Spermiogenesis and spermatozoa ultrastructure in Salminus and Brycon, two primitive genera in Characidae (Teleostei: Ostariophysi: Characiformes)

In Salminus, spermiogenesis is cystic and gives origin to a type I aquasperm. Spermatid differentiation is characterized by chromatin condensed into thick fibres, nuclear rotation, nuclear fossa formation, cytoplasmic channel formation, mitochondrial fusion producing long and ramified mitochondria, and the presence of several membranous concentric rings around the plasma membrane that encircles the cytoplasmic channel. In Salminus and Brycon, spermatozoa are very similar. They exhibit a spherical nucleus and chromatin condensed into fibre clusters, and a deep nuclear fossa. They show a long midpiece with few elongate mitochondria at the initial region and a cytoplasmic channel completely encircled by one or two membranous concentric rings. The flagellar axis is perpendicular to the nucleus and exhibits the classic axoneme (9 + 2). The very strong similarity observed between Salminus and Brycon spermatozoa supports the hypothesis that these subfamilies are likely to have a monophyletic origin.     

Sperm and spermatozeugma ultrastructure in the inseminating species Tyttocharax cochui, T. tambopatensis, and Scopaeocharax rhinodus (Pisces: Teleostei: Characidae: Glandulocaudinae: Xenurobryconini)

This article presents the scanning and transmission electron microscopy of the spermatozoa and sperm packets of three inseminating species of the glandulocaudine tribe Xenurobryconini. All three species, Scopaeocharax rhinodus, Tyttocharax cochui, and T. tambopatensis produce unencapsulated sperm packets (= spermatozeugmata) of similar morphology. The external anterior surface of each spermatozeugma is comprised of elongate sperm heads arranged in parallel, and the posterior part is made up of tightly packed flagella. The interior of the anterior portion consists of alternating layers of sperm heads and flagella. The remarkable integrity of each packet appears to be maintained through an electron-dense secretion seen among all parts of the cells. Spermatozeugma formation takes place within the spermatocysts at the end of spermiogenesis and at spermiation fully formed packets are released. Morphology of the mature spermatozoa was similar in all three species. Each nucleus is elongate, flattened along most of its length, and tapers at either end. The two centrioles are nearly parallel to one another and are located just anterior to the nucleus. Elongate mitochondria are located along the nucleus. The single flagellum, which lacks axonemal fins, is initially contained within a short cytoplasmic collar. Accessory microtubules run parallel to the long axis of the nucleus just beneath the plasma membrane. During spermiogenesis, no nuclear rotation occurs and the cytoplasmic canal containing the flagellum elongates along with the nucleus. However, prior to spermiation all but the anterior portion of the collar degenerates. The sperm modifications observed in these species are discussed as adaptations to the unique reproductive habit of insemination.     

Sperm ultrastructure in the inseminating Macropsobrycon uruguayanae (Teleostei: Characidae: Cheirodontinae)

Macropsobrycon uruguayanae is a small, inseminating characid (tetra) of the tribe Compsurini. Although spermatozoa can be found within the ovarian cavity close to oocytes, the exact moment of fertilization has not yet been determined. Spermatozoa have moderately elongate nuclei with electron-dense chromatin. During spermiogenesis, nuclear rotation takes place. Elongate mitochondria with lamellar cristae are found posterior to the nucleus. Centrioles are parallel to one another with the proximal centriole slightly anterior to the longer distal one. The anterior tip of the proximal centriole is located within a shallow nuclear fossa. Electron-dense spurs are associated within the anterior and posterior ends of the distal centriole. Striated centriolar rootlets radiate both anteriorly and posteriorly from the distal centriole. Nine longitudinal accessory microtubules surround the axoneme in the proximal flagellum. The flagellum has a typical 9 + 2 axoneme with no intratubular differentiation. Atypical spermatozoa are also found in the testicular lumen. These cells resemble spermatozoa in most aspects, except that their nuclei are variable in shape, with the granular chromatin less electron-dense than that seen in spermatozoa. The origin and function of these cells could not be determined. The specializations seen in the spermatozoa are discussed as possible adaptations related to the habit of insemination.     

Sperm transfer and reproductive biology in species of hermaphroditic bivalves (Galeommatoidea: Montacutidae)

The histology of the reproductive organs is studied in the protandric hermaphroditic Tellimya ferruginosa. In NW Europe the species reproduces from May through August. Sperm transfer takes place when mature testis follicles are transplanted to the gills or walls of the mantle cavity in recipient hermaphroditic or female bivalves. Transplantation is accompanied by histological changes and sperm cells are released when transplants perish with age. Details are given on the reproduction in Montacuta percompressa which takes place from March through October in North Carolina, USA. All shelled bivalves are females and it is postulated that spermatogenic bodies attached to gills or other surfaces in the female's mantle cavity and previously considered to be dwarf males arise from transplanted larval gonads. The ultrastructure of the euspermatozoa and/or the anucleate paraspermatozoa is described in T. ferruginosa, T. tenella, and M. percompressa. The sperm of the first two species share a number of significant apomorphies with those of another montacutid, Brachiomya stigmatica. In the simultaneous hermaphroditic M. substriata the nucleate paraspermatozoa associate with the euspermatozoa to form spherical spermatozeugmata that are stored in the testis.     

