comparative morphology and ultrastructure of the duf ... · general aspect of a monolayered...

11(3/4):

165-181 ISSN: 0171-8177Entomol. Gener. Stuttgart 1986-05

EGT-Nr 517 VII

Comparative Morphology and Ultrastructureof the Duf~ Gland in Ants (Hymenoptera: Formicidae)*

IiJohan P. J. Dillen **

Received: 1985-02-25 Accepted: 1985-09-13

Billen, J. P. J. [Zool. Inst., Univ., B-3000 Leuven]: Comparative Morphology and Ultra-structure 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 monolayeredglandular epithelium. The gland cells are characterized by a well developed smooth-sur-faced endoplasmic reticulum and numerous but rather small mitochondria. Numerousmultilamellar inclusions probably represent some stage of secretion. -Considerabledifferences, however, can be observed in the cellular organization in the several ant sub-familiae, as was revealed by a comparative study of 60 species belonging to 8 subfamiliae.In this way, a rather simple epithelium without special modifications was found in mostof the Myrmicinae and Ponerinae. In the African Dorylinae, the epithelium has a crenel-lated appearance and numerous basal invaginations, while the New World Ecitoninae havea 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 avery thick basement membrane.

Billen, J. P. J. [Zool. Inst., Univ., B-3000 Leuven]: Vergleichende Morphologie und Ultra-struktur 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 ein-schichtigen Driisenepithelium. Die Driisenzellen sind gekennzeichnet duTch ein gutent-wickeltes glattes endoplasmatisches Retikulum und enthalten viele kleine Mitochondrien.Zahlreiche multi1amellare Korperchen wiederspiegeln erne bestimmte Phase in del Sekre-tion. -Eine vergleichende Untersuchung von 60 Arten, 8 Unterfamilien angehorend,zeigt jedoch, d~ betriichtliche Unterschiede in der Zellorganisation zwischen verschie-denen Unterfamilien existieren. So ist in den meisten Myrmicinae und Ponerinae einziemlich einfaches Epithelium ohne besondere Kennzeichen vorhanden. Bei den afri-kanischen Dorylinae sieht das Epithelium zinnenformig aus mit vielen basalen Einstiil-pungen, wiihrend die Ecitoninae aus der Neuen Welt ein gleichformiges Epithelium zeigenmit einer basalen Schicht von Membranfaltungen. Myrmeciinae, Pseudomyrmecinae undDolichoderinae haben aile ihren Eigentyp von apikalen Mikrovilli, wohingegenFormicinaeerne charakteristische subkutikulare Schicht von Mitochondrien sowie erne sehr dickeBasalmembran besitzen.

* Paper delivered: XVII Internat. Congress of Entomology; Hamburg/FRG: 1984-08-20/26

** Senior research assistant of 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 theDufour glanq is very limited. The gland is found in the workers [~~]l and queens [2C?rof all social Hymenoptera, and originally is an accessory gland of the female reproductivesystem. In old literature, it therefore has often been referred to as 'accessory gland', orhas been given the chemically misleading name 'alcalic gland'. Information on the Dufourgland [D-G]3 in Formicidae (as well as in Apidae) so far mainly focused on the chemicalanalysis and biological activity of the secretion.

The attribution of a well-defined and general function to Dufour's gland, however, seemsmost precarious. Its relationship with the female reproductive system for a long time hassuggested a function as a sting lubricant facilitating egg deposition. Many bee species usetheir Dufour gland secretion for brood cell lining [Cane 1981], or mix it with the pollenballs [Duffield et alii 1983]. In both situations it serves as food for the growing larvae[Norden et alii 1980]. The Dufour gland in ants has been reported as the source of alarmpheromones in Formicinae [Wilson & Regnier 1971], Myrmeciinae [Robertson 1971] andMyrmicinae [Cammaerts-Tricot 1974]. Some other myrmicine species are known toproduce their trail substances in the Dufour gland [Ritter et alii 1977; Vander Meer et alii1981]. Another function assigned to Dufour's gland in a number of species is one ofterritorial marking [Holldobler & Lumsden 1980]. In most groups, however, the functionof the gland is unknown or insufficiently investigated.

