the location of the mandible during movement (electronic
supplementary material S2).
Mandible movement in Diplura is a combination of
protraction –adduction with retraction –abduction as countermovements (electronic supplementary material, movie S1a).
The three interaction points serve as crucial guiding structures for the mandibles during food uptake. The stipital
stud prevents a lateral evasion of the posterior part of the
mandible, while the apodemes of head and hypopharynx
collectively serve as ‘splints’ preventing dorsal and ventral
sheering out of the mandibles during movement (electronic
supplementary material, movie S1a).
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Ma
400
Holometabola
Psocodea
Condylognatha
Polyneoptera
Palaeoptera
Palaeodyct.
Zygentoma
Archaeognatha
Diplura
Collembola
Protura
DEV
loss of SMI
SIL
450
ORD
first occurrence of SMI
origin of terrestrial fungi
500
interactions between mouthparts
mandible
maxilla
axis of rotation
mandible interactions with the head and/or endoskeleton
mandible movement
maxilla movement
Figure 2. Evolution of structural mouthpart interactions in insects mapped on a transcriptome-based phylogenetic tree and divergence time estimates [11]. Shapes
of mouthparts and articulation points are shown as simplified models, mandible and maxilla movements with red and blue arrows respectively. Note that the same
forms of interaction points indicate putative homologous structures across taxa. Also note the differing SMI solutions to achieve mandible stabilization during food
uptake in Protura, Collembola, Diplura and Archaeognatha. The common ancestor of insects (Hexapoda) probably already possessed a mandible – maxilla SMI. The
occurrence of SMI can be correlated with the origin of fungi during the Ordovician [29], one of the principal diets of recent Collembola and Protura [4,23,30].
In bristletails (Archaeognatha), an anterior mandibular articulation (dicondyly) evolved [31], which made other supporting or stabilizing structures obsolete
during the further evolution of dicondyly in silverfish (Zygentoma) and winged insects (Pterygota). Structural mouthpart interaction again occurs in extinct Palaeodictyopterida, extant Condylognatha (true bugs and thrips), and a large parts of Holometabola (e.g. bees, butterflies and flies), where mouthparts function as
guiding structures for other mouthparts or even fuse together. The occurrence of these new mouthpart types again can be correlated with the evolution of
food sources such as diverse plant and animal fluids [2,32].
mandible during protraction (figure 2; electronic supplementary material, three-dimensional model S5 and [30]). Owing
to these morphological differences, the SMIs of Archaeognatha
and Protura appear not homologous to the SMI in Collembola
and Diplura.
It has been suggested that patterns of Hox gene expression
are correlated with the evolution of novel mouthpart morphologies [37–39]. In Protura, Collembola and Diplura,
Hox gene expression in developing mouthparts has not been
studied yet; therefore, the influence of these regulatory mechanisms on the general principle is unclear. It could be
rewarding to investigate gene expression patterns in Protura,
Collembola and Diplura in order to clarify the evolution
of gene expression patterns characteristic for structurally
interacting mouthparts.
It remains equally unclear until which point SMIs are exhibited in the stemline of early insects before this principle occurs
again in more derived insects (figure 2). The enormous, winged
Palaeodictyopterida, the only major insect group to have
become extinct, had stylet-like paired mandibles and maxillae,
and a hypopharynx [40]. These were interlocked with each
other [2,40], thus representing the basic principle of SMI.
Evidence suggests that their diet consisted mainly of plant
fluids [2,32]. The phylogenetic placement of Palaeodictyopterida is a matter of debate (figure 2). They are placed as
sistergroup to modern dragonflies (Odonata [1]), as sistergroup
to Palaeoptera (Ephemeroptera þ Odonata [41]) or even as
sistergroup to Neoptera [42].
Regardless of the position of Palaeodictyopterida, the
biting–chewing mouthpart type with mandibles connected to
the head via articulations, as shown in Archaeognatha, can no
longer be attributed as the plesiomorphic condition in insects.
Rather, the entognathous piercing–sucking functional mouthpart unit with elongated, distally pointed mandibles appears
ancestral. Exposed, structurally uncoupled mouthparts are a
groundplan apomorphy of silverfish and winged insects.
It is assumed that mouthpart diversification enabled the
exploration of new food sources [43,44], and accordingly was
probably triggered by the evolution of vascular plants
(approx. 415 Ma [45]) and trees (approx. 380 Ma [46]), the
radiation of seed plants (approx. 340–280 Ma [47]) and the
radiation of flowering plants (approx. 120–70 Ma [48,49]).
