Ultrastructural analysis of spermatozoa of Korscheltell us lupulinus L. (Lepidoptera : Hepialidae) and Micropterix calthella L. (Lepidoptera : Micropterigidae)

Morphology of the male reproductive system and spermatozoa of Smicridea (Rhyacophylax) iguazu Flint, 1983 (Trichoptera, Hydropsychidae)

The Trichoptera, holometabolous aquatic insects found worldwide except in Antarctica, exhibit a unique feature in their sperm, which are solely nucleated (eupyrene). Current knowledge on Trichoptera sperm is limited to Old World species. To enhance our understanding of their reproductive biology and contribute to systematic discussions, we describe the male reproductive system and spermatozoa of Smicridea (Rhyacophylax) iguazu Flint, 1983 (Hydropsychidae). This species lacks seminal vesicles, possesses piriform to oval-shaped testes with spermatozoa grouped in apical bundles and dense filamentous material filling other areas. The vasa deferentia are long and a pair of elongated accessory glands displays distinct proximal and distal regions. The relatively short (∼40 μm) spermatozoa are nucleated, aflagellated, and immobile. Further research could explore variations and assess the taxonomic utility of these features for genus identification within Hydropsychidae.

Field and Laboratory Studies on the Ecology, Reproduction, and Adult Diapause of the Asian Comma Butterfly, Polygonia c-aureum L. (Lepidoptera: Nymphalidae)

Adult diapause and reproduction of a nymphalid butterfly, Polygonia c-aureum L., were investigated in field and laboratory examinations. Laboratory studies showed that old virgin male butterflies of non-diapausing generations had heavy accessory glands and simplex, which were suppressed in diapausing generations. The number of eupyrene sperm bundles in the duplex increased with adult age, whereas testis size decreased with age. Field examinations indicated that reproductive development of both sexes of diapausing generations in autumn was suppressed, and developed in spring. We attempted to estimate the physiological age of wild-caught males, as adult male age can be estimated from the testis size. We also attempted to determine whether or not wild male butterflies had mated from the development of the accessory glands and simplex, as well as the number of eupyrene sperm bundles in the duplex, by comparing unmated males with mated males. Field examinations suggest that almost all females in a population of non-diapausing generations mated and showed a tendency toward polyandry, while in the diapausing generation, in spring, monoandry rather than polyandry predominated. This suggests a different mating strategy between non-diapausing and diapausing generations.

Effects of pre-overwintering conditions on eupyrene and apyrene spermatogenesis after overwintering in Polygonia c-aureum (Lepidoptera: Nymphalidae)

Sperm polymorphism is widely known in invertebrates. In insects, Lepidoptera has two types of sperm: nucleated eupyrene (fertile) sperm and anucleated apyrene (unfertile) sperm. These sperm types are produced during post-embryogenesis, and eupyrene spermatogenesis precedes apyrene spermatogenesis. During overwintering, spermatogenesis stops and a portion of undifferentiated-stage spermatocytes degenerate. After overwintering, spermatogenesis restarts with unaffected spermatogonia. However, how new spermatozoa arise in the adult testes after overwintering is not known in Lepidoptera. In this study, we investigated the spermatogenesis events in the nymphalid butterfly Polygonia c-aureum after overwintering under various environmental conditions. Our results indicate that both eupyrene and apyrene spermatogenesis restart at any stopping stage and sperm of these types are regenerated in no particular order after adult insect overwintering. This suggests that the spermatogenesis occurring after overwintering proceeds without embryogenetic restrictions related to the developmental sequence.

Structure and Evolution of Insect Sperm: New Interpretations in the Age of Phylogenomics

This comprehensive review of the structure of sperm in all orders of insects evaluates phylogenetic implications, with the background of a phylogeny based on transcriptomes. Sperm characters strongly support several major branches of the phylogeny of insects-for instance, Cercophora, Dicondylia, and Psocodea-and also different infraordinal groups. Some closely related taxa, such as Trichoptera and Lepidoptera (Amphiesmenoptera), differ greatly in sperm structure. Sperm characters are very conservative in some groups (Heteroptera, Odonata) but highly variable in others, including Zoraptera, a small and morphologically uniform group with a tremendously accelerated rate of sperm evolution. Unusual patterns such as sperm dimorphism, the formation of bundles, or aflagellate and immotile sperm have evolved independently in several groups.

