Skin glands,poison and mimicry in dendrobatid and leptodactylid amphibians

In amphibians, secretions of toxins from specialized skin poison glands play a central role in defense against predators. The production of toxic secretions is often associated with conspicuous color patterns that warn potential predators, as it is the case of many dendrobatid frogs, including Ameerega picta. This species resembles the presumably nontoxic Leptodactylus lineatus. This study tests for mimicry by studying the morphology and distribution of skin glands, components of skin secretion, and defensive behavior. Dorsal skin was studied histologically and histochemically, and skin secretions were submitted to sodium dodecyl sulfate polyacrylamide gel electrophoresis, reversed phase high performance liquid chromatography and assays for proteolytic activity. We found that poison glands in A. picta are filled with nonprotein granules that are rich in carbohydrates, while L. lineatus glands present protein granules. Accordingly, great amounts of proteins, at least some of them enzymes, were found in the poison of L. lineatus but not in that of A. picta. Both species differ greatly on profiles of gland distribution: In L. lineatus, poison glands are organized in clusters whose position coincides with colored elements of the dorsum. These regions are evidenced through a set of displays, suggesting that poison location is announced to predators through skin colors. In contrast, A. picta presents lower densities of glands, distributed homogeneously. This simpler profile suggests a rather qualitative than quantitative investment in chemical defense, in agreement with the high toxicity attributed to dendrobatids in general. Our data suggest that both species are toxic or unpalatable and transmit common warning signals to predators, which represents a case of Müllerian mimicry. J. Morphol. 2012. © 2011 Wiley Periodicals, Inc.     

Identification of male-specific exocrine secretions from predatory stink bugs (Hemiptera,pentatomidae)

In the nearctic predaceous stink bugs (Asopinae), Perillus bioculatus and Stiretrus anchorago, and the neotropical asopine, Oplomus severus, males possess conspicuous sternal glands that are absent in females. In each of these species, the male sternal gland secretion contains predominantly a single compound; 6,10,13-trimethyltetradecyl isovalerate in the allopatric species, P. bioculatus and O. severus, and 6,10,13-trimethyltetradecanol in S. anchorago, a species sympatric with P. bioculatus. The function of the sternal gland secretions from asopine hemipterans is unknown.     

Colony composition,queen behavior,specialized predation on millipedes,and exocrine glands in the ponerine ant Myopias conicara Xu, 1998 (Hymenoptera: Formicidae)

We collected a queenright colony of the very rare Myopias conicara Xu in Vietnam (1 dealate queen, 41 workers and 38 larvae). Both the queen and workers fed on xystodesmid millipedes. After paralyzing a millipede, its head was first removed by the workers, and then the larvae were put on the opening of the collum (anteriormost ring of the trunk). After the inner tissue of the collum was consumed, the exoskeleton of the collum was discarded. The feeding sequence was then repeated on the following rings of the trunk, until the entire prey was consumed. The ring‐shaped exoskeletons of the prey were deposited next to the nest entrance. The exocrine system of the workers (excluding the legs) contains 15 glands of which the structural features are similar to these of other ponerine ants. The presence of an oblong plate gland is interesting, as this gland had only been found previously in Myopias hollandi (Forel). However, none of the novel thoracic glands that were recently described in M. hollandi occur in M. conicara, which illustrates the variation within the genus Myopias. A unique characteristic of the class‐3 glands of Myopias ants is the gradual widening of the ducts, which has never been found in other insects, although the functional significance remains unknown.     

Group hunting in a ponerine ant,Leptogenys nitida Smith

Field observations on the emigration and foraging behaviours of the southern African ponerine ant, Leptogenys nitida, were undertaken at Mtunzini, Natal, South Africa. These colonies have a single ergatoid queen and 200–1000 workers. The nest sites are found in the leaf litter and these nests are moved frequently over distances ranging from 0.5 to 5 m. Leptogenys nitida is a diurnal predator of arthropods dwelling in the leaf litter. Up to 500 workers participate in each foraging trail, and are not led by definite scouts. Ants form clear trunk trails and fan out at various intervals to search for prey. The prey is searched for and retrieved cooperatively. From laboratory tests it was determined that ants will follow pygidial gland extracts, with the poison gland extract eliciting a limited response. The type of army ant behaviour observed in L. nitida seems to be different to that observed in other ponerine ants.     

