Phylogenetic relationships among the holometabolous insect orders were inferred from cladistic analysis of nucleotide sequences of 18S ribosomal DNA (rDNA) (85 exemplars) and 28S rDNA (52 exemplars) and morphological characters. Exemplar outgroup taxa were Collembola (1 sequence), Archaeognatha (1), Ephemerida (1), Odonata (2), Plecoptera (2), Blattodea (1), Mantodea (1), Dermaptera (1), Orthoptera (1), Phasmatodea (1), Embioptera (1), Psocoptera (1), Phthiraptera (1), Hemiptera (4), and Thysanoptera (1). Exemplar ingroup taxa were Coleoptera: Archostemata (1), Adephaga (2), and Polyphaga (7); Megaloptera (1); Raphidioptera (1); Neuroptera (sensu stricto = Planipennia): Mantispoidea (2), Hemerobioidea (2), and Myrmeleontoidea (2); Hymenoptera: Symphyta (4) and Apocrita (19); Trichoptera: Hydropsychoidea (1) and Limnephiloidea (2); Lepidoptera: Ditrysia (3); Siphonaptera: Pulicoidea (1) and Ceratophylloidea (2); Mecoptera: Meropeidae (1), Boreidae (1), Panorpidae (1), and Bittacidae (2); Diptera: Nematocera (1), Brachycera (2), and Cyclorrhapha (1); and Strepsiptera: Corioxenidae (1), Myrmecolacidae (1), Elenchidae (1), and Stylopidae (3). We analyzed approximately 1 kilobase of 18S rDNA, starting 398 nucleotides downstream of the 5' end, and approximately 400 bp of 28S rDNA in expansion segment D3. Multiple alignment of the 18S and 28S sequences resulted in 1,116 nucleotide positions with 24 insert regions and 398 positions with 14 insert regions, respectively. All Strepsiptera and Neuroptera have large insert regions in 18S and 28S. The secondary structure of 18S insert 23 is composed of long stems that are GC rich in the basal Strepsiptera and AT rich in the more derived Strepsiptera. A matrix of 176 morphological characters was analyzed for holometabolous orders. Incongruence length difference tests indicate that the 28S + morphological data sets are incongruent but that 28S + 18S, 18S + morphology, and 28S + 18S + morphology fail to reject the hypothesis of congruence. Phylogenetic trees were generated by parsimony analysis, and clade robustness was evaluated by branch length, Bremer support, percentage of extra steps required to force paraphyly, and sensitivity analysis using the following parameters: gap weights, morphological character weights, methods of data set combination, removal of key taxa, and alignment region. The following are monophyletic under most or all combinations of parameter values: Holometabola, Polyphaga, Megaloptera + Raphidioptera, Neuroptera, Hymenoptera, Trichoptera, Lepidoptera, Amphiesmenoptera (Trichoptera + Lepidoptera), Siphonaptera, Siphonaptera + Mecoptera, Strepsiptera, Diptera, and Strepsiptera + Diptera (Halteria). Antliophora (Mecoptera + Diptera + Siphonaptera + Strepsiptera), Mecopterida (Antliophora + Amphiesmenoptera), and Hymenoptera + Mecopterida are supported in the majority of total evidence analyses. Mecoptera may be paraphyletic because Boreus is often placed as sister group to the fleas; hence, Siphonaptera may be subordinate within Mecoptera. The 18S sequences for Priacma (Coleoptera: Archostemata), Colpocaccus (Coleoptera: Adephaga), Agulla (Raphidioptera), and Corydalus (Megaloptera) are nearly identical, and Neuropterida are monophyletic only when those two beetle sequences are removed from the analysis. Coleoptera are therefore paraphyletic under almost all combinations of parameter values. Halteria and Amphiesmenoptera have high Bremer support values and long branch lengths. The data do not support placement of Strepsiptera outside of Holometabola nor as sister group to Coleoptera. We reject the notion that the monophyly of Halteria is due to long branch attraction because Strepsiptera and Diptera do not have the longest branches and there is phylogenetic congruence between molecules, across the entire parameter space, and between morphological and molecular data.

The Strepsiptera problem: phylogeny of the holometabolous insect orders inferred from 18S and 28S ribosomal DNA sequences and morphology.

Publisher Summary This chapter discusses germ plasm and the differentiation of the germ cell line. Germ plasm is defined as a substance present in the cytoplasm of gametes, which is segregated into specific cells during blastulation and determines that those cells shall become the progenitors of the germ cell line during subsequent development. The composition of germ plasm is discussed. The histochemical evidence for the presence of RNA in polar granules of insects and germinal plasm of amphibians indicates that RNA is present only in eggs and early embryos, while a protein component is present throughout the germ cell cycle. Good morphological and experimental evidence for the presence of germ plasm is available for only a few animal species. The germinal cells of chaetognaths were present in early stages of embryonic development and identified a group of cells at the bottom of the archenteron cavity in gastrulas of Sagitta as the primordium of the germ line. Experimental studies are given to determine the role of germinal plasm in anuran eggs by altering the cytoplasm in which it is contained.