Likewise, a correlation of the piercing–sucking functional
mouthpart unit with the appearance of non-symbiotic terrestrial fungi [29,50] or bryophytes [46] in the mid-Ordovician is
a likely scenario given the potential origin and diversification
of Collembola and Diplura at the same time as indicated by
recent dating analyses (figure 2) [11]. In this scenario, the
mandibles of the earliest insects are protracted and retracted
through a narrow oral opening (entognathy), and they are
stabilized by the maxillae and hypopharynx to penetrate the
thin cell walls of fungi and plants.
Proc. R. Soc. B 282: 20151033
homologous
SMI type
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Remipedia
5
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Ethics. All research was conducted under appropriate licences for collecting insects ( personal licence 45/7/3).
research program of the DAAD and the University of Tsukuba
(ID 57060275).
6
Data accessibility. All electronic supplements are deposited in the Dryad
Acknowledgements.
rspb.royalsocietypublishing.org
repository at http://dx.doi.org/10.5061/dryad.gf643.
Authors’ contributions. A.B., R.M., M.S., P.V., F.W., K.U. and B.M.
designed the experiments; A.B., P.T.R., R.M., P.V., K.U. and F.W. conducted the experiments; A.B., P.T.R., R.M. and B.M. analysed the
data; and A.B., R.M. and B.M. wrote the manuscript. All authors
read and approved the final version of the manuscript.
Competing interests. We declare we have no competing interests.
Funding. The study received funding from DESY (ID: I-20120065), PSI
References
1.
Grimaldi D, Engel MS. 2005 Evolution of the Insects.
Cambridge, UK: Cambridge University Press.
2. Labandeira CC. 1997 Insect mouthparts: ascertaining
the paleobiology of insect feeding strategies. Annu.
Rev. Ecol. Syst. 28, 153–193. (doi:10.1146/annurev.
ecolsys.28.1.153)
3. von Lieven AF. 2000 The transformation from
monocondylous to dicondylous mandibles in the
Insecta. Zool. Anz. 239, 139–146.
4. Koch M. 2001 Mandibular mechanisms and the
evolution of hexapods. Ann. Soc. Entomol. Fr. NS 37,
129–174.
5. Wolter H. 1963 Vergleichende Untersuchungen zur
Anatomie und Funktionsmorphologie der stechendsaugenden Mundwerkzeuge der Collembolen. Zool.
Jahrb. Anat. 81, 27 –100.
6. Pass G, Szucsich NU. 2011 100 years of research on
the Protura: many secrets still retained. Soil Org. 83,
309–334.
7. Schaller F. 1970 Collembola (Springschwänze).
Berlin, Germany: Walter de Gruyter.
8. Dallai R. 1998 New findings on dipluran
spermatozoa. In The Fifth European Congress of
Entomology, p. 291. Ceské Budejovice, Czech
Republic: European Congress of Entomology.
9. Tomizuka S, Machida R. 2015 Embryonic
development of a collembolan, Tomocerus
cuspidatus Börner, 1909: with special reference to
the development and developmental potential of
serosa (Hexapoda: Collembola, Tomoceridae).
Arthropod Struct. Dev. 44, 157 –172. (doi:10.1016/j.
asd.2014.12.004)
10. Ikeda Y, Machida R. 2001 Embryogenesis of the
dipluran Lepidocampa weberi Oudemans (Hexapoda:
Diplura, Campodeidae): formation of dorsal organ
and related phenomena. J. Morphol. 249,
242–251. (doi:10.1002/jmor.1052)
11. Misof B et al. 2014 Phylogenomics resolves the
timing and pattern of insect evolution. Science 346,
763–767. (doi:10.1126/science.1257570)
12. Beckmann F, Herzen J, Haibel A, Müller B, Schreyer
A. 2008 High density resolution in synchrotronradiation-based attenuation-contrast
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
microtomography. Proc. SPIE 7078, 70781D –
70781D-13. (doi:10.1117/12.794617)
Stampanoni M, Marone F, Modregger P, Pinzer B,
Thüring T, Vila-Comamala J, David C, Mokso R. 2010
Tomographic hard X-ray phase contrast micro- and
nano-imaging at TOMCAT. AIP Conf. Proc. 1266,
13 –17. (doi:10.1063/1.3478189)
Uesugi K, Hoshino M, Takeuchi A, Suzuki Y, Yagi N.
2012 Development of fast and high throughput
tomography using CMOS image detector at
SPring-8. Proc. SPIE 8506, 85060I. (doi:10.1117/12.
929575)
Ogurreck M, Wilde F, Herzen J, Beckmann F,
Nazmov V, Mohr J, Haibel A, Müller M, Schreyer A.
2013 The nanotomography endstation at the PETRA
III imaging beamline. J. Phys. Conf. Ser. 425,
182002. (doi:10.1088/1742-6596/425/18/182002)
Uesugi K. 2015 In preparation. The full field X-ray
microscope at BL47XU (SPring-8, Japan).
