Comparative Morphology and Ultrastructure of the Duf

11(3/4):
Entomol.Gener.
165-181
Stuttgart 1986-05
ISSN: 0171-8177
VII
EGT-Nr 517
Comparative Morphology and Ultrastructure
of the Duf~ Gland in Ants (Hymenoptera: Formicidae)*
Ii
JohanP.J. Dillen**
Received: 1985-02-25
Accepted: 1985-09-13
Billen, J. P. J. [Zool. Inst., Univ., B-3000 Leuven]: Comparative Morphology and Ultrastructure of the Dufour Gland in Ants (Hymenoptera: Formicidae). -Entomol. Gener.
11(3/4): 165-181; Stuttgart 1986. -[Article].
The Dufour gland in ants essentially is a sac-like reservoir which is lined by a monolayered
glandular epithelium. The gland cells are characterized by a well developed smooth-surfaced endoplasmic reticulum and numerous but rather small mitochondria. Numerous
multilamellar inclusions probably represent some stage of secretion. -Considerable
differences, however, can be observed in the cellular organization in the several ant subfamiliae, as was revealed by a comparative study of 60 speciesbelonging to 8 subfamiliae.
In this way, a rather simple epithelium without special modifications was found in most
of the Myrmicinae and Ponerinae. In the African Dorylinae, the epithelium has a crenellated appearance and numerous basal invaginations, while the New World Ecitoninae have
a very uniform epithelium with a basal layer of membrane foldings. Myrmeciinae,
Pseudomyrmecinae and Dolichoderinae, each show a different kind of apical microvilli,
whereas Formicinae exhibit a characteristic subcuticular layer of mitochondria and a
very thick basementmembrane.
Billen, J. P.J. [Zool. Inst., Univ., B-3000 Leuven]: Vergleichende Morphologie und Ultrastruktur der Dufour-Druse bei Ameisen (Hymenoptera: Formicidae). -Entomol. Gener.
11(3/4): 165-181; Stuttgart 1986. -[Abhandlung].
Die Dufourdriise del Ameisen ist ein sackformiger Speicher, bekleidet von einem einschichtigen Driisenepithelium. Die Driisenzellen sind gekennzeichnet duTch ein gutentwickeltes glattes endoplasmatisches Retikulum und enthalten viele kleine Mitochondrien.
Zahlreiche multi1amellare Korperchen wiederspiegelnerne bestimmte Phasein del Sekretion. -Eine vergleichende Untersuchung von 60 Arten, 8 Unterfamilien angehorend,
zeigt jedoch, d~ betriichtliche Unterschiede in der Zellorganisation zwischen verschiedenen Unterfamilien existieren. So ist in den meisten Myrmicinae und Ponerinae ein
ziemlich einfaches Epithelium ohne besondere Kennzeichen vorhanden. Bei den afrikanischen Dorylinae sieht das Epithelium zinnenformig aus mit vielen basalen Einstiilpungen, wiihrend die Ecitoninae aus der Neuen Welt ein gleichformiges Epithelium zeigen
mit einer basalen Schicht von Membranfaltungen. Myrmeciinae, Pseudomyrmecinaeund
Dolichoderinae haben aile ihren Eigentyp von apikalen Mikrovilli, wohingegenFormicinae
erne charakteristische subkutikulare Schicht von Mitochondrien sowie erne sehr dicke
Basalmembranbesitzen.
* Paperdelivered: XVII Internat. Congressof Entomology; Hamburg/FRG: 1984-08-20/26
** Senior research assistantof the Belgian National Fund for Scientific Research.
0171-8177/86/0011-0165$ 4.25
@ 1986 E. Schweizerbart'sche Verlagsbuchi!andlung.
D-7000 Stuttgart 1
166 -Johan P.J. Bil1en
Introduction
Although its first description by L. Dufour dates from 1841, the actual knowledge on the
Dufour glanq is very limited. The gland is found in the workers [~~]l and queens [2C?r
of all social Hymenoptera, and originally is an accessorygland of the female reproductive
system. In old literature, it therefore has often been referred to as 'accessorygland', or
has been given the chemically misleading name 'alcalic gland'. Information on the Dufour
gland [D-G]3 in Formicidae (as well as in Apidae) so far mainly focused on the chemical
analysis and biological activity of the secretion.
