Morphology of a thermosensitive multipolar neuron in the infrared organ of Merimna atrata (Coleoptera, Buprestidae)

Two pairs of infrared (IR) organs are situated ventrolaterally on the second and third abdominal sternites of the Australian fire beetle Merimna atrata (Buprestidae). In ventral view, each IR organ has a round IR absorbing area under which a sensory complex is attached to the epidermis. The main component of the complex is a single large multipolar neuron and its mass of highly branched dendrites. All parts of this neuron are enveloped in glial cells. The proximal primary dendrites, which arise from the soma, finally branch into several hundred tightly packed terminal dendrites, which contain many mitochondria. We term this unusual morphology of the dendritic region a terminal dendritic mass (TDM). Additionally, two chordotonal organs were found in each sensory complex. Their somata are integrated in the complex and the dendrites extend to the periphery of the absorbing area. The bauplan of the dendritic region is reminiscent of the thermosensitive trigeminal nerve fibers innervating the absorbing structures in the IR receptors in boid and crotalid snakes. Because this multipolar neuron also functions as a thermoreceptor, another example of a functional analogy between insect and vertebrate sensory systems could be demonstrated.     

Bimodal innervation of the infrared organ of Merimna atrata (Coleoptera,Buprestidae) by thermo- and mechanosensory units

The pyrophilous Australian “fire-beetle” Merimna atrata approaches forest fires and possesses abdominal infrared (IR) organs. Each round IR organ is centrally innervated by a sensory complex showing two different units: one thermoreceptive multipolar neuron and one mechanosensitive chordotonal organ (CO) consisting of two scolopidia. We investigated the CO and found that the scolopidia are mononematic (the scolopale cap remains below the cuticle) and monodynal (one sensory cell per scolopidium). The dendrites of the scolopidia extend anteriorly and are attached by their caps to the cuticle about in the middle of the absorbing area. Structural features at the site of innervation suggest that the CO measures minute thermal deformations caused by IR absorption. Therefore, an additional photomechanic component which has been described for the IR receptors of pyrophilous jewel beetles of the genus Melanophila can be proposed for the IR organ of Merimna. Because scolopidia can measure displacements in the subnanometer range, the CO may enhance the sensitivity of the IR organ. The sensory complex of the Merimna IR organ shows the same units and similar cuticular modifications as the tympanal organs of some noctuid moths. Therefore, a parallel evolution of insect ears and the Merimna IR organ is discussed.     

Thermomechanical properties of the stimulus transducing cuticle in the infrared organ of Merimna atrata (Coleoptera,Buprestidae)

The pyrophilous Australian “fire‐beetle” Merimna atrata strongly depends on the occurrence and localization of forest fires for its reproduction. As a special adaptation to its unusual biology, elaborate infrared (IR) organs have evolved in this species. The IR‐organs consist of a specialized cuticular portion, the absorbing area, innervated by a sensory complex. The sensory complex contains a thermosensitive multipolar neuron with a specialized dendritic region, the terminal dendritic mass, and a mechanosensitive unit represented by a chordotonal organ (CO). Evidence for the IR‐receptive function so far has only been provided for the multipolar neuron. Based on morphological data, it has been hypothesized that the CO could also be involved in IR‐reception by measuring minute thermal deformations of the absorbing area. To test this hypothesis, we investigated structural features like cuticle thickness, reduced Young's modulus and hardness of the absorbing area. The results were used in finite element simulations to analyze the thermomechanical behavior and performance of the IR‐organ. Our findings indicate that considerable thermal deformation of the absorbing area occurs, supporting the hypothesis that the CO could function as photomechanical IR‐receptor. Interestingly, at the innervation site of the CO the lowest relative displacements of the absorbing area were found. This may indicate that the CO as putative photomechanic IR‐receptor has not been adapted according to the requirements of highest sensitivity. Probable benefits of the bimodal innervation by a thermosensory and a mechanosensory unit and their possible interaction for an improved performance of the IR‐organ are discussed. J. Morphol. 275:991–1003, 2014. © 2014 Wiley Periodicals, Inc.     

