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Anatomy and ultrastructure of dermal glands in an adult water mite, Teutonia cometes (Koch, 1837) (Acariformes: Hydrachnidia: Teutoniidae)
Arthropod Structure & Development 42 (2013) 115e125
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Anatomy and ultrastructure of dermal glands in an adult water mite, Teutonia cometes (Koch, 1837) (Acariformes: Hydrachnidia: Teutoniidae) Andrew B. Shatrov* Zoological Institute of the Russian Academy of Science, Universitetskaya nab. 1, 199034 St.-Petersburg, Russia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 10 May 2012 Received in revised form 28 October 2012 Accepted 29 October 2012
Organization of dermal glands in adult water mites Teutonia cometes (Koch, 1837) was studied using light-optical, SEM and TEM methods for the first time. These glands are large and occur in a total number of ten pairs at the dorsal, ventral and lateral sides of the body. The slit-like external openings of the glands (glandularia) are provided with a cone-shaped sclerite, and are combined with a single small trichoid seta (hair sensillum), which is always situated slightly apart from the anterior aspect of the gland opening. Each gland is formed by an epithelium encompassing a very large lumen (central cavity) normally filled with secretion that stains in varying intensity on toluidine blue stained sections. The epithelium is composed of irregularly shaped secretory cells with an electron-dense cytoplasm and infolded basal portions. The cells possess a large irregularly shaped nucleus and are filled with tightly packed slightly dilated cisterns and vesicles of rough endoplasmic reticulum (RER) with electron lucent contents. Dense vesicles are also present in the apical cell zone. Some cells undergo dissolution, occupy an upper position within the epithelium and have a lighter cytoplasm with disorganized RER. Muscle fibers are regularly present in the deep folds of the basal cell portions and may serve to squeeze the gland and eject the secretion into the external milieu. The structure of these dermal glands is compared with the previously described idiosomal glands of the same species and a tentative correlation with the glandularia system of water mites is given. Possible functions of the dermal glands of T. cometes are discussed. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Morphology Dermal glands Water mites Teutoniidae Teutonia cometes
1. Introduction Dermal glands are known as constantly present in representatives of water mites (Croneberg, 1878; Michael, 1895; Thor, 1902, 1904; Lundblad, 1930; Schmidt, 1935; Sokolov, 1940; Stout, 1953; Wiles, 1997; Alberti and Coons, 1999) and thought to function in different ways, such as protection against enemies (fishes) (Elton, 1922; Stout, 1953; Kerfoot, 1982), mating behavior (Smith and Hagman, 2002), dampening in unfavorable conditions (Croneberg, 1878). Unfortunately, very little is known about the anatomy and ultrastructure of dermal glands in different water mite taxa (Alberti and Coons, 1999; Shatrov, 2008; Smit and Alberti, 2009); thus questions about their functions, homology, and evolution are premature. The number of dermal glands and their distribution throughout the mite body as indicated by the gland openings (termed ‘glandularia’) are considered species-specific and
* Tel.: þ7 812 714 01 51; fax: þ7 812 714 04 44. E-mail address: [email protected]. 1467-8039/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.asd.2012.10.006
constant (Lundblad, 1930; Sokolov, 1940; Daochao and Longshu, 1997; Wiles, 1997) and may be important in evaluating the particular evolution of water mites. The external openings of dermal glands are always combined with a single hair sensillum, which is thought to serve as a ‘trigger’ mechanism for releasing the secretion (Halik, 1929; Kerfoot, 1982; Shatrov, 2008). In adult water mites, Teutonia cometes, one pair of ‘unusual’ idiosomal glands has been already described (Shatrov, 2008). These occupy the ventral position in the posterior half of the idiosoma and obviously correspond to the ‘pre-anal external’ glandularia (Tuzovskiy, 1987) or epimeroglandularia 4 (Wiles, 1997). The main purpose of the present study is to give a detailed morphological and ultrastructural description of the conspicuous ‘normal’ dermal glands in adult mites of T. cometes in comparison with the data available on the structure and function of these glands in other water mites studied so far. This work is the first attempt of a thorough fine structural examination of dermal glands in a given water mite species in order to serve as a basis for further comparative, taxonomic, phylogenetic and functional considerations.
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2. Materials and methods
3. Results
2.1. Material and collecting procedure
3.1. Anatomy
Adult mites were collected by the author in the two fresh-water lakes “Krivoe” and “Krugloe” in the region of the Chupa Bay basin of the Kandalaksha Gulf of the White Sea in the vicinity of the White Sea Biological Station “Kartesh” of the Zoological Institute of the Russian Academy of Science during the summereautumn periods of 2000e2003. Collecting was carried out by “mowing” with a net along the lakeside up to a depth of 1 m. A certain number of mites was fixed for TEM study mostly on the day of or on the next day after capture, and the remaining mites were placed in 70% ethyl ethanol for further species identification. The latter was kindly carried out afterward by Dr. P.V. Tuzovskiy (Institute of Biology of the Internal Waters of the Russian Academy of Science, Borok, Russia). Additionally, some adult mites of this species were kindly sent to the author by Dr. R. Gerecke (Institute of Evolution and Ecology of Invertebrates, University of Tübingen, Tübingen, Germany). Besides this, whole-mount specimens of T. cometes (N 8302, males and N 8410, females) from the water mite collection kept in the Institute of Biology of the Internal Waters of the Russian Academy of Science, Borok, Russia, were kindly given to the author by Dr. P.V. Tuzovskiy and were also used to observe terminal gland openings.
Using both whole-mount preparations and semi-thin sections, I counted ten pairs of the ‘normal’ dermal glands, which occupy a constant position at the dorsal, ventral and lateral sides of the mite body. All these glands belong to one morphological type and supposedly correspond to the following glandularia: pre- and postantennal glandularia, dorsoglandularia 1e4; ventroglandularia 3 and 4; lateroglandularia 4 and epimeroglandularia 2 (Wiles, 1997) (Fig. 1). An 11th pair of glands, the ‘unusual’ idiosomal glands studied by me previously (Shatrov, 2008) corresponds to the epimeroglandularia 4. Although the dermal glands are large and occupy a comparatively large body volume, the presence of the glands may be identified externally only by the glandularia, i.e. the extremely small gland openings associated with a single small seta (hair sensillum), which is always situated slightly apart from the anterior aspect of the opening (Figs. 2 and 3F). The glands are surrounded by the haemocoelic space but may directly contact organs and tissues, such as epidermis, salivary glands, midgut, hemocytes and tracheae (Figs. 3AeD, 4A and 5A). Inside, the gland openings are provided with a cone-shaped sclerite extending into the body cavity (Figs. 3E, 6B and 8).
2.2. Light-optical observations For anatomical observations, serial semi-thin sections of mites in transverse and longitudinal planes were stained with toluidine or methylene blue and investigated and photographed with a Leica DM LS-2 light-optical microscope combined with a Leica EC-3 digital camera. The gland openings were also examined and photographed in mites mounted on slides in Berlese solution using the same microscope under oil immersion (magnification 100). 2.3. Transmission electron microscopy (TEM) For TEM study, the mites were initially fixed in 2.5% glutaraldehyde in 0.1 M phosphate buffer (pH 7.2e7.4) for 2e4 h. After immersion into the fixative fluid, the integument of the mites was carefully ruptured from the dorsal side with tiny insect pins for a better penetration of the fixative, or the mites were left intact. Mites were then washed in several changes of 0.2 M phosphate buffer, postfixed in 2% osmium tetroxyde in 0.1 M phosphate buffer for 12 h to overnight, dehydrated in ethanol and acetone series, and finally embedded in an araldite mixture. Serial ultra-thin sections both in transverse and longitudinal planes were made on a Leica UC-6 ultramicrotome and, after staining with uranyl acetate and lead citrate, were examined with LEO-900 (negative film slides) and Morgagni 268D (digital visualization) transmission electron microscopes at 50 and 80 kV, respectively. 2.4. Scanning electron microscopy (SEM) For SEM study of the terminal gland’s openings, mites were washed in alcohol series and then treated with hexamethyldisilazane (HMDS) for 5e10 min as an alternative method to critical point drying for preserving the natural shape and size of the mite body. Immediately after these procedures specimens were covered with a platinum layer in an Eiko IB-5 apparatus, and examined with a JEOL JSM-6510LA scanning electron microscope at 30 kV.
