Subtle effect of Xenos vesparum (Xenidae, Strepsiptera) on the reproductive apparatus of its male host: Parasite or parasitoid?

Parasitic castration is an adaptive strategy where parasites usurp the hosts' reproductive physiology to complete their life cycle. The alterations in the host traits vary in their magnitude, from subtle changes in the host morpho-physiology and behaviour to the production of complex aberrant phenotypes, which often depend on the host gender. The strepsipteran macroparasite Xenos vesparum induces dramatic behavioural and physiological changes in its female host, the paper wasp Polistes dominula, while its effect on the male phenotype is largely unknown. In this study we investigated how a single X. vesparum parasite influences the functional morphology of P. dominula male reproductive apparatus. We performed morphometry and ultrastructure characterization of corpora allata, testes, seminal vesicles and accessory glands in parasitized and unparasitized males, and also in young and old males to control for the effect of age on the natural deterioration of these organs. Our results show that age significantly affects the development of male reproductive apparatus. A low parasite load - one parasite per host is the common prevalence in the field - has only a marginal impact on the reproductive morphology of P. dominula males, affecting quantitatively but not qualitatively the protein content of male accessory glands. Thus, in male P. dominula wasps, X. vesparum appears to behave as a true "parasite", in clear opposition to the role of "parasitoid" that it takes in female hosts where castration causes the reproductive death.

Development: a deep breath for endocrine organ evolution.

Developmental biologists have made surprising discoveries on the evolutionary origins of cell types, organs and body plans. Now, an elegant study in Drosophila raises interesting questions about the origin of two major endocrine organs of insects.

Common origin of insect trachea and endocrine organs from a segmentally repeated precursor.

Segmented organisms have serially repeated structures [1] that become specialized in some segments [2]. We show here that the Drosophila corpora allata, prothoracic glands, and trachea have a homologous origin and can convert into each other. The tracheal epithelial tubes develop from ten trunk placodes [3, 4], and homologous ectodermal cells in the maxilla and labium form the corpora allata and the prothoracic glands. The early endocrine and trachea gene networks are similar, with STAT and Hox genes inducing their activation. The initial invagination of the trachea and the endocrine primordia is identical, but activation of Snail in the glands induces an epithelial-mesenchymal transition (EMT), after which the corpora allata and prothoracic gland primordia coalesce and migrate dorsally, joining the corpora cardiaca to form the ring gland. We propose that the arthropod ectodermal endocrine glands and respiratory organs arose through an extreme process of divergent evolution from a metameric repeated structure.

Homology of insect corpora allata and vertebrate adenohypophysis?

Animal species of various phyla possess neuroendocrine glands whose hormonal products regulate developmental and physiological mechanisms and directly impact behavior. Two examples, the corpora allata of insects and the vertebrate adenohypophysis have previously been regarded as analogous tissues that evolved independently from diffuse epidermal nerve nets of early metazoans. More recent developmental and functional studies accumulated evidence suggesting that the bilaterian nervous systems including its modern parts (e.g. pallium or cortex and mushroom bodies) and its neuroendocrine appendages (that are considered to be more ancient structures) possess a single evolutionary origin. The corpora allata of insects and the vertebrate adenohypophysis share a number of characteristics in respect of morphology, control of hormone release by RFamides, metabolites produced by closely related cytochrome P450 enzymes and gene expression during embryonic development. This review incorporates latest findings into an extensive description of similarities between insect corpora allata and vertebrate adenohypophysis that should encourage further studies about the onto- and phylogenetic origin of these neuroendocrine glands.

Morph-specific diurnal variation in allatostatin immunostaining in the corpora allata of Gryllus firmus: implications for the regulation of a morph-specific circadian rhythm for JH biosynthetic rate.

