Jacques Bitsch

Phylogenetic relationships of basal hexapods among the mandibulate arthropods: a cladistic analysis based on comparative morphological characters

In this paper we propose a reappraisal of the relationships between the basal hexapod lineages (the former ‘apterygote’ insects) and the other major groups of mandibulate arthropods. It results from a cladistic analysis including 72 characters based on external morphology, internal anatomy and development. Detailed comments are provided on the various characters used and the scoring of their states. The 35 terminal taxa include 12 hexapods (9 of which are basal ‘apterygote’ representatives), 7 myriapods, 13 crustaceans, and 3 chelicerates taken as outgroups. The results of our analyses are discussed in detail for each of the taxonomic groupings, and compared with those recently obtained by other authors using different approaches based on morphological, palaeontological, developmental or molecular sequence data. Our results support the monophyly of the Mandibulata, Crustacea, Atelocerata (Tracheata) and Hexapoda, but the assemblage of Myriapoda appears poorly supported. A close relationship between Crustacea and Hexapoda, as hypothesized by several authors, is not found in any of our analyses. Within Hexapoda, the Protura and the Collembola appear as independent clades, whereas the two unresolved dipluran taxa are grouped with the monophyletic Ectognatha (Archaeognatha, Zygentoma and Pterygota).

Ecdysteroids in the haemolymph and the ovaries of the firebrat Thermobia domestica (Packard) (Insecta, Thysanura): Correlations with integumental and ovarian cycles

Abstract Ecdysteroids were analysed with radioimmunoassay (RIA) and high-performance liquid chromatography (HPLC) in females of the apterygotous insect Thermobia domestica , which ahs overlapping moulting and reproductive cycles. During each moulting cycle, a peak in the haemolymph concentration of ecdysteroids occurs at day 9 (in the 11-day standard cycle), which can be correlated with apolysis and the beginning of new cuticle deposition. The ovaries show a peak of ecdysteroids at day 5 (i.e. one day before egg-laying), which suggests that these hormones are also involved in the reproductive cycle. In both cases, HPLC analysis combined with RIA suggests that the main ecdysteroid is 20-hydroxyecdysone. This duality in the function of ecdysteroids is discussed.

The endoskeletal structures in arthropods: cytology, morphology and evolution

The paper proposes an overview of the endoskeletal structures of the head and trunk in the different arthropod groups: Chelicerata, Crustacea, Myriapoda and Hexapoda (=Insecta s.l.). Two major endoskeletal systems are reported with their cytological characteristics: those made up of connective tissue derived from muscular tendons, and those consisting of cuticular rods or plates arising from integumentary ingrowths. The morphological value of the various endoskeletal structures, their possible homologies in different groups, and their presumed evolutionary changes are discussed. This survey may be considered as a first step to use morphological characteristics of the endoskeleton in future cladistic analyses to assess the phylogeny of arthropods.

Modifications ultrastructurales des glandes vésiculaires des Machilidae (Insecta, Thysanura) au cours des cycles de mue

SummaryDuring the period between apolysis and ecdysis, the vesicular glands show many important transformations which affect not only the cuticular ductules, but all the cells. The cytoplasm of the glandular cells undergoes a partial autolysis, whereas other parts of the cells present a high secretory activity. Immediately after the apolysis the cellular reservoir empties and disappears almost completely; soon after, refills with secretion. The most interesting transformations concern each ciliary cell, always associated with a glandular cell. In the first phase of the moulting cycle, the dendrite of the ciliary cell grows a ciliumlike extension (= distal region of the dendrite), which penetrates into the corresponding ductule; the new intima of this ductule is laid around the cilium. At the same time, the proximal region of the dendrite forms a circular fold around the base of the cilium and begins to secrete a material which will form the end apparatus. This latter is finished during the second phase of the cycle. The third phase is characterized by the degeneration of the distal region of the dendrite and the circular fold. Thus, the end apparatus is not a secretion of the ductule-carrying cell, but of the ciliary cell. At the end of the moulting period, just before ecdysis, the vesicular gland again takes the structure characteristic of the intermoult: the reservoir of the glandular cell is very large; the cuticular apparatus is almost formed; the dendrite of the ciliary cells shows, at its apex, a short “cilium” (= ciliary region s. str. + short distal region) surrounded by microvilli, free in the secretion of the reservoir.

The phylogenetic position of early hexapod lineages: morphological data contradict molecular data

Abstract.  A review of different studies on the phylogenetic relationships of the early Hexapoda lineages shows that analyses based on molecular sequence data have led to labile and sometimes incongruous results, introducing doubt as to the reliability of the cladograms as a whole. In a recent analysis using molecular data, the Collembola, usually considered as early branching hexapods, appear to occupy a position outside the assemblage of Crustacea and Insecta, leading to the rejection of the traditional view of hexapod monophyly. However, many morphological features, as well as the results of cladistic analyses based on morphological and developmental information, contradict these conclusions. More generally, it appears that in the present state of the analytical strategies, hypotheses concerning arthropod phylogenies obtained from morphological and developmental criteria and combined analyses involving molecular and morphological data provide more reliable results than those generated by molecular information alone.