Fig. 1. Schematic drawing illustrating the approximate position of the gland openings (glandularia) on the body surface of the water mite Teutonia cometes reflecting the presence of dermal glands. Black circles indicate dorsally located glandularia, white circles e glandularia on the ventral surface. Small dots anterior to the glandularia point to the position of the hair sensilla. Proposed names of the glandularia (after Wiles, 1997): A1, A2 e pre- and post-antennal glandularia; D1eD4 e dorsoglandularia 1e 4; E2, E4 e epimeroglandularia 2 and 4 (epimeroglandularia 4 correspond to the idiosomal glands); L4 e lateroglandularia 4; V3, V4 e ventroglandularia 3 and 4.
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Fig. 2. (AeD). External morphology of an adult water mite Teutonia cometes and of the dermal gland openings. SEM. A e general view of a mite from the dorso-frontal aspect. Scale bar e 200 mm; B e anterior dorsal body surface with extremely small gland openings e glandularia (arrows). Scale bar e 100 mm; C e dorsal view of the button-like gland opening (dorsoglandularia 2) formed of external and internal folds and associated with a hair sensillum (trichoid hair, broken at the middle portion) situated slightly apart from the anterior aspect of the opening. Scale bar e 5 mm; D e anterior horizontal view of the gland opening (dorsoglandularia 3) composed of the same components. Note the long but thin trichoid hair adhering to the body surface. Scale bar e 2 mm. A1 e pre-antennal glandularia of the both side of the body; A2 e post-antennal glandularium of the left body side; D1 e dorsoglandularium 1 of the left body side; EF e external fold; GO e gland orifice; IF e internal fold; Lg e legs; Pa e palp; TH e trichoid hair.
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3.2. Morphology and ultrastructure A single-layered epithelium forms the gland wall encompassing a very large lumen (central cavity). The lumen is normally filled with secretion that stains in varying intensity on toluidine blue stained sections (Fig. 3AeD). The epithelium is composed of irregularly shaped cells with an electron-dense cytoplasm and infolded basal portion (Figs. 4, 5C and 7). The epithelium rests on the flat basal lamina of moderate electron density, which rarely forms indentations into the epithelial cells (Figs. 4C and 5B). The basal plasma membrane remains flat and does not form invaginations. The lateral cell borders are tightly apposed to each other forming contacts with a rather narrow intercellular space of high electron density, where septa may be hardly distinguished (Figs. 5D and 6A). The cells possess a large irregularly shaped centrally located nucleus with a large nucleolus (Figs. 4B and 7). The cytoplasm is filled with tightly packed slightly dilated RER cisterns with electron lucent contents frequently forming whorls (Figs. 4C, 5A, D and 7). The RER cisterns, and especially RER vesicles pinched off the RER cisterns, come close to the apical plasma membrane. Occasionally, these vesicles may open into the lumen (Figs. 4 insert, C, 5B, D and 7). Besides RER cisterns, electron-dense vesicles may be also present in the apical cell zones (Figs. 5F, 6A and 7). Conspicuous Golgi bodies were not observed in the epithelial cells. Round mitochondria with a matrix of moderate electron density (sometimes partly destroyed) are numerous (Figs. 4C and 5A, E). Two kinds of vacuoles may be observed in the epithelial cells. The first one is represented by electron-lucent round vacuoles of various sizes scattered freely within the cells without obvious orientation (Figs. 4A, 5B and 7). Their origin is obscure. Typically, they are only rarely seen to contact the apical plasma membrane (Fig. 4C) and direct release of contents into the lumen was never observed. The second one are variously shaped vacuoles with a matrix of moderate electron density frequently represented by the same granulation as in the lumen (see below) (Figs. 5B, D and 7). These vacuoles contact the cell surface and their contents fuse with the secretion in the lumen (Fig. 5B). Apical cell regions within the epithelium may display a lighter cytoplasm with loosely packed poorly organized RER (Figs. 4A, 5A, E and 7) and appear as if dissolving. Mitoses in the basally located cells were not observed. Fibers of somatic muscles running along the gland wall are constantly present in the deep invaginations of the basal portions of the epithelial cells (Figs. 4A, C and 5C). The secretion in the gland lumen displays various electron densities and contains rather numerous small dense granules of unknown origin (Figs. 4C, 5B, F and 7). A layer of the homogenous secretion of moderate electron density, in which various cell processes may be observed, frequently separates the cell surface and the main portion of the granulated secretion (Figs. 4C and 5B, F). Long and narrow cell extensions divide the secretion situated close to the cell surface into compartments (Figs. 3B, C, 4A and 5A). Close to the gland opening the epithelium becomes much thinner and no longer shows extensive RER (Fig. 6A), but there are
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numerous extensions of the apical surface projecting into the lumen. Immediately beneath of the cone-shaped sclerite flanking the gland ’mouth’, prominent somatic muscles are found attached to the thickened basal lamina of the epithelium (Fig. 6A, C). 3.3. Gland opening Externally in SEM, the gland opening looks like an extremely small round ‘button’ with a thickened external rim. A slit-like orifice is situated along the middle line of this ‘button’ (Figs. 2Be D and 8). TEM examinations show that a large external circular fold of the body cuticle flanks the gland opening. Two internal smaller folds (valves) formed mostly of electron-dense epicuticle, organize the orifice as such (Figs. 2C, 3E, 6B, C and 8). A circular cone-shaped sclerite extends from the deep portion of the internal folds into the body cavity in the form of a bell (Figs. 6B, C and 8). 3.4. Hair sensilla According to their organization, the hair sensilla near the gland opening belong to the ‘no pore single-walled sensilla’ (NP-SW) type (Ivanov, 2000; Leonovich, 2005) and supposedly have a mechanoreceptive function (Fig. 6D). In T. cometes, these sensilla are characterized by a very large cup-shaped sensillum lymph space into which envelope cells extend their long curved microvilli-like processes. A dendritic sheath with round electron-dense plaques on the inner side surrounds the thick tubular bodies of the receptive cell cilia (Fig. 6D). The sensory hair is composed of a thickened basal portion with a large sensillum lymph space and a thin but long tapering trichoid hair provided with a small axial cavity in its basal portion (Figs. 2C, D and 6D). The number of sensory cells and dendrites, unfortunately, could not be determined. 4. Discussion 4.1. Anatomy and ultrastructure The number of dermal glands found in the present study is in contrast with the drawing given by Tuzovskiy (1987), where the presence of 14 pairs of glandularia is indicated in T. cometes. It is remarkable, however, that some of the glands of any gland pair in the mites studied may be lacking, and in these cases the corresponding glandularium is also absent. Due to a total absence of any signs of segmentation of the mite body, the homology of the glands with the glandularia in the scheme of Wiles (1997) seems to be highly arbitrary and reflects only the general position of the glands. This study shows that adult water mites, T. cometes, possess two types of the large dermal glands e one pair of the ‘unusual’ idiosomal glands (Shatrov, 2008) and at least ten pairs of the ‘normal’ dermal glands. Morphologically, these gland types are significantly different (Fig. 3D). In contrast to the sac-like ‘normal’ dermal glands, the idiosomal glands are arranged along the axis of the body with their openings on the epimere IV, thus corresponding to the epimeroglandularia 4 (Wiles, 1997). They have a comparatively flat epithelium, a large lumen with single solid electron-dense
Fig. 3. (AeF). Anatomical organization of dermal glands in adult water mites, Teutonia cometes. Semi-thin toluidine blue stained sections (AeE), whole-mount preparation (F). A e transverse section through the very posterior body region showing two pairs of dermal glands. Note that the deep horizontal fold of the body wall creates the impression that the excretory organ divides into two, dorsal and ventral, portions. Scale bar e 50 mm; B e large dermal gland in the posterior body region corresponding to dorsoglandularia 4 with the lumen filled with secretion. Scale bar e 25 mm; C e dermal gland corresponding to lateroglandularia 4 adjacent to testis with the gland orifice and secretion in the lumen. Scale bar e 20 mm; D e transverse section through the ventral half in the middle body region showing relationship of the ‘unusual’ idiosomal gland and ‘normal’ dermal gland corresponding ventroglandularia 3. Scale bar e 50 mm; E e orifice of the gland and the lumen filled with secretion. Scale bar e 10 mm; F e external view of the gland opening showing orifice as such, cuticular folds and the hair sensillum. Scale bar e 10 mm. Cu e cuticle; D4 e dermal gland corresponding dorsoglandularia 4; DG e dermal gland; EF e external fold; EO e excretory organ; GO e gland orifice; HS e haemocoelic space; HSe e hair sensillum; IF e internal fold; IG e idiosomal gland; L e gland lumen; MG e midgut; Ms e body muscles; Sc e cone-shaped sclerite; SE e secretory epithelium; Te e testis; V4 e dermal gland corresponding to ventroglandularia 4.