Previous studies have documented a circadian cycle in juvenile hormone (JH) biosynthesis in the long-winged, flight-capable morph, but not in the short-winged flightless morph of the cricket Gryllus firmus. One rapid and reversible inhibitor of in vitro JH biosynthesis by the corpora allata (CA) in crickets is the neuropeptide Phe-Gly-Leu/Ile-amide type of allatostatins (ASTs). To investigate the possible role of allatostatin regulation of the morph-specific circadian cycle of JH production, the quantity of this type of AST in the nerves within the CA was determined by the density of anti-AST-immunostaining in confocal images using the Image J program. The density of immunostaining was inversely related to the rate of JH biosynthesis: Immunostaining in the CA was high and did not differ between morphs early in the photophase when the in vitro rate of JH biosynthesis is low and equivalent in the morphs. However, during the end of the photophase, when the rate of JH biosynthesis rises dramatically in the flight-capable morph, but not in the flightless morph, immunostaining was significantly lower in the flight-capable compared to the flightless morph. These results indicate that morph-specific differences in delivery of AST to the CA and its probable release likely regulate the morph-specific circadian pattern of JH biosynthesis. Also, the negative correlation between AST density and JH production provides evidence for predicting the periods of altered release of these rapid-acting paracine regulators of JH biosynthesis.

Effect of juvenile hormone III on the ultrastructure of the corpora allata in Melipona quadrifasciata (Hymenoptera,. Apidae, Meliponýný)

Changes in hormonal levels can produce alternative phenotypes. Juvenile hormone III plays an importantrole in the regulation of metamorphosis, caste determination and age in bees. In this work, we examined theultrastructure of corpora allata cells from stingless bees (Melipona quadrifasciata) treated with juvenilehormone during development. The corpora allata cells of M. quadrifasciata queens showed greater activitythan those of workers. The topical application of juvenile hormone III altered the cellular ultrastructureand either delayed development (as shown by fewer mitochondria and greater chromatin condensation) orenhanced development (looser chromatin and numerous mitochondria) when compared to untreated (control)bees. Our results show that corpora allata cells differ in their ultrastructural characteristics and that thecessation of juvenile hormone production by these cells in M. quadrifasciata is not synchronous.

Variation in cuticular hydrocarbon signatures, hormonal correlates and establishment of reproductive dominance in a polistine wasp.

In many social insects the relationship between reproductive dominance and physiological correlates is poorly understood. Recent evidence now strongly suggests that cuticular hydrocarbons are important in reproductive differentiation in these societies where they are used as signals of ovarian activity in reproductive females. In this study we investigated the relationship between reproductive dominance, size of the corpora allata (CA, producer of Juvenile Hormone, JH) and the proportions of cuticular hydrocarbons present on the cuticle in overwintering foundresses and both associative (polygynous) and solitary (monogynous) pre-emergence colonies of the social wasp Polistes dominulus. Size of the CA was positively correlated with ovarian development in polygynous colonies. In contrast, solitary foundresses possessed significantly smaller CAs than dominant foundresses from polygynous nests, yet ovarian activity was similar for both female types. CA size variation was associated with variation in cuticular hydrocarbon proportions. Overwintering, solitary, dominant and subordinate (from associative nests) females all possessed distinctive cuticular chemical profiles revealed by multivariate discriminant analyses. Our data indicate that the social environment strongly affects reproductive physiology in this wasp, and we discuss the role of cuticular hydrocarbons in reproductive signaling in P. dominulus and other social insects.

Allatostatins and allatotropin in the corpus cardiacum/corpus allatum complex of larval and adult lepidopterans studied by confocal laser scanning microscopy: correlation to juvenile hormone biosynthesis.

Peptidergic innervation of the corpus cardiacum/corpus allatum (CC/CA) retrocerebral complex, and neurosecretory areas of the brain of the lepidopterans Lacanobia oleracea, Heliothis virescens and Manduca sexta was studied by immunocytochemistry linked to confocal laser scanning microscopy. The patterns of immunostaining resulting from the simultaneous application of fluorochrome-conjugated antibodies against Manduca sexta allatostatin (Mas-AS), M. sexta allatotropin (Mas-AT), and a representative of the -Y/FXFGL-NH(2) superfamily of allatostatins was correlated with the physiological effects of these putative allatoregulatory peptides on juvenile hormone (JH) biosynthesis by the corpora allata. Whereas the two types of allatostatin immunoreactivity are present in both larval and adult CA of the three species, allatotropin immunoreactivity occurs only in the adult gland. The conclusion that withdrawal of the stimulatory effect of allatotropin is unlikely to be involved in the downregulation of CA activity prior to the onset of metamorphosis, but that an inhibitory influence of at least Mas-AS is important, is borne out in physiological experiments on JH biosynthesis in M. sexta larvae (Mas-AS inhibitory, Mas-AT without effect). Immunoreactivity to the Y/FXFGL-NH(2) allatostatins is present in both larval and adult CA and CC, frequently co-localised with Mas-AS. The function of this peptide family in the retrocerebral complex remains enigmatic since experiments on JH biosynthesis, either when the peptide is administered alone, or together with Mas-AS, show no effect on JH biosynthesis.