Information on the Dufour gland morphology in ants mainly refers to some generalanatomical and light microscopical data [Callahan et alii 1959;Hermann& Blum 1967a,b;Robertson 1967; Wilson & Regnier 1971; Beck 1972]. Ultrastructural investigations so farare restricted to a rather short contribution on Camponotus rnfipes [Gama & CruzLandim 1977] and a few other Israeli Formicinae [Hefetz & Orion 1982], and to adescription of the Dufour gland closing apparatus in Formica sanguinea [Billen 1982].We here report on the Dufour gland morphology-and ultrastructure in 60 species belongingto 8 sub familiae: Myrmicinae, Ponerinae, Dorylinae, Ecitoninae, Myrmeciinae, Pseudo-myrmecinae, Dolichoderinae and Formicinae.

2 Material and methods

Over 300 1(1( and 29 representing 60 species from allover the world have been investi-gated in this study. For convenience, they will be mentioned per subfamilia along withthe corresponding results.The ants after air shipment to Belgium were killed by momentary immersion in liquidnitrogen and prepared for electron microscopy. Either abdominal halves or dissectedDufour glands were fixed in 2 % cold glutaraldehyde (buffered with 0.05 M sodiumcacodylate and 0.15 M saccharose) and postfixed in 2 % osmium tetroxide. Uranyl acetatebloc-stained samples were dehydrated in acetone, embedded in Araldite, and sectionedwith a Reichert llitracut microtome. Double-stained grids were viewed in a Philips EM400 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 theabdominal tip in the stingless Formicinae. A single layer of epithelial cells both acts as thesite of glandular activity and as the reservoir lining. The general appearance of the glandcan be small and pear-shaped as in Dolichoderinae, Dorylinae and Ecitoninae, and mostMyrmicinae. In other Myrmicinae (such as Harpagaxenus and Messar) as well as inMyrmeciinae, Pseudomyrmecinae and Ponerinae it is narrow and tubiform. MostFormicinae are characterized by a heart-shaped Dufour gland (Fig 1). Although thegeneral aspect of a monolayered epithelium, lined with a cuticula and surrounded by abasement membrane [B-M]4, sounds very simple, we find a considerable variation amongthe numerous species investigated. For that reason, the several subfamiliae will be de-scribed separately.

Fig 1: Variation of the Dufour glandwith a tubular, pear- or heart-shapedappearance. The gland opens in thestingbase or, as in the stinglessFormicinae, near the abdominal tip(drawn in black).

TrinidadU.S.A.CorsicaTrinidadVenezuelaBrasilGuyanaU.S.A.CorsicaItalyItalySpainCorsicaSpainTurkeyTurkeyBelgiumZambiaU.S.A.Sri Lanka

3.1 Myrmicinae

List of species investigated, together with their locality of origin:

Acromyrmex octospinosus (Reichert 1793) Santa Cruz ValleyAphaenogaster fulva Roger 1863 Utica, New YorkAphaenogaster spinosa nitida (Emery 1895) CalviAtta cephalotes (Linnaeus 1758) Santa Cruz ValleyAtta laevigata F. Smith 1858 Ca1abosoA tta sexdens rubropilosa Forel1908 SaD PauloAtta sex dens sexdens (Linnaeus 1758) Timheri Int'lCrematogaster lineolata (Say 1836) Utica, New YorkCrematogaster scutellaris (Olivier 1791) CalviHarpagoxenus sublaevis (Nylander 1856) DobiaccoLeptothorax acervorum (Fabricius 1793) DobiaccoMessor capitatus (Latreille 1798) BarcelonaMessor minor (Andre 1881) SolenzaraMessor sanctus bouvieri Bondroit 1918 BenidormMessor structor (Latreille 1798) IstanbulMonomorium salomonis sommieri Emery 1908 IstanbulMyrmica rubra (Linnaeus 1758) AIkenMyrmicaria baumi Fore1 1901 LusakaPogonomyrmex occidentalis (Cresson 1879) Denver, ColoradoSolenopsis geminata (Fabricius 1804) Galle

basement membrane; in further text: B-M

168 -Johan P. J. Bi11en

Strongylognathus testaceus (Schenck 1852) Heythuyzen NetherlandsTetramorium caespitum (Linnaeus 1758) Heythuyzen NetherlandsTetramorium semilaeve Andre 1881 Calvi Corsica