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secretion globule (Fig. 3D); a narrow layer of connective tissue cells encompasses the glandular epithelium from the outside. No regular muscle ‘net’, like in the ‘normal’ dermal glands, is found surrounding the idiosomal glands. The excretory duct of these glands is very elaborate (Shatrov, 2008) and much bigger than in the ‘normal’ glands, where only a short ‘mouth’ is observed. The presence of the epimeroglandularia 4 in most water mite species (Wiles, 1997) suggests that all corresponding glands are homological to each other. At the same time, the epimeroglandularia 4 frequently migrate anterior from their initial position on the epimere IV (Wiles, 1997). For instance, in Lebertia, Oxus and Frontipoda these glands, termed “Glandulae globulosae” (Thor, 1902), do not open on the epimere IV but far anterior. Conversely, in Limnesia maculata (Müller) such glands called “Glandula Limnesiae” open, like in T. cometes, on the ventral body surface not far from the genital opening (Thor, 1902). All these glands in the above mentioned species have a large lumen with intensively staining secretion material. These findings suggest that T. cometes and L. maculata with E4 located on the epimere IV are more basally positioned in comparison with the advanced species, where E4 have moved forward. L. maculata, besides one pair of the “Glandula Limnesiae”, also displays several pairs of large dermal glands containing a peculiar spindle-like secretion (Croneberg, 1878; Thor, 1904; Schmidt, 1935). This secretion is discharged from the gland on the body surface as solid waveform yellowish fibers (Croneberg, 1878). Glands of a very similar morphology have been also described in Eylais extendens (Müller) (Schmidt, 1935). Other mites studied so far may have, at least, two types of dermal glands (Lundblad, 1930; Smit and Alberti, 2009). Most of these glands, except for one gland type of Arrenurus globator (Müller) (Lundblad, 1930), do not display a large lumen (Croneberg, 1878; Michael, 1895; Thor, 1904; Stout, 1953; etc.). In Litarachna, one pair of dermal glands is extremely large and is filled with secretion “occupied by myriads of small granules” (Smit and Alberti, 2009, p. 76), just like in T. cometes. The origin of secretion in the lumen is not quite clear in T. cometes. Evidently the RER produces precursors of the protein secretion that is discharged from the cells most likely by means of the Golgi body dense vesicles. The Golgi bodies, however, are not clearly seen when the glands are full of secretion and probably become distinct only after the glands are depleted and start a new secretion cycle. Dissolved cells and RER vesicles, occasionally opening into the lumen, may play an additional role in the secretion process. Cell degradation and related changes in the epithelium are probably very slow, so that mitoses and active regeneration of the epithelium could not be observed. The ejection mechanism of the secretion in T. cometes may be as follows: the muscles surrounding the gland from its periphery squeeze the gland volume to push the secretion toward the orifice, whereas the muscles attached to the epithelium close to the gland opening widen the gland mouth facilitating evacuation of the secretion. A similar organization of the gland opening provided with a cone-shaped sclerite is found in Litarachna (Smit and Alberti, 2009) and in the majority of water mites (see Croneberg, 1878;
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Michael, 1895; Schmidt, 1935; Alberti and Coons, 1999; etc.), where glands are rich in secretion. However, nearly the same sclerite at the base of the orifice is shown in the mite Hydrachna globosa, De Geer (Thor, 1904), in which dermal glands are devoid of the large lumen. A great similarity in the organization of the gland openings leads to a supposition that initially all dermal glands were identical in their origin and organization and, probably, have appeared anew in water mites as a synapomorphic character. Their association with a hair sensillum may result in a trigger mechanism for the gland secretion (Kerfoot, 1982). 4.2. Functions Adult mites of T. cometes are actively swimming and have a brown or dark-red coloration (Sokolov, 1940). It is considered that fishes may more readily swallow these than brightly red colored mites (Kerfoot, 1982). As a result, Teutonia might have elaborated an effective protective mechanism against enemies in the form of the large and numerous dermal glands containing rejecting secretion. On the other hand, “red mites are most abundant in temporary water bodies, which lack fish” (Proctor and Garga, 2004, p. 129) and “redness may not be a novel trait ., but is rather a symplesiomorphy that first arose on land” (ibid. p. 129). Among four proposed types of the glandularia arrangements, the lebertoides type, to which Teutonia belongs, is considered to be the highest and evolutionary the youngest (Daochao and Longshu, 1997). Functions of the idiosomal glands are expected to be different. Their terminal apertures are situated on the epimere IV not far from the genital opening and it is speculated that these glands may play a role in sexual behavior releasing pheromones (Smith and Hagman, 2002; Shatrov, 2008). Observations on the living mites in the laboratory show that representatives of different genera, such as Limnesia and Piona, produce thin white filaments while walking upon the substrate. These threads stretch from the postero-ventral body portion by one to several pairs of the parallel lines. After producing large amounts of these threads, the mite gathers them into a knot or a net by movements of the forth pair of legs (Soldatenko, personal communication). This finding indicates that a certain gland type may be involved in the net production of still unknown biological role. Until now, very little is known about the biochemistry of the dermal glands secretion (Kirstein and Martin, 2009, 2010) and its direct effects on enemies. Biochemical tests show that different mite species contain secretion proteins with different atomic masses. It was found, however, that components with lowmolecular weight with combination of still unknown certain proteins more likely act on fish (Kirstein and Martin, 2010). At the same time, behavior experiments have found out that ‘naive’ fish attack all mites, irrespectively of their species attribution and coloration, but immediately spit them out without any damages to mites (Kirstein and Martin, 2010). Fish learn this experience and do not any more attack mites in experiments. Thus, the dermal glands may have given the mites a significant biological potential in a water life competition.
Fig. 4. (AeC). Ultrastructure of dermal glands in adult water mites, Teutonia cometes. TEM. A e general view of the secretory epithelium showing muscle fibers in the infoldings of the basal cell portions, large electron-lucent vacuoles and gland lumen with electron-dense secretion. Scale bar e 5 mm; Insert e apical cell zone showing opening (arrowheads) of dilated RER vesicles pinched off from the RER cisterns into the gland lumen. Scale bar e 0.5 mm; B e Part of the relatively flat epithelial cell with dilated RER cisterns and nucleus. Note the electron-dense lumen and muscle fibers under the epithelium. Scale bar e 3 mm; C e portion of the gland wall with large invaginations of the basal cell zone containing muscle fibers. Note cell processes extending into the lumen from the apical cell zone and the lumen filled with secretion of varying electron density containing granulation in one of the lumen compartments. Arrows indicate RER cisterns coming close to the cell surface, double arrow shows invagination of the basal lamina, arrowhead points to a vacuole fusing with the apical plasma membrane. Scale bar e 3 mm. BL e basal lamina; CP e cell processes; HS e haemocoelic space; L e gland lumen; LV e electron-lucent vacuoles; M e mitochondria; Ms e muscle fibers; N e nucleus; RER e rough endoplasmic reticulum.
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Fig. 6. (AeD). Ultrastructure of dermal glands, terminal opening and hair sensillum in adult water mites, Teutonia cometes. TEM. A e flat epithelial layer close to the gland opening with muscle attached to the basal cell surface. Note the group of dense vesicles in the vesiculated zone closely adjacent to the cell surface. Arrows indicate fusion of dense vacuoles with the gland lumen; arrowheads point to cell contacts. Scale bar e 1 mm; B e longitudinal section through the gland opening showing cuticular folds forming the orifice and the cone-shaped sclerite extending into the body cavity. Scale bar e 3 mm; C e releasing of secretion through the gland orifice. Note muscles attached to the thickened basal lamina of the flat epithelium. Scale bar e 3 mm; D e longitudinal section through the hair sensillum. Scale bar e 1 mm. AP e arthrodial pit; Cu e cuticle; DV e electron-dense vacuole; DVe e electron-dense vesicles; DS e dendrite sheath; EC e envelope cells; EF e external folds; Ep e epidermis; GO e gland orifice; IF e internal folds; IF1 e internal fold 1; IF2 e internal fold 2; L e gland lumen; Ms e muscles; Mv e microvilli; Sc e cone-shaped sclerite; Sec e secretion; SLS e sensillum lymph space; TB e tubular body; TH e trichoid hair.