Morphology of the sternal and tergal glands producing the sexual pheromones and the aphrodisiacs among the cockroaches of the subfamily oxyhaloinae

Among cockroaches in the subfamily of Oxyhaloinae, the adult males produce two essential and successively active chemical signals: the sex pheromone attracting females from a distance secreted by the sternal glands, and the aphrodisiac required for mating which is secreted by the tergal glands. The adult males of the seven species studied, Nauphoeta cinerea, Henschoutedenia flexivitta, Leucophaea maderae, Jagrehnia madecassa, Gromphadorhina portentosa, G. laevigata, and G. chopardi, possess well-developed sternal and tergal glands whose number varies according to the species and methods of mating (three to six sternal glands and four to seven tergal glands). These glands are basically composed of type three glandular units (glandular cell + duct cell) and type 2 cells (modified oenocytes) which exhibit no significant external cuticular modification except for tergite 2 of L. maderae. The extreme variance in development of these glands can be linked to sexual behavior. The hypothesis put forward here is that of a regressive evolution of the tergal glands, related to a modification of the role played by the aphrodisiacs which they secrete.     

Host colony usurpation by the queen of the Japanese pirate ant, Polyergus samurai (hymenoptera: formicidae)

Colony usurpations by newly mated queens of Polyergus samurai were observed under artificial conditions. Newly mated queens of P. samurai were introduced into three kinds of Formica japonica host colonies: queenright, queenless (artificially orphaned), and workerless (only a queen remaining) colonies. In the queenright condition, the P. samurai queen intruded into the host nest and killed the host queen, and was subsequently adopted by the host workers. In all queenright and queenless host colonies, seven of 13 queens of P. samurai succeeded in colony usurpation, although the starting time of grooming, a nestmate behavior, by host workers in the queenright condition occurred earlier than in the queenless condition. In workerless conditions, four of five P. samurai queens ignored the F. japonica queen. The results suggest that while host-queen killing is not necessary, it is important to win acceptance by host workers.     

A blend of formic acid,benzoic acid,and aliphatic alkanes mediates alarm recruitment responses in western carpenter ants,Camponotus modoc

Formicine ants in distress spray alarm pheromone which typically recruits nestmates for help. Studying the western carpenter ant, Camponotus modoc Wheeler (Hymenoptera: Formicidae), our objectives were to (1) determine the exocrine glands that contain alarm recruitment pheromone, (2) identify the key alarm recruitment pheromone components, and (3) ascertain the pheromone components that are discharged by distressed ants. In Y-tube olfactometer experiments, extracts of poison glands, but not of Dufour’s glands, elicited anemotactic responses from worker ants. Gas chromatographic-mass spectrometric analyses of poison gland extracts revealed the presence of (1) aliphatic alkanes (undecane, tridecane, pentadecane, heptadecane), (2) aliphatic alkenes [(Z)-7-pentadecene, (Z)-7- and (Z)-8-heptadecene], (3) two acids (formic, benzoic), and (4) other oxygenated compounds (hexadecan-1-ol, hexadecyl formate, hexadecyl acetate). Testing the responses of worker ants in Y-tube olfactometers to complete and partial synthetic blends of these compounds revealed that the acids and the alkanes are essential alarm pheromone components. In two-choice arena bioassays, micro-locations treated with synthetic alarm pheromone recruited worker ants. Acids and alkanes were abundant in the poison gland and the Dufour’s gland, respectively, suggesting that the alarm pheromone components originate from both glands. Moreover, alarm pheromone sprays of ants differed in that all sprays contained formic acid but only some also contained alkanes, implying that ants can independently discharge the content of either one or both glands in accordance with the type of distress incident they experience.     

Bracelet salt glands of the recretohalophyte Limonium bicolor: Distribution,morphology, and induction

Halophytes complete their life cycles in saline environments. The recretohalophyte Limonium bicolor has evolved a specialized salt secretory structure,the salt gland, which excretes Na⁺to avoid salt damage. Typical L. bicolor salt glands consist of 16 cells with four fluorescent foci and four secretory pores. Here, we describe a special type of salt gland at the base of the L. bicolor leaf petiole named bracelet salt glands due to their beaded-bracelet-like shape of blue auto-fluoresc...     

