Colette 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).

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.

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.

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.

Effects of ovarian maturation and insemination on the length of intermoult in Thermobia domestica

ABSTRACT. A study of the individual variability in the length of intermoult periods allows correlations to be established between reproductive and moulting cycles in adult females of Thermobia domestica (Packard) (Thysanura, Lepismatidae). By keeping the females without or with males and by changing the day of insemination, it is shown that the intermoult periods vary with the rate of ovarian maturation from the beginning of each stadium. Females with slow oocyte growth are never inseminated, even in the presence of males; they have short intermoults. Females with rapid oocyte growth can be inseminated and the timing of insemination regulates the length of the intermoults. It appears that the variability in duration of the intermoult only concerns the first part of the stadium (postecdysial period of the reproductive cycle=period of intense vitellogenesis), whereas the second part of the stadium (pre‐ecdysial period=previtellogenesis) has an almost constant length. The endocrine mechanisms involved are considered, taking into account the cyclic changes in hormonal levels already described in other papers.

Inhibition of phospholipase A2 modulates fecundity in the primitive insect Thermobia domestica (Thysanura)

Abstract Phospholipase A 2 (PLA 2 ) activity was tested in the seminal receptacle of the firebrat female during an ovarian cycle and in relation to insemination. The PLA 2 activity was weak up to the time of insemination, while a strong increase of the enzyme activity occurred at the end of the ovarian cycle in both inseminated and non-inseminated females, indicating that PLA 2 is an endogenous enzyme not transferred by the spermatophore. Females received various drugs whose anti-PLA 2 effects were checked on the seminal receptacle tissues. The effects of the drugs were investigated on ovarian maturation and on the number of eggs layed by inseminated females. Dose-response relationships provide crucial indications that PLA 2 inhibition interferes with the firebrat fecundity. The emergent picture is that oocyte maturation is insensitive to PLA 2 activity, but that the treatments which reduce the release of arachidonic acid from cellular phospholipids interrupt some physiological link leading to egg deposition. The arachidonate metabolites are designated as the primer of the ovulation mechanisms; the possible role of development hormones in PLA 2 regulation is discussed.

Comparison between endogenous and exogenous yolk proteins along an ovarian cycle in the firebat thermobia domestica (insecta, thysanura)

Abstract 1. 1. In the primitive insect, Thermobia domestica , the two sex-specific proteins of the female are generated by both the fat body and the ovaries. 2. 2. Production from both origins was studied along an ovarian cycle and in relation to the moulting cycle. Data designate the ovaries as the highly preponderant source of yolk proteins, but only the fat body metabolism appears clearly stimulated after insemination. 3. 3. In the ovaries, the early yolk protein synthesis and its high specific activity from the onset of a reproductive cycle indicate early translation and gene amplification necessary to support the massive endogenous production.

Synthesis and maturation of the major yolk protein by the ovaries of the firebrat, Thermobia domestica (Insecta, thysanura)

1. 1. Ovaries of Therobia domestica, dissected from inseminated females and incubated with tritiated amino acids, synthesize labeled proteins, the major fraction of which is indistinguishable from the major vitellogenin secreted by the fat body, when considering the electrophoretic mobility, the polypeptide composition and the immunoreactivity. 2. 2. Peptide mapping, using two different proteases, shows a striking structural similarity between the proteins of both origins and reveals interrelationships between their subunits. 3. 3. The ovary synthesizes the 210–212 kD precursors of the major vitellogenin, as does the fat body, and processes them intensively into smaller subunits (176–182, 57 and 46 kD). The follicle cells are tentatively nominated for both roles. 4. 4. The quantitative contribution of the two ovaries to the vitellogenin pool was found to be much higher than that of the fat body.