The attribution of a well-defined and general function to Dufour's gland, however,seems
most precarious. Its relationship with the female reproductive system for a long time has
suggesteda function as a sting lubricant facilitating egg deposition. Many bee speciesuse
their Dufour gland secretion for brood cell lining [Cane 1981], or mix it with the pollen
balls [Duffield et alii 1983]. In both situations it servesas food for the growing larvae
[Norden et alii 1980]. The Dufour gland in ants has been reported as the source of alarm
pheromones in Formicinae [Wilson & Regnier 1971], Myrmeciinae [Robertson 1971] and
Myrmicinae [Cammaerts-Tricot 1974]. Some other myrmicine species are known to
produce their trail substancesin the Dufour gland [Ritter et alii 1977; Vander Meer et alii
1981]. Another function assigned to Dufour's gland in a number of species is one of
territorial marking [Holldobler & Lumsden 1980]. In most groups, however,the function
of the gland is unknown or insufficiently investigated.
Information on the Dufour gland morphology in ants mainly refers to some general
anatomical and light microscopical data [Callahan et alii 1959;Hermann& Blum 1967a,b;
Robertson 1967; Wilson & Regnier 1971; Beck 1972]. Ultrastructural investigations so far
are restricted to a rather short contribution on Camponotus rnfipes [Gama & Cruz
Landim 1977] and a few other Israeli Formicinae [Hefetz & Orion 1982], and to a
description of the Dufour gland closing apparatus in Formica sanguinea [Billen 1982].
We here report on the Dufour gland morphology-and ultrastructure in 60 speciesbelonging
to 8 subfamiliae: Myrmicinae, Ponerinae, Dorylinae, Ecitoninae, Myrmeciinae, Pseudomyrmecinae, Dolichoderinae and Formicinae.
2 Material and methods
Over 300 1(1(and 29 representing 60 species from allover the world have been investigated in this study. For convenience, they will be mentioned per subfamilia along with
the corresponding results.
The ants after air shipment to Belgium were killed by momentary immersion in liquid
nitrogen and prepared for electron microscopy. Either abdominal halves or dissected
Dufour glands were fixed in 2 % cold glutaraldehyde (buffered with 0.05 M sodium
cacodylate and 0.15 M saccharose)and postfixed in 2 % osmium tetroxide. Uranyl acetate
bloc-stained samples were dehydrated in acetone, embedded in Araldite, and sectioned
with a Reichert llitracut microtome. Double-stained grids were viewed in a Philips EM
400 electron microscope.
1 worker(s);in further text: ~(IIII)
2 queen(s); in further text: !i>(W)
3 Dufour gland; in further text: D-G
Morphology
and Ultrastructure
of Dufour Gland -167
3 Results
The Dufour gland essentially is a simple sac that opens in the sting base or near the
abdominal tip in the stinglessFormicinae. A single layer of epithelial cells both acts as the
site of glandular activity and as the reservoir lining. The general appearanceof the gland
can be small and pear-shapedas in Dolichoderinae, Dorylinae and Ecitoninae, and most
Myrmicinae. In other Myrmicinae (such as Harpagaxenus and Messar) as well as in
Myrmeciinae, Pseudomyrmecinae and Ponerinae it is narrow and tubiform. Most
Formicinae are characterized by a heart-shaped Dufour gland (Fig 1). Although the
general aspect of a monolayered epithelium, lined with a cuticula and surrounded by a
basement membrane [B-M]4, sounds very simple, we find a considerable variation among
the numerous species investigated. For that reason, the several subfamiliae will be described separately.
Fig 1: Variation of the Dufour gland
with a tubular, pear- or heart-shaped
appearance. The gland opens in the
stingbase or, as in the stingless
Formicinae, near the abdominal tip
(drawn in black).
