Ovariole structure supports sistergroup relationship of Neuroptera and Coleoptera

Abstract

Insect ovaries consist of functional units, the ovarioles. Each ovariole is a polarized tube with a germarial region at its anterior end. Undifferentiated germarial germ cells may differentiate either into oocytes alone (so-called panoistic ovarioles) or in oocytes and nurse cells (so-called meroistic ovarioles). Whenever nurse cells accompany an oocyte through all growth periods in a separated physiological unit – the follicle – the subtype is called polytrophic meroistic. In telotrophic meroistic ovarioles all nurse cells remain in an anterior trophic chamber and contribute their products finally into all growing oocytes via nutritive cords. Differences in the mode of germ cell cluster formation and the specifi c interaction of germ cells with the somatic tissues were causing these different types. All three types are constant at the family to order level or even at a supra-order level. Therefore the characters which lead to these types are excellent candidates to unravel order and supraorder ranked taxa. Data from the analysis of germ cell cluster formation are presented which corroborate the sistergroup relationship of Neuropterida and Coleoptera.