Sperm structure and ultrastructure of the fire ant Solenopsis invicta (Buren) (Hymenoptera, Formicidae)

Sperm Bundles in the Seminal Vesicle of the Crematogaster victima (Smith) Adult Males (Hymenoptera: Formicidae)

This study establishes the presence of spermatodesm in the seminal vesicles of sexually mature males of Crematogaster victima (Smith). In this species, the spermatozoa are maintained together by an extracellular matrix in which the acrosomal regions are embedded. This characteristic has not yet been observed in any other Aculeata. However, the sperm morphology in this species is similar to that described for other ants. The spermatozoa measure on average 100 μm in length, and the number of sperm per bundle is up to 256. They are composed of a head formed by the acrosome and nucleus; this is followed by the flagellum, which is formed by the centriolar adjunct, an axoneme with a 9 + 9 + 2 microtubule pattern, two mitochondrial derivatives, and two accessory bodies. The acrosome is formed by the acrosomal vesicle and perforatorium. The nucleus is filled with compact chromatin with many areas of thick and non-compacted filaments. Both mitochondrial derivatives have the same shape and diameters. The presence of sperm bundles in sexually mature males differentiates C. victima from other ants; however, the similarities in the sperm ultrastructure support the monophyly of this insect group.

Sperm bundles in the seminal vesicles of sexually mature Lasius ant males

In many insects, sperm cells are produced in bundles with their heads being held together by a glycoprotein matrix secreted by a cyst cell. Mature sperm cells in the seminal vesicles are usually free, but in sawflies and several other insects, such structures (spermatodesmata) remain intact and sperm cells may be ejaculated as bundles. Here we report the occurrence of spermatodesmata in mature males of the ant Lasius pallitarsis. Microscopic investigations of the abdominal contents of males immediately prior to their nuptial flights showed that the anterior ends of numerous sperm cells were embedded in an oval-shaped 20 by 30 micrometer extracellular fibrous cap. Individual sperm ranged in length from 55 to 75 micrometers with an average overall length of 65 micrometers. The bulb-shaped heads of the sperm were relatively small, only about 1.5 micrometers in length and about 1.1 micrometers in diameter. The diameter of the sperm tails was approximately 1 micrometer. Observations of live preparations of the spermatodesmata showed increasingly active undulating wave-like movement of the sperm tails as the slide preparations aged. This appears to be the first case of sperm bundles being present in the seminal vesicles of mature ant males--males that are immediately poised to complete their nuptial mating flight.

Morphology of the male reproductive system and sperm ultrastructure of the egg parasitoid Gryon pennsylvanicum (Ashmead) (Hymenoptera, Platygastridae)

Gryon pennsylvanicum is a platygastrid hymenopteran that has lately received increasing attention in Europe due to its possible use in biological control of the conifer seed bug pest Leptoglossus occidentalis. Here the male reproductive system and the spermatogenesis of this species, along with those of Gryon muscaeformis, are examined ultrastructurally for the first time. The male genital system is formed by a pair of testes, each containing only one follicle, a pair of accessory glands and deferent ducts connected to a single ejaculatory duct. All the stages of spermatogenesis are described in detail. Characteristic features of the Gryon spp. sperm, which are 100 μm long, are the presence of a polygonal nucleus, only one mitochondrial derivative, the occurrence of the centriole adjunct and a typical insect 9 + 9 + 2 flagellar axoneme. The single derivative, however, results from a process in which one of the two mitochondria is lost during spermiogenesis. Unlike in other insects, two centrioles occur in spermatids as a consequence of the ameiotic parthenogenesis. These characteristics stand as a valuable tool for phylogenetic inferences. Furthermore this study suggests a useful strategy for laboratory mass rearing.

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

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.

The descriptions of new microanatomical structures of the male reproductive system and sperm of Myschocyttarus cassununga (Hymenoptera: Vespidae)

The male reproductive system of Mischocyttarus cassununga consists of two testes, each one with three follicles, as occurs in most Vespidae. The seminal vesicle is divided in two chambers, separated by a constriction, so that the anterior locus is a little larger. In the testicular follicles, the spermatozoa are organized in cysts, with approximately 128 per cyst, where the nuclei are oriented toward the follicle center. The spermatozoa of M. cassununga is about 97 μm in length, which makes them the shortest sperm described for Vespidae. Sperm ultrastructure of M. cassununga is very similar of the others Vespidae. But, despite these similarities, the bilobated mitochondrial derivative represents an autapomorphy for M. cassununga. The subdivision of the seminal vesicle has never been observed in any other Vespidae. Thus, this study supports the validity of insect sperm morphology as a tool for phylogenetic analysis within Hymenoptera.