D’Haese CA. 2003 Morphological appraisal of
Collembola phylogeny with special emphasis on
Poduromorpha and a test of the aquatic origin
hypothesis. Zool. Scr. 32, 563 –586. (doi:10.1046/j.
1463-6409.2003.00134.x)
D’Haese CA. 2002 Were the first springtails semiaquatic? A phylogenetic approach by means of 28S
rDNA and optimization alignment. Proc. R. Soc. Lond.
B 269, 1143–1151. (doi:10.1098/rspb.2002.1981)
Xiong Y, Gao Y, Yin W, Luan Y. 2008 Molecular
phylogeny of Collembola inferred from ribosomal
RNA genes. Mol. Phylogenet. Evol. 49, 728–735.
(doi:10.1016/j.ympev.2008.09.007)
Fiala JC. 2005 Reconstruct: a free editor for serial
section microscopy. J. Microsc. 218, 52 –61. (doi:10.
1111/j.1365-2818.2005.01466.x)
Yushkevich PA, Piven J, Hazlett HC, Smith RG, Ho S,
Gee JC, Gerig G. 2006 User-guided 3D active contour
segmentation of anatomical structures: significantly
improved efficiency and reliability. NeuroImage
31, 1116–1128. (doi:10.1016/j.neuroimage.2006.
01.015)
Manton SM, Harding JP. 1964 Mandibular
mechanisms and the evolution of Arthropods. Phil.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
Trans. R. Soc. Lond. B. 247, 1 –183. (doi:10.1098/
rstb.1964.0001)
Hoffmann RW. 1908 Über die Morphologie und
Funktion der Kauwerkzeuge und über das
Kopfnervensystem von Tomocerus plumbeus L. (III.
Beitrag zur Kenntnis der Collembolen). Z. für Wiss.
Zool. 89, 598 –689 (þ5 plates).
Manton SM. 1977 The Arthropoda: habits, functional
morphology and evolution. Oxford, UK: Clarendon
Press.
Snodgrass RE. 1935 Principles of insect morphology.
Ithaca, NY: Cornell University Press.
Snodgrass RE. 1947 The insect cranium and the
‘epicranial suture’. Smithson. Misc. Collect. 107,
1–52.
DuPorte EM. 1946 Observations on the morphology
of the face in insects. J. Morphol. 79, 371– 417.
(doi:10.1002/jmor.1050790303)
DuPorte EM. 1957 The comparative morphology of
the insect head. Annu. Rev. Entomol. 2, 55– 70.
(doi:10.1146/annurev.en.02.010157.000415)
Redecker D, Kodner R, Graham LE. 2000 Glomalean
fungi from the Ordovician. Science 289,
1920– 1921. (doi:10.1126/science.289.5486.1920)
Tuxen SL. 1964 The Protura. Paris, France:
Hermann.
Blanke A, Machida R, Szucsich NU, Wilde F, Misof B.
2015 Mandibles with two joints evolved much
earlier in the history of insects: dicondyly is a
synapomorphy of bristletails, silverfish and winged
insects. Syst. Entomol. 40, 357 –364. (doi:10.1111/
syen.12107)
Labandeira C, Phillips TL. 1996 Insect fluid-feeding
on Upper Pennsylvanian tree ferns
(Palaeodictyoptera, Marattiales) and the early
history of the piercing-and-sucking functional
feeding group. Ann. Entomol. Soc. Amer. 89,
157–183. (doi:10.1093/aesa/89.2.157)
Beutel RG, Gorb SN. 2006 A revised interpretation
of the evolution of attachment structures in
Hexapoda with special emphasis on
Mantophasmatodea. Arthropod Syst. Phylogeny
64, 3 –25.
Proc. R. Soc. B 282: 20151033
(ID: 20110069 & 20140056) and SPring-8 (ID: 2014B1046) for the
beamline experiments. A.B. was supported by the Japanese Society
for the Promotion of Science (JSPS, ID: P14071) and R.M. by a
Grant-in-Aid from the JSPS (Scientific Research C, ID: 25440201).
A.B. and P.T.R. were additionally partly supported by the joint
Cyrille A. D’Haese provided specimens of
Megaphorura arctica, Lepidocyrtus lignorum, Orchesella sp., Dicyrtoma sp.,
Triacanthella rosea, Neotropiella carli and Brachystomellides neuquensis.
