Sperm ultrastructure of shrimps from the family Penaeidae (Crustacea: Dendrobranchiata) in a phylogenetic context

Morphology of the gastric mill teeth in dotillid crabs (Crustacea: Brachyura: Dotillidae) from Indonesia

The gastric mill is a prominent structure in the digestive system of brachyuran crabs, consisting of a median tooth plate and a pair of lateral tooth plates. Among crab species that are deposit feeders, the morphology and size of the gastric mill teeth are correlated with the preferred substrate types and food spectrum. In this study, we provide a detailed description of the morphology of the median and lateral teeth of the gastric mills in eight species of dotillid crabs from Indonesia, and compare them in relation to habitat preferences and molecular phylogeny. Ilyoplax delsmani, Ilyoplax orientalis, and Ilyoplax strigicarpus have comparatively simple shapes of their median and lateral teeth, with fewer teeth on each lateral tooth plate compared to Dotilla myctiroides, Dotilla wichmanni, Scopimera gordonae, Scopimera intermedia, and Tmethypocoelis aff. ceratophora, which have more complexly shaped median and lateral teeth, with a greater number of teeth on each lateral tooth plate. The number of teeth on lateral tooth correlates with habitat preference, that is, dotillid crabs inhabiting muddy substrata have fewer teeth on the lateral tooth plate, and those inhabiting sandy substrata have a more teeth. Phylogenetic analysis using partial COI and 16S rRNA genes supports that teeth morphology is similar among closely related species. Therefore, the description of median and lateral teeth of the gastric mill is expected to contribute to the systematic study of dotillid crabs.

The ultrastructure of spermatozoa of two species of Aegla (A. parana and A. quilombola) (Crustacea, Decapoda) endemic to Brazil

The previously published ultrastructure of Aegla spermatozoa contributed to the phylogenetics of this unique taxon. The present study describes the spermatozoa of two additional aeglids, Aegla parana and A. quilombola. The spermatozoa consist of two hemispheres of the approximate same size and a bilayered acrosomal vesicle; both characteristics of the genus Aegla. The similarity of spermatozoa ultrastructure observed between A. parana and A. quilombola and the endemic Australian anomuran, Lomis hirta (Lomidae) reflects a sister group relationship, even though both are from different regions of the world and different environments today. Aeglid spermatozoa share the same organization with Lomis including the two equal size hemispheres separated by a membrane also two layers in the acrosomal vesicle with the external layer being surrounded by another membrane. The number of spermatozoa microtubular arms is unclear in Aegla, however, they are present in both the nucleus and cytoplasm. This observation does not agree with the presence of spermatozoa arms only in the nucleus, as an exclusive character for Aegla, as proposed previously. The presence of lipid-droplets and peroxisomes was observed only in the spermatozoa of A. quilombola. The greatly reduced number of spermatozoa observed in all specimens analyzed raises concerns about the conservation of several threatened species. In addition, the absence of any spermatophores seems to be a characteristic of the Aeglidae to date.

Spermiogenic histone transitions and chromatin decondensation in Decapoda

Decapoda are among of the most diverse groups of Crustacea with an important economic value, and have thus been the focus of various reproductive biology studies. Although spermatozoa are morphologically diverse, decapod spermatozoa possess common features, such as being non-motile and having uncondensed nuclear chromatin. Many scholars have studied uncondensed chromatin in decapod spermatozoa; however, the role of biologically regulated decondensation in spermatozoa remains unclear. In this study, histone changes in the spermatozoa of five commercially relevant aquatic crustacean species (Eriocheir sinensis, Scylla paramamosain, Procambarus clarkii, Fenneropenaeus chinensis, and Macrobrachium nipponense) were studied via liquid chromatography-tandem mass spectrometry (LC-MS/MS) and immunofluorescence. The LC-MS/MS results confirmed that all four core histones were present in the sperm nuclei of the five Decapoda species. Positive fluorescent signals from histones H2A, H2B, H3, and H4 were detected in the spermatozoa nuclei of E. sinensis, S. paramamosain and M. nipponense via immunofluorescence. Histone H2A was first identified in the membrane sheets or cytoplasm of mature sperm in P. clarkii and F. chinensis, whereas H3 and H4 were generally distributed in the nucleus of the spermatozoa. Histone H2B gradually disappeared during spermiogenesis and was not found in the sperm of P. clarkii and F. chinensis eventually. Our data suggest that core histones are instructive and necessary for chromatin decondensation in decapods spermatozoa. Thus, our results may help resolve the complex sperm histone code and provide a reference for the study of spermatozoa evolution in Decapoda.