The glandular units of the spermathecae of machilids (Microcoryphia): ultrastructure and modifications during moulting

Abstract The spermathecae of 4 species of Microcoryphia (Lepismachilis targionii, Trigoniophthalmus alternatus, Machilis sp. and Machilinus rupestris) present characteristics related to the primitive phylogenetic position of these apterygote insects. They are paired organs situated in the 8th abdominal segment on each side of the rudimentary genital chamber. Each spermatheca includes 2 different tissues: (a) a simple epithelium surrounding 2 spermathecal capsules and communicating with the genital chamber by short ducts; (b) a complex glandular tissue composed of numerous functional units, each made up of several cell types — a large glandular cell with a subapical reservoir, 2 basal cells, a ductule cell and enveloping cells. One of the basal cells, called the ciliary cell, presents a dendrite-like process containing 2 apical centrioles in alignment. Several ductules of neighbouring units join together before opening in the genital chamber, independently of the ducts of the spermathecal capsules. The spermathecae undergo marked changes during moulting periods. Apolysis is followed by a partial dedifferentiation of the glandular cells, then the formation of new ductule cavities and the growth of a pseudocilium at the apex of the dendrite-like process of each ciliary cell. Afterwards, cuticular material is laid down around the pseudocilia, forming the intima of the new ductules, which results from the secretions of at least the ciliary and ductule cells. The pseudocilia degenerate before ecdysis. A comparison is made with the organogenesis of analogous organs described in different insect species.

Antigonadotropic and antiallatal effects of precocene II in the firebrat, Thermobia domestica (Thysanura, Lepismatidae)

Abstract The sensitivity of an apterygote insect to precocene II was investigated for the first time in females of Thermobia domestica. Topical applications of this compound, which has been said to possess anti-juvenile hormone activity, were carried out at various times in the postecdysial period of a reproductive cycle, during intense vitellogenesis in the terminal oocytes. The effects of treatment were observed on mortality, fecundity, insemination and also on the ultrastructure of corpora allata; they depend on the dose used and on the day of treatment. A single application of 10 μg/insect at the beginning of the postecdysial period induces antigonadotropic effects in females reared both with and without males. The effects of precocene add to those of non-insemination, which also elicits inhibition of oocyte maturation. In addition, the cytotoxic action of precocene, leading to degeneration of the corpora allata, which is most probably irreversible, was demonstrated.

Les etapes de la vitellogenese chez Thermobia Domestica (Packard) (Thysanura: Lepismatidae)

Abstract Study of the ultrastructural modifications of the follicular epithelium and of the oocytes during the high growth period of the terminal follicles has allowed us to characterize 4 successive phases and to pin-point their synchronisation with the moulting cycles in adults. During phase 1, which takes place near the end of a moulting cycle, the terminal oocytes still undergo previtellogenic growth, followed by the beginning of micropinocytosis and vitellogenesis (lipid droplets at first, then little protein granules), whereas the follicular cells remain joined together. The 2nd phase starts a little before ecdysis; this phase and the third one correspond to 2 steps of intense vitellogenesis, with simultaneous deposition of lipid and glycoprotein. Endogenous protein synthesis seems to be very limited, unlike most other Apterygota. The follicular cells gradually differentiate proteosynthetic organelles, but continue dividing; the intercellular spaces become greatly distended during the 2nd and 3rd phases. Vitellogenesis can be completed only if insemination takes place at the beginning of each moulting cycle. The 4th phase is marked by the formation of the vitelline envelope and of the chorion, while the follicular cells, once more joined together, become very flat and poor in organelles. Oviposition takes place in the middle of the intermoult period.

Morphologie abdominale des machilides (Thysanura)—II. Squelette et musculature des segments génitaux femelles

Abstract A detailed description and a morphological interpretation of the VIIIth and the IXth abdominal segments of the female machilids is given in this paper. The median gonopore is situated in the posterior part of the VIIth segment and followed in the VIIIth segment by a sagittal cleft in which open 2 pairs of receptacula seminis . The VIIIth sternite is reduced to a transverse bar bearing the insertions of the anterior arms of the endosternites. In the IXth segment the sternal area is entirely membranous, but there is also a transverse bridge which we interpret as resulting from the union of 2 sclerites detached from the anterior part of the coxites. The large gonocoxites IX delimit a genital chamber in which are placed the gonapophyses bases. At the latero-anterior part of each IXth gonocoxite there is also a little sclerite, the laterocoxite or gonangulum , which probably corresponds to the second valvifer of the orthopteroids. The morphological value of the 2 pairs of gonapophyses is then discussed; we believe that these formations are coxalia interna carried by an area homologous to this, which gives rise to the eversible sacs in the pregenital segments.

Ultrastructure de l'epithelium glandulaire dureceptacle seminal chez thermobia domestica (packard) (thysanura : lepismatidae)

Abstract The present paper gives an ultrastructural description of the glandular epithelium of the receptaculum seminis of Thermobia domestica . The functional units of this epithelium, belonging to the third type, are composed of 4 apically surrounding cells: a central ciliary cell, which is permanent (only the “cilium” degenerates at each molt), a glandular cell and 2 enveloping cells. An efferent ductule allows the secretory products to be released into the central lumen of the receptaculum, lined by a thick intima. During each moulting cycle, the glandular cell shows several phases of secretory activity. The role of the receptaculum seminis is considered, both as a storage organ for seminal liquid, and as a possible source for some kind of information required for complete maturation of oocytes.