La glande sternale dans l'évolution des Termites

Résumé Des différenciations glandulaires de l'épiderme au niveau de certains sternites abdominaux (glandes sternales) existent chez tous les Termites.Mastotermes darwiniensis possède une glande sur chacun des sternites 3, 4 et 5; dans les sous-familles des Stolotermitinæ, Porotermitinæ, Hodotermitinæ, la glande sternale, unique, est située sur le 4^e sternite; tous les autres Termites examinés ont une glande sternale sur le 5^e sternite. Ces glandes existent dans toutes les castes, mais subissent une régression chez les sexués fonctionnels, qu'ils soient imaginaux ou néoténiques.

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Summary Glandular swellings of the epidermis in the region of some abdominal sternites (sternal glands) are always present in Termites.Mastotermes darwiniensis shows 3 glands, one on each of the 3rd, 4th and 5th sternites; in the sub-families Stolotermitinæ, Porotermitinæ and Hodotermitinæ, there is a single sternal gland on the 4th sternite; in all other Termites examined, one finds this sternal gland on the 5th sternite. These glands have been observed in every caste, but they regress in functional reproductives, both imaginal and neoteinic.

     

Electrophysiological characterization of the multipolar thermoreceptors in the "fire-beetle" Merimna atrata and comparison with the infrared sensilla of Melanophila acuminata (both Coleoptera,Buprestidae)

A thermosensitive multipolar neuron innervates each of the four abdominal receptors of the Australian buprestid beetle Merimna atrata. The neuron is spontaneously active within a broad range of body temperatures (tested between 10°C and 40°C). We heated the receptors with a red diode laser (=0.66 µm) at intensities ranging from 5.3 mW cm^–2 up to 1.3 W cm^–2. In general, warming caused an increase of receptor activity. Peak discharge frequencies were reached 100–300 ms after onset of irradiation. After peak frequencies were reached, distinct adaptation took place within seconds. A linear increase in irradiation intensity caused an exponential increase in peak frequencies. Lowest threshold was found to be at 40 mW cm^–2 where latencies were 47 ms. At the highest intensity tested (1.3 W cm^–2), peak frequencies increased up to about 300 Hz and latencies decreased to 24 ms. Considering the pyrophilous behaviour of Merimna and the morphological data from previous studies, our results support the hypothesis that the abdominal receptors are infrared receptors. We also recorded the responses of the photomechanic infrared sensilla of Melanophila acuminata under the same experimental conditions. These results show that the photomechanic sensillum of Melanophila has a higher sensitivity, and that the latencies are considerably shorter.     

Interactions of cardiac glycosides with cells and membranes Properties and structural aspects of two receptor sites for ouabain in erythrocytes

The existence of two types of binding sites for ouabain in human erythrocyte membranes is described. Receptor sites designated as ‘type I’, which may be identical to the K⁺-insensitive sites of intact cells, were detected at concentrations of ouabain as low as 10⁻⁷ M. The ‘type II’ receptor sites require the inclusion of Mg²⁺ + P_i to form complexes with ouabain; they may be identical to the K⁺-sensitive sites of intact cells. These sites were saturated at approx. 5 · 10⁻⁷ M ouabain but could not be detected at higher concentrations. The range of ouabain concentrations at which ‘type I’ receptors start to predominate (i.e. 5 · 10⁻⁸–5 · 10⁻⁷ M) was termed ‘critical digitalis concentrations’. The process of binding reached equilibrium within 1 and 4 h for ‘type I’ and ‘type II’ sites, respectively. The dissociation constant for ‘type II’ receptor-ouabain complexes was 7.6 · 10⁻⁹ M.Under similar experimental conditions, rat erythrocyte membranes exhibited only non-saturable sites.Alterations in the proportions of the two types of receptors were demonstrated by preincubation of the membranes, in the presence or absence of Mg²⁺ + P_i, prior to the addition of ouabain. In the first case, ‘type II receptor-ouabain’ complexes were stabilized at about 50% of the untreated membranes and ‘type I-ouabain’ complexes slowly approached equilibrium over a period of 24 h. In the latter instance, ‘type I’ receptors were not detected, and only ‘type II-ouabain’ complexes prevailed.     