The Dufour gland epithelium in the Myrrnicinae generally has a uniform thickness thatvaries 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 slightlyexceptional with an irregular and more or less crenellated epithelial wall [Billen et alii1984] .Nuclei are rounded and display a dispersed chromatin (Fig 2). The cytoplasm is character-ized by a very well developed smooth-surfaced endoplasmic reticulum and Golgi complex(Fig 3), while mitochondria and multilamellar inclusions are also fairly numerous. Lipiddroplets generally are rare, except for the basal region of the epithelium in Aphaenogasterspinosa v. nitida (Fig 4). Apart from a few microvillar projections, the apical and basal cellmembranes closely adhere to the cuticle and B-M, respec. The cuticle has a thickness from0.2-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 tracheolesand nerve fibres.

3.2 Ponerinae

Ectatomma quadridens (Fabricius 1793) Caracas VenezuelaEctatomma ruidum Roger 1861 Tuxt1a Chico MexicoEctatomma tuberculatum (Olivier 1791) Tuxt1a Chico MexicoGnamptogenys strigata (Norton 1871) Rancho del Carmen MexicoMegaponera foetens Mayr 1862 Kizu, Mayombe ZaireNeoponera apicalis (Latreille 1802) Tuxt1a Chico MexicoOdontomachus assiniensis Emery 1892 Kigali RuandaPachycondyla soror Emery 1899 Mwebe Zaire

The Dufour gland of Ponerinae strongly resembles that in the Myrmicinae. The epithelialthickness within a single individual is very constant, though it may vary considerably,ranging from 1-25 p.m, among conspecific and especially heterospecific individuals.The cytoplasm shows a similar composition as in the Dufour gland of Myrmicinae withthe very well elaborated smooth endoplasmic reticulum in a predominant appearance(Fig 5,6). The apical cell membrane tightly adjoins the cuticle, the thickness of whichvaries bet. 0.2 & 0.5 .urn (Fig 5). Basal invaginations may occur, but are not nearly as welldeveloped as in some other sub familiae (Fig 6). The epithelium is surrounded by a thinB-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 1858Anomma nigricans (Illiger 1802)Dorylus affinis Shuckard 1840Dorylus wilverthi Emery 1899

RuandaKenyaRuandaRuandaZaire

KigaliNairobiKigaliKigaliKizu, Mayombe

Figs 2-6: Electron micrographs of Dufour gland epithelium in Myrmicinae (2-4) andPonerinae (5-6), showing the well developed smooth endoplasmic reticulum as a majorcytoplasmic element. -2: epithelium in Tetramorium caespitum (Linnaeus 1758) [x7,700].


3: apical cytoplasm and cuticle in Messor structor (Latreille 1798) [x 12,400]. 4: basalcytoplasm and surrounding muscle fibres in Aphaenogaster spinosa nitida (Emery 1895)[x7,850]. S: apical cytoplasm in Odontomachusassiniensis Emery 1892 [x 8,000]. 6: basalcytoplasm 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. Theepithelium, with a thickness bet. 10 & 20 .urn, displays numerous apical projections at5-10 .urn intervals, resulting in a crenellated appearance when sectioned (Fig 7). Creneltops as a rule correspond with the apical region of intercellular junctions. Moreover, basalinvaginations and the very much folded lateral cell membranes [C-M]5 give a very capri-cious aspect to the cell shape. The apical CoM closely follows the cuticular lining withoutany microvillar differentiation. The cuticular thickness varies from 0.5 up to and over1.um.Nuclei of the doryline Dufour gland epithelium are found in the basal half of the cellsand are slightly lobate. The cytoplasm contains numerous multilamellar inclusions inaddition to the smooth endoplasmic reticulum and mitochondria (Fig 7). Only a fewmuscle 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 species was available, namely Eciton burchelli urichiFore11899, originating from Arima Valley in Trinidad. The Dufour gland epithelium ofthese Eciton ~~ is markedly different from that in the Old World Dorylinae by its veryuniform thickness (7-l0jJ.m). Most of the basal epithelium half is occupied by an abun-dance of horizontally occurring membrane foldings (Fig 8). These correspond to theextremely twisted lateral CoM and are not to be considered as basal invaginations. Thebasal CoM itself indeed very closely adheres without any appearance of invagination to theB-M which is about 70 nm thick. Also the apical CoM does not show any differentiationand runs parallel to the cuticle. The latter has a thickness of approx. 0.5 jJ.m, and is pro-vided with numerous small epicuticular fringes (Fig 8).The cytoplasm contains the usual organelles such as mitochondria, multilamellar andmultivesicular inclusions, and smooth endoplasmic reticulum, though its contents may beheavily masked due to the many membrane folds. The more or less flattened nuclei arefound in the apical epithelium half.The gland is surrounded by a well developed and continuous muscle layer, a few tracheolesand nerve fibres.