Biosynthesis of formic acid by the poison glands of formicine ants

The biosynthesis of formic acid in the poison glands of formicine ants is closely related to the C-1 metabolism of the glandular cells. Experiments utilizing radiolabeled amino acids revealed that serine is a major precursor, contributing both its α and β carbons to formic acids. 5,10[¹⁴C]methylene H₄folate and 5,10[¹⁴C]methenyl H₄folate also serve as precursors of formic acid in the poison gland, suggesting that they are intermediates in the pathway. Furthermore, these H₄folate derivatives were isolated from poison glands following incubation with [3-¹⁴C]serine and proved radioactive. The glandular cells are also exceptionally rich in the enzymes responsible for these reactions, supporting the proposed pathway.Although this pathway has been established in various organism, the uniqueness of the poison gland system is that it accumulates formic acid to large extent, yet avoids its cytotoxicity. This is made possible by a combination of the biochemical characteristics of the pathway and the special morphological features of the poison gland.     

Multiple glandular origins of queen pheromones in the fire ant Solenopsis invicta

The poison sac of the fire ant Solenopsis invicta is the only identified glandular source of pheromones produced by a functional ant queen. This structure, which contains the poison gland, has previously been shown to be the source of a releaser pheromone that mediates queen recognition and tending by workers. The poison sac has also been demonstrated to be the source of a primer pheromone that inhibits winged, virgin queens from shedding their wings (dealating) and developing their ovaries. To determine if the poison sac was the only source of these pheromones, we excised the poison sac from queens and observed whether operated queens retained their pheromonal effects. In a first experiment, the poison sac was removed from functional (egg-laying) queens which were then paired with unoperated nestmate queens in small colonies. Counts of the workers surrounding each queen two weeks after the operation showed that queens without poison sac were as effective as their unoperated nestmates in attracting worker retinues. In a second experiment, we removed the poison sacs of virgin queens which had not yet begun laying eggs and thus had not begun producing queen pheromone. After allowing them to develop their ovaries, these individuals produced amounts of queen recognition pheromone comparable to those secreted by unoperated or sham operated virgin queens as determined by bioassay. Testing the head, thorax and abdomens of functional queens separately revealed that the head was the most attractive region in relation to its relative surface area. Bioassays of extracts of two cephalic glands-the mandibular gland and postpharyngeal gland-showed that the postpharyngeal gland is a second source of the queen recognition pheromone. Finally, we found that virgin queens whose poison sacs were removed before they began producing queen pheromone initiated production of a primer pheromone that inhibits winged virgin queens from dealating, indicating that this pheromonal effect also has an additional but as yet undetermined source. These results parallel those on the honey bee in which several of the pheromonal effects of functional queens appear to have multiple glandular sources.     

Scent gland apparatus in the Western conifer seed bug Leptoglossus occidentalis Heidemann (Heteroptera: Coreidae)

The coreid Leptoglossus occidentalis is a Nearctic bug responsible for severe seed losses to pine orchards. When disturbed, adults and nymphs emit a defensive secretion deemed an allomone. Here we describe the gross morphology of the scent gland apparatus and the related evaporatory structures in nymphs and adults of L. occidentalis, through light microscopy and scanning electron microscopy. Adults of both sexes possess a metathoracic scent gland complex (MTG) including a central orange‐yellow reservoir and a pair of white lateral glands, connected by ducts to the reservoir. The MTG belongs to the diastomian type, with two ostioles located on the metathorax associated with a microsculptured cuticular accumulation area, i.e. evaporatory area, which can prevent the spread of the secretion on to non‐evaporative cuticle and increase scent fluid evaporation. A high number of male‐specific sternal gland pores were observed. These pores and associated glands are likely the source of an attractant pheromone, which could be extremely useful in monitoring and combating this invasive pest. In nymphs, MTG is replaced by two dorsal abdominal scent glands (DAGs) located between the 4th and the 6th urotergites. DAGs are reddish cuticle‐lined sacs with gland cells forming the gland wall; the scent substances are released through two orifices lying on the mid‐dorsal abdominal line between urotergites IV–V and V–VI. Also in nymphs, peculiar cuticular evaporatory areas surround both orifices.     