Structural and ultrastructural characteristics of male reproductive tract and spermatozoa in two Cryptinae species (Hymenoptera: Ichneumonidae)

This study represents the first characterization of male reproductive tracts and ultrastructural description of sperm of Cryptinae species. In Lymeon dieloceri and Pachysomoides sp., the male reproductive tract is formed by a pair of testis, two deferent ducts, two accessory glands and one ejaculatory duct. The spermatozoa are similar to those described for other Hymenoptera, with: (1) the acrosome formed by the acrosomal vesicle covering the perforatorium, which has its base inserted in a cavity located in the nucleus point; (2) a thin nucleus with electron-dense chromatin; (3) an electron-dense centriolar adjunct located between the nucleus and one of the two mitochondrial derivatives; (4) an axoneme with a 9 + 9 + 2 microtubule arrangement; (5) two long mitochondrial derivatives with peripheral cristae and; (6) two accessory bodies located between the two mitochondrial derivatives and the axoneme. These ichneumonids present structural characteristics similar to other parasitic wasps, such as presence of a single follicle per testis, layer of extracellular material enveloping the acrosome and accessory microtubules ending before others in final portion of the flagellum. However, male reproductive system and the spermatozoa presented morphological characteristics that allowed their differentiation, such as oval shapes accessory glands and the symmetric mitochondrial derivatives in L. dieloceri compared to the spherical accessory glands and asymmetrical derivatives observed in Pachysomoides sp. Taken together, data presented here demonstrates that diversity of morphological characteristic from the male reproductive tract and spermatozoa in Hymenoptera might provide a character system that can be used, in association with other systems, to resolve various uncertainties about the evolutionary relationships of this insect group.

Morphology of the male reproductive system and spermiogenesis in Hypanthidium foveolatum (Alfken, 1930) (Hymenoptera: Apidae: Megachilinae)

The morphological aspects of male reproductive tract, spermiogenesis and spermatozoa are typical for each species and reflect its evolution, establishing a unique source of characters, which has been used to help solve phylogenetic problems. In Hypanthidium foveolatum the reproductive tract is composed of the testes comprising 28 testicular tubules, deferent ducts, seminal vesicles, accessory glands and an ejaculatory duct. The differentiation of spermatids occurs within cysts of up to 128 germ line cells each one. During the early spermatid phase, the nucleus resembles that of somatic cells. There follows a gradual chromatin condensation with an increase in nuclear electron density. In the spermatozoon, the nucleus contains heterogeneous chromatin with a loose appearance. The acrosome, shaped with the active participation of the Golgi complex, shows an electron-dense perforatorium involved by four electron-lucent acrosomal vesicle projections. The sperm tail presents an axoneme with a 9+9+2 microtubule pattern and two mitochondrial derivatives, which appear with different sizes. A dense crystalloid is formed initially in the mitochondrial matrix of the large derivative. The mitochondrial derivatives' differentiation occurs concomitantly with an axoneme outgrowth. The centriolar adjunct is observed near the axoneme, anterior to the smaller mithocondrial derivative and exhibits an approximately triangular shape in cross-sections. Microtubules were observed around the head region and flagellar components during spermiogenesis.

Sperm ultrastructure of the European hornet Vespa crabro (Linnaeus, 1758) (Hymenoptera: Vespidae)

This study represents the first sperm description of a Vespinae species (Vespa crabro). The acrosome consists of an acrosomal vesicle and a perforatorium. The nucleus has compact chromatin and shows lenticular structures on the nuclear envelope. These structures, which have never been observed in a hymenopteran sperm, could be clusters of nuclear pores. The centriolar adjunct has an asymmetric pattern and shows a structured periphery. The centriole consists of 9 accessory microtubules and 9 doublet microtubules devoid of arms and spokes. The axoneme has a 9+9+2 microtubule pattern and the accessory microtubules have 16 protofilaments. The mitochondrial derivatives differ in length and diameter. The larger one is adjacent to the nuclear base, while the smaller one begins below the centriolar adjunct. They possess three distinct areas and a large paracrystalline region, which occurs only in the large one. The large mitochondrial derivative ends first, followed by the small one. The axoneme gradually disorganizes: first the central microtubules disappear, then the doublets, which show opened B-tubules, and finally the accessory microtubules. The sperm morphology of V. crabro is very similar to that of the polistine wasp, Agelaia vicina. This can indicate that, in Vespidae, sperm morphology is maintained without important variations among subfamilies and/or that this similarity indicates close phylogenetic relationship between these two subfamilies. Although Vespidae phylogenetically related to Formicidae, these data suggest that the former more closely related to Apoidea than to Formicidae.