3.1 Myrmicinae
List of speciesinvestigated, together with their locality of origin:
Acromyrmex octospinosus (Reichert 1793)
Aphaenogasterfulva Roger 1863
Aphaenogaster spinosa nitida (Emery 1895)
Atta cephalotes (Linnaeus 1758)
Atta laevigata F. Smith 1858
A tta sexdensrubropilosa Forel1908
Atta sexdens sexdens (Linnaeus 1758)
Crematogasterlineolata (Say 1836)
Crematogasterscutellaris (Olivier 1791)
Harpagoxenus sublaevis (Nylander 1856)
Leptothorax acervorum (Fabricius 1793)
Messor capitatus (Latreille 1798)
Messorminor (Andre 1881)
Messor sanctus bouvieri Bondroit 1918
Santa Cruz Valley
Utica, New York
Calvi
Santa Cruz Valley
Ca1aboso
SaDPaulo
Timheri Int'l
Utica, New York
Calvi
Dobiacco
Dobiacco
Barcelona
Solenzara
Benidorm
Messor structor (Latreille 1798)
Monomorium salomonis sommieri Emery 1908
Istanbul
Istanbul
Myrmica rubra (Linnaeus 1758)
Myrmicaria baumi Fore1 1901
Pogonomyrmex occidentalis (Cresson 1879)
Solenopsisgeminata (Fabricius 1804)
AIken
Lusaka
Denver,Colorado
Galle
basementmembrane; in further text: B-M
Trinidad
U.S.A.
Corsica
Trinidad
Venezuela
Brasil
Guyana
U.S.A.
Corsica
Italy
Italy
Spain
Corsica
Spain
Turkey
Turkey
Belgium
Zambia
U.S.A.
Sri Lanka
168 -Johan P.J. Bi11en
Strongylognathus testaceus(Schenck 1852)
Tetramorium caespitum (Linnaeus 1758)
Tetramorium semilaeveAndre 1881
Heythuyzen
Heythuyzen
Calvi
Netherlands
Netherlands
Corsica
The Dufour gland epithelium in the Myrrnicinae generally has a uniform thickness that
varies from approx 5 J,lm (Harpagoxenus, Myrmica, Tetramorium; Fig 2) up to 20 J,lm
(Aphaenogaster,Monomorium). Only the leaf-cutting ants (Acromyrmex, Atta) are slightly
exceptional with an irregular and more or less crenellated epithelial wall [Billen et alii
1984] .
Nuclei are rounded and display a dispersed chromatin (Fig 2). The cytoplasm is characterized by a very well developed smooth-surfaced endoplasmic reticulum and Golgi complex
(Fig 3), while mitochondria and multilamellar inclusions are also fairly numerous. Lipid
droplets generally are rare, except for the basal region of the epithelium in Aphaenogaster
spinosav. nitida (Fig 4). Apart from a few microvillar projections, the apical and basal cell
membranes closely adhere to the cuticle and B-M, respec.The cuticle has a thickness from
0.2-O.7J,lm, and shows an electron-dense but thin epicuticular layer and an electron-lucid,
fibrillar endocuticle (Fig 3). The thickness of the thin B-M varies bet. 30-80 nm.
Surrounding the epithelium are numerous muscle fibres (Figs 2,4) and a few tracheoles
and nerve fibres.
3.2 Ponerinae
Ectatomma quadridens (Fabricius 1793)
Ectatomma ruidum Roger 1861
Ectatomma tuberculatum (Olivier 1791)
Gnamptogenys strigata (Norton 1871)
Megaponera foetens Mayr 1862
Neoponera apicalis (Latreille 1802)
Odontomachus assiniensisEmery 1892
Pachycondyla soror Emery 1899
Caracas
Tuxt1a Chico
Tuxt1a Chico
Rancho del Carmen
Kizu, Mayombe
Tuxt1a Chico
Kigali
Mwebe
Venezuela
Mexico
Mexico
Mexico
Zaire
Mexico
Ruanda
Zaire
The Dufour gland of Ponerinae strongly resemblesthat in the Myrmicinae. The epithelial
thickness within a single individual is very constant, though it may vary considerably,
ranging from 1-25 p.m,among conspecific and especiallyheterospecific individuals.
The cytoplasm shows a similar composition as in the Dufour gland of Myrmicinae with
the very well elaborated smooth endoplasmic reticulum in a predominant appearance
(Fig 5,6). The apical cell membrane tightly adjoins the cuticle, the thickness of which
varies bet. 0.2 & 0.5 .urn(Fig 5). Basalinvaginations may occur, but are not nearly as well
developed as in some other subfamiliae (Fig 6). The epithelium is surrounded by a thin
B-M (approx 35 nm), a well developed muscle layer, tracheoles and a few nerve fibres.