Antennal ampullary glands of Helicoverpa zea (Lepidoptera: Noctuidae).

In adult moths, the cephalic aorta terminates in an apical sack from which extends a pair of optic and antennal vessels that lie on either side of the esophagus, at the dorsoanterior surface of the brain. The base of each antennal vessel is dilated to form an ampulla that contains an oval mass of tissue, the antennal ampullary gland (AAG). An ultrastructural study revealed that the AAG of the corn earworm moth, Helicoverpa zea (Lepidoptera, Noctuidae), is composed of a single type of 40-50 parenchymal cells that produce secretory granules. The secretory material is released into the lymph channel of the ampullary vessel, suggesting that the AAG is an endocrine gland. Unlike the prothoracic gland and the corpus allatum, the AAG does not receive direct neural innervation; however, portions of the aortal muscle, associated with the ampullary wall, contain neurosecretory terminals and some of their products may also affect the AAG. No morphological differences were found between the AAG of males and females, with the exception that the glands in males were slightly larger. The function of the AAG remains unknown at this time. Because the AAG is located within the ampulla of the antennal vessel, one could assume that the product(s) of this gland may influence the response of the antennal sensory neurons to external stimuli.

Multifactorial control of the release of hormones from the locust retrocerebral complex.

The retrocerebral complex of locusts consists of the corpus cardiacum, the corpora allata, and the nerves that connect these glands with the central nervous system. Both corpus cardiacum and corpora allata are neuroendocrine organs and consist of a glandular part, which synthesizes adipokinetic hormones and juvenile hormone, respectively, and of a neurohemal part. The glandular adipokinetic cells in the corpus cardiacum appear to be subjected to a multitude of regulatory stimulating, inhibiting, and modulating substances. Neural influence comes from secretomotor cells in the lateral part of the protocerebrum. Up to now, only peptidergic factors have been established to be present in the neural fibres that make synaptic contact with the adipokinetic cells. Humoral factors that act on the adipokinetic cells via the hemolymph are of peptidergic and aminergic nature. In addition, high concentrations of trehalose inhibit the release of adipokinetic hormones. Although there is evidence that neurosecretory cells in the protocerebrum are involved in the control of JH biosynthesis, the nature of the factors involved remains to be resolved.

Allatostatin-immunoreactive neurons projecting to the corpora allata of adult Diploptera punctata.

A monoclonal antibody against allatostatin I was used to demonstrate the allatostatin-immunoreactive pathways between the brain and the corpus cardiacum-corpus allatum complex in the adult cockroach Diploptera punctata. The antibody was two to three orders of magnitude more sensitive to allatostatin I than to the other four known members of the allatostatin family. Whole and sectioned brains in which immunoreactivity was localized with horseradish peroxidase-H2O2-diaminobenzidine reaction showed strongly immunoreactive cells in the pars lateralis of the brain with axons leading to and arborizing in the corpus cardiacum and the corpus allatum. Although many neurosecretory cells of the pars intercerebralis project to the corpora allata only, four strongly immunoreactive cells were evident here (two pairs on either side), and these did not project to the corpus cardiacum and corpus allatum but rather terminated within the protocerebrum in areas in which lateral cells also formed arborizations. Immunoreactivity was found in many other cells in the brain, especially in the tritocerebrum.

The cerebral neurosecretory cells and retrocerebral endocrine complex in several representatives of staphyliniformic beetles (Coleoptera, Staphyliniformia).

The cerebral neurosecretory cells and retrocerebral endocrine complex were histologically studied in 20 species representing 4 families of the series Staphyliniformia (Coleoptera, Polyphaga). In their brains, the neurosecretory cells are clustered in one usually unpaired median group of the pars intercerebralis and in paired dorso-lateral and lateral groups. Up to 5 distinct neurosecretory cell types were found in the pars intercerebralis. In Hydrophilidae, Staphylinidae and in Nicrophorus species (Silphidae), the median group includes generally 20 type I neurosecretory cells and 16 type II neurosecretory cells. In Histeridae and Silphini species, the number of type I and II neurosecretory cells reaches 60-90 each. In staphyliniformic beetles, as in other Coleoptera, the number of type III and V neurosecretory cells is equal to 4. The corpora cardiaca are paired and fused with lateral aorta walls. In Hydrophilidae, Staphylinidae and Silphini, two pairs of the nervi corporis cardiaci innervate the corpora cardiaca. There is only one pair of the nervi corporis cardiaci in Histeridae and Nicrophorus species. The corpora allata join directly the corresponding corpora cardiaca. They contain frequently the neurosecretory products of cerebral neurosecretory cells.

