Synaptonemal complexes in female and male meiotic prophase of ephestia kuehniella (Lepidoptera)

Synaptonemal complex (SC) complements of oocyte and spermatocyte pachytene nuclei in the Mediterranean flour moth, Ephestia kuehniella, were investigated using a microspreading technique and electron microscopy. In both sexes, three autosomal SCs could be identified by their morphological landmarks; one SC has a prominent knob and two SCs have nucleolus organizer regions. In a later stage of SC development in oocytes, the two nucleolar SCs displayed electron dense terminal modifications of the lateral elements. In some oocytes, the sex chromosome bivalent was inconspicuous but in the majority it was recognized by heterochromatin tangles associated with the W chromosome, a shorter W chromosome axis and/or incomplete pairing. Male synaptonemal complexes in contrast to female ones contained recombination nodules (RNs). Almost every bivalent was associated with one RN, rarely none or two RNs. Along the SCs, RNs were preferentially located in distal positions. The presence of RNs in male SCs and their absence in female SCs corresponds with the presence of crossing over and chiasmata in male meiosis and their absence in female meiosis. The mean total length of SC complements was greater in males than in females, but in both sexes, variation was considerable. We assume that male SCs become longer with progression of the pachytene stage while in female SCs a period of elongation is followed by a period of shortening.