3.3 Dorylinae
Anomma kohli (Wasmann 1904)
Anomma molestum Gerstaecker 1858
Anomma nigricans (Illiger 1802)
Dorylus affinis Shuckard 1840
Dorylus wilverthi Emery 1899
Kigali
Nairobi
Kigali
Kigali
Kizu, Mayombe
Ruanda
Kenya
Ruanda
Ruanda
Zaire
Figs 2-6: Electron micrographs of Dufour gland epithelium in Myrmicinae (2-4) and
Ponerinae (5-6), showing the well developed smooth endoplasmic reticulum as a major
cytoplasmic element. -2: epithelium in Tetramorium caespitum(Linnaeus 1758)[x7,700].
Morphology and Ultrastructure of Dufour Gland -169
3: apical cytoplasm and cuticle in Messor structor (Latreille 1798) [x 12,400]. 4: basal
cytoplasm and surrounding muscle fibres in Aphaenogaster spinosa nitida (Emery 1895)
[x7,850]. S: apical cytoplasm in OdontomachusassiniensisEmery 1892 [x 8,000]. 6: basal
cytoplasm in Ectatomma quadridens (Fabricius 1793) [x 17,300].
170 -Johan P. J. Billen
The African army ants or Dorylinae investigated all show a very characteristic D-G. The
epithelium, with a thickness bet. 10 & 20 .urn, displays numerous apical projections at
5-10 .urn intervals, resulting in a crenellated appearance when sectioned (Fig 7). Crenel
tops as a rule correspond with the apical region of intercellular junctions. Moreover, basal
invaginations and the very much folded lateral cell membranes [C-M]5 give a very capricious aspect to the cell shape. The apical CoMclosely follows the cuticular lining without
any microvillar differentiation. The cuticular thickness varies from 0.5 up to and over
1.um.
Nuclei of the doryline Dufour gland epithelium are found in the basal half of the cells
and are slightly lobate. The cytoplasm contains numerous multilamellar inclusions in
addition to the smooth endoplasmic reticulum and mitochondria (Fig 7). Only a few
muscle fibres, compared to most other subfamilies, lie beneath the epithelium and its thin
(30-100 nm) B-M.
3.4 Ecitoninae
Only one single New World army ant specieswas available, namely Eciton burchelli urichi
Fore11899, originating from Arima Valley in Trinidad. The Dufour gland epithelium of
these Eciton ~~ is markedly different from that in the Old World Dorylinae by its very
uniform thickness (7-l0jJ.m). Most of the basal epithelium half is occupied by an abundance of horizontally occurring membrane foldings (Fig 8). These correspond to the
extremely twisted lateral CoM and are not to be considered as basal invaginations. The
basal CoMitself indeed very closely adheres without any appearanceof invagination to the
B-M which is about 70 nm thick. Also the apical CoMdoes not show any differentiation
and runs parallel to the cuticle. The latter has a thickness of approx. 0.5 jJ.m,and is provided with numerous small epicuticular fringes (Fig 8).
The cytoplasm contains the usual organelles such as mitochondria, multilamellar and
multivesicular inclusions, and smooth endoplasmic reticulum, though its contents may be
heavily masked due to the many membrane folds. The more or less flattened nuclei are
found in the apical epithelium half.
The gland is surrounded by a well developed and continuous muscle layer, a few tracheoles
and nerve fibres.
3.5 Mynneciinae
Myrmecia
Myrmecia
gulosa (Fabricius 1775)
vindex Fr. Smith 1858
Sydney
Bentley
NSW, Australia
W.-Australia
The epithelial thickness of the mynneciine Dufour gland can vary from 5 to 40 .urn
according to the individual. Within the same ~, the epithelium is fairly uniform, though
several basal protrusions are observed that give a characteristic appearanceto the gland
(Fig 10). A typical feature is the interruption of the muscle layer in these areas,that can
have a diameter from less than 5 up to severaltens of micrometres.
Another characterizing feature in Myrmecia is the apical border with rather short and
robust microvilli, that have a length of approx. 0.5 .urn and a diameter of 0.1 .urn(Fig 9).
Underneath the microvillar area a considerable network of microtubules is found. Most of
the cytoplasm is occupied by small vesicles of smooth endoplasmic reticulum, numerous
small mitochondria and a large number of multilamellar bodies (Figs 10 and 11). The
5 cell membrane; in further text: C-M
Morphology
--
and Ultrastructure
of Dufour Gland -171
Figs 7-8: Dufour gland epithelium in the Old and New World army ants. -7: crenelated
epithelium in Anomma nigricans (llliger 1802) with basalinvaginations (Old World Dorylinae). Intercellular junctions correspond with crenel tops [x 5,000]. 8: uniform epithelium
in Eciton burchelli urichi Forel1899 (New World Ecitoninae), showing very much folded
lateral cell membranes in the basal region [x5,000].