Metamorphic changes in the cephalic neurosecretory cells and the retrocerebral neuroendocrine complex of Pericalia ricini Fabricius (Lepidoptera: Arctidae).

Aldehyde Fuchsin-positive (AF-positive) A-cells first appear in the pars intercerebralis of 4d old 1st instar larva. First sign of secretory activity is noted in 3d old 2nd instar. A gradual increase in the number of neurosecretory cells (NSC) is noted during successive larval instars. The secretion of neurosecretory material (NSM) is followed by the coalescence and finally release phases. This is a regular phenomenon, however, various NSC exhibit different phases of secretory activities at a particular time. In 4d old pupa, A4 and D-cells are absent in the tritocerebral region and in 7d, decrease in the number and size of AF-positive cells is noted. In 4-7d old pupae A4-cells are absent in the lateral region but are present in 8-10d old pupae. In unmated females 6A4-cells are present in the lateral region of the brain which are absent in unmated males. The optic region of unmated males and females have A4 and B2-cells whereas A2-cells are absent in the tritocerebrum of both the sexes. The total number of NSC in females is more than males. A1 and A3-cells of mated males and all the NSC of laid females lack NSM.

The cephalic neuroendocrine system in the beetle, Mylabris pustulata (thunb) (Meloidae: Coleoptera).

The cephalic neuroendocrine system in Mylabris pustulata includes neurosecretory cells in the brain, a pair of corpora cardiaca and corpora allata. There are three groups of the neurosecretory cells in each hemisphere of the brain-medial and lateral in the protocerebrum and central in tritocerebrum. They are classified into three types viz., A, B and C on the basis of staining affinities they exhibit. The axons of the medial, lateral and ventral neurosecretory cells constitute independently the medial, lateral and ventral neurosecretory pathways respectively inside the brain. The medial neurosecretory pathways emerge out of the brain as nervi corporis cardiaci I while the lateral and ventral neurosecretory pathways form collectively the other nerve, nervi corporis cardiaci II and innervate the CC. The CC contain two types of cells viz., the chromophilic, which are AF-positive and the chromophobic cells, which take the counterstain. The corpora allata are compact bodies and contain cells of one type but fluctuations in the nuclear size and the gland are occur frequently.

Changes in the neuroendocrine system during post-embryonic development in the buffalo-fly, Lyperosia exigua (De Meijere) (Diptera: Muscidae).

The neurosecretory cells of the pars intercerebralis and ring gland are examined in histological sections of larva, pupa and adult of buffalo-fly, Lyperosia exigua fixed at various intervals during the rpost-embryonic development. Three paired medial groups of the neurosecretory cells are observed in the larval brain. These groups show their displacement during the larval-pupal-adult moult. The medial neurosecretory A cells exhibit secretory activity by undergoing cyclic changes of synthesis and release during post-embryonic development. The ecdysial glands and a single corpus allatum also undergo cyclical changes in volume and histological appearance in accordance with the larval-pupal-adult moult.

Cephalic neuroendocrine system of the buffalo-fly, Lyperosia exigua (De Meijere) (Diptera: Muscidae).

In the adult buffalo-fly, L. exigua three groups of neurosecretory cells are present in each half of the brain; medial and lateral groups in the protocerebrum and ventral group in the tritocerebral region. The cerebral neurosecretory cells are classified as A and B cells. Both the cells are present in the medial, lateral and ventral groups. Histochemically, the neurosecretory material of these cells is composed of neutral mucopolysaccharides and proteins. The A cells are rich in cystine or cysteine amino acids, whereas B cells either lack them or may contain in negligible quantity but are rich in basic amino acids. A single pair or nerves, nervi corporis cardiaci, emerges out of the brain and merges with the recurrent nerve which later on enters the corpus cardiacum and terminates into the hypocerebral ganglion. The corpus cardiacum primarily functions as storage organ for cerebral neurosecretory material and secondarily may also produce its own hormone. The corpus allatum is composed of a single type of cells and some times it appears as syncytial structure. Cerebral neurosecretory material is never found in the corpus allatum.