Germ plasm and the differentiation of the germ cell line.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1096-0031.2001.tb00115.x

The Phylogeny of the Extant Hexapod Orders

Attachment devices of representatives of most higher taxa of hexapods were examined. Short descriptions of tibial, tarsal and pretarsal adhesive structures for each order are presented. In their evolution, hexapods have developed two distinctly different mechanisms to attach themselves to a variety of substrates: hairy surfaces and smooth flexible pads. The flexible properties of pad material guarantees a maximal contact with surfaces, regardless of the microsculpture. These highly specialized structures are not restricted to one particular area of the leg. They may be located on different parts, such as claws, derivatives of the pretarsus, tarsal apex, tarsomeres, or tibia. The 10 characters of the two alternative designs of attachment devices – smooth and hairy – were coded and analysed together with a data matrix containing 105 additional morphological characters of different stages and body parts. The analysis demonstrates, that similar structures (arolium, euplantulae, hairy tarsomeres) have evolved independently in several lineages. Nevertheless, some of them support monophyletic groups (e.g. Embioptera + Dermaptera; Dictyoptera + Phasmatodea + Grylloblattodea + Orthoptera; Dictyoptera + Phasmatodea; Hymenoptera + Mecopterida; Neuropterida + Strepsiptera + Coleoptera). Other structures such as claw pads (Ephemeroptera), balloon-shaped eversible pads (Thysanoptera), or fossulae spongiosae (Reduviidae) are unique for larger or smaller monophyletic units. It is plausible to assume that the evolution of flight and the correlated necessity to cling to vegetation or other substrates was a major trigger for the evolution of adhesive structures. Groups with a potential to evolve a great variety of designs of adhesive pads are Hemiptera and Diptera. Even though characters of the adhesive pads are strongly subject to selection, they can provide phylogenetic information. The results of the cladistic analyses are largely congruent with current hypotheses of hexapod phylogeny. A sistergroup relationship between Diplura and Insecta and between Zygentoma (excl. Tricholepidion) and Pterygota is confirmed. Plecoptera are probably the sistergroup of the remaining Neoptera. Dermaptera are the sistergroup of Embioptera and Dictyoptera the sistergroup of Phasmatodea. Paurometabola excl. Dermaptera + Embioptera are monophyletic. A sistergroup relationship between Zoraptera and a clade comprising Paraneoptera + Endopterygota is only supported by weak evidence. Coleoptera + Strepsiptera are the sistergroup of Neuropterida and Hymenoptera the sistergroup of Mecopterida.

Ultrastructure of attachment specializations of hexapods (Arthropoda): evolutionary patterns inferred from a revised ordinal phylogeny

Publisher Summary This chapter focuses on the problem of pattern specification in early insect embryogenesis, essentially on the formal level characteristic of “classical” developmental physiology. In the field of pattern formation, optimal use can be made of these new methods of study only if they are applied with the proper questions in mind; starting off from the wrong hypothesis may mean years of detour. This consideration requires integrating old and new data from an animal group, which, such as the insects, holds much promise for the developmental biologist, especially from the genetical point of view. Any embryonic cell or group of cells, which later on, will give rise to a particular part of the body, must be instructed by appropriate signals, which specific pathway of development they should follow; this process will be called cellular instruction. Specification of a pattern occurs when different instructing signals are provided in a spatially coordinated manner. In order to respond to a specific instructing signal by producing a particular visible pattern element, an embryonic cell or group of cells must become committed to the developmental pathway indicated by that signal. Much evidence concerning pattern specification is derived from the study of egg fragments; parts of the system isolated functionally by removal or denaturation (cautery) of the remaining parts.

Specification of the Basic Body Pattern in Insect Embryogenesis1

In endoplasm close to the posterior pole of the egg ofPimpla one finds conglomerated oosome material, rich in RNA. Investigations after various operations in the oosome region (10% of egg length), before cleavage were intended to show whether pole cells develop, how many segments form and if gonads contain primordial germ cells.

Experimente am ungefurchten Ei vonPimpla turionellae L. (Hymenoptera) zur Funktionsanalyse des Oosombereichs

Von einigenRaphidia-Arten,Inocellia crassicornis Schumm. (Raphidioptera),Sialis lutaria L.,Sialis fuliginosa Pict. (Megaloptera) undOsmylus fubicephalus Scop. (Neuroptera=Planipennia) wurden Skelett und Muskulatur der beiden ersten Abdomensegmente beschrieben und mit anderen Megaloptera und Neuroptera verglichen.