Fig. 5. (AeF). Ultrastructure of dermal glands in adult water mites Teutonia cometes. TEM. A e portion of the gland wall adjacent to the midgut. Arrowheads indicate zones of remnants of the totally dissolved epithelial cell. Scale bar e 5 mm; B e Part of the epithelium showing electron-dense vacuoles and deep invagination of the cell surface (arrowheads). Arrow indicates invagination of the basal lamina into the epithelial cell. Scale bar e 3 mm; C e the basal cell zone penetrated by a muscle fiber adjacent to the body wall. Scale bar e 3 mm; D e the apical cell zone containing dilated RER cisterns partly organized as a whorl and an electron-dense vacuole. Note apical cell processes projecting into the lumen. Arrow indicates cell junction. Scale bar e 1 mm; E e part of the epithelium showing upper, “dissolving”, cell region with poorly organized dilated RER cisterns and a lighter cytoplasm in comparison with basal situated cell regions. Scale bar e 3 mm; F e apical cell surface with electron-dense vesicles coming close to the apical plasma membrane. Note fine granulation of the secretion within the lumen. Scale bar e 0.2 mm. CP e cell processes; Cu e cuticle; DC e “dissolving” cell; DV e electron-dense vacuoles; DVe e electron-dense vesicles; HS e haemocoelic space; L e gland lumen; LV e electron-lucent vacuoles; M e mitochondria; MG e midgut; Ms e muscles; RER e rough endoplasmic reticulum; Tr e trachea.
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Fig. 7. Schematic drawing showing ultrastructural organization of the gland epithelial cell and portion of the gland lumen in adult water mites, Teutonia cometes. BL e basal lamina; CP e cell processes; DC e “dissolving” cell; DV e electron-dense vacuole; DVe e electron-dense vesicles; L e gland lumen; LV e electron-lucent vacuoles; M e mitochondria; Ms e muscle fibers; N e nucleus; Nu e nucleolus; RER e rough endoplasmic reticulum.
of Tübingen, Tübingen, Germany) for additional material on this species. I wish also to thank A.E. Tenison, T.K. Zogoev and P.I. Henkin, engineers of the Department of the Electron Microscopy of the Laboratory of Parasitology, Zoological Institute RAS, St.-Petersburg, for their qualified assistance with the electron microscopy. Special thanks to Dr. O.L. Galankina (Institute of Geology and Geochronology of Pre-Cambrian RAS, St.-Petersburg) for her assistance in working on SEM JEOL and to Dr. E.V. Soldatenko (Smolensk State University, Smolensk, Russia) for her patience in observing on different mite species living in the laboratory.
References
Fig. 8. Schematic drawing of a longitudinal section through the dermal gland opening in adult water mites Teutonia cometes. Cu e cuticle; EF e external fold; IF1 e internal fold 1; IF2 e internal fold 2; Ms e muscles; Sc e cone-shaped sclerite; Sec e secretion.
Acknowledgments This study is supported by a grant N 12-04-00354-a from the Russian Foundation for Fundamental Research. I am very thankful to Dr. P.V. Tuzovskiy (Institute of Biology of the Internal Waters RAS, Borok) for the identification of the mite species used in this study and for the whole-mount preparations of mites and to Dr. R. Gerecke (Institute of Evolution and Ecology of Invertebrates, University
Alberti, G., Coons, L.B., 1999. Acari e mites. In: Harrison, F.W. (Ed.), Microscopic Anatomy of Invertebrates, vol. 8C. Wiley-Liss, New York, pp. 515e1265. Croneberg, A.I., 1878. On the organization of Eylais extendens (O.F. Müller) with remarks on some relative forms. Proceedings of the Imperial Society of Amateurs of Natural History, Anthropology and Ethnography 29, 1e37 (in Russian). Daochao, J., Longshu, L., 1997. On glandularia morphology of water mites (Acari, Actinedida, Hydrachnellae) and evolutionary theory of the mite soma. Acta Entomologica Sinica 40, 231e246. Elton, C.S., 1922. On the colours of water mites. Proceedings of the Zoological Society of London, 1231e1239. Halik, L., 1929. Beitrag zur Kenntnis der Sinnesborsten bei Hydracarinen. Zoologischer Anzeiger 83, 164e168. Ivanov, V.P., 2000. The Sensory Organs of Insects and Other Arthropods. Nauka, Moscow (in Russian). Kerfoot, W.C., 1982. A question of taste: crypsis and warning coloration in freshwater zooplankton communities. Ecology 63, 538e554. Kirstein, K.-G., Martin, P., 2009. Die Glandularien der Wassermilben (Hydrachnidia, Acari) e ihre Funktion als Wehrdrüsen. Deutsche Gesellschaft fur Limnologie (DGL), Erweiterte Zusammenfassungen der Jahrestagung 2008 (Konstanz), Hardegsen 2009, pp. 571e575.
A.B. Shatrov / Arthropod Structure & Development 42 (2013) 115e125 Kirstein, K.-G., Martin, P., 2010. Die Glandularien der Wassermilben (Hydrachnidia, Acari) e Die Wehrdrüsensekrete im Vergleich. Deutsche Gesellschaft fur Limnologie (DGL), Erweiterte Zusammenfassungen der Jahrestagung 2009 (Oldenburg), Hardegsen 2010, pp. 433e437. Leonovich, S.A., 2005. Sensory Systems of Parasitic Ticks and Mites. Nauka, St.Petersburg. Lundblad, O., 1930. Über die Anatomie von Arrhenurus mediorotundatus und die Hautdrüsen der Arrhenurus-Arten. Zeitschrift für Morphologie und Ökologie der Tiere 17, 302e338. Michael, A.D., 1895. A study of the internal anatomy of Thyas petrophilus, an unrecorded Hydrachnid found in Cornwall. Proceedings of the Zoological Society of London, 174e209. Proctor, H.C., Garga, N., 2004. Red, distasteful water mites: did fish make them that way? Experimental and Applied Acarology 34, 127e147. Schmidt, U., 1935. Beiträge zur Anatomie und Histologie der Hydrachniden, besonders von Diplodontus despiciens O.F. Müller. Zeitschrift für Morphologie und Ökologie der Tiere 30, 99e176. Shatrov, A.B., 2008. Organization of unusual idiosomal glands in a water mite, Teutonia cometes (Teutoniidae). Experimental and Applied Acarology 44, 249e263.
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Smit, H., Alberti, G., 2009. The water mite family Pontarachnidae, with new data on its peculiar morphological structures (Acari: Hydrachnidia). In: Sabelis, M.W., Bruin, J. (Eds.), Trends in Acarology. Springer, Dordrecht, pp. 71e79. Smith, B.P., Hagman, J., 2002. Experimental evidence for a female sex pheromone in Arrenurus manubriator (Acari: Hydrachnidia: Arrenuridae). Experimental and Applied Acarology 27, 257e263. Sokolov, I.I., 1940. Faune de l’URSS. Arachnides. In: N 2 Hydracarina (1-re partie: Hydrachnellae), vol. V. Edition de l’Academie des Sciences de l’URSS, Moscou, Leningrad (in Russian). Stout, V.M., 1953. Eylais waikawae n.sp. (Hydracarina) and some features of its life history and anatomy. Transactiona of the Royal Society of New Zealand 81, 389e416. Thor, S., 1902. Eigenartige, bisher unbekannte Drüsen bei einzelnen “Hydrachniden” Formen. Zoologischer Anzeiger 25, 401e409. Thor, S., 1904. Recherches sur l’anatomie comparée des Acariens prostigmatiques. Annales des Sciences Naturelles. Sér. 8 Zoologie 19, 1e190. Tuzovskiy, P.V., 1987. Morphology and Postembryonic Development of Water Mites. Nauka, Moscow (in Russian). Wiles, P.R., 1997. The homology of glands and glandularia in the water mites (Acari: Hydrachnidia). Journal of Natural History 31, 1237e1251.