172 -Johan P. J. Billen
Figs 9-13: Dufour gland in Myrmicinae (9-11) and Pseudomyrmecinae (12-13). 9: cuticula and apical microvillar border with underlaying network of microtubules in
172 -Johan P. J. Billen
Figs 9-13: Dufour gland in Myrmicinae (9-11) and Pseudomyrmecinae (12-13).9: cuticula and apical microvillar border with underlaying network of microtubules in
Morphology and Ultrastructure of Dufour Gland
173
cuticle of the myrmeciine D-G has a thicknessthat variesbet. 0.5 & 2.0 lim. The B-M
measuresapprox. 70 nm. -Nerve fibres (Fig 10),tracheolesand musclessurroundthe
gland,the musclefibres,however,beinginterruptedby the protrusionsmentionedabove.
3.6 Pseudomyrmecinae
The only pseudomyrmecine speciesavailable for this study wasPseudomyrmex termitarius
Fr. Smith 1855, originating from Caracas,Venezuela. Its Dufour gland epithelium has a
more or less wavy appearance with a thickness of approx. 5 llm (Fig 13). Nuclei are
slightly flattened, while other cytoplasmic constituents mainly refer to smooth endoplasmic reticulum, numerous mitochondria and some multilamellar bodies. The gland's
most distinguishing feature are the locally grouped microvillar clusters, that are separated
from each other by areascovered with an undifferentiated apical CoM(Figs 12,13). These
clusters often occur in association with intercellular junctions, the microvilli being formed
by both contributing cells (Fig 12). This association, however,is facultative, while similar
clusters are also observed 'within' a single cell. The D-G cuticle in Pseudomyrmex has a
thickness of approx 0.5 llm, its B-M measuresaround 20 nm. A well developed muscle
layer surrounds the gland.
3.7 Dolichoderinae
Bothriomyrmex decapitans Santschi 1911
Ouka'imeden
Dolichoderus quadripunctatus (V on Linne 1771) Wiirzburg
Iridomyrmex humilis (Mayr 1868)
Barcelona
Tapinoma nigerrimum (Nylander 1856)
Calvi
Morocco
Germany
Spain
Corsica
The dolichoderine Dufour gland epithelium has a very uniform thickness ranging bet. 10
& 20 IJ.maccording to the species.Its nuclei are very rounded and occur in the basal cell
half (Fig 14). The cytoplasm, in addition to the smooth endoplasmic reticulum and
relatively few mitochondria, contains fairly numerous and conspicuous vacuoles,that can
reach a diameter of up to 3 IJ.m.The apical CoMshows some irregularly arrangedmicrovilli with a length up to 2 J.J.In
and a diameter bet. 100 and 150 nm (Fig 15). These seem
to penetrate into the very clear and structureless basal part of the cuticula. Also the
epicuticula, at least in Tapinoma nigemmum, has an electron-lucid appearancein comparison with other subfamiliae. The overall thickness of the cuticula varies from 0.5-3IJ.m.
The basal CoM closely follows the thin B-M, that has a thickness of SOnm. Muscle and
nerve fibres, and tracheoles, in contrast to most other subfarniliae, are rarely found
around the D-G of Dolichoderinae.
3.8 Formicinae
Acantholepis velox Santschi 1917
Camponotus aethiops (Latreille 1798)
Istanbul
Calvi
Turkey
Corsica
Myrmecia gulosa (Fabricius 1775) [x21,700]. 10: basal protrusion of the epithelium in
M. gulosa. Note the presence of nerve fibres and the interruption of the muscle layer
[xl,600]. 11: detail of cytoplasm in M. gulosa, showing numerous multilamellar bodies
and vesicles of smooth endoplasmic reticulum [x7,000]. 12: cuticula and apical cytoplasm
in Pseudomyrmex termitarius Fr. Smith 1855, with cluster of microvilli [x 15,200].
13: epithelium in P. termitarius with surrounding muscle fibres. The apical cell membrane
shows local clusters oj microvilli (arrows) [x5,900].
