Origin and fate of germ cells in male and female embryos of Haplothrips verbasci (Osborn) (Insecta, Thysanoptera, Phlaeothripidae)

Abstract

Comparison of germ cells in male and female embryos of the arrhenotokous thrips, Haplothrips verbasci, yields the following observations: A mean of 11 cleavage energids enter the posterior pole plasm of the egg after the sixth cleavage division and apparently become pole cells when they take up polar granules in their cytoplasm. The cells proliferate asynchronously prior to and during anatrepsis to yield a mean of 36 germ cells in male embryos and 31 in females. Visible sexual differentiation of germ cells begins during germ band elongation and is completed shortly after the appearance of appendages. Female germ cells are larger than those of the males and may contain two nucleoli. The germ cells separate into two groups just before katatrepsis and mesodermal cells collect about these to form the primary epithelial sheaths of the gonads and the primordia of the gonoducts shortly after revolution is completed. Each gonad contains a mean of 13 germ cells in male embryos and 7 in females - a number that persists until mitosis resumes after hatching. During ketatrepsis, a mean of 11 germ cells in male embryos and 2.6 in females fail to be enclosed within the gonads, become dispersed in the yolk and perhaps transform into vitellophages. Germ cell development in H. verbasci embryos resembles similar events taking place in psocid embryos, providing additional evidence for a close phylogenetic relationship between Thysanoptera and Psocoptera.

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

“…In Polyneoptera, the embryo is formed by a pair of blastoderm regions with higher cellular density (e.g., Dermaptera: Shimizu, ; Embioptera: Jintsu, ; Phasmatodea: Bedford, ; Orthoptera: Miyawaki et al, ; Nakamura et al, ; Zoraptera: Mashimo et al, ; Grylloblattodea: Uchifune & Machida, ). In Palaeoptera and Acercaria (e.g., Ephemeroptera: Tojo & Machida, ; Odonata: Ando, ; Psocodea: Goss, ; Thysanoptera: Haga, ; Heming, ), cells near the posterior pole concentrate in one area and proliferate to form the embryo. This type is also found in the apterygote ectognathan orders Archaeognatha (Machida, Nagashima, & Ando, ) and Zygentoma (Masumoto & Machida, ), clearly suggesting that this is a plesiomorphic condition belonging to the groundplan of the Ectognatha and Pterygota.…”

The Phylogenetic Origin of oskar Coincided with the Origin of Maternally Provisioned Germ Plasm and Pole Cells at the Base of the Holometabola

“…Since germ cells arise at the posterior pole just after gastrulation in some hemimetabolous species [16], [67], [68], it is possible that factors that predispose posterior nuclei to take germline fate are also localized at the posterior pole in these species. The molecular nature of any such factor, and whether its role is direct or indirect, remains to be determined.…”

Evidence against a germ plasm in the milkweed bugOncopeltus fasciatus, a hemimetabolous insect

“…Cytological studies of three paraneopteran species, a book louse (Psocoptera (Goss, 1952)), a thrip (Thysanoptera (Heming, 1979)) and an aphid (Hemiptera (Chang et al, 2009)) suggested the presence of germ plasm in oocytes or early embryos, as did expression studies of vasa , piwi and nanos expression during asexual development of the pea aphid Acyrthosiphon pisum (Chang et al, 2006; Chang et al, 2007; Chang et al, 2009; Lu et al, 2011). However, A. pisum embryogenesis is highly modified relative to that of other hemimetabolous insects and even relative to other members of the same order (Miura et al, 2003).…”