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Anatomy and ultrastructure of dermal glands in an adult water mite, Teutonia cometes (Koch, 1837) (Acariformes: Hydrachnidia: Teutoniidae) Andrew B. Shatrov* Zoological Institute of the Russian Academy of Science, Universitetskaya nab. 1, 199034 St.-Petersburg, Russia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 10 May 2012 Received in revised form 28 October 2012 Accepted 29 October 2012
Organization of dermal glands in adult water mites Teutonia cometes (Koch, 1837) was studied using light-optical, SEM and TEM methods for the first time. These glands are large and occur in a total number of ten pairs at the dorsal, ventral and lateral sides of the body. The slit-like external openings of the glands (glandularia) are provided with a cone-shaped sclerite, and are combined with a single small trichoid seta (hair sensillum), which is always situated slightly apart from the anterior aspect of the gland opening. Each gland is formed by an epithelium encompassing a very large lumen (central cavity) normally filled with secretion that stains in varying intensity on toluidine blue stained sections. The epithelium is composed of irregularly shaped secretory cells with an electron-dense cytoplasm and infolded basal portions. The cells possess a large irregularly shaped nucleus and are filled with tightly packed slightly dilated cisterns and vesicles of rough endoplasmic reticulum (RER) with electron lucent contents. Dense vesicles are also present in the apical cell zone. Some cells undergo dissolution, occupy an upper position within the epithelium and have a lighter cytoplasm with disorganized RER. Muscle fibers are regularly present in the deep folds of the basal cell portions and may serve to squeeze the gland and eject the secretion into the external milieu. The structure of these dermal glands is compared with the previously described idiosomal glands of the same species and a tentative correlation with the glandularia system of water mites is given. Possible functions of the dermal glands of T. cometes are discussed. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Morphology Dermal glands Water mites Teutoniidae Teutonia cometes
1. Introduction Dermal glands are known as constantly present in representatives of water mites (Croneberg, 1878; Michael, 1895; Thor, 1902, 1904; Lundblad, 1930; Schmidt, 1935; Sokolov, 1940; Stout, 1953; Wiles, 1997; Alberti and Coons, 1999) and thought to function in different ways, such as protection against enemies (fishes) (Elton, 1922; Stout, 1953; Kerfoot, 1982), mating behavior (Smith and Hagman, 2002), dampening in unfavorable conditions (Croneberg, 1878). Unfortunately, very little is known about the anatomy and ultrastructure of dermal glands in different water mite taxa (Alberti and Coons, 1999; Shatrov, 2008; Smit and Alberti, 2009); thus questions about their functions, homology, and evolution are premature. The number of dermal glands and their distribution throughout the mite body as indicated by the gland openings (termed ‘glandularia’) are considered species-specific and
* Tel.: þ7 812 714 01 51; fax: þ7 812 714 04 44. E-mail address: [email protected]. 1467-8039/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.asd.2012.10.006
constant (Lundblad, 1930; Sokolov, 1940; Daochao and Longshu, 1997; Wiles, 1997) and may be important in evaluating the particular evolution of water mites. The external openings of dermal glands are always combined with a single hair sensillum, which is thought to serve as a ‘trigger’ mechanism for releasing the secretion (Halik, 1929; Kerfoot, 1982; Shatrov, 2008). In adult water mites, Teutonia cometes, one pair of ‘unusual’ idiosomal glands has been already described (Shatrov, 2008). These occupy the ventral position in the posterior half of the idiosoma and obviously correspond to the ‘pre-anal external’ glandularia (Tuzovskiy, 1987) or epimeroglandularia 4 (Wiles, 1997). The main purpose of the present study is to give a detailed morphological and ultrastructural description of the conspicuous ‘normal’ dermal glands in adult mites of T. cometes in comparison with the data available on the structure and function of these glands in other water mites studied so far. This work is the first attempt of a thorough fine structural examination of dermal glands in a given water mite species in order to serve as a basis for further comparative, taxonomic, phylogenetic and functional considerations.
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2. Materials and methods
3. Results
2.1. Material and collecting procedure
3.1. Anatomy
Adult mites were collected by the author in the two fresh-water lakes “Krivoe” and “Krugloe” in the region of the Chupa Bay basin of the Kandalaksha Gulf of the White Sea in the vicinity of the White Sea Biological Station “Kartesh” of the Zoological Institute of the Russian Academy of Science during the summereautumn periods of 2000e2003. Collecting was carried out by “mowing” with a net along the lakeside up to a depth of 1 m. A certain number of mites was fixed for TEM study mostly on the day of or on the next day after capture, and the remaining mites were placed in 70% ethyl ethanol for further species identification. The latter was kindly carried out afterward by Dr. P.V. Tuzovskiy (Institute of Biology of the Internal Waters of the Russian Academy of Science, Borok, Russia). Additionally, some adult mites of this species were kindly sent to the author by Dr. R. Gerecke (Institute of Evolution and Ecology of Invertebrates, University of Tübingen, Tübingen, Germany). Besides this, whole-mount specimens of T. cometes (N 8302, males and N 8410, females) from the water mite collection kept in the Institute of Biology of the Internal Waters of the Russian Academy of Science, Borok, Russia, were kindly given to the author by Dr. P.V. Tuzovskiy and were also used to observe terminal gland openings.
Using both whole-mount preparations and semi-thin sections, I counted ten pairs of the ‘normal’ dermal glands, which occupy a constant position at the dorsal, ventral and lateral sides of the mite body. All these glands belong to one morphological type and supposedly correspond to the following glandularia: pre- and postantennal glandularia, dorsoglandularia 1e4; ventroglandularia 3 and 4; lateroglandularia 4 and epimeroglandularia 2 (Wiles, 1997) (Fig. 1). An 11th pair of glands, the ‘unusual’ idiosomal glands studied by me previously (Shatrov, 2008) corresponds to the epimeroglandularia 4. Although the dermal glands are large and occupy a comparatively large body volume, the presence of the glands may be identified externally only by the glandularia, i.e. the extremely small gland openings associated with a single small seta (hair sensillum), which is always situated slightly apart from the anterior aspect of the opening (Figs. 2 and 3F). The glands are surrounded by the haemocoelic space but may directly contact organs and tissues, such as epidermis, salivary glands, midgut, hemocytes and tracheae (Figs. 3AeD, 4A and 5A). Inside, the gland openings are provided with a cone-shaped sclerite extending into the body cavity (Figs. 3E, 6B and 8).
2.2. Light-optical observations For anatomical observations, serial semi-thin sections of mites in transverse and longitudinal planes were stained with toluidine or methylene blue and investigated and photographed with a Leica DM LS-2 light-optical microscope combined with a Leica EC-3 digital camera. The gland openings were also examined and photographed in mites mounted on slides in Berlese solution using the same microscope under oil immersion (magnification 100). 2.3. Transmission electron microscopy (TEM) For TEM study, the mites were initially fixed in 2.5% glutaraldehyde in 0.1 M phosphate buffer (pH 7.2e7.4) for 2e4 h. After immersion into the fixative fluid, the integument of the mites was carefully ruptured from the dorsal side with tiny insect pins for a better penetration of the fixative, or the mites were left intact. Mites were then washed in several changes of 0.2 M phosphate buffer, postfixed in 2% osmium tetroxyde in 0.1 M phosphate buffer for 12 h to overnight, dehydrated in ethanol and acetone series, and finally embedded in an araldite mixture. Serial ultra-thin sections both in transverse and longitudinal planes were made on a Leica UC-6 ultramicrotome and, after staining with uranyl acetate and lead citrate, were examined with LEO-900 (negative film slides) and Morgagni 268D (digital visualization) transmission electron microscopes at 50 and 80 kV, respectively. 2.4. Scanning electron microscopy (SEM) For SEM study of the terminal gland’s openings, mites were washed in alcohol series and then treated with hexamethyldisilazane (HMDS) for 5e10 min as an alternative method to critical point drying for preserving the natural shape and size of the mite body. Immediately after these procedures specimens were covered with a platinum layer in an Eiko IB-5 apparatus, and examined with a JEOL JSM-6510LA scanning electron microscope at 30 kV.