Diversity and morphology of abdominal glands in workers of the ant genus Myopias (Formicidae,Ponerinae)

Histological examination of serial sections through the abdomen of workers of three species of Myopias ants revealed the presence of several exocrine glands. These include the common venom and Dufour glands as well as the pygidial gland, but also more specific sternal glands and glands associated with the sting base and the gonostyli. Two of these glands have not been reported previously among ants: one is the paired oblong plate gland, that occurs next to the oblong plate and may have a pheromonal function. The other novel gland is the paired sting shaft gland, that occurs at the dorsal side in the proximal region of the sting shaft. A remarkable characteristic of these Myopias ants is that all glands of class-3 show ducts with gradually widening internal diameter. Myopias emeryi shows a clearly more simple variety of abdominal glands than Myopias maligna and M. sp.1.     

Coordination of Raiding and Emigration in the Ponerine Army Ant Leptogenys distinguenda (Hymenoptera: Formicidae: Ponerinae): A Signal Analysis

Several glandular sources of trail pheromones have been discovered in army ants in general. Nevertheless, at present the understanding of the highly coordinated behavior of these ants is far from complete. The importance of trail pheromone communication for the coordination of raids and emigrations in the ponerine army ant Leptogenys distinguenda was examined, and its ecological function is discussed. The secretions of at least two glands organize the swarming activities of L. distinguenda. The pygidial gland is the source of an orientation pheromone holding the group of raiding workers together. The same pheromone guides emigrations to new nest sites. In addition, the poison sac contains two further components: one with a weak orientation effect and another which produces strong, but short-term attraction and excitement. The latter component is important in prey recruitment and characterizes raid trails. This highly volatile recruitment pheromone allows the extreme swarm dynamic characteristic of this species. Emigration trails lack the poison gland secretion. Due to their different chemical compositions, the ants are thus able to distinguish between raid and emigration trails. Nest emigration is not induced chemically, but mechanically, by the jerking movements of stimulating workers.     

Absence of reproductive conflict during queen rearing in Apis cerana

Polyandry in honeybee queens (Apis) causes many patrilines (subfamilies) within a colony, which may lead to a potential conflict of interest among workers. This may be most apparent during queen rearing when nepotistic worker behavior could influence the genetics of future generations. Several studies have searched for such conflict in European honeybees (A. mellifera), but studies on other Apis species remain lacking. We investigated the presence of reproductive conflict in A. cerana japonica by comparing the patriline proportion of queen larvae to that of adult workers. We determined the patrilines of 272 workers and 57 queen larvae using four polymorphic microsatellite markers that were sampled from queenless colonies originally derived from four naturally mated queen-right colonies. The number of patrilines in each colony was 9, 12, 8, and 7, respectively, which is lower than that observed in continental Asia. We found no difference in patriline proportion between adult workers and queen larvae. Our data support neither genetic variance for royalty or existence of worker nepotism in A. cerana japonica.     

Primer effect of queen pheromone on juvenile hormone biosynthesis in adult worker honey bees

Juvenile hormone synthesis in adult worker honey bees was measured by an in vitro corpora allata bioassay. Adult queenless workers exhibit higher rates of juvenile hormone biosynthesis than queenright workers. Hormone synthesis is not correlated with the volume of the glands. Extract of queen mandibular glands, applied to a dummy, reduces juvenile hormone biosynthesis in caged queenless workers to the level of queenright workers. The same result was obtained with synthetic (E)-9-oxo-2-decenoic acid, the principal component of the queen mandibular gland secretion. This pheromonal primer effect may function as a key regulating element in maintaining eusocial colony homeostasis. The presence of brood does not affect the hormone production of the corpora allata.Abbreviations BSA bovine serum albumin - CA Corpora allata - JH juvenile hormone - 9-ODA (E)-9-oxo-2-decnoic acid     

Ultimobranchial gland ultrastructure of larval axolotls,Ambystoma mexicanum shaw,with some observations on the newt,Pleurodeles waltlii Micahelles

Summary The fine structure of the ultimobranchial (UB) glands of two common laboratory urodeles, viz., larval axolotls, Ambystoma mexicanum Shaw and adult Pleurodeles waltlii Micahelles, is described and compared in what is believed to be the first ultrastructural report on urodele UB glands. The axolotl UB gland shows a wide variety of form, being represented by an elongated diffuse series of follicles and sometimes by one or two large discrete terminal follicular bodies. In these axolotl UB glands up to four cell categories are distinguishable including a tonofilamentous cell and a secretory cell that is possibly homologous with calcitonin-producing C cells of anurans or other vertebrates. These two cell categories are also found in the Pleurodeles gland. The possible significance of the various cells is considered.We are indebted to the Central Research Fund of London University and the Science Research Council for awards making this research possible. We would also like to thank Dr. Eyal of the Dept. of Zoology, The Hebrew University, Jerusalem for the gift of the Pleurodeles and Mr. Raynor L. Jones for his excellent technical assistance.     