Scanning and Transmission Electron Microscopical Observations on the Larvae of Priapulus caudatus (Priapulida)

Abstract Scanning electron microscopical studies revealed four distinct morphological larva-types (not instars) of Priapulus caudatus whose lorica-length measured 82–860 μm. The smallest of the larvae are round to oval, have 20 longitudinal ridges, a series of transverse ridges, and have two pairs of laterally situated tubuli near the posterior limits. The second larva-type is dorsoventrally compressed, has a single dorsal and single unsculptured ventral plate each with a prominent midridge near the anterior limits, three infolded lateral plates with a pair of tubuli near the posterior limits. The third and fourth larva-types remain dorsoventrally flattened; the third larva-type has less pronounced sculpturing than the fourth larva-type and is smaller; two pairs of tubuli are situated as in the previous stage. The number and arrangement of scalids on the introvert and pharyngeal teeth differ according to each of the four larva-types and are described. The ultrastructure of all organ systems is described. All scalids are sensilla equipped with ciliated receptor cells. The cuticle is similar to the cuticle in the adult and differs fundamentally from the cuticle of larval Halicryptus. The trunk is richly supplied with sensory structures. Trunk tubuli contain secretory cells. Posteriorly, a gland complex was found which presumably is the precursor of the equivalent gland in postlarvae and adults. The implications of the first larva-type's structural similarity to the larva of Tubiluchus are discussed.     

Age and size at maturity in mountain and lowland populations of the expanding moss <Emphasis Type="Italic">Pogonatum dentatum</Emphasis>

The moss Pogonatum dentatum has expanded its distribution in Fennoscandia from mountainous areas into the lowlands. This recent expansion appears to be associated with changes in important life-history parameters in female shoots. We examined shoot age and size at first production of sex organs and mature spores in P. dentatum to investigate this phenomenon. Female shoots produced mature spores for the first time in the lowlands in their second year but in their third year in the mountains. However, sex organs were produced by second year plants in both areas. There was no size difference between the mountain and lowland female shoots at the time of spore production. Among mountain females reproducing for the first time, 41% of the shoots branched, making them potentially ‘iteroparous’. Branching was not observed among lowland females. Male shoots showed no difference in production of sex organs, and were produced by second year shoots in both areas. Female shoots in the lowlands have earlier spore production and exhibit ‘semelparous’ behaviour by not producing branches. This suggests that the lowland phenotypes of P. dentatum are more ‘invasive’ than the mountain phenotypes. Earlier studies showing high rates of diaspore establishment in lowland areas also support this observation.     

Abdominal plates,spiracles and sternites in the ventral mesosoma of embryos of the desert scorpion Paruroctonus mesaensis (Scorpiones,Vaejovidae)

Summary

The scanning electron microscope was used to study changes in the ventral mesosoma of the vaejovid scorpion, Paruroctonus mesaensis. Observations are compared with those from scorpion fossils. The oldest fossils are from the Silurian period; migration from water to land occurred in the Carboniferous and Permian periods. All recent scorpions are terrestrial with four pairs of booklungs and spiracles in mesosomal sternites. Ancient eurypterids and scorpions had flap-like abdominal plates attached to the ventral surface of five mesosomal segments. The abdominal plates were apparently an aquatic adaptation, and authors have described possible gill tissue in the chamber above. In scorpion embryos, rectangular (holostem) plate-like structures precede the formation of sternites in the ventral mesosoma. Transverse folds were seen in the space above the abdominal plates. The lack of elaborate gill-like structures here supports an earlier hypothesis that aquatic scorpions had other mesosomal respiratory sites (e.g., pectines), resulting in less reliance on respiratory tissues above the abdominal plates. Spiracles initially appear as round or ovoid patterns in the epidermis at the latero-posterior margins of the ventral plates. The booklung spiracles are positioned farther anterior in sternites, but the developmental sequence for this transition is still unclear and may occur later than the stages of this study. The abdominal plates lengthen and enlarge laterally and/or epidermis is added at the lateral edges so that broad, overlapping sternites eventually cover the ventral surface of the mesosoma.     