3.5 Mynneciinae

Myrmecia gulosa (Fabricius 1775) Sydney NSW, AustraliaMyrmecia vindex Fr. Smith 1858 Bentley W.-Australia

The epithelial thickness of the mynneciine Dufour gland can vary from 5 to 40 .urnaccording to the individual. Within the same ~, the epithelium is fairly uniform, thoughseveral basal protrusions are observed that give a characteristic appearance to the gland(Fig 10). A typical feature is the interruption of the muscle layer in these areas, that canhave a diameter from less than 5 up to several tens of micrometres.Another characterizing feature in Myrmecia is the apical border with rather short androbust 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 ofthe cytoplasm is occupied by small vesicles of smooth endoplasmic reticulum, numeroussmall mitochondria and a large number of multilamellar bodies (Figs 10 and 11). The

5 cell membrane; in further text: C-M


--Figs 7-8: Dufour gland epithelium in the Old and New World army ants. -7: crenelatedepithelium in Anomma nigricans (llliger 1802) with basal invaginations (Old World Dory-linae). Intercellular junctions correspond with crenel tops [x 5,000]. 8: uniform epitheliumin Eciton burchelli urichi Forel1899 (New World Ecitoninae), showing very much foldedlateral cell membranes in the basal region [x5,000].


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


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 thickness that varies bet. 0.5 & 2.0 lim. The B-Mmeasures approx. 70 nm. -Nerve fibres (Fig 10), tracheoles and muscles surround thegland, the muscle fibres, however, being interrupted by the protrusions mentioned above.

3.6 Pseudomyrmecinae

The only pseudomyrmecine species available for this study wasPseudomyrmex termitariusFr. Smith 1855, originating from Caracas, Venezuela. Its Dufour gland epithelium has amore or less wavy appearance with a thickness of approx. 5 llm (Fig 13). Nuclei areslightly flattened, while other cytoplasmic constituents mainly refer to smooth endo-plasmic reticulum, numerous mitochondria and some multilamellar bodies. The gland'smost distinguishing feature are the locally grouped microvillar clusters, that are separatedfrom each other by areas covered with an undifferentiated apical CoM (Figs 12,13). Theseclusters often occur in association with intercellular junctions, the microvilli being formedby both contributing cells (Fig 12). This association, however, is facultative, while similarclusters are also observed 'within' a single cell. The D-G cuticle in Pseudomyrmex has athickness of approx 0.5 llm, its B-M measures around 20 nm. A well developed musclelayer surrounds the gland.