Morphology of testicular and post-testicular spermatozoa in Microstigmus arlei Richards, 1972 and M. nigrophthalmus Melo, 1992 (Hymenoptera: Apoidea: Pemphredoninae) with phylogenetic consideration

The sperm of Microstigmus arlei and Microstigmus nigrophthalmus are twisted in a spiral and consist of two regions: the head, formed by an acrosome and a nucleus, and the flagellum, formed by two asymmetric mitochondrial derivatives, a long centriolar adjunct, an axoneme (9+9+2) and two accessory bodies. The head shows a characteristic morphology. The acrosome is very long and is basically made up of a paracrystalline structure. In the central head region, the acrosome is inserted into the nucleus, which is observed coiling laterally around the paracrystalline structure. In the subsequent part of the spermatozoon the nucleus appears round in transverse sections, and over some length it is still penetrated by the acrosome until shortly distal to the flagellar insertion. At this point the nucleus forms an inverted cone-shaped projection. These morphological characteristics of acrosome and nucleus of the Microstigmus wasp have not been previously described in Apoidea and are useful for phylogenetic evaluation of this superfamily.

Centriole/basal body morphogenesis and migration during ciliogenesis in animal cells

Cilia, either motile or immotile, exist on most cells in the human body. There are several different mechanisms of ciliogenesis, which enable the production of many kinds of cilia and flagella: motile and immotile, transient and long-lived. These can be linked to the cell cycle or associated with differentiation. A primary cilium is extended from a basal body analogous to the mitotic centrioles, whereas the several hundred centrioles needed to form the cilia of a multi-ciliated cell can be generated by centriolar or acentriolar pathways. Little is known about the molecular control of these pathways and most of our knowledge comes from ultrastructural studies. The increasing number of genetic diseases linked to dysfunctional cilia and basal bodies has renewed interest in this area, and recent proteomic and cell biological studies in model organisms have helped to shed light on the molecular components of these enigmatic organelles.

The evolution of male traits in social insects

Pair formation in social insects mostly happens early in adult life and away from the social colony context, which precludes promiscuity in the usual sense. Termite males have continuous sperm production, but males of social Hymenoptera have fixed complements of sperm, except for a few species that mate before female dispersal and show male-fighting and lifelong sperm production. We develop an evolutionary framework for testing sexual selection and sperm competition theory across the advanced eusocial insects (ants, wasps, bees, termites) and highlight two areas related to premating sexual selection (sexual dimorphism and male mate number) that have remained understudied and in which considerable progress can be achieved with relatively simple approaches. We also infer that mating plugs may be relatively common, and we review further possibilities for postmating sexual selection, which gradually become less likely in termite evolution, but for which eusocial Hymenoptera provide unusual opportunities because they have clonal ejaculates and store viable sperm for up to several decades.

Structure and ultrastructure of spermatozoa in Meliponini (stingless bees) (Hymenoptera: Apidae)

In spite of their importance in the reproduction of phanerograms, few bees have received an adequate description of their sperm ultrastructure. In this study, we concluded that it was possible to define a characteristic pattern for Meliponini spermatozoa. However, we have also found species-specific differences that could be used, for example, in a taxonomic or phylogenetic evaluation. Meliponini spermatozoa are made up of a head and a flagellar region. The head includes an acrosome containing the perforatorium, covered by the acrosomal vesicle and a nucleus. In transverse sections, the acrosome is circular at the tip but becomes triangular as it nears the nucleus. The perforatorium base penetrates into a small cavity in the nuclear tip. The flagellum consists of an axoneme, a pair of mitochondrial derivatives, a centriolar adjunct and a pair of accessory bodies. The axoneme has a typical 9+9+2 microtubule pattern. In the final portion, the axoneme becomes gradually disorganized with the accessory microtubules terminating last. The mitochondrial derivatives are asymmetric in length and diameter. In cross-section, they are ellipsoidal and the larger one has a paracrystalline region. The centriolar adjunct begins at the nuclear base and extends parallel to the axoneme up to the anterior end of the smaller mitochondrial derivative.