Ultrastructure of spermatozoa in two solitary bee species with an emphasis on synapomorphic traits shared in the family apidae

Abstract

Morphology of spermatozoa in bees has provided promising results for phylogenetic analyses. In this work, the structure and ultrastructure of spermatozoa from Thygater (Thygater) analis and Melitoma segmentaria were characterized and the synapomorphies shared in the family Apidae are discussed. In these species, spermatozoa bundles which are undone in the seminal vesicle possess, on average, 50 cells. Spermatozoa consist of a head and a flagellar region. The head includes an acrosome containing the perforatorium, covered by the acrosomal vesicle and a nucleus. The flagellum is formed by two mitochondrial derivatives, which are asymmetric in diameter and length, with one centriolar adjunct, one axoneme (9 + 9 + 2), and two accessory bodies. In cross section the centriolar adjunct is asymmetric and the accessory bodies are triangular in shape. In the distal region of the flagellum, the derivative terminates before the axoneme and the small derivative terminates first. The axoneme is gradually disorganized and the accessories microtubules are the last to terminate. In these two species, spermatozoa share diverse synapomorphies with those of other bee species previously described in the literature, which allows for the establishment of a morphological pattern for spermatozoa of the family Apidae.