3.7 Dolichoderinae

Bothriomyrmex decapitans Santschi 1911 Ouka'imeden MoroccoDolichoderus quadripunctatus (V on Linne 1771) Wiirzburg GermanyIridomyrmex humilis (Mayr 1868) Barcelona SpainTapinoma nigerrimum (Nylander 1856) Calvi Corsica

The dolichoderine Dufour gland epithelium has a very uniform thickness ranging bet. 10& 20 IJ.m according to the species. Its nuclei are very rounded and occur in the basal cellhalf (Fig 14). The cytoplasm, in addition to the smooth endoplasmic reticulum andrelatively few mitochondria, contains fairly numerous and conspicuous vacuoles, that canreach a diameter of up to 3 IJ.m. The apical CoM shows some irregularly arranged micro-villi with a length up to 2 J.J.In and a diameter bet. 100 and 150 nm (Fig 15). These seemto penetrate into the very clear and structureless basal part of the cuticula. Also theepicuticula, at least in Tapinoma nigemmum, has an electron-lucid appearance in compar-ison 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 SO nm. Muscle andnerve fibres, and tracheoles, in contrast to most other subfarniliae, are rarely foundaround the D-G of Dolichoderinae.

IstanbulCalvi

TurkeyCorsica

3.8 Formicinae

Acantholepis velox Santschi 1917Camponotus aethiops (Latreille 1798)

Myrmecia gulosa (Fabricius 1775) [x21,700]. 10: basal protrusion of the epithelium inM. 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 bodiesand vesicles of smooth endoplasmic reticulum [x7,000]. 12: cuticula and apical cytoplasmin Pseudomyrmex termitarius Fr. Smith 1855, with cluster of microvilli [x 15,200].13: epithelium in P. termitarius with surrounding muscle fibres. The apical cell membraneshows local clusters oj microvilli (arrows) [x5,900].


Figs 14-17: Dufour gland epithelium in Dolichoderinae (14-1 5).'and Formicinae (16-17),-14: epithelium in Tapinoma nigerrimum (Nylander 1856), showing irregularly arrangedapical microvilli [x4,550]. 15: detail of microvilli penetrating into lower cuticular layer in


Camponotus fulvopilosus (De Geer 1778) Lusaka ZambiaCamponotus lateralis (Olivier 1791) Calvi CorsicaCamponotus pictiventris Mayr 1901 Louis Trichardt South-AfricaCataglyphis nodus (Brulle 1832) Elazi~ TurkeyFormica cunicularia Latreille 1798 Heythuyzen NetherlandsFormica fusca Linnaeus 1758 Heythuyzen NetherlandsFormica pratensis Retzius 1783 Heythuyzen NetherlandsFormica sanguinea Latreille 1798 Heythuyzen NetherlandsLasius flavus (Fabricius 1781) Heythuyzen NetherlandsLasius flavus nearcticus Wheeler 1906 Utica, New York U.S.A.Lasius fuliginosus (Latreille 1798) Heythuyzen NetherlandsLasius niger (L~naeus 1758) Heythuyzen NetherlandsPlagiolepis pygmaea (Latreille 1798) Calvi CorsicaPolyrhachis militaris cupreopubescens Forel1858 Kigali Ruanda

Formicinae show a Dufour gland epithelium with a very uniform thickness, that, accord-ing to the individual may range 5-20 .urn. The rounded nuclei occur in the basal half ofthe epithelium, or are more or less flattened in the low epithelium (Fig 16). The cytoplasmcontains a very elaborate smooth endoplasmic reticulum and Golgi complex, but isespecially characterized by the conspicuous subcuticular layer of mitochondria (Fig 16).Other mitochondria are scattered in the cytoplasm along with fairly numerous multi-lamellar bodies. In a few occasions the latter were even observed in the gland lumen.The apical CoM runs parallel to the cuticula, which has a mean thickness of 0.3 .urn. Basalinvaginations are quite common and may penetrate a few micrometres into the epithe-lium. A very constant feature is the very thick B-M, the thickness of which varies from0.5-0.8 and even over 1 .urn (Fig 17). A very well developed muscle layer, numeroustracheoles 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 glandduct. In the stingless Forrnicinae both glands open near the abdominal tip in a similarrelative relationship. The D-G epithelium in this region considerably differs from theactual reservoir part. In both stinging and non-stinging species the duct has a slit-likeappearance. A very extensive supply of muscle fibres insert on both its dorsal and ventralside (Fig 18). The basal outline of the duct epithelium is very irregular due to the numer-ous muscle attachments, that deeply penetrate between the duct cells. The duct cellnuclei are found in the sunken basal part (Fig 19). The cytoplasm mainly containsbundles of microtubules that ensure the structural link between the muscle fibres and thecuticula. The bundles of myofilaments and micro tubules from both sides adhere to theconfluent basement membrane layer of the muscle fibre and duct cell by means ofhemidesmosomes (Figs 18 and 19). A similar organization ofhemidesmosome attachmentis observed in the microtubular part reaching the cuticular lining of the duct.