Die Abdomenbasis der Neuropteroidea (Insecta, Holometabola)

In endoplasm close to the posterior pole of the egg ofPimpla one finds conglomerated oosome material, rich in RNA. Investigations after various operations in the oosome region (10% of egg length), before cleavage were intended to show whether pole cells develop, how many segments form and if gonads contain primordial germ cells.Oosome material was squashed with a blunt glass needle. The uninjured part of the egg in front of the oosome region develops blastoderm but no pole cells. It gives rise to a fully segmentated larva with germ cells in the gonads.After ligation of up to 15% of egg length complete embryos with germ cells can develop. The smaller the anterior isolates, the more abdominal segments are missing.By ligation and invagination of the hindpole of eggs with a blunt glass needle, anteriorly material from the oosome region is combined with ooplasm situated more. Translocation of only a small amount of ooplasm results in the same number of abdominal segments in the anterior isolate as in ordinary ligated eggs. Translocation of much ooplasm yields a significantly greater number of abdominal segments. It is immaterial for the metameric segmentation of the embryo whether the oosome is situated before or behind the ligature or is destroyed. But the depth of the invagination and how many segments result do not seem to be correlated.A completely segmentated embryo can develop also after extirpation of the oosome provided care is taken not to injure the hindpole-plasm. No pole-cells result when the complete oosome is missing and the hindpole-plasm is present; loss of part of the oosome results in the development of only a few pole-cells. Thus oosome material is a necessary and quantitative condition for pole-cell differentiation. In one favourable case pole-cells developed in the extraovate because the oosome was followed after some hours by endoplasm and cleavage nuclei.Functions of the oosome are discussed: together with cleavage nuclei it is responsible for pole-cell development. As pole-cells are not invariable precursors of germ-cells, the oosome cannot contain determinants for them. Possibly it includes postembryonic growth modifiers or it could be active in gametogenesis later on. As an egg without oosome-region is able to develop an embryo, this region does not or exclusively contain an activation-center (e. g.Platycnemis), or special hind-pole factors (e. g.Euscelis). In any case the oosome itself does not include these factors. A greater number of segments in the anterior isolate after translocation of ooplasm could be due to its special quality, as inEuscelis andBruchidius whose metameric organisations originate from a bipolar ooplasmic reaction system. Also it could depend only on the increase of ooplasm competent for differentiation-factors in the middle and anterior egg parts.

Experiments on the uncleared egg ofPimpla turionellae L. (Hymenoptera) for the functional analysis of the oosome region

Prospective diapause eggs ofBombyx mori become permeable to water in or after contact with paraffin, and they die before reaching diapause. If the eggs are hindered from drying up, their germ anlagen develop to diapausing germ bands. Prospective diapause eggs opened in paraffin, always develop without egg diapause, but their degree of organogenesis depends on the chorion: When eggs are completely dechorionized most of them develop to hatching or nearly hatching larvae; when eggs are completely dechorionized, but their chorion remains in the paraffin, the degree of organogenes is issignificantly lower; and when the opened eggs keep 1/2–3/4 of the chorion, their organogenesis is significantly lower than in the two previous experiments.

Nondormanz-Entwicklung prospektiver Diapause-Eier vonBombyx mori mit oder ohne Chorion unter Paraffinöl

Prospective diapause eggs ofBombyx mori become permeable to water in or after contact with paraffin, and they die before reaching diapause. If the eggs are hindered from drying up, their germ anlagen develop to diapausing germ bands. Prospective diapause eggs opened in paraffin, always develop without egg diapause, but their degree of organogenesis depends on the chorion: When eggs are completely dechorionized most of them develop to hatching or nearly hatching larvae; when eggs are completely dechorionized, but their chorion remains in the paraffin, the degree of organogenes is issignificantly lower; and when the opened eggs keep 1/2-3/4 of the chorion, their organogenesis is significantly lower than in the two previous experiments.It is discussed that nondormancy development ofprospective diapause eggs in vitro is not a specific effect of culture media containing water but is possible in paraffin oil too. It is not only possible to stop but also to prevent egg diapause. Nothing, as yet, can be said about the prospective significance of the chorion's reducing factor in organogenesis.

Michael Achtelig

Papers

Experimente am ungefurchten Ei vonPimpla turionellae L. (Hymenoptera) zur Funktionsanalyse des Oosombereichs

Die Abdomenbasis der Neuropteroidea (Insecta, Holometabola)

Experiments on the uncleared egg ofPimpla turionellae L. (Hymenoptera) for the functional analysis of the oosome region

Nondormanz-Entwicklung prospektiver Diapause-Eier vonBombyx mori mit oder ohne Chorion unter Paraffinöl

Development without dormancy of prospective diapause eggs ofBombyx mori in paraffin oil with or without chorion