|Budget Amount *help
¥2,200,000 (Direct Cost : ¥2,200,000)
Fiscal Year 1997 : ¥800,000 (Direct Cost : ¥800,000)
Fiscal Year 1996 : ¥1,400,000 (Direct Cost : ¥1,400,000)
In this project, major groups of primitive hexapods of which embryological knowledge is requisite to the phylogenetical accounts but fragmental and insufficient, i. e., the Diplura, Ephemeroptera and Archaeognatha, are comparative embryologically examined, aiming at the deeper comprehension of hexapod ground plan and phylogeny in higher levels.
Achievements produced in this project are as follows.
1-1. The entognathy formation of Rhabdura closely resembles that of Dicellurata but significantly differs from that of Collembola. This strongly supports the monophyly of Diplura but requires a careful reexamination of monophyletic status of Entognatha.
1-2.A second embryonic membrane or the amnion, which has been regarded as an autapomorphy of Ectognatha, is found to be produced in association with the formation of primary dorsal organ, also in Diplura. This may suggest the monophyly of the Diplura and Ectognatha, but reinforces doubts on the monophyletic status of Entognatha.
2-1. The embryonic developmental process, of which our knowledge still remains fragmented, is described in detail, focusing on the metamerism. The caudal filament has been unconditionally recognized to be an elongation of eleventh abdominal tergum, but it is revealed that this structure represents the telson independent of the eleventh segment. This is the first reference to and identification of the telson in the entomology.
2-2. The developmental process from the maturation to cleavage is described in detail, by aid of the semi-thin resin serial sections and time-lapse video system. An extensive and circuitous migration of male pronucleus is found to be involved in the fertilization. The primitiveness of Ephemeroptera may lend additional importance to this finding in the field of biology of the insect fertilization.
3. Functional specialization between the embryo proper and embryonic membranes in the Hexapoda and Atelocerata
3-1. Reviewed are the evolutionary changes of the embryo proper and embryonic membranes and the evolutionary transition of functional specialization between them in Atelocerata. It is shown that a deeper insight to the amnioserosal fold in Ectognatha can be given in context of the transition of functional specialization between the embryo proper and embryonic membranes. Less