Giant spiral shaped spermatozoa of Diasemopsis comoroensis (Diptera, Diopsidae) with a unique ultrastructural component

The ultrastructure of the spermatheca of Mordellistena brevicauda (Coleoptera, Tenebrionoidea) and the associated bacterial cells

The ultrastructural study on the female reproductive system of the beetle M. brevicauda (Mordellidae) confirmed the positive correlation between the length of the sperm and the size of the female seminal receptacle (Spermatheca). The spermatheca of the species is characterized by an apical bulb-like structure where the spermathecal duct forms numerous folds filled with sperm. At this level many bacterial cells are present intermingled with the duct folds. Some are organized in large structures, such as bacteriomes, while other are single bacteriocytes. The latter are often found near the basal lamina of duct epithelium. In addition, some bacteria are visible in the cytoplasm of the duct epithelial cells. Interestingly, bacterial cells have never been observed in the duct lumen. The possible function of the bacterial cells is discussed.

Coevolution between female seminal receptacle and sperm morphology in the semiaquatic measurer bug Hydrometra stagnorum L. (Heteroptera, Hydrometridae)

The coevolution between sperm length and size of the female sperm-storage organs is described for the first time within Heteroptera. The long sperm of the measurer bug Hydrometra stagnorum is characterized by the unusually long acrosome with its anterior region helically arranged, and by a very short nucleus. The sperm flagellum has a 9 + 9+2 conventional axoneme and crystallized mitochondrial derivatives. The female spermatheca consists of an extraordinarily long spermathecal duct ending with an apical spermathecal bulb into which flows also the secretions of a relatively short spermathecal gland. Both spermathecal duct and gland have a thin epithelium lined by a cuticle, beneath which a complex of secretory and duct forming cells are present. The secretions of these two structures flow into the apical spermathecal bulb. A thick layer of muscle fibers surrounds the epithelium. These results confirm the opinion that the dimensions of the female reproductive sperm-storage organs are able to drive the sperm morphology.

Morphology and ultrastructure of the spermatozoa of Lonchoptera lutea Panzer, 1809 (Diptera: Lonchopteridae)

Lonchoptera lutea males produce giant spermatozoa that are more than 2000 μm long and 1.4 μm wide. Unlike the typical brachyceran spermatozoon, they have a highly asymmetrical cross-section with only a single, albeit very large, mitochondrial derivative and a pair of massive accessory bodies, one of which extends throughout the entire length of the sperm tail. The accessory bodies consist of an electron-dense matrix in which numerous peculiar electron-lucid substructures are embedded. In the mated female, the giant spermatozoa are found inside two tubular spermathecae which are also extremely long, measuring 4000 μm or more.

Reproductive context of extremely short sperm in the parasitic wasp Cotesia congregata (Hymenoptera: Braconidae)

Among adaptive traits under sexual selection, the length of spermatozoa shows high interspecific variation. In insects, extremes exist for both short and long sperm. The spermatozoa of the endoparasitic wasp Cotesia congregata (Say) are the shortest flagellated sperm described in animals, 6.6 µm in length. By comparison, the sperm of Drosophila bifurca are almost 6000 times longer. Thus, C. congregata has the potential to shed light on the selection pressures that drive variation in sperm length in relation to their production and use. The reproductive organs, sperm counts, controlled oviposition and sex ratios were investigated. The testes showed stratified differentiation stages of spermatogenesis, and sperm counts revealed continuous spermatogenesis in the late pupal stage. The small female spermatheca stored ~1000 sperm, resulting in an extremely high sperm concentration. The number of progeny per brood decreased over time until depletion of eggs. Females produced up to 370 daughters, corresponding to the effective use of 34% of the average sperm stock. Haploid males made up a greater proportion of broods in later parasitisms. Sperm miniaturization may be an adaptation to transfer increased quantities for the entire reproductive life of females in the absence of sperm competition but in the reduced space offered by the spermatheca.

Giant spermatozoa of Diasemopsis (Diopsidae, Diptera) - Structural, ultrastructural and functional aspects

The spermatozoa of Diasemopsis comoroensis and Diasemopsis meigenii differ from the conventional brachyceran type in several respects. Not only are they very long but they are also extraordinarily wide, especially at the very end of the tail. The latter is effected by two cellular components: oversized mitochondrial derivatives and a prominent central band, which is a peculiar structure not known from any other spermatozoa. Based on its position with respect to the other organelles and its origin during early spermiogenesis, the central band is interpreted as a derivative of the centriolar adjunct material. Like the axoneme, the mitochondrial derivatives and the central band extend through the entire length of the spermatozoon tail. The spermatozoon tail is helical and can be coiled up into a tight cone-shaped spiral with a peculiar corkscrew shaped end portion. The potential adaptive significance of these features and their coevolution with the morphology of the female's multi-chambered ventral receptacle are discussed, as are sperm competition and cryptic female choice.

Overview on spermatogenesis and sperm structure of Hexapoda

The main characteristics of the sperm structure of Hexapoda are reported in the review. Data are dealing with the process of spermatogenesis, including the aberrant models giving rise to a reduced number of sperm cells. The sperm heteromorphism and the giant sperm exceeding the usual sperm size for length and width are considered. The characteristics of several components of a typical insect sperm are described: the plasma membrane and its glycocalyx, the nucleus, the centriole region and the centriole adjunct, the accessory bodies, the mitochondrial derivatives and the flagellar axoneme. Finally, a detailed description of the main sperm features of each hexapodan group is given with emphasis on the flagellar components considered to have great importance in phylogenetic considerations. This study may be also useful to those requiring an introduction to hexapod reproduction.