Osteology of Priocharax and remarkable developmental truncation in a miniature Amazonian fish (Teleostei: Characiformes: Characidae)

Establishing phylogenetic relationships of miniature fishes is challenging in taxa with developmental truncation. Within the Characiformes, developmental truncation appears to be relatively rare, with the Neotropical genus Priocharax being an example. Priocharax includes three miniature species among the smallest of the order and has been hypothesized to belong to the Heterocharacinae. The pronounced reduction in its skeleton, however, prevented a clearer evaluation of its relationships. The present detailed osteological study was designed to address this question and revealed that 21 bones are absent and nine other skeletal structures are simplified in Priocharax when compared to other characids. Comparison of the skeleton of adult Priocharax with early developmental stages of other characids demonstrated that most of the absences and simplifications can be interpreted as developmental truncations. The most striking developmental truncations are in the pectoral girdle, in which the endoskeleton remains entirely cartilaginous. Other interesting truncations are in the ethmoid region of the skull, infraorbital series, and Weberian apparatus, in which the claustrum is absent. Our study also revealed some unusual sexual dimorphisms in the pelvic girdle. Two cladistic analyses were performed to assess the relationships of Priocharax within the Heterocharacinae. The first consisted of a traditional analysis in which all absences and reductions of Priocharax were coded in the same way as in the remaining taxa. This resulted in three equally most parsimonious topologies, all of which have Priocharax as the most basal taxon of the Heterocharacinae. The second analysis incorporated ontogenetic information, and most absences and reductions of Priocharax were reinterpreted as apomorphic conditions and thus, coded differently from similar conditions in outgroups. This resulted in a single phylogenetic hypothesis with Priocharax and Gnathocharax as sister groups based on seven synapomorphies. Our approach demonstrates the importance of developmental studies to better understand morphological evolution of miniaturized, truncated taxa, and to generate hypotheses of their relationships. J. Morphol. 277:65–85, 2016. © 2015 Wiley Periodicals, Inc.     

Functional morphology of the reproductive system of Galathea intermedia (Decapoda: Anomura)

Spermatophore formation in Galathea intermedia begins in the proximal part of the vas deferens. The contents subsequently form a spermatophoric ribbon, the so-called "secondary spermatophore," in its distal part. A strongly muscular ductus ejaculatorius is present in the coxa of the fifth pereiopod which builds up pressure for the extrusion of the spermatophoric ribbon. After extrusion, the ribbon is caught by the first gonopod, while the second gonopod dissolves the matrix of the ribbon. During copulation the spermatophores are randomly placed on the sternum of the female, near the genital opening, by the fifth pereiopods of the male. Subsequent ovulation of the female via the genital opening, an active process accomplished through muscular activity, results in fertilization of the eggs by the exploding spermatophores. External intersexes are characterized by both male and female external sexual characters, but in all individuals only male gonads are present. No trace of a female reproductive system could be detected. Thus, these external intersexes are exclusively functional males.     

Microsatellite markers for the cardinal tetra Paracheirodon axelrodi,a commercially important fish from central Amazonia

The cardinal tetra Paracheirodon axelrodi is a very popular aquarium fish and the most important ornamental fishery resource for riverine communities inhabiting the Rio Negro floodplain in central Amazonia. Here we describe the isolation and characterization of 14 microsatellite DNA loci for cardinal tetras. Number of alleles and heterozygosity per locus in a sample of 30 fish ranged from 2 to 22 and from 0.49 to 0.92, respectively. These markers provide powerful tools for studies on conservation and management of cardinal tetra resources and for investigating evolutionary processes underlying population diversification in Amazonian flooded forest fishes.     

Annual cycle of stored spermatozoa within the ovaries of Helicolenus dactylopterus dactylopterus (Teleostei, Scorpaenidae)

The aim of this work was to analyse the ultrastructure of storage crypts and stored spermatozoa, and to describe changes during the annual reproductive cycle of the bluemouth Helicolenus dactylopterus dactylopterus , which has internal fertilization and a zygoparous mode of reproduction. Spermatozoa had elongated heads and long midpieces, two characteristics which are thought to be fairly advanced and correlated with internal fertilization, as is the case of the bluemouth. A remarkable spermatozoon feature was the retention of a significant quantity of cytoplasm around the head, a condition that appeared to be related to nourishment during the long storage period, up to 10 months in the intraovarian crystal structures of the female. Male sex cells' protection against the female immune system was ensured by junctional complexes between the crypt cells composed of tight junctions and desmosomes.     

Taxonomic revision of the South American fish