The distribution of zinc, cadmium, lead and copper within the hepatopancreas of a woodlouse

The distribution of metals within the hepatopancreas of Oniscus asellus (Crustacea, Isopoda) from two uncontaminated sites, and two sites contaminated with zinc, cadmium and lead, has been studied by atomic absorption spectrophotometry, light microscopy, transmission and scanning electron microscopy and X-ray microanalysis. The hepatopancreas contains two types of intracellular granule. The first type, in the S cells, are spherical granules which contain copper, sulphur and calcium. In woodlice from contaminated sites, these ‘copper’ granules, also contain zinc, cadmium and lead. The second type, in the B cells, are flocculent deposits which contain iron. In woodlice from contaminated sites, these ‘iron’ granules also contain zinc and lead. Moribund woodlice from contaminated sites have large numbers of ‘copper’ and ‘iron’ granules in the hepatopancreas and a fine deposit of zinc and lead on the membranes of the cells. There are numerous microorganisms in close association with the microvillous border of the hepatopancreas of woodlice from all four sites. Within the microorganisms of Oniscus asellus from contaminated sites, there are deposits of material which contain zinc, lead, calcium and phosphorus ‘Copper’ and ‘iron’ granules could have evolved as storage sites for essential metals to be utilized when demand from the body exceeds uptake from the food. Woodlice in contaminated sites may be able to ‘detoxify’ potentially harmful amounts of essential and non-essential metals by storing them in a relatively insoluble form within these granules.     

Modelling a historic oil-tank fire allows an estimation of the sensitivity of the infrared receptors in pyrophilous Melanophila beetles

Pyrophilous jewel beetles of the genus Melanophila approach forest fires and there is considerable evidence that these beetles can detect fires from great distances of more than 60 km. Because Melanophila beetles are equipped with infrared receptors and are also attracted by hot surfaces it can be concluded that these infrared receptors are used for fire detection.The sensitivity of the IR receptors is still unknown. The lowest threshold published so far is 0.6 W/m(2) which, however, cannot explain the detection of forest fires by IR radiation from distances larger than approximately 10 km. To investigate the possible sensitivity of the IR receptors we assumed that beetles use IR radiation for remote fire detection and we made use of a historic report about a big oil-tank fire in Coalinga, California, in 1924. IR emission of an oil-tank fire can be calculated by "pool fire" simulations which now are used for fire safety and risk analysis. Assuming that beetles were lured to the fire from the nearest forests 25 and 130 km away, our results show that detection from a distance of 25 km requires a threshold of the IR receptors of at least 3×10(-2) W/m(2). According to our investigations most beetles became aware of the fire from a distance of 130 km. In this case the threshold has to be 1.3×10(-4) W/m(2). Because such low IR intensities are buried in thermal noise we suggest that the infrared sensory system of Melanophila beetles utilizes stochastic resonance for the detection of weak IR radiation. Our simulations also suggest that the biological IR receptors might be even more sensitive than uncooled technical IR sensors. Thus a closer look into the mode of operation of the Melanophila IR receptors seems promising for the development of novel IR sensors.     

A second cell-binding domain on fibronectin (RGDS-independent) for neurite extension of human neuroblastoma cells

