The embryology of the jumping bristletail, Pedetontus unimaculatus Machida (Insecta, Microcoryphia, Machilidae)

Thesis--University of Tsukuba, D.Sc.(A), no. 123, 1982. 3. 2

Embryological evidence substantiates the subcoxal theory on the origin of pleuron in insects

The lateral body plate pleuron is a significant structure in insects that contributes to the development and elaboration of wings and limbs (appendages). Although the pleuron is thought to originate from the proximal-most appendicular segment, the subcoxa, details remain unclear, and the morphological boundary between the dorsal body plate tergum and appendage (BTA) has not been clearly specified. Employing low-vacuum scanning electron microscopy (SEM) and the nano-suit method for SEM, we followed, in detail, the development of the thoracic segments of the two-spotted cricket Gryllus bimaculatus and succeeded in clearly defining the BTA. This study demonstrates the subcoxal origin of the pleuron, suggests the tergal origin of spiracles, and reveals that the wing proper originates exclusively from the tergum, whereas the wing hinge and direct muscles may be appendicular in origin, suggesting the dual origin (i.e., tergal plus appendicular origin) of wings

Embryonic development of Eucorydia yasumatsui Asahina, with special reference to external morphology (Insecta: Blattodea, Corydiidae)

As the first step in the comparative embryological study of Blattodea, with the aim of reconstructing the groundplan and phylogeny of Dictyoptera and Polyneoptera, the embryonic development of a corydiid was examined and described in detail using Eucorydia yasumatsui. Ten to fifteen micropyles are localized on the ventral side of the egg, and aggregated symbiont bacterial “mycetomes” are found in the egg. The embryo is formed by the fusion of paired blastodermal regions, with higher cellular density on the ventral side of the egg. This type of embryo formation, regarded as one of the embryological autapomorphies of Polyneoptera, was first demonstrated for “Blattaria” in the present study. The embryo undergoes embryogenesis of the short germ band type, and elongates to its full length on the ventral side of the egg. The embryo undergoes katatrepsis and dorsal closure, and then finally, it acquires its definitive form, keeping its original position on the ventral side of the egg, with its anteroposterior axis never reversed throughout development. The information obtained was compared with that of previous studies on other insects. “Micropyles grouped on the ventral side of the egg” is thought to be a part of the groundplan of Dictyoptera, and “possession of bacteria in the form of mycetomes” to be an apomorphic groundplan of Blattodea. Corydiid embryos were revealed to perform blastokinesis of the “non-reversion type (N)”, as reported in blaberoid cockroaches other than Corydiidae (“Ectobiidae,” Blaberidae, etc.) and in Mantodea; the embryos of blattoid cockroaches (Blattidae and Cryptocercidae) and Isoptera undergo blastokinesis of the “reversion type (R),” in which the anteroposterior axis of the embryo is reversed during blastokinesis. Dictyopteran blastokinesis types can be summarized as “Mantodea (N) + Blattodea [= Blaberoidea (N) + Blattoidea (R) + Isoptera (R)]”

Four myriapod relatives – but who are sisters? No end to debates on relationships among the four major myriapod subgroups

BackgroundPhylogenetic relationships among the myriapod subgroups Chilopoda, Diplopoda, Symphyla and Pauropoda are still not robustly resolved. The first phylogenomic study covering all subgroups resolved phylogenetic relationships congruently to morphological evidence but is in conflict with most previously published phylogenetic trees based on diverse molecular data. Outgroup choice and long-branch attraction effects were stated as possible explanations for these incongruencies. In this study, we addressed these issues by extending the myriapod and outgroup taxon sampling using transcriptome data.ResultsWe generated new transcriptome data of 42 panarthropod species, including all four myriapod subgroups and additional outgroup taxa. Our taxon sampling was complemented by published transcriptome and genome data resulting in a supermatrix covering 59 species. We compiled two data sets, the first with a full coverage of genes per species (292 single-copy protein-coding genes), the second with a less stringent coverage (988 genes). We inferred phylogenetic relationships among myriapods using different data types, tree inference, and quartet computation approaches. Our results unambiguously support monophyletic Mandibulata and Myriapoda. Our analyses clearly showed that there is strong signal for a single unrooted topology, but a sensitivity of the position of the internal root on the choice of outgroups. However, we observe strong evidence for a clade Pauropoda+Symphyla, as well as for a clade Chilopoda+Diplopoda.ConclusionsOur best quartet topology is incongruent with current morphological phylogenies which were supported in another phylogenomic study. AU tests and quartet mapping reject the quartet topology congruent to trees inferred with morphological characters. Moreover, quartet mapping shows that confounding signal present in the data set is sufficient to explain the weak signal for the quartet topology derived from morphological characters. Although outgroup choice affects results, our study could narrow possible trees to derivatives of a single quartet topology. For highly disputed relationships, we propose to apply a series of tests (AU and quartet mapping), since results of such tests allow to narrow down possible relationships and to rule out confounding signal