1: nigerrimum [x 13,900]. 16: epithelium in Formica sanguinea Latreille 1798. (Note thesubcuticular layer of mitochondria, the multilamellar inclusions and thick basementmembrane) [x7,500]. 17: basal cytoplasm with plasmalemma invaginations, and under-laying thick basement membrane, tracheoles and muscle fibres (Formica pratensis Retzius1783) [x7,850].


Figs 18-19: Cross section electron micrographs through the Dufour gland duct, illustratingthe gland's opening and closing mechanism. -18: dorsally and ventrally inserting musclefibres upon contraction cause the slit-like duct to open. Closure is probably achieved by


4 Discussion

The Dufour gland consists of class-1 glandular cells according to the classification ofNoirot & Quennedey [1974]. Consequently, their secretion simply has to cross the over-laying cuticle in order to reach the central lumen. In all ant species investigated, we finda glandular epithelium with a very well developed smooth-surfaced endoplasmic reticulum,fairly numerous mitochondria as well as very characteristic multilamellar or multivesicularinclusions.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 agreement withthe above mentioned cytological characteristics. The large numbers of multilamellarbodies according to Hefetz & Orion [1982] ought to be related to secretory micelles thatafter migration and transcuticular passage accumulate in the gland lumen as an oilysecretion. This hypothesis is supported at least by the occurrence of similar multilamellarbodies in the gland lumen as we could observe in a few formicine species. Moreover, theappearance of multilamellar inclusions represents a general feature of insect epidermalglands [Bazire-Benazet & Zylberberg 1979, Delfino et alii 1983, Grandperrin & Cassier1983; Heroin & Ramade 1970; Noirot & Quennedey 1974, Plattner et alii 1972, Quen-nedey & Brossut 1975, Stein 1962]. Some of these inclusions most probably are involvedin cellular autophagy and therefore form part of the lysosome system. Their involvementin cellular degeneration is clearly illustrated by the exuberant appearance in the finalstages of ovariole regression in 1111 ants [Billen 1985 a]. A similar lysosomal function is alsoattributed to the lamellar inclusions in the DoG of the formicine species Camponotusrufipes [Gama & Cruz Landim 1977]. They often, however, are far too abundant for thisinterpretation and therefore seem to support the hypothesis that they have to be con-sidered as secretion figures [Noirot & Quennedey 1974].Notwithstanding the simple general structure with merely epithelial cells, considerabledifferences were observed in the DoG of species belonging to different subfamilies (Fig 20).This variation in general is very constant within a group and mainly refers to particulararrangements of the CoM. Apical microvilli occur in Myrmeciinae, Pseudomyrmecinae andDolichoderinae, although their appearance is different for each group. In Dolichoderinaethey are rather irregularly arranged, long and slender structures that seem to penetrateinto the lower cuticular region. The myrmeciine microvilli, on the other hand, are morerobust and constitute a more regular pattern, while in Pseudomyrmex they are clusteredin local groups. Apart perhaps from a few myrmicine species, all other subfamiliae have aDufour gland with an undifferentiated apical cell membrane tightly appressed to thecuticle.Invaginations of the basal C-M are most obvious in Dorylinae and Formicinae, while basalprotrusions of the epithelium were only found in Myrmeciinae. Folded lateral C-M mayoccur in all species, but are extremely conspicuous in the Ecitoninae.In addition, Dorylinae are characterized by the crenellated aspect of their DoG and For-micinae by the subcuticular layer of mitochondria and the thick B-M. Both formicinecharacters confirm earlier observations in Camponotus rufipes [Gama & Cruz Landim

return of the thickened cuticular intima to a rest position (Tetramorium semilaeve Andre1881) [x9,600]. 19: ventral region of the Dufour gland duct in Myrmica rubra (Linnaeus1758), showing myofilaments that deeply penetrate between the duct cells (*). Muscularforces on the cuticle are transmitted by bundles of microtubules that cross the duct wall[x8,800].