Human neuroblastoma cells (Platt and La-N1) have previously been shown to adhere and extend neurites on tissue-culture substrata coated with a 120K chymotryptic cell-binding fragment (CBF) of plasma fibronectin (pFN), a fragment which lacks heparan sulfate- and collagen-binding activities, and to adhere to—but not extend neurites on—substrata coated with the heparan sulfate (HS)-binding protein, platelet factor-4 (PF4) ([3.]). The mechanisms of these processes on CBF, on the intact pFN molecule, or on heparin-binding fragments of pFN have been tested using a heptapeptide (peptide A) containing the Arg---Gly---Asp---Ser (RGDS) sequence which recognizes a specific ‘receptor’ on the surface of a variety of cells or a control peptide with a single amino acid substitution. Adherence and neurite extension were completely inhibited on the 120K CBF by peptide A but not by control peptide; these results indicate that the RGDS-dependent ‘receptor’ is solely responsible for adhesive responses to the 120K CBF-containing region of the pFN molecule. When peptide A was added to cells on CBF which had already formed neuntes to test reversibility, retraction of all neurite processes was induced by 1 h and cells eventually detached. In contrast, on intact pFN, peptide A had very limited effects on either initial adherence or neurite extension, revealing a second ‘cell-binding’ domain on the fibronectin molecule outside of the 120K region competent for neurite differentiation; addition of peptide A at later times to pFN-adherent, neurite-containing cells could induce only a small subset of neurites to retract, thus supporting evidence for the presence of this second domain. A second ‘cell-binding’ domain was further confirmed by quantitation of neurite outgrowth on these substrata and by analyses of cells on substrata coated with mixtures of CBF/PF4. When substrata coated with chymotrypsin-liberated HBF were tested in a similar fashion, adherence was rapid but neurite outgrowth required much longer times and was completely sensitive to RGDS peptides; supplementation of cells with the complex ganglioside GT1b could not induce RGDS-resistant neurites on heparin-binding fragments (HBF). These latter results indicate that neurite extension on HBF is a consequence of a low concentration of RGDS-dependent activity in HBF (but not to HS-binding activity as characterized by Tobey et al. [3]) and that the second ‘cell-binding’ domain is sensitive to chymotrypsin digestion of pFN during the liberation of HBF. Possible candidate molecules for this second activity as well as its preliminary location in the pFN molecule are discussed and evidence, is provided in ref. [37] ([37.]) for the potential role for one class of molecules as a ‘receptor’. These neural tumor cells therefore have multiple and alternative mechanisms of adherence and differentiation on fibronectin matrices.     

Larval structures associated with larva-to-adult trophallaxis in Platythyrea (Hymenoptera : Formicidae)

Larvae of Platythyrea arnoldi, P. modesta, P. schultzei and P. sp. (Hymenoptera : Formicidae) were found to have a well-developed, distinctive median tubercle on their 7th abdominal sternites. The first 2 species also had a tubercle on the 8th abdominal sternite. Specialised epithelial cells surround a deep invagination that opens through an orifice to the base of the tubercle on the 7th abdominal sternite of at least 3 of the species. P. lamellosa has a poorly developed tubercle. A secretion was seen at the base of the tubercle of a P. arnoldi larva, and adult ants of this species and of P. sp. and P. schultzei were often seen licking the posterior face of the tubercles for extended periods. They were feeding on a secretion originating from the orifice beneath the tubercle.     

Larval development and morphogenesis of the sea spider Pycnogonum litorale (Ström, 1762) and the tagmosis of the body of Pantopoda

Aspects of pantopod ontogeny have been known for a long time, but specific information is available for only a few species. Our account of the postembryonic development of Pycnogonum litorale is based on laboratory-reared individuals and SEM studies. We documented particularly all early developmental stages, with emphasis on morphogenetic changes of head structures and appendages. In P. litorale the protonymphal limbs, the chelicerae and two more uniramous legs, degenerate already during the larval phase; only the third one, the ovigers, reappears in male juveniles. Other Pantopoda vary in this aspect from retention of all three protonymphal appendages to their complete reduction, as in P. litorale. Accordingly, the two post-cheliceral larval appendages are separate legs in front of the walking legs in the adults, the ‘parapalps’ and the ‘ovigers’, but they do not occur in all pantopods. The scarcity of studies of the ontogeny of Pantopoda prevents us from a more conclusive picture, but our data are promising to state that additional such studies will increase the usability of ontogenetic data for a phylogenetic analysis of Pantopoda, the crown group of the Pycnogonida. We also discuss the phylogenetic implications of our data in the light of new information from Hox genes and developmental-biological data on body segmentation and tagmosis of the Chelicerata. These suggest the homology of chelicerae and antenn(ul)ae of other euarthropods. Accepting this, we conclude that the adult pycnogonid/pantopod head, the cephalosoma, corresponds to the euarthropod head and that the protonymph with three appendage-bearing segments may represent an even shorter, possibly phylogenetically older larval type than the euarthropod ‘head larva’ bearing four pairs of appendages. In further consequence, the fourth walking legs of Pycnogonida/Pantopoda should correspond to the first opisthosomal appendages, the chilaria, of euchelicerates. This implies that within Pycnogonida the post-prosomal region became compacted during evolution to a single leg-bearing segment plus a tubular end piece. Accordingly, neither the anterior nor the posterior functional boundaries of the walking-leg region correspond to the original tagma borders.     

