REDUCTIONS AND NEW INVENTIONS DOMINATE OOGENESIS OF STREPSIPTERA (INSECTA)

The endoparasitic life of strepsipterans (Insecta), especially neoteni c females, reduces to a great extent external and internal organs. Lig ht and electron microscopic investigation of ovaries of Elenchus tenui cornis (Kirby) confirms the following: (1) somatic tissues of ovaries are totally reduced, with the exception of some cells surrounding germ cell clusters; (2) a previtellogenic growth phase of oocytes is reduc ed; (3) nurse cells remain diploid and their membranes degenerate at t he onset of vitellogenesis; (4) vitellogenesis is reduced, vitellin an d fat vacuoles contribute only 50% to the final egg volume; and (5) ch orionogenesis is reduced to a vitellin membrane. However, some feature s of normal development remain, allowing classification of the ovary t ype as polytrophic meroistic: (1) germ cells undergo synchronized, inc omplete divisions, following the 2(n) rule, where all former intercell ular bridges become localized in one cystocyte, while the other has no ne; and (2) only one cell is determined as the oocyte, all other cysto cytes serve as nurse cells and the surrounding somatic cells transform into follicular cells. Novel events in oogenesis of strepsipterans in clude fission of clusters during the phase of cluster mitoses, and pro tection of oocyte nuclei, while nurse cell nuclei degenerate in the sa me cytoplasm. (C) 1998 Elsevier Science Ltd, All rights reserved.