Fig. 1. Schematic drawing illustrating the approximate position of the gland openings (glandularia) on the body surface of the water mite Teutonia cometes reflecting the presence of dermal glands. Black circles indicate dorsally located glandularia, white circles e glandularia on the ventral surface. Small dots anterior to the glandularia point to the position of the hair sensilla. Proposed names of the glandularia (after Wiles, 1997): A1, A2 e pre- and post-antennal glandularia; D1eD4 e dorsoglandularia 1e 4; E2, E4 e epimeroglandularia 2 and 4 (epimeroglandularia 4 correspond to the idiosomal glands); L4 e lateroglandularia 4; V3, V4 e ventroglandularia 3 and 4.
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Fig. 2. (AeD). External morphology of an adult water mite Teutonia cometes and of the dermal gland openings. SEM. A e general view of a mite from the dorso-frontal aspect. Scale bar e 200 mm; B e anterior dorsal body surface with extremely small gland openings e glandularia (arrows). Scale bar e 100 mm; C e dorsal view of the button-like gland opening (dorsoglandularia 2) formed of external and internal folds and associated with a hair sensillum (trichoid hair, broken at the middle portion) situated slightly apart from the anterior aspect of the opening. Scale bar e 5 mm; D e anterior horizontal view of the gland opening (dorsoglandularia 3) composed of the same components. Note the long but thin trichoid hair adhering to the body surface. Scale bar e 2 mm. A1 e pre-antennal glandularia of the both side of the body; A2 e post-antennal glandularium of the left body side; D1 e dorsoglandularium 1 of the left body side; EF e external fold; GO e gland orifice; IF e internal fold; Lg e legs; Pa e palp; TH e trichoid hair.
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3.2. Morphology and ultrastructure A single-layered epithelium forms the gland wall encompassing a very large lumen (central cavity). The lumen is normally filled with secretion that stains in varying intensity on toluidine blue stained sections (Fig. 3AeD). The epithelium is composed of irregularly shaped cells with an electron-dense cytoplasm and infolded basal portion (Figs. 4, 5C and 7). The epithelium rests on the flat basal lamina of moderate electron density, which rarely forms indentations into the epithelial cells (Figs. 4C and 5B). The basal plasma membrane remains flat and does not form invaginations. The lateral cell borders are tightly apposed to each other forming contacts with a rather narrow intercellular space of high electron density, where septa may be hardly distinguished (Figs. 5D and 6A). The cells possess a large irregularly shaped centrally located nucleus with a large nucleolus (Figs. 4B and 7). The cytoplasm is filled with tightly packed slightly dilated RER cisterns with electron lucent contents frequently forming whorls (Figs. 4C, 5A, D and 7). The RER cisterns, and especially RER vesicles pinched off the RER cisterns, come close to the apical plasma membrane. Occasionally, these vesicles may open into the lumen (Figs. 4 insert, C, 5B, D and 7). Besides RER cisterns, electron-dense vesicles may be also present in the apical cell zones (Figs. 5F, 6A and 7). Conspicuous Golgi bodies were not observed in the epithelial cells. Round mitochondria with a matrix of moderate electron density (sometimes partly destroyed) are numerous (Figs. 4C and 5A, E). Two kinds of vacuoles may be observed in the epithelial cells. The first one is represented by electron-lucent round vacuoles of various sizes scattered freely within the cells without obvious orientation (Figs. 4A, 5B and 7). Their origin is obscure. Typically, they are only rarely seen to contact the apical plasma membrane (Fig. 4C) and direct release of contents into the lumen was never observed. The second one are variously shaped vacuoles with a matrix of moderate electron density frequently represented by the same granulation as in the lumen (see below) (Figs. 5B, D and 7). These vacuoles contact the cell surface and their contents fuse with the secretion in the lumen (Fig. 5B). Apical cell regions within the epithelium may display a lighter cytoplasm with loosely packed poorly organized RER (Figs. 4A, 5A, E and 7) and appear as if dissolving. Mitoses in the basally located cells were not observed. Fibers of somatic muscles running along the gland wall are constantly present in the deep invaginations of the basal portions of the epithelial cells (Figs. 4A, C and 5C). The secretion in the gland lumen displays various electron densities and contains rather numerous small dense granules of unknown origin (Figs. 4C, 5B, F and 7). A layer of the homogenous secretion of moderate electron density, in which various cell processes may be observed, frequently separates the cell surface and the main portion of the granulated secretion (Figs. 4C and 5B, F). Long and narrow cell extensions divide the secretion situated close to the cell surface into compartments (Figs. 3B, C, 4A and 5A). Close to the gland opening the epithelium becomes much thinner and no longer shows extensive RER (Fig. 6A), but there are
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numerous extensions of the apical surface projecting into the lumen. Immediately beneath of the cone-shaped sclerite flanking the gland ’mouth’, prominent somatic muscles are found attached to the thickened basal lamina of the epithelium (Fig. 6A, C). 3.3. Gland opening Externally in SEM, the gland opening looks like an extremely small round ‘button’ with a thickened external rim. A slit-like orifice is situated along the middle line of this ‘button’ (Figs. 2Be D and 8). TEM examinations show that a large external circular fold of the body cuticle flanks the gland opening. Two internal smaller folds (valves) formed mostly of electron-dense epicuticle, organize the orifice as such (Figs. 2C, 3E, 6B, C and 8). A circular cone-shaped sclerite extends from the deep portion of the internal folds into the body cavity in the form of a bell (Figs. 6B, C and 8). 3.4. Hair sensilla According to their organization, the hair sensilla near the gland opening belong to the ‘no pore single-walled sensilla’ (NP-SW) type (Ivanov, 2000; Leonovich, 2005) and supposedly have a mechanoreceptive function (Fig. 6D). In T. cometes, these sensilla are characterized by a very large cup-shaped sensillum lymph space into which envelope cells extend their long curved microvilli-like processes. A dendritic sheath with round electron-dense plaques on the inner side surrounds the thick tubular bodies of the receptive cell cilia (Fig. 6D). The sensory hair is composed of a thickened basal portion with a large sensillum lymph space and a thin but long tapering trichoid hair provided with a small axial cavity in its basal portion (Figs. 2C, D and 6D). The number of sensory cells and dendrites, unfortunately, could not be determined. 4. Discussion 4.1. Anatomy and ultrastructure The number of dermal glands found in the present study is in contrast with the drawing given by Tuzovskiy (1987), where the presence of 14 pairs of glandularia is indicated in T. cometes. It is remarkable, however, that some of the glands of any gland pair in the mites studied may be lacking, and in these cases the corresponding glandularium is also absent. Due to a total absence of any signs of segmentation of the mite body, the homology of the glands with the glandularia in the scheme of Wiles (1997) seems to be highly arbitrary and reflects only the general position of the glands. This study shows that adult water mites, T. cometes, possess two types of the large dermal glands e one pair of the ‘unusual’ idiosomal glands (Shatrov, 2008) and at least ten pairs of the ‘normal’ dermal glands. Morphologically, these gland types are significantly different (Fig. 3D). In contrast to the sac-like ‘normal’ dermal glands, the idiosomal glands are arranged along the axis of the body with their openings on the epimere IV, thus corresponding to the epimeroglandularia 4 (Wiles, 1997). They have a comparatively flat epithelium, a large lumen with single solid electron-dense
Fig. 3. (AeF). Anatomical organization of dermal glands in adult water mites, Teutonia cometes. Semi-thin toluidine blue stained sections (AeE), whole-mount preparation (F). A e transverse section through the very posterior body region showing two pairs of dermal glands. Note that the deep horizontal fold of the body wall creates the impression that the excretory organ divides into two, dorsal and ventral, portions. Scale bar e 50 mm; B e large dermal gland in the posterior body region corresponding to dorsoglandularia 4 with the lumen filled with secretion. Scale bar e 25 mm; C e dermal gland corresponding to lateroglandularia 4 adjacent to testis with the gland orifice and secretion in the lumen. Scale bar e 20 mm; D e transverse section through the ventral half in the middle body region showing relationship of the ‘unusual’ idiosomal gland and ‘normal’ dermal gland corresponding ventroglandularia 3. Scale bar e 50 mm; E e orifice of the gland and the lumen filled with secretion. Scale bar e 10 mm; F e external view of the gland opening showing orifice as such, cuticular folds and the hair sensillum. Scale bar e 10 mm. Cu e cuticle; D4 e dermal gland corresponding dorsoglandularia 4; DG e dermal gland; EF e external fold; EO e excretory organ; GO e gland orifice; HS e haemocoelic space; HSe e hair sensillum; IF e internal fold; IG e idiosomal gland; L e gland lumen; MG e midgut; Ms e body muscles; Sc e cone-shaped sclerite; SE e secretory epithelium; Te e testis; V4 e dermal gland corresponding to ventroglandularia 4.