Karen Meusemann helped to collect Podura aquatica, Alex Böhm collected Catajapyx aquilionaris and Kaoru Sekiya provided Occasjapyx
japonicus, O. akiyamae and Lepidocampa weberi. Atlasjapyx cf. atlas was
kindly provided by Thomas Wesener. Felix Beckmann and Julia
Herzen (both Helmholtz-Zentrum Geesthacht) helped during the experiments at DESY beamlines DORIS III/BW2 and PETRA III/IBLP05. We
furthermore thank Sina David, Karen Meusemann, Björn von Reumont,
Katrin Wittig, Susanne Düngelhoef, Thorsten Klug, Makiko Fukui,
Toshiki Uchifune and Yoshie Jintsu-Uchifune for their help during the
beamline experiments. Nikola Szucsich gave useful advice during
the preparation of the manuscript. Hans Pohl and Torsten Wappler
did the vector drawings of insects in figure 2.
Downloaded from http://rspb.royalsocietypublishing.org/ on June 17, 2017
41.
42.
44.
45. Steemans P, Hérissé AL, Melvin J, Miller MA, Paris F,
Verniers J, Wellman CH. 2009 Origin and radiation
of the earliest vascular land plants. Science 324,
353. (doi:10.1126/science.1169659)
46. Kenrick P, Crane PR. 1997 The origin and early
evolution of plants on land. Nature 389, 33 –39.
(doi:10.1038/37918)
47. Pryer KM, Schneider H, Smith AR, Cranfill R, Wolf
PG, Hunt JS, Sipes SD. 2001 Horsetails and ferns are
a monophyletic group and the closest living
relatives to seed plants. Nature 409, 618–622.
(doi:10.1038/35054555)
48. Doyle JA. 2012 Molecular and fossil evidence on
the origin of angiosperms. Annu. Rev. Earth
Planet. Sci. 40, 301– 326. (doi:10.1146/annurevearth-042711-105313)
49. Nel A et al. 2013 The earliest known
holometabolous insects. Nature 503, 257–261.
(doi:10.1038/nature12629)
50. James TY et al. 2006 Reconstructing the
early evolution of fungi using a six-gene
phylogeny. Nature 443, 818–822. (doi:10.1038/
nature05110)
7
Proc. R. Soc. B 282: 20151033
43.
evidence. Can. J. Zool. 68, 1807 –1834. (doi:10.
1139/z90-262)
Kukalová-Peck J. 2008 Phylogeny of higher taxa
in Insecta: finding synapomorphies in the extant
fauna and separating them from homoplasies.
Evol. Biol. 35, 4 – 51. (doi:10.1007/s11692-0079013-4)
Sroka P, Staniczek AH, Bechly G. 2014 Revision of
the giant pterygote insect Bojophlebia prokopi
Kukalová-Peck, 1985 (Hydropalaeoptera:
Bojophlebiidae) from the Carboniferous of the Czech
Republic, with the first cladistic analysis of fossil
palaeopterous insects. J. Syst. Palaeontol. 0, 1 –20.
(doi:10.1080/14772019.2014.987958)
Bernays EA, Jarzembowski EA, Malcolm SB. 1991
Evolution of insect morphology in relation to plants.
Phil. Trans. R. Soc. Lond. B 333, 257–264. (doi:10.
1098/rstb.1991.0075)
Krenn HW. 2010 Feeding mechanisms of
adult lepidoptera: structure, function, and
evolution of the mouthparts. Annu. Rev. Entomol.
55, 307– 327. (doi:10.1146/annurev-ento-112408085338)
rspb.royalsocietypublishing.org
34. Fortey RA. 1998 Arthropod relationships. Berlin,
Germany: Springer.
35. Schram FR. 1986 Crustacea. New York, NY: Oxford
University Press.
36. François J, Dallai R, Yin WY. 1992 Cephalic anatomy
of Sinentomon erythranum Yin (Protura:
Sinentomidae). Int. J. Insect Morphol. Embryol. 21,
199–213. (doi:10.1016/0020-7322(92)90016-G)
37. Angelini DR, Kaufman TC. 2004 Functional analyses
in the hemipteran Oncopeltus fasciatus reveal
conserved and derived aspects of appendage
patterning in insects. Dev. Biol. 271, 306 –321.
(doi:10.1016/j.ydbio.2004.04.005)
38. Angelini DR, Liu PZ, Hughes CL, Kaufman TC. 2005
Hox gene function and interaction in the
milkweed bug Oncopeltus fasciatus (Hemiptera).
Dev. Biol. 287, 440 – 455. (doi:10.1016/j.ydbio.
2005.08.010)
39. Angelini DR, Kaufman TC. 2005 Insect appendages
and comparative ontogenetics. Dev. Biol. 286,
57 –77. (doi:10.1016/j.ydbio.2005.07.006)
40. Shear WA, Kukalová-Peck J. 1990 The ecology
of Paleozoic terrestrial arthropods: the fossil