Morphological and biochemical characterization of the cutaneous poison glands in toads (<Emphasis Type="Italic">Rhinella marina</Emphasis> group) from different environments

Background

Amphibian defence against predators and microorganisms is directly related to cutaneous glands that produce a huge number of different toxins. These glands are distributed throughout the body but can form accumulations in specific regions. When grouped in low numbers, poison glands form structures similar to warts, quite common in the dorsal skin of bufonids (toads). When accumulated in large numbers, the glands constitute protuberant structures known as macroglands, among which the parotoids are the most common ones. This work aimed at the morphological and biochemical characterization of the poison glands composing different glandular accumulations in four species of toads belonging to group Rhinella marina (R. icterica, R. marina, R. schneideri and R. jimi). These species constitute a good model since they possess other glandular accumulations together with the dorsal warts and the parotoids and inhabit environments with different degrees of water availability.

Results

We have observed that the toads skin has three types of poison glands that can be differentiated from each other through the morphology and the chemical content of their secretion product. The distribution of these different glands throughout the body is peculiar to each toad species, except for the parotoids and the other macroglands, which are composed of an exclusive gland type that is usually different from that composing the dorsal warts. Each type of poison gland presents histochemical and biochemical peculiarities, mainly regarding protein components.

Conclusions

The distribution, morphology and chemical composition of the different types of poison glands, indicate that they may have different defensive functions in each toad species.

     

Microanatomy of the digestive tract and accessory organs of the Japanese flathead (Inegocia japonica Cuvier, 1829) (Scorpaeniformes,Platycephalidae)

The Japanese flathead, Inegocia japonica Cuvier, 1829 is a commercially important fish in small-scale coastal fisheries in Thailand; however, an explanation of its digestive biology is missing. This study describes the digestive tract and accessory organs of I. japonica, using morphological and histological methods. The fish (10 individual fish, 24.5 ± 0.98 cm in total length) were obtained from Libong Island, Thailand. Integrated morphological and histological data showed that the digestive tract was composed of oesophagus, stomach, pyloric caeca and intestine, with accessory organs. All digestive tracts consisted of four layers, including mucosa, submucosa, muscularis and serosa. Two stomach regions were identified (cardiac and pyloric stomachs). Several clusters of gastric glands were identified in the cardiac stomach. Each gland was a unicellular structure. The apical surface of this gland contained the vacuolar cell. The intestine was lined with a simple columnar structure with goblet cells that was similar to pyloric caecum. Goblet cells were rare in the anterior intestine, in contrast to the posterior intestine where goblet cells were abundant. The numerous of hepatocyte was mostly observed in the liver, whereas an exocrine acinar cell of pancreas was also identified. The results of our observations provided the first information of the digestive tract of I. japonica and can be applied to advanced study, such as physiology and histopathology.     

Serous gland dimorphism in the skin of Melanophryniscus stelzneri (Anura: Bufonidae)

Two serous gland types (I and II) in the skin of the Argentine toad Melanophryniscus stelzneri were discovered using light and electron microscopy. Glands of the two types differ in several traits: features of the products (both mature and immature), organelles involved in biosynthesis, and paths of serous maturation. No consistent differences, however, were detected between the myoepithelial sheaths encircling the secretory units. Type I glands manufacture vesicles containing a single dense body with a repeating substructure and conform to the fundamental secretory line of bufonid skin, a secretory line involved in biosynthesis of steroids. Type II glands synthesize granules of varying densities and seem to belong to a line of glands that secrete proteinaceous products. The occurrence of the two serous gland types in Melanophryniscus stelzneri is discussed in a comparison with current literature on the morphofunctional characteristics of anuran poison glands, which perform both regulative and defensive roles. It is suggested that di- or polymorphism in serous glands is an adaptive trait that allows differential release of active molecules on the body surface. J. Morphol. 237:19–32, 1998. © 1998 Wiley-Liss, Inc.