Comparative Embryology of Arctoperlaria (Insecta: Plecoptera) January 2019 Shodo MTOW Comparative Embryology of Arctoperlaria (Insecta: Plecoptera) A Dissertation Submitted to the Graduate School of Life and Environmental Sciences, the University of Tsukuba in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Science (Doctoral Program in Biological Sciences) Shodo MTOW CONTENTS ABSTRACT .................................................................................................................... 1 INTRODUCTION .......................................................................................................... 3 MATERIALS AND METHODS ................................................................................. 10 1. Materials ................................................................................................................. 10 2. Fixation ................................................................................................................... 10 3. External morphology ............................................................................................... 11 4. Histology ................................................................................................................ 12 5. Transmission electron microscopy ......................................................................... 13 RESULTS ...................................................................................................................... 14 1. Eggs and embryonic development of Euholognatha .............................................. 15 1.1 Scopura montana (Scopuridae) ........................................................................ 15 1.1.1 Egg ............................................................................................................. 15 1.1.2 Embryonic Development ........................................................................... 16 1.2 Obipteryx sp. (Taeniopterygidae) ..................................................................... 24 1.2.1 Egg ............................................................................................................. 24 1.2.2 Embryonic Development ........................................................................... 25 1.3 Paraleuctra cercia (Leuctridae) ....................................................................... 25 1.3.1 Egg ............................................................................................................. 26 1.3.2 Embryonic Development ........................................................................... 26 1.4 Apteroperla tikumana (Capniidae) ................................................................... 26 1.4.1 Egg ............................................................................................................. 26 1.4.2 Embryonic Development ........................................................................... 27 1.5 Protonemura towadensis (Nemouridae) ........................................................... 27 i 1.5.1 Egg ............................................................................................................. 28 1.5.2 Embryonic Development ........................................................................... 28 2. Eggs and embryonic development of Systellognatha ............................................. 28 2.1 Calineuria stigmatica (Perlidae) ...................................................................... 29 2.1.1 Egg ............................................................................................................. 29 2.1.2 Embryonic Development ........................................................................... 29 2.2 Sweltsa sp. (Chloroperlidae) ............................................................................. 30 2.2.1 Egg ............................................................................................................. 30 2.2.2 Embryonic Development ........................................................................... 30 2.3 Ostrovus sp. (Perlodidae).................................................................................. 31 2.3.1 Egg ............................................................................................................. 31 2.3.2 Embryonic Development ........................................................................... 31 2.4 Yoraperla uenoi (Peltoperlidae) ........................................................................ 32 2.4.1 Egg ............................................................................................................. 32 2.4.2 Embryonic Development ........................................................................... 33 DISCUSSION ................................................................................................................ 35 1. Egg .......................................................................................................................... 35 2. Embryonic development ......................................................................................... 39 2.1 Formation of the embryo .................................................................................. 39 2.2 Germ band type ................................................................................................ 41 2.3 Thickened serosa and serosal cuticle beneath the embryo ............................... 42 2.4 Blastokinesis ..................................................................................................... 45 2.4.1 Anatrepsis and formation of the embryo ................................................... 45 2.4.2 Intertrepsis ................................................................................................. 47 ii 2.4.3 Katatrepsis ................................................................................................. 48 2.5 Egg tooth .......................................................................................................... 50 3. Concluding remarks ................................................................................................ 51 ACKNOWLEDGMENTS ............................................................................................ 54 LETERATURE CITED ............................................................................................... 55 TABLES ......................................................................................................................... 72 FIGURES ...................................................................................................................... 74 iii ABSTRACT Plecoptera is one of the most controversial groups in reconstruction of interordinal relationships of insects. Aiming at 1) the detailed description of the embryonic development of Plecoptera, and 2) the reconstruction of the groundplan and phylogeny of Plecoptera and Polyneoptera, the comprehensive comparative embryological study of Plecoptera was conducted, using nine arctoperlarian stoneflies from nine families, i.e., Scopuridae, Taeniopterygidae, Leuctridae, Capniidae, and Nemouridae of Euholognatha, and Perlidae, Chloroperlidae, Perlodidae, and Peltoperlidae of Systellognatha. The egg structure and embryonic development of nine arctoperlarian plecopterans were examined and described with spherical reference to Scopura montana (Scopuridae). Euholognatha has eggs characterized by a thin, transparent chorion, while the eggs of Systellognatha are characterized by a collar and anchor plate at the posterior pole. These features represent an apomorphic groundplan for each group. The embryos are formed by the concentration of blastoderm cells toward the posterior pole of the egg. Soon after the formation of the embryo, amnioserosal folds are formed and fused with each other, resulting in a ball-shaped “embryo-amnion composite” that is a potential autapomorphy of Plecoptera. As an embryological autapomorphy of Polyneoptera, embryo elongation occurs on the egg surface, supporting the affiliation of Plecoptera to Polyneoptera. After its elongation on the egg surface, the embryo sinks into the yolk with its cephalic and caudal ends remaining on the egg surface. This unique embryonic posture may be regarded as an apomorphic groundplan of Plecoptera. 1 The serosa converges beneath the embryo to form a thickened serosa, comprising cells in a radial arrangement, in association with the formation of the amnioserosal fold. The thickened serosa then deposits the thickened serosal cuticle, consisting of four layers differing in fine structure and electron density. These serosal derivatives may also be regarded as an embryological autapomorphy of Plecoptera. Arctoperlarian plecopterans perform three types of katatrepsis: 1) the first type, in which the embryo’s anteroposterior and dorsoventral axes change in reverse during katatrepsis, is found in Capniidae, Nemouridae, Perlidae, Chloroperlidae, and Perlodidae, and this sharing is symplesiomorphic; 2) the second one, in which the embryo’s axes are not changed during katatrepsis, is found in Scopuridae, Taeniopterygidae, and Leuctridae, and this may be regarded as synapomorphic to them; 3) the third one, in which the embryo rotates around its anteroposterior axis by 90° during katatrepsis as known for Pteronarcyidae, is found in Peltoperlidae, and this type may be synapomorphic to these two families. 2 INTRODUCTION Hexapoda are the most diverse group among the organisms which have ever appeared in the 3-billion-year