178 -Johan P. J. Bi11en

PONERINAEMYRMICINAE

DORYLINAE ECITONINAE

~,-.c,

-I

~

PSEUDOMYRMECINAEMYRMECIINAE

? '?

,."..".",""."."""

(

DOLICHODERINAE FORMICINAE

Fig 20: Schematical representation of the Dufour gland epithelium in the 8 subfamiliaeinvestigated [Hymenoptera: Formicidae].

Morphology and Ultrastructure of Dufour Gland

79

1977] and a few other Camponotus, Cataglyphis and Polyrhachis species [Hefetz & Orion1982]. Only Myrrnicinae and Ponerinae lack such features that are distinguishing for thegroup.It is clear from these observations that the morphology of the D-G coincides with theexisting subfamily classification. Whether this variation has any phylogenetic implication,however, remains an open question. A functional interpretation of the different epitheliumtypes therefore is required but seems most precarious so far.The clear differences between the doryline and ecitonine D-G at least illustrate thediphyletic origin of the army ants [Billen 1985 b]. The hypothesis of a triphyletic originwith the Aenictini as a third group according to Gotwald [1979] is a strong incitation tocheck the Dufour gland morphology in Aenictus species. Moreover, the number of speciesinvestigated per subfamily should be increased for some groups to allow a more generalinterpretation. In this regard, especially Ecitoninae, Myrmeciinae and Pseudomyrmecinaeneed more representatives to be checked morphologically. This also applies to both thetropical Leptanillinae, that were not available so far, as to the rare but taxonomicallycritical species Aneuretus simoni and Nothomyrmecia macrops.Finally, a common feature of the D-G are the muscle and nerve fibres that surround thereservoir sac, and that have a role in the discharge of secretion. A conspicuous muscularsupply inserting on the gland's duct acts as a precise control mechanism for ejection. Bothin stinging and non-stinging species, the duct has a slit-like appearance. It is suggested thatthe dorsal and ventral muscles upon contraction cause an opening of the duct, whileclosure could be the passive result of a return of the much thickened cuticular intima to arest position [Billen 1982]. It should be noted that therefore this opening and closingmechanism of the D-G is independent from the poison gland secretion mechanism, so thatboth glands can discharge their contents separately and independently.

5 Abbreviations

bm basement membranect cuticulaga Golgi apparatushd hemidesmosomeLd lipid droplet

N nucleusNF nerve fibretr tracheoleV vacuole

MF muscle fibremlb multilamellar bodyMT micro tubulesmv microvillimvb multivesicular body

6 Acknowledgements

Numerous ant species investigated in this study were kindly provided by Prof A. Buschin-ger, 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 dedicatingthis paper to him on the occasion of his seventieth birthday. I am also very grateful toE. Plaum for preparing the microscope sections, and to Prof M. Van Poucke and ProfK. Schmidt for reading the manuscript.

7

References

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Author's address -Anschrift des Verfassers: Dr Johan P. J. Billen, Laboratorium voorSystematiek en Ecologie, Zoologisch Instituut K. U. Leuven, Naamsestraat 59, B-3000Leuven; 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 ofadaptations of insects to their environment: 1. Metabolic and Enzyme Adaption toTemperature (K. H. Hoffmann), 2. Temperature and Insect Development (H. T. Ratte),3. Environmental Aspects of Insect Dormancy (W. Behrens), 4. Metabolic Energy Expend-iture 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 ofInsect Bioluminescence (K. H. Hoffmann). An extensive list of references (895) and asubject and taxonomic index are included.The single articles contain a short introduction and conclusion, the results and models areillustrated by several figures and tables. Beside the description of the experimental find-ings main emphasis is laid on an understanding of the underlying mechanisms.This book can be recommended to both physiologists and ecologists and the single arti-cles are also good introductions for advanced students.

Klaus-Diether Spindler (Dusseldorf)

comparative morphology and ultrastructure of the duf ... · general aspect of a monolayered...

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