SUBSTRUCTURE OF THE AXONEME OF PTERYGOTE INSECT SPERMATOZOA - PHYLOGENETIC CONSIDERATIONS

Spermatozoa from a great number of insect species were fixed in a tann ic acid-containing fixative and the ultrastructure of the flagellar ax oneme was examined in a search for apomorphies. Most of the examined s pecies, representing a majority of insect orders, have accessory tubul es outside the axoneme (hence a 9 + 9 + 2 pattern), and these consist of 16 protofilaments. Some important apomorphies concern the number of protofilaments in the accessory tubules: 13 (plus 7 inner elements) i n Ephemeroptera, 13 in the (elliptic) tubules of Psocoptera + Anoplura + Mallophaga (thus a synapomorphy), 13 in Tipulidae + Brachycera, 15 in the dipteran families Dixidae + Chironomidae (with a 9 + 9 + 2 axon eme) and Culicidae + Bibionidae (with a 9 + 9 + ''1'' axoneme), 17 in Phasmatodea, and 17-20 in Trichoptera. Other apomorphies concern the a ppearance of the so-called intertubular material outside the microtubu lar doublets, the appearance of the interior of the various microtubul es, and the loss, in some taxa, of outer or inner dynein arms of both dynein arms. In some cases, the flagellum is completely abnormal; the sperm tail of Thysanoptera, for example, consists of 27 elements of 3 different kinds. The different taxa within orders Diptera and Trichopt era have sperm tail axonemes of different appearances, where those fro m other orders have a rather uniform appearance. The conclusions that can be drawn from this spermatological study, generally agree with dat a from classical studies, except with some variations, in some cases.