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secretion globule (Fig. 3D); a narrow layer of connective tissue cells encompasses the glandular epithelium from the outside. No regular muscle ‘net’, like in the ‘normal’ dermal glands, is found surrounding the idiosomal glands. The excretory duct of these glands is very elaborate (Shatrov, 2008) and much bigger than in the ‘normal’ glands, where only a short ‘mouth’ is observed. The presence of the epimeroglandularia 4 in most water mite species (Wiles, 1997) suggests that all corresponding glands are homological to each other. At the same time, the epimeroglandularia 4 frequently migrate anterior from their initial position on the epimere IV (Wiles, 1997). For instance, in Lebertia, Oxus and Frontipoda these glands, termed “Glandulae globulosae” (Thor, 1902), do not open on the epimere IV but far anterior. Conversely, in Limnesia maculata (Müller) such glands called “Glandula Limnesiae” open, like in T. cometes, on the ventral body surface not far from the genital opening (Thor, 1902). All these glands in the above mentioned species have a large lumen with intensively staining secretion material. These findings suggest that T. cometes and L. maculata with E4 located on the epimere IV are more basally positioned in comparison with the advanced species, where E4 have moved forward. L. maculata, besides one pair of the “Glandula Limnesiae”, also displays several pairs of large dermal glands containing a peculiar spindle-like secretion (Croneberg, 1878; Thor, 1904; Schmidt, 1935). This secretion is discharged from the gland on the body surface as solid waveform yellowish fibers (Croneberg, 1878). Glands of a very similar morphology have been also described in Eylais extendens (Müller) (Schmidt, 1935). Other mites studied so far may have, at least, two types of dermal glands (Lundblad, 1930; Smit and Alberti, 2009). Most of these glands, except for one gland type of Arrenurus globator (Müller) (Lundblad, 1930), do not display a large lumen (Croneberg, 1878; Michael, 1895; Thor, 1904; Stout, 1953; etc.). In Litarachna, one pair of dermal glands is extremely large and is filled with secretion “occupied by myriads of small granules” (Smit and Alberti, 2009, p. 76), just like in T. cometes. The origin of secretion in the lumen is not quite clear in T. cometes. Evidently the RER produces precursors of the protein secretion that is discharged from the cells most likely by means of the Golgi body dense vesicles. The Golgi bodies, however, are not clearly seen when the glands are full of secretion and probably become distinct only after the glands are depleted and start a new secretion cycle. Dissolved cells and RER vesicles, occasionally opening into the lumen, may play an additional role in the secretion process. Cell degradation and related changes in the epithelium are probably very slow, so that mitoses and active regeneration of the epithelium could not be observed. The ejection mechanism of the secretion in T. cometes may be as follows: the muscles surrounding the gland from its periphery squeeze the gland volume to push the secretion toward the orifice, whereas the muscles attached to the epithelium close to the gland opening widen the gland mouth facilitating evacuation of the secretion. A similar organization of the gland opening provided with a cone-shaped sclerite is found in Litarachna (Smit and Alberti, 2009) and in the majority of water mites (see Croneberg, 1878;
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Michael, 1895; Schmidt, 1935; Alberti and Coons, 1999; etc.), where glands are rich in secretion. However, nearly the same sclerite at the base of the orifice is shown in the mite Hydrachna globosa, De Geer (Thor, 1904), in which dermal glands are devoid of the large lumen. A great similarity in the organization of the gland openings leads to a supposition that initially all dermal glands were identical in their origin and organization and, probably, have appeared anew in water mites as a synapomorphic character. Their association with a hair sensillum may result in a trigger mechanism for the gland secretion (Kerfoot, 1982). 4.2. Functions Adult mites of T. cometes are actively swimming and have a brown or dark-red coloration (Sokolov, 1940). It is considered that fishes may more readily swallow these than brightly red colored mites (Kerfoot, 1982). As a result, Teutonia might have elaborated an effective protective mechanism against enemies in the form of the large and numerous dermal glands containing rejecting secretion. On the other hand, “red mites are most abundant in temporary water bodies, which lack fish” (Proctor and Garga, 2004, p. 129) and “redness may not be a novel trait ., but is rather a symplesiomorphy that first arose on land” (ibid. p. 129). Among four proposed types of the glandularia arrangements, the lebertoides type, to which Teutonia belongs, is considered to be the highest and evolutionary the youngest (Daochao and Longshu, 1997). Functions of the idiosomal glands are expected to be different. Their terminal apertures are situated on the epimere IV not far from the genital opening and it is speculated that these glands may play a role in sexual behavior releasing pheromones (Smith and Hagman, 2002; Shatrov, 2008). Observations on the living mites in the laboratory show that representatives of different genera, such as Limnesia and Piona, produce thin white filaments while walking upon the substrate. These threads stretch from the postero-ventral body portion by one to several pairs of the parallel lines. After producing large amounts of these threads, the mite gathers them into a knot or a net by movements of the forth pair of legs (Soldatenko, personal communication). This finding indicates that a certain gland type may be involved in the net production of still unknown biological role. Until now, very little is known about the biochemistry of the dermal glands secretion (Kirstein and Martin, 2009, 2010) and its direct effects on enemies. Biochemical tests show that different mite species contain secretion proteins with different atomic masses. It was found, however, that components with lowmolecular weight with combination of still unknown certain proteins more likely act on fish (Kirstein and Martin, 2010). At the same time, behavior experiments have found out that ‘naive’ fish attack all mites, irrespectively of their species attribution and coloration, but immediately spit them out without any damages to mites (Kirstein and Martin, 2010). Fish learn this experience and do not any more attack mites in experiments. Thus, the dermal glands may have given the mites a significant biological potential in a water life competition.
Fig. 4. (AeC). Ultrastructure of dermal glands in adult water mites, Teutonia cometes. TEM. A e general view of the secretory epithelium showing muscle fibers in the infoldings of the basal cell portions, large electron-lucent vacuoles and gland lumen with electron-dense secretion. Scale bar e 5 mm; Insert e apical cell zone showing opening (arrowheads) of dilated RER vesicles pinched off from the RER cisterns into the gland lumen. Scale bar e 0.5 mm; B e Part of the relatively flat epithelial cell with dilated RER cisterns and nucleus. Note the electron-dense lumen and muscle fibers under the epithelium. Scale bar e 3 mm; C e portion of the gland wall with large invaginations of the basal cell zone containing muscle fibers. Note cell processes extending into the lumen from the apical cell zone and the lumen filled with secretion of varying electron density containing granulation in one of the lumen compartments. Arrows indicate RER cisterns coming close to the cell surface, double arrow shows invagination of the basal lamina, arrowhead points to a vacuole fusing with the apical plasma membrane. Scale bar e 3 mm. BL e basal lamina; CP e cell processes; HS e haemocoelic space; L e gland lumen; LV e electron-lucent vacuoles; M e mitochondria; Ms e muscle fibers; N e nucleus; RER e rough endoplasmic reticulum.
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Fig. 6. (AeD). Ultrastructure of dermal glands, terminal opening and hair sensillum in adult water mites, Teutonia cometes. TEM. A e flat epithelial layer close to the gland opening with muscle attached to the basal cell surface. Note the group of dense vesicles in the vesiculated zone closely adjacent to the cell surface. Arrows indicate fusion of dense vacuoles with the gland lumen; arrowheads point to cell contacts. Scale bar e 1 mm; B e longitudinal section through the gland opening showing cuticular folds forming the orifice and the cone-shaped sclerite extending into the body cavity. Scale bar e 3 mm; C e releasing of secretion through the gland orifice. Note muscles attached to the thickened basal lamina of the flat epithelium. Scale bar e 3 mm; D e longitudinal section through the hair sensillum. Scale bar e 1 mm. AP e arthrodial pit; Cu e cuticle; DV e electron-dense vacuole; DVe e electron-dense vesicles; DS e dendrite sheath; EC e envelope cells; EF e external folds; Ep e epidermis; GO e gland orifice; IF e internal folds; IF1 e internal fold 1; IF2 e internal fold 2; L e gland lumen; Ms e muscles; Mv e microvilli; Sc e cone-shaped sclerite; Sec e secretion; SLS e sensillum lymph space; TB e tubular body; TH e trichoid hair.