A multigene and morphological analysis expands the diversity of the seabod shrimp Xiphopenaeus Smith, 1869 (Decapoda: Penaeidae), with descriptions of two new species

After being stable for nearly a century, the taxonomic history of the genus Xiphopenaeus has been marked by many changes in the last three decades. The taxonomic status of the Atlantic species has a low resolution, and many species are still undefined and grouped as cryptic species. Here we employed an integrative approach to define the species of Xiphopenaeus and the morphological characters needed to differentiate them. We combined the analyses of two molecular markers (COI and 16 S rDNA), scanning electron microscopy and light microscopy. Based on specimens from 17 localities from the Atlantic and Pacific oceans, we detected five divergent genetic groups, three in the Atlantic (A1, A2, A3) and two in the Pacific (P1, P2). Male secondary sexual characters were able to differentiate four out of the five genetic groups. Group A1 corresponds to X. kroyeri, and A2 and A3 correspond to new species. We redescribed the genus and two new species are described and illustrated: Xiphopenaeus dincao nov. sp. (A2) and Xiphopenaeus baueri nov. sp. (A3). Since the holotype of X. riveti was missing and the specimen analysed from group P2 was a female, the status of the species of Xiphopenaeus from the Pacific remains unresolved.

Ultrastructure of spermiogenesis and the distribution of spermatozoal nuclear histones in the Japanese mantis shrimp, Oratosquilla oratoria (Crustacea: Stomatopoda)

The Japanese mantis shrimp Oratosquilla oratoria (Stomatopoda; Crustacea) is one of the most economically important aquatic species of Pacific shrimp and it is distributed from Japan to the coast of China, the Philippines, the Malay Peninsula, and the Hawaiian Islands. Early studies described certain characteristics of spermatogenesis and the sperm ultrastructure in Stomatopoda, but the composition of sperm basic nuclear proteins (SBNPs) remains completely unknown. We studied the sperm ultrastructure of O. oratoria using transmission electron microscopy and the histone composition using immunofluorescence and immunoelectron microscopy. We found that the spherical nucleus is adjacent to the electron translucent external coat, which occurs in early spermatids. The acrosomal structure begins to form at the junction of the nucleus and the external coat. At the mid-spermatid stage, part of the chromatin appears to be more electron-dense than the external coat side. The aflagellate sperm of O. oratoria, are rounded or slightly ovoid in shape and have a consistent granular nucleus, an acrosome structure of pushpin shape and a spherical vesicular body in which faintly granular material is scattered. The acrosome consists of an acrosomal vesicle, perforatorium, and subacrosomal material. The sperm contains histones H2A, H2B, H3, H4, H3.3, H2AX, and H2AZ as well as some histone modifications, that is, H3K9me3, H3K4me2, H3S10ph, H4Kac, and H2A + H4S1ph. Histones are localized not only in the nucleus of the sperm but also in other structures outside the nucleus. The results may provide new perspectives for systematic studies of crustaceans and their sperm chromatin components. These findings extend the study of the sperm structure of Stomatopoda and provide basic data to elucidate the epigenetic mechanism of fertilization.