Evidence from embryology for reconstructing the relationships of hexapod basal clades

Hexapod basal clades are discussed and their relationships reconstructed based on comparative embryological evidence. Monophylies of Diplura, Dicondylia and Ectognatha is strongly supported but no embryological evidence supports mono-phyly of the Entognatha. The developmental potential of the embryonic membrane (it forms part of the dorsal body wall) suggests that proturans may be basal to all other hexapod

The homology of cephalic muscles and endoskeletal elements between Diplura and Ectognatha (Insecta)

Diplura (two-pronged bristletails) are key to our understanding of hexapod head evolution. A sister group relationship with Ectognatha (=Insecta), comprising bristletails, silverfish and winged insects, is advocated in most modern studies, however, homologization of head muscles and endoskeletal elements between Diplura and Ectognatha is still lacking. Here, we present the first homologization of a number of head muscles and endoskeletal structures between Diplura and Ectognatha. A homologization of these structures is possible if a range of species, both from Japygidae and Campodeidae, are studied in order to reconstruct the potential groundplan characteristics and account for inner anatomy variations within Diplura. Japygidae and Campodeidae show differences in the origin, insertion, and presence of mandibular and maxillary muscles as well as the shape of the maxillary cardo. Taking into account recent embryological studies on the formation of the endoskeleton in Protura, Collembola and Diplura, we furthermore reconstruct the potential evolution of the endoskeleton in early Hexapoda. The tentorium is a defining feature of dicondylic insects (including Archaeognatha) while anterior and posterior cephalic invaginations (the later tentorial pits of dicondylic insects) are groundplan features of Hexapoda. Additionally, we clarify the composition of the gnathal pouches (i.e. the type of entognathy) in Diplura and Collembola. The pouches in Diplura are posteriorly separated, similar to the state encountered in Collembola. This contrasts to former studies emphasizing the differences in the ellipuran and dipluran type of entognathy

Notes on mating and oviposition of a primitive representative of the higher Forficulina, Apachyus chartaceus de Haan (Insecta: Dermaptera: Apachyidae)

Mating, oviposition, and selected details of the egg surface in the basalmost clade of the higher Forficulina, Apachyidae, were described, using Apachyus chartaceus (de Haan, 1842) as a representative. The mating of A. chartaceus is of the endtoend type with the partners being dorsoventrally reversed. Throughout copulation, the male tightly holds the female’s postabdomen using his forceps. This manner of mating is unique in Dermaptera, likely autapomorphic to Apachyidae, and perhaps correlated with life under bark. The eggs of A. chartaceus have an adhesive substance, by which they attach to the substratum; this is also found in basal Forficulina but is uniquely plesiomorphic for higher Forficulina. A. chartaceus does not show intensive maternal care; this is overall a secondary condition or may be accidentally caused under rearing, while the absence of some aspects of brood care (especially transport of eggs) is more likely plesiomorphic. Apachyus thus shows a mixture of unique apomorphic features and features that are uniquely plesiomorphic for higher Forficulina

Reproductive biology and postembryonic development in the basal earwig Diplatys flavicollis (Shiraki) (Insecta: Dermaptera: Diplatyidae)

Based on captive breeding, reproductive biology including mating, egg deposition and maternal brood care, and postembryonic development were examined and described in detail in the basal dermapteran Diplatys flavicollis (Shiraki, 1907) (Forficulina: Diplatyidae). The eggs possess an adhesive stalk at the posterior pole, by which they attach to the substratum. The mother cares for the eggs and offspring, occasionally touching them with her antennae and mouthparts, but the maternal care is less intensive than in the higher Forficulina. The prelarva cuts open the egg membranes with its egg tooth, a structure on the embryonic cuticle, to hatch out, and, simultaneously, sheds the cuticle to become the first instar. The number of larval instars is eight or nine. Prior to eclosion, the final instar larva eats its own filamentous cerci, with only the basalmost cercomeres left, and a pair of forceps appears in the adult. The present observations were compared with previous information on Dermaptera. The adhesive substance is an ancestral feature of Dermaptera, and the adhesive stalk may be a characteristic of Diplatyidae. The attachment of the eggs and less elaborate maternal brood care are regarded as plesiomorphic in Dermaptera. The number of larval instars in D. flavicollis (eight or nine) is remarkably larger than that in the higher Forficulina (generally four or five) and also exceeds that in another representative of basal Dermaptera or Pygidicranidae (six or seven). The largest number of larval instars among Dermaptera having been found in D. flavicollis confirms the perception of Diplatyidae being very primitive earwigs