Inflorescence patterns in the woody Brazilian genus Diplusodon (Lythraceae)

The Brazilian genus Diplusodon is the second largest genus within Lythraceae. Their 85 species occupy diverse habitats within the ‘cerrado’ vegetation, and range from shrubs and treelets to dwarf, xylopodium-bearing subshrubs. A comparative-morphological survey of their inflorescence structures using Trollian typology is here presented, as well as some evolutionary considerations drawn from mapping inflorescence characters onto a preliminary phylogeny. The inflorescences of Diplusodon are mostly polytelic, ranging from single racemes to more or less complex double-, triple-, and multiple-racemes. Frondose, compound racemes are plesiomorphic within the genus. Nevertheless, an array of derived features has been found among their species, including production of lateral cymes, proliferation of the main axis, diverse patterns of internode elongation, reduction of subtending leaves to bracts, development of accessory branches, paedomorphic flowering, and, in three species, reversion to monotely.     

The Role of Olfactory Cues in Short-Range Mate Finding by the Emerald Ash Borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae)

We investigated the relative importance of olfaction versus vision in the mate-finding behavior of Agrilus planipennis. When coupled in male–female, male–male and female–female pairs, attempts to mate occurred only in the male–female pairs, suggesting that beetles can identify the opposite sex before attempting to mate. In a set of sensory deprivation experiments with male–female pairs, we evaluated whether males could find females when deprived of their sense of olfaction, vision or both. Males whose antennae were blocked with model paint took significantly longer to find females and spent less time in copula compared to untreated males. Males whose eyes were similarly blocked did not differ in their mate finding capacity compared to untreated males. In a third experiment that compared both olfaction and vision, olfactorily impaired beetles never mated whereas the mate finding potential of visually impaired beetles did not differ from that of untreated beetles. Our results indicate that males can identify females before coming into physical contact with them, and that at short range (≤5 cm), volatile cues detected by olfaction are involved in mate finding by A. planipennis.     

Distinguishing kinds of prior dominance and subordination experiences in males of green swordtail fish (Xiphophorus helleri)

In experiments, there are usually two general ways of obtaining dominants and subordinates to test for the effect of recent experience upon ulterior behavior and dominance. One is to ‘impose’ such an experience on the contestants by a priori deciding which individual of the pair will become the dominant and which will become the subordinate through the use of rigged contests. The second technique is to let contestants ‘self-select’ the winner and loser by waiting for the spontaneous outcome of dyadic encounters between two usually well matched opponents. These two techniques of obtaining dominants and subordinates probably represent extreme cases on a single continuum of investment made by animals to settle dominance. To test this, we compared dominants and subordinates obtained from these two techniques in Xiphophorus fish males. It was found that pairs obtained through rigged contest (R) were much more aggressive in subsequent encounters than pairs in which the dominant and subordinate could self-select (S). They recuperated more rapidly from handling, initiated contact earlier, took more time to assess each other, and fought for a longer period of time. Prior-winners and prior-losers of the R condition more frequently relied on aggressive behavior during contest than that of the S condition. As a consequence, prior-winners and prior-losers of the R condition won equally the subsequent contest. On the contrary, prior-winners of the S condition defeated their prior-loser opponent in a majority of cases. These results can be tentatively explained by the following principle, winning or losing against a well matched opponent would leave more ‘experience’ than winning over a much weaker opponent, or losing to a much stronger one. This reinforces the hypothesis that prior-experiences are not qualitative states but come in various degrees.     

Persistent larval sensory neurons in adult Drosophila melanogaster

Using a combination of lineage tracing and laser ablation, we have identified a segmentally repeated array of embryonically produced sensory neurons that persist through metamorphosis into adult stages of Drosophila development. The persistent sensory neurons are found in all unfused abdominal segments, but there is segment-specific variation in the number of neurons observed. There are 12 persistent neurons in the first abdominal segment (A1), 18 in the second (A2), and 16 in segments A3-A7. Most are internal sensory neurons (dendritic arborization neurons and bipolar dendrite neurons), but two are associated with external sensilla on the sternite. All of these neurons and their axons define specific adult sensory pathways in the periphery and their locations and persistence through metamorphosis suggest a role in guiding the growth of adult sensory and motor axons.