Neuroendocrine system and storage of neurosecretory material in the dorsal aorta in a bug Chrysocoris stollii Wolf (Heteroptera: Pentatomidae).

The neuroendocrine system of Chrysocoris stollii has been described with the help of PF bulk-stained preparations and sections. Two groups of median neurosecretory cells (NSC), each consisting of 5 A-cells in females and 7 A-cells in male individuals together with 3 B-cells, have been observed in the pars intercerebralis medialis of the brain. The lateral neurosecretory cells are absent. The axons of the two groups of median neurosecretory cells give off two bundles of neurosecretory axonal pathways which decussate in the anterodorsal part of the protocerebrum. From the point of decussation the two pathways run deep into the protocerebrum and deutocerebrum and emerge from the tritocerebrum as nervi corporis I (NCC I). The NCC I of both the sides enter into the aorta wall. The NSM is present in the aorta wall only, which comes from the bain through the NCC I. The nervi corporis cardiaci II (NCC II) are two short nerves originating from the tritocerebrum and entering the corpora cardiaca of its side. Two posteriorly fused oval corpora cardiaca are present below the aorta and dorsal to the oesophagus. A single semicircular corpus allatum is present behind the corpora cardiaca. Two oval A-type neurosecretory cells are present in the suboesophageal ganglion whereas other ganglia of the nerve cord lack the NSC. The aorta acts as a neurohaemal organ in this insect.

Pathways and fine structure of neurons forming the nervi corporis allati II of the cockroach Periplaneta americana (L.).

By back-filling the nervus corporis allati II (NCA2) with Co2+ and precipitating the sulfide, two groups of somata (A and B) are revealed on the ipsilateral side of the subesophageal ganglion (SG). These occur anteroventrally, adjacent to the midsaggital plane. Group A consists of two cells; group B of five. Their processes form two discrete tracts issuing dorsoposteriorly into the neuropile between and slightly behind the circumesophageal connectives (CEC). After producing separate arborization fields in the dorsal neuropile, the tracts circumscribe the base of the ipsilateral CEC, unite, and their seven fibers enter NCA2 anteriorly. Prograde diffusion reveals 4--6 NCA2 axons penetrating the corpus allatum (CA) near a cap-like neurohemal organ. These axons form the transverse allatal tract (TAT), from whence they branch amongst the CA cells, and into the "cap", the postallatal nerves, and the opposite CA. Electron microscopy of transverse sections demonstrates nine neurosecretory axons entering the SG through NCA2. Proximal to the CA, NCA2 consists of a central bundle of neurosecretory axons and a peripheral zone confluent with the CA "cap". Depending upon the level of sectioning, there are 7--20 axons at the center, and seven pass into the TAT. The peripheral zone has the structure of a neurohemal organ.

Studies on the neuroendocrine system of the mangohopper, Idiocerus atkinsoni Leth. (Homoptera : Jassidae).

The neuroendocrine system of the homopteran, Idiocerus atkinsoni has been described, employing a neurosecretory stain. Two groups of medial neurosecretory cells (NSC) of one tinctorial type are present in the pars intercerebralis of the brain. Processes believed to be dendrites of the neurosecretory neurons lie superficially underneath the neurilemma and enclose neurosecretory material (NSM). Both the nervi corporis cardiaci, NCCI and NCCII, are branched. The branches of the former join to form an oesophageal nerve that runs on the oesophageal surface and terminates on the midgut, and those of the latter, innervate the oesophageal dilator muscles. Besides being present in the dendrite-like processes and NSC, the NSM is also seen in the NCCI, anterior part of the aorta and oesophageal nerve but not in the NCCII, corpora cardiaca (CC) and the corpus allatum (CA). It is suggested that the release of NSM into the circulation in this insect occurs through two main routes: the dendrites and the aorta. The evolution of the aorta as an exclusive neurohaemal organ in Hemiptera is discussed.

Neuroendocrine organs of the lemon-butterfly, Papilio demoleus L. III. Metamorphic changes in the retocerebral endocrine organs.

The retrocerebral endocrine organs, the corpora cardiaca and corpora allata were studied in different developmental stages of the lemon-butterfly. The organs were found to undergo several changes in respect of their position, size, structure and the number of nerves associated with them.