Sperm handling in aquatic animals for artificial reproduction

Artificial reproduction involves collection and handling of gametes in a way that secures their quality and maximizes the fertilization outcome. In addition to initial sperm quality, numerous steps can affect the final result of fertilization, from the sperm collection process until gamete mixing (or co-incubation) when the spermatozoon enters or fuses with the oocyte. In this review, we summarize the whole process of sperm handling, from collection until fertilization for fish, penaeid shrimp, bivalve mollusks and marine mammals. To obtain sperm from captive animals, techniques vary widely across taxa, and include stripping by abdominal massage or testis surgical removal in fish, spermatophore collection in penaeid shrimps, gonadal scarification or temperature shock in bivalve mollusks, and voluntary collection via positive reinforcement in mammals. In most cases, special care is needed to avoid contamination by mucus, seawater, urine, or feces that can either activate sperm motility and/or decrease its quality. We also review techniques and extender solutions used for refrigerated storage of sperm across the aforementioned taxa. Finally, we give an overview of the different protocols for in vivo and in vitro fertilization including activation of sperm motility and methods for gamete co-incubation. The present study provides valuable information regarding breeder management either for animal production or species conservation.

Comparative spermatozoal ultrastructure and molecular analysis in dromiid crabs and their phylogenetic implications for Dromiidae and Podotremata (Decapoda: Brachyura)

We described the spermatozoal ultrastructure and conducted a molecular analysis of Dromiidae Hypoconcha parasitica, Hypoconcha arcuata, Moreiradromia antillensis and Dromia erythropus. To elucidate the relationship between the different species of this brachyuran group, we also compared the spermatozoal morphologies and phylogenetic positioning among species of Dromiidae, Dromioidea and Podotremata. Specimens were collected from the northern coast of São Paulo, Brazil and were fixed and processed followed by transmission electron microscopy and molecular analysis routines. The Dromiidae spermatozoa studied are characterized by a discoidal acrosome, with three or four concentric zones, which are centrally separated by a bilaterally capitate perforatorial chamber, with a "mushroom"-shaped apex in the Hypoconchinae and a "T-shape" in Dromiinae. Above the perforatorial chamber, there is an apical protuberance, continuous with the subopercular region and the operculum, which forms a low, centrally perforated dome. Under differential interference contrast microscopy, the spermatozoa show 3 to 4 radial arms. The spermatozoal characters in Hypoconchinae and Dromiinae do not separate these subfamilies from the Dromiidae and Dromioidea. Ultrastructural differentiation was only found between representative Dromioidea and other Podotremata. Thus, the spermiotaxonomy of these Hypoconcha, Moreiradromia and Dromia species corroborated previous morphological and molecular studies, supporting the monophyly of Dromiidae and Dynomenidae in relation to Homolidae and Latreilliidae.

Ultrastructure of spermatozoa of spider crabs, family Mithracidae (Crustacea, Decapoda, Brachyura): Integrative analyses based on morphological and molecular data

Recent studies based on morphological and molecular data provide a new perspective concerning taxonomic aspects of the brachyuran family Mithracidae. These studies proposed a series of nominal changes and indicated that the family is actually represented by a different number and representatives of genera than previously thought. Here, we provide a comparative description of the ultrastructure of spermatozoa and spermatophores of some species of Mithracidae in a phylogenetic context. The ultrastructure of the spermatozoa and spermatophore was observed by scanning and transmission electron microscopy. The most informative morphological characters analysed were thickness of the operculum, shape of the perforatorial chamber and shape and thickness of the inner acrosomal zone. As a framework, we used a topology based on a phylogenetic analysis using mitochondrial data obtained here and from previous studies. Our results indicate that closely related species share a series of morphological characteristics of the spermatozoa. A thick operculum, for example, is a feature observed in species of the genera Amphithrax, Teleophrys, and Omalacantha in contrast to the slender operculum observed in Mithraculus and Mithrax. Amphithrax and Teleophrys have a rhomboid perforatorial chamber, while Mithraculus, Mithrax, and Omalacantha show a wider, deltoid morphology. Furthermore, our results are in agreement with recently proposed taxonomic changes including the separation of the genera Mithrax (previously Damithrax), Amphithrax (previously Mithrax) and Mithraculus, and the synonymy of Mithrax caribbaeus with Mithrax hispidus. Overall, the spermiotaxonomy of these species of Mithracidae represent a novel set of data that corroborates the most recent taxonomic revision of the family and can be used in future taxonomic and phylogenetic studies within this family.