Characterisation of the Manduca sexta sperm proteome: Genetic novelty underlying sperm composition in Lepidoptera

The application of mass spectrometry based proteomics to sperm biology has greatly accelerated progress in understanding the molecular composition and function of spermatozoa. To date, these approaches have been largely restricted to model organisms, all of which produce a single sperm morph capable of oocyte fertilisation. Here we apply high-throughput mass spectrometry proteomic analysis to characterise sperm composition in Manduca sexta, the tobacco hornworm moth, which produce heteromorphic sperm, including one fertilisation competent (eupyrene) and one incompetent (apyrene) sperm type. This resulted in the high confidence identification of 896 proteins from a co-mixed sample of both sperm types, of which 167 are encoded by genes with strict one-to-one orthology in Drosophila melanogaster. Importantly, over half (55.1%) of these orthologous proteins have previously been identified in the D. melanogaster sperm proteome and exhibit significant conservation in quantitative protein abundance in sperm between the two species. Despite the complex nature of gene expression across spermatogenic stages, a significant correlation was also observed between sperm protein abundance and testis gene expression. Lepidopteran-specific sperm proteins (e.g., proteins with no homology to proteins in non-Lepidopteran taxa) were present in significantly greater abundance on average than those with homology outside the Lepidoptera. Given the disproportionate production of apyrene sperm (96% of all mature sperm in Manduca) relative to eupyrene sperm, these evolutionarily novel and highly abundant proteins are candidates for possessing apyrene-specific functions. Lastly, comparative genomic analyses of testis-expressed, ovary-expressed and sperm genes identified a concentration of novel sperm proteins shared amongst Lepidoptera of potential relevance to the evolutionary origin of heteromorphic spermatogenesis. As the first published Lepidopteran sperm proteome, this whole-cell proteomic characterisation will facilitate future evolutionary genetic and developmental studies of heteromorphic sperm production and parasperm function. Furthermore, the analyses presented here provide useful annotation information regarding sex-biased gene expression, novel Lepidopteran genes and gene function in the male gamete to complement the newly sequenced and annotated Manduca genome.

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.

Unusual Axonemes of Hexapod Spermatozoa

Hexapod spermatozoa exhibit a great variation in their axoneme structure. The 9+2 pattern organization is present in a few basal taxa and in some derived groups. In most hexapods, a crown of nine accessory microtubules surrounds the 9+2 array, giving rise to the so-called 9+9+2 pattern. This general organization, however, displays a number of modifications in several taxa. In this review, the main variations concerning the number and localization of the accessory tubules, microtubular doublets, central microtubules, dynein arms, and axonemal length are summarized. We discuss the phylogenetic significance of all this structural information as well as the current hypotheses relating the sperm size and sperm polymorphism with reproductive success of some hexapod species. Also described are the biochemical data and the motility patterns which are currently known on some peculiar aberrant axonemes, in light of the contribution these models may give to the comprehension of the general functioning of the conventional 9+2 axoneme. Finally, we summarize methodological developments for the study of axoneme ultrastructure and the new opportunities for the molecular analysis of hexapod axonemes.

Ultrastructural observations of eu- and paraspermiogenesis in the cottid fish Hemilepidotus gilberti (Teleostei: Scorpaeniformes: Cottidae)

The developmental process of eu- and paraspermatozoa in the cottid fish, Hemilepidotus gilberti, was observed by electron microscopy. Euspermatozoa of H. gilberti consist of a thin disk-like sperm head (about 3 microm in length), a short middle piece, and a long flagellum, but lack an acrosome. On the other hand, during spermiogenesis, aberrant spermatids, rich in cytoplasm and possessing binuclei, develop into cysts containing spermatids. The developing aberrant spermatids connect with normal spermatids and euspermatozoa by intercellular bridges. The early phase of chromatin condensation in aberrant spermatids is almost identical to that in normal spermatids, but the nuclei in the later phase develop into a mass of highly electron-dense globules. Since the aberrant spermatids complete karyokinesis but not cytokinesis at telophase of the second meiotic division, they are considered to develop into hyperpyrenic cells due to incomplete cytokinesis of the second meiotic division. These spermatids are oval in shape (5-7 microm in diameter) and lack a flagellum. The aberrant spermatids of H. gilberti are shed along with euspermatozoa and amount to about 50% of semen in volume. Judging from their form and developmental process, aberrant spermatids produced in H. gilberti are considered hyperpyrenic paraspermatozoa.

The long and short of sperm polymorphisms in insects

Production of more than one morphological type of sperm in a common testis has been documented for a variety of invertebrates, including gastropods, spiders, centipedes, and insects. This unusual phenomenon is difficult to explain by current theory, particularly since available evidence indicates that one sperm type is often incapable of effecting fertilization. In this review we critically examine evidence on the distribution and development of sperm heteromorphisms among insects in light of competing hypotheses for the evolutionary origin, maintenance, and function of a non-fertilizing class of sperm. To date, no single hypothesis, including alternatives which assume non-fertilizing sperm are non-adaptive, or that they provision, facilitate, or compete with fertilizing sperm, has received strong empirical support by any group of insects. The diversity of sperm heteromorphisms suggests that non-fertilizing sperm may have different functions in different clades or even serve multiple functions within a clade. We suggest that insight could be gained from (1) new models for the evolution of sperm polymorphism, (2) comparative studies that focus on multiple traits simultaneously (e.g. sperm number, proportion, length, and remating rate) and utilize clades in which more than one gain or loss of sperm heteromorphism has been documented (e.g. Pentatomidae, Carabidae, or Diopsidae), and (3) experimental studies that exploit individual variation or directly manipulate the composition of the male ejaculate.