Embryogenesis of the dipluranLepidocampa weberiOudemans (Hexapoda: Diplura, Campodeidae): Formation of dorsal organ and related phenomena

Abstract

The developmental changes of embryonic membranes of a dipluran Lepidocampa weberi, with special reference to dorsal organ formation, are described in detail by light, scanning, and transmission electron microscopies. Newly differentiated germ band and serosa secrete the blastodermic cuticle at the entire egg surface beneath the chorion. Soon after, the serosal cells start to move dorsad. All the serosal cells finally concentrate at the dorsal side of the egg and form the dorsal organ. During their concentration, the serosal cells attenuate their cytoplasm to form filaments. The extensive area from which the serosa has receded is occupied by a second embryonic membrane, the amnion, which originates from the embryonic margin. The embryo and newly emerged amnion then secrete three fine cuticular layers, "cuticular lamellae I, II, and III," above which the filaments of the (developing) dorsal organ are situated. With the progression of definitive dorsal closure, the amnion reduces its extension, the dorsal organ is incorporated into the body cavity of the embryo, and the amnion and dorsal organ finally degenerate. The dorsal organ of diplurans is formed by the concentration of whole serosal cells, while that of collembolans is formed by the direct differentiation of a part of serosal cells. However, the dorsal organs of diplurans and collembolans closely resemble each other in major aspects, including that of ultrastructural features, and there is no doubt regarding their homology. The amnion, which has been regarded as being a characteristic of Ectognatha, also develops in the Diplura. This might suggest a closer affinity between the Diplura and Ectognatha than previously believed.

The genome of the blind soil-dwelling and ancestrally wingless dipluranCampodea augens, a key reference hexapod for studying the emergence of insect innovations

“…Phylogenomic analysis employing a supermatrix of 358 concatenated single-copy protein-coding genes of 14 arthropods support the idea of "Enthognatha" being paraphyletic and Diplura representing the sister group of Insecta (Figure 2, Panel a). This result is in agreement with previous phylogenetic studies that analysed phylogenomic data (Misof et al 2014), Sanger-sequenced nuclearencoded protein-coding genes (Regier et al 2004), or studied fossil (Kukalová-Peck 1987), morphological (Giribet et al 2004) and comparative embryological (Ikeda & Machida 2001;Tomizuka & Machida 2015) evidence. However, more extensive sampling of genomes of Collembola, Diplura and Protura is desirable to improve confidence in the inferred phylogenetic relationships.…”

Insect morphology in the age of phylogenomics: innovative techniques and its future role in systematics

“…Machida et al . , 1994a; Tojo & Machida ; Ikeda & Machida ; Uchifune & Machida ; Jintsu et al . ; Mashimo et al .…”

“…Machida et al . , 1994a; Ikeda & Machida ; Niitsu ; Tsutsumi et al . ; Uchifune & Machida ; Niitsu & Kobayashi ; Jintsu & Machida ; Mashimo et al .…”

“…1, e.g. Machida et al 1990Machida et al , 1994aTojo & Machida 1998;Ikeda & Machida 2001;Uchifune & Machida 2005;Jintsu et al 2010;Mashimo et al 2011). Additionally, Machida developed an automatic vacuum infiltrator which greatly improved the infiltration efficiency and minimized deformation (Machida et al 1994b;R Machida, pers.…”

“…Notable exceptions are the laboratories of R. Machida (University of Tsukuba), T. Tsutsumi (Fukushima University) and S. Niitsu (Tokyo Metropolitan University), where TEM is used routinely (e.g. Machida et al 1990Machida et al , 1994aIkeda & Machida 2001;Niitsu 2001;Tsutsumi et al 2005;Uchifune & Machida 2005;Niitsu & Kobayashi 2008;Jintsu & Machida 2009;Mashimo et al 2011;Niitsu et al 2011). Obviously the application of this demanding technique depends on the aim of the research.…”