174 -Johan P. J. Billen
Figs 14-17: Dufour gland epithelium in Dolichoderinae (14-1 5).'andFormicinae (16-17),
-14: epithelium in Tapinoma nigerrimum (Nylander 1856), showing irregularly arranged
apical microvilli [x4,550]. 15: detail of microvilli penetrating into lower cuticular layer in
Morphology
and Ultrastructure
Camponotus fulvopilosus (De Geer 1778)
Camponotus lateralis (Olivier 1791)
Camponotus pictiventris Mayr 1901
Cataglyphis nodus (Brulle 1832)
Formica cunicularia Latreille 1798
Formica fusca Linnaeus 1758
Formica pratensis Retzius 1783
Formica sanguinea Latreille 1798
Lasius flavus (Fabricius 1781)
Lasius flavus nearcticus Wheeler 1906
Lasius fuliginosus (Latreille 1798)
Lasius niger (L~naeus 1758)
Plagiolepis pygmaea (Latreille 1798)
Polyrhachis militaris cupreopubescensForel1858
of Dufour Gland -175
Lusaka
Calvi
Louis Trichardt
Elazi~
Heythuyzen
Heythuyzen
Heythuyzen
Heythuyzen
Heythuyzen
Utica, New York
Heythuyzen
Heythuyzen
Calvi
Kigali
Zambia
Corsica
South-Africa
Turkey
Netherlands
Netherlands
Netherlands
Netherlands
Netherlands
U.S.A.
Netherlands
Netherlands
Corsica
Ruanda
Formicinae show a Dufour gland epithelium with a very uniform thickness, that, according to the individual may range 5-20 .urn. The rounded nuclei occur in the basalhalf of
the epithelium, or are more or less flattened in the low epithelium (Fig 16). The cytoplasm
contains a very elaborate smooth endoplasmic reticulum and Golgi complex, but is
especially characterized by the conspicuous subcuticular layer of mitochondria (Fig 16).
Other mitochondria are scattered in the cytoplasm along with fairly numerous multilamellar bodies. In a few occasionsthe latter were evenobserved in the gland lumen.
The apical CoMruns parallel to the cuticula, which has a mean thickness of 0.3 .urn. Basal
invaginations are quite common and may penetrate a few micrometres into the epithelium. A very constant feature is the very thick B-M, the thickness of which varies from
0.5-0.8 and even over 1 .urn (Fig 17). A very well developed muscle layer, numerous
tracheoles and a few nerve fibres surround the gland (Fig 17).
3.9 The Dufour gland duct
The Dufour gland enters the sting base in a ventral position refering to the poison gland
duct. In the stingless Forrnicinae both glands open near the abdominal tip in a similar
relative relationship. The D-G epithelium in this region considerably differs from the
actual reservoir part. In both stinging and non-stinging species the duct has a slit-like
appearance. A very extensive supply of muscle fibres insert on both its dorsal and ventral
side (Fig 18). The basal outline of the duct epithelium is very irregular due to the numerous muscle attachments, that deeply penetrate between the duct cells. The duct cell
nuclei are found in the sunken basal part (Fig 19). The cytoplasm mainly contains
bundles of microtubules that ensure the structural link between the muscle fibres and the
cuticula. The bundles of myofilaments and micro tubules from both sides adhere to the
confluent basement membrane layer of the muscle fibre and duct cell by means of
hemidesmosomes(Figs 18 and 19). A similar organization ofhemidesmosome attachment
is observed in the microtubular part reaching the cuticular lining of the duct.
1: nigerrimum [x 13,900]. 16: epithelium in Formica sanguineaLatreille 1798. (Note the
subcuticular layer of mitochondria, the multilamellar inclusions and thick basement
membrane) [x7,500]. 17: basal cytoplasm with plasmalemma invaginations, and underlaying thick basement membrane, tracheoles and muscle fibres (Formica pratensis Retzius
1783) [x7,850].
176 -Johan P. J. Billen
Figs 18-19: Cross section electron micrographs through the Dufour gland duct, illustrating
the gland's opening and closing mechanism. -18: dorsally and ventrally inserting muscle
fibres upon contraction cause the slit-like duct to open. Closure is probably achieved by
Morphology
and Ultrastructure
of Dufour Gland -177
4 Discussion
The Dufour gland consists of class-1 glandular cells according to the classification of
Noirot & Quennedey [1974]. Consequently, their secretion simply has to cross the overlaying cuticle in order to reach the central lumen. In all ant speciesinvestigated,we find
a glandular epithelium with a very well developed smooth-surfaced endoplasmic reticulum,
fairly numerous mitochondria as well as very characteristic multilamellar or multivesicular
inclusions.