Fig. 5. (AeF). Ultrastructure of dermal glands in adult water mites Teutonia cometes. TEM. A e portion of the gland wall adjacent to the midgut. Arrowheads indicate zones of remnants of the totally dissolved epithelial cell. Scale bar e 5 mm; B e Part of the epithelium showing electron-dense vacuoles and deep invagination of the cell surface (arrowheads). Arrow indicates invagination of the basal lamina into the epithelial cell. Scale bar e 3 mm; C e the basal cell zone penetrated by a muscle fiber adjacent to the body wall. Scale bar e 3 mm; D e the apical cell zone containing dilated RER cisterns partly organized as a whorl and an electron-dense vacuole. Note apical cell processes projecting into the lumen. Arrow indicates cell junction. Scale bar e 1 mm; E e part of the epithelium showing upper, “dissolving”, cell region with poorly organized dilated RER cisterns and a lighter cytoplasm in comparison with basal situated cell regions. Scale bar e 3 mm; F e apical cell surface with electron-dense vesicles coming close to the apical plasma membrane. Note fine granulation of the secretion within the lumen. Scale bar e 0.2 mm. CP e cell processes; Cu e cuticle; DC e “dissolving” cell; DV e electron-dense vacuoles; DVe e electron-dense vesicles; HS e haemocoelic space; L e gland lumen; LV e electron-lucent vacuoles; M e mitochondria; MG e midgut; Ms e muscles; RER e rough endoplasmic reticulum; Tr e trachea.
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Fig. 7. Schematic drawing showing ultrastructural organization of the gland epithelial cell and portion of the gland lumen in adult water mites, Teutonia cometes. BL e basal lamina; CP e cell processes; DC e “dissolving” cell; DV e electron-dense vacuole; DVe e electron-dense vesicles; L e gland lumen; LV e electron-lucent vacuoles; M e mitochondria; Ms e muscle fibers; N e nucleus; Nu e nucleolus; RER e rough endoplasmic reticulum.
of Tübingen, Tübingen, Germany) for additional material on this species. I wish also to thank A.E. Tenison, T.K. Zogoev and P.I. Henkin, engineers of the Department of the Electron Microscopy of the Laboratory of Parasitology, Zoological Institute RAS, St.-Petersburg, for their qualified assistance with the electron microscopy. Special thanks to Dr. O.L. Galankina (Institute of Geology and Geochronology of Pre-Cambrian RAS, St.-Petersburg) for her assistance in working on SEM JEOL and to Dr. E.V. Soldatenko (Smolensk State University, Smolensk, Russia) for her patience in observing on different mite species living in the laboratory.
References
Fig. 8. Schematic drawing of a longitudinal section through the dermal gland opening in adult water mites Teutonia cometes. Cu e cuticle; EF e external fold; IF1 e internal fold 1; IF2 e internal fold 2; Ms e muscles; Sc e cone-shaped sclerite; Sec e secretion.
Acknowledgments This study is supported by a grant N 12-04-00354-a from the Russian Foundation for Fundamental Research. I am very thankful to Dr. P.V. Tuzovskiy (Institute of Biology of the Internal Waters RAS, Borok) for the identification of the mite species used in this study and for the whole-mount preparations of mites and to Dr. R. Gerecke (Institute of Evolution and Ecology of Invertebrates, University
Alberti, G., Coons, L.B., 1999. Acari e mites. In: Harrison, F.W. (Ed.), Microscopic Anatomy of Invertebrates, vol. 8C. Wiley-Liss, New York, pp. 515e1265. Croneberg, A.I., 1878. On the organization of Eylais extendens (O.F. Müller) with remarks on some relative forms. Proceedings of the Imperial Society of Amateurs of Natural History, Anthropology and Ethnography 29, 1e37 (in Russian). Daochao, J., Longshu, L., 1997. On glandularia morphology of water mites (Acari, Actinedida, Hydrachnellae) and evolutionary theory of the mite soma. Acta Entomologica Sinica 40, 231e246. Elton, C.S., 1922. On the colours of water mites. Proceedings of the Zoological Society of London, 1231e1239. Halik, L., 1929. Beitrag zur Kenntnis der Sinnesborsten bei Hydracarinen. Zoologischer Anzeiger 83, 164e168. Ivanov, V.P., 2000. The Sensory Organs of Insects and Other Arthropods. Nauka, Moscow (in Russian). Kerfoot, W.C., 1982. A question of taste: crypsis and warning coloration in freshwater zooplankton communities. Ecology 63, 538e554. Kirstein, K.-G., Martin, P., 2009. Die Glandularien der Wassermilben (Hydrachnidia, Acari) e ihre Funktion als Wehrdrüsen. Deutsche Gesellschaft fur Limnologie (DGL), Erweiterte Zusammenfassungen der Jahrestagung 2008 (Konstanz), Hardegsen 2009, pp. 571e575.
A.B. Shatrov / Arthropod Structure & Development 42 (2013) 115e125 Kirstein, K.-G., Martin, P., 2010. Die Glandularien der Wassermilben (Hydrachnidia, Acari) e Die Wehrdrüsensekrete im Vergleich. Deutsche Gesellschaft fur Limnologie (DGL), Erweiterte Zusammenfassungen der Jahrestagung 2009 (Oldenburg), Hardegsen 2010, pp. 433e437. Leonovich, S.A., 2005. Sensory Systems of Parasitic Ticks and Mites. Nauka, St.Petersburg. Lundblad, O., 1930. Über die Anatomie von Arrhenurus mediorotundatus und die Hautdrüsen der Arrhenurus-Arten. Zeitschrift für Morphologie und Ökologie der Tiere 17, 302e338. Michael, A.D., 1895. A study of the internal anatomy of Thyas petrophilus, an unrecorded Hydrachnid found in Cornwall. Proceedings of the Zoological Society of London, 174e209. Proctor, H.C., Garga, N., 2004. Red, distasteful water mites: did fish make them that way? Experimental and Applied Acarology 34, 127e147. Schmidt, U., 1935. Beiträge zur Anatomie und Histologie der Hydrachniden, besonders von Diplodontus despiciens O.F. Müller. Zeitschrift für Morphologie und Ökologie der Tiere 30, 99e176. Shatrov, A.B., 2008. Organization of unusual idiosomal glands in a water mite, Teutonia cometes (Teutoniidae). Experimental and Applied Acarology 44, 249e263.
125
Smit, H., Alberti, G., 2009. The water mite family Pontarachnidae, with new data on its peculiar morphological structures (Acari: Hydrachnidia). In: Sabelis, M.W., Bruin, J. (Eds.), Trends in Acarology. Springer, Dordrecht, pp. 71e79. Smith, B.P., Hagman, J., 2002. Experimental evidence for a female sex pheromone in Arrenurus manubriator (Acari: Hydrachnidia: Arrenuridae). Experimental and Applied Acarology 27, 257e263. Sokolov, I.I., 1940. Faune de l’URSS. Arachnides. In: N 2 Hydracarina (1-re partie: Hydrachnellae), vol. V. Edition de l’Academie des Sciences de l’URSS, Moscou, Leningrad (in Russian). Stout, V.M., 1953. Eylais waikawae n.sp. (Hydracarina) and some features of its life history and anatomy. Transactiona of the Royal Society of New Zealand 81, 389e416. Thor, S., 1902. Eigenartige, bisher unbekannte Drüsen bei einzelnen “Hydrachniden” Formen. Zoologischer Anzeiger 25, 401e409. Thor, S., 1904. Recherches sur l’anatomie comparée des Acariens prostigmatiques. Annales des Sciences Naturelles. Sér. 8 Zoologie 19, 1e190. Tuzovskiy, P.V., 1987. Morphology and Postembryonic Development of Water Mites. Nauka, Moscow (in Russian). Wiles, P.R., 1997. The homology of glands and glandularia in the water mites (Acari: Hydrachnidia). Journal of Natural History 31, 1237e1251.