Chemical analysis reveals that the Dufour gland is a unique hydrocarbon source [Blum &
Hermann 1978; Attygalle & Morgan 1984]. Such a type of secretion is in agreementwith
the above mentioned cytological characteristics. The large numbers of multilamellar
bodies according to Hefetz & Orion [1982] ought to be related to secretory micelles that
after migration and transcuticular passageaccumulate in the gland lumen as an oily
secretion. This hypothesis is supported at least by the occurrence of similar multilamellar
bodies in the gland lumen as we could observe in a few formicine species.Moreover, the
appearance of multilamellar inclusions represents a general feature of insect epidermal
glands [Bazire-Benazet & Zylberberg 1979, Delfino et alii 1983, Grandperrin & Cassier
1983; Heroin & Ramade 1970; Noirot & Quennedey 1974, Plattner et alii 1972, Quennedey & Brossut 1975, Stein 1962]. Some of these inclusions most probably are involved
in cellular autophagy and therefore form part of the lysosome system. Their involvement
in cellular degeneration is clearly illustrated by the exuberant appearance in the final
stagesof ovariole regressionin 1111
ants [Billen 1985a]. A similar lysosomal function is also
attributed to the lamellar inclusions in the DoG of the formicine species Camponotus
rufipes [Gama & Cruz Landim 1977]. They often, however,are far too abundant for this
interpretation and therefore seem to support the hypothesis that they have to be considered as secretion figures [Noirot & Quennedey 1974].
Notwithstanding the simple general structure with merely epithelial cells, considerable
differences were observed in the DoGof speciesbelonging to different subfamilies (Fig 20).
This variation in general is very constant within a group and mainly refers to particular
arrangements of the CoM.Apical microvilli occur in Myrmeciinae, Pseudomyrmecinaeand
Dolichoderinae, although their appearanceis different for eachgroup. In Dolichoderinae
they are rather irregularly arranged, long and slender structures that seemto penetrate
into the lower cuticular region. The myrmeciine microvilli, on the other hand, are more
robust and constitute a more regular pattern, while in Pseudomyrmex they are clustered
in local groups. Apart perhaps from a few myrmicine species,all other subfamiliae have a
Dufour gland with an undifferentiated apical cell membrane tightly appressed to the
cuticle.
Invaginations of the basal C-M are most obvious in Dorylinae and Formicinae, while basal
protrusions of the epithelium were only found in Myrmeciinae. Folded lateral C-M may
occur in all species,but are extremely conspicuous in the Ecitoninae.
In addition, Dorylinae are characterized by the crenellated aspect of their DoGand Formicinae by the subcuticular layer of mitochondria and the thick B-M. Both formicine
characters confirm earlier observations in Camponotus rufipes [Gama & Cruz Landim
return of the thickened cuticular intima to a rest position (Tetramorium semilaeveAndre
1881) [x9,600]. 19: ventral region of the Dufour gland duct in Myrmica rubra (Linnaeus
1758), showing myofilaments that deeply penetrate between the duct cells (*). Muscular
forces on the cuticle are transmitted by bundles of microtubules that cross the duct wall
[x8,800].
~
178 -Johan
P. J. Bi11en
MYRMICINAE
PONERINAE
DORYLINAE
ECITONINAE
~
.
,-
c,
-I
PSEUDOMYRMECINAE
MYRMECIINAE
? '?
(
,."..".",""."."""
DOLICHODERINAE
FORMICINAE
Fig 20: Schematical representation of the Dufour gland epithelium in the 8 subfamiliae
investigated [Hymenoptera: Formicidae].
79
7
Morphology and Ultrastructure of Dufour Gland
1977] and a few other Camponotus,Cataglyphis and Polyrhachis species[Hefetz & Orion
1982]. Only Myrrnicinae and Ponerinae lack such features that are distinguishing for the
group.
It is clear from these observations that the morphology of the D-G coincides with the
existing subfamily classification. Whether this variation has any phylogenetic implication,
however, remains an open question. A functional interpretation of the different epithelium
types therefore is required but seemsmost precarious so far.
The clear differences between the doryline and ecitonine D-G at least illustrate the
diphyletic origin of the army ants [Billen 1985b]. The hypothesis of a triphyletic origin
with the Aenictini as a third group according to Gotwald [1979] is a strong incitation to
check the Dufour gland morphology in Aenictus species.Moreover, the number of species
investigated per subfamily should be increased for some groups to allow a more general
interpretation. In this regard, especially Ecitoninae, Myrmeciinae and Pseudomyrmecinae
need more representatives to be checked morphologically. This also applies to both the
tropical Leptanillinae, that were not available so far, as to the rare but taxonomically
critical speciesAneuretus simoni and Nothomyrmecia macrops.
Finally, a common feature of the D-G are the muscle and nerve fibres that surround the
reservoir sac, and that have a role in the discharge of secretion. A conspicuous muscular
supply inserting on the gland's duct acts as a precise control mechanism for ejection. Both
in stinging and non-stinging species,the duct has a slit-like appearance.It is suggestedthat
the dorsal and ventral muscles upon contraction cause an opening of the duct, while
closure could be the passiveresult of a return of the much thickened cuticular intima to a
rest position [Billen 1982]. It should be noted that therefore this opening and closing
mechanism of the D-G is independent from the poison gland secretion mechanism,so that
both glands can discharge their contents separatelyand independently.
5 Abbreviations
bm
ct
ga
hd
Ld
basementmembrane
cuticula
Golgi apparatus
hemidesmosome
lipid droplet
MF
mlb
MT
mv
mvb
muscle fibre
multilamellar body
micro tubules
microvilli
multivesicular body
N
NF
tr
V
nucleus
nerve fibre
tracheole
vacuole
6 Acknowledgements
Numerous ant speciesinvestigated in this study were kindly provided by Prof A. Buschinger, Dr J. M. Cherrett, Dr R. H. Crozier, Mr L. Erasmus, Dr X. Espadaler,Dr D. Fresneau,
Dr K. Jaffe, Dr J. D. Majer,Dr E.E. Martens,Prof E. R. Schockaert,and Dr H.H. W.Velthuis.
In this regard, I especially thank Prof J. K. A. van Boven, and take pleasure in dedicating
this paper to him on the occasion of his seventieth birthday. I am also very grateful to
E. Plaum for preparing the microscope sections, and to Prof M. Van Poucke and Prof
K. Schmidt for reading the manuscript.
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'
Author's address -Anschrift
des Verfassers: Dr Johan P. J. Billen, Laboratorium voor
Systematiek en Ecologie, Zoologisch Instituut K. U. Leuven, Naamsestraat 59, B-3000
Leuven; Belgium, and Limburgs Universitair Centrum, Dept. SBM, Universitaire Campus,
B-36l0 Diepenbeek; Belgium.
Hoffmann, K. H. (Editor): Environmental Physiology and Biochemistry of Insects. [IV x 296 pages, 78 figures, size 127 x 248 mm, balacron hard cover]. -Publishers:
Springer Verlag Berlin -Heidelberg -New York -Tokyo 1985; ISBN: 3-540-13762-9;
price: DM 98.-. ---[EGR-Nr
1071].
The carefully edited book of Hoffmann summarizes in 9 articles different aspects of
adaptations of insects to their environment: 1. Metabolic and Enzyme Adaption to
Temperature (K. H. Hoffmann), 2. Temperature and Insect Development (H. T. Ratte),
3. Environmental Aspects of Insect Dormancy (W. Behrens),4. Metabolic Energy Expenditure and Its Hormonal Regulation (R. Ziegler), 50 Anaerobic Energy Metabolism (G.
Gade),6. Respiration and Respiratory Water Loss (P. Kestler), 7. Water and Salt Relations
(F. Hevert), 8. Color and Color Changes(K. Ho Hoffmann), 9. Environmental Aspects of
Insect Bioluminescence (K. H. Hoffmann). An extensive list of references (895) and a
subject and taxonomic index are included.
The single articles contain a short introduction and conclusion, the results and models are
illustrated by severalfigures and tables. Beside the description of the experimental findings main emphasisis laid on an understanding of the underlying mechanisms.
This book can be recommended to both physiologists and ecologists and the single articles are also good introductions for advancedstudents.
Klaus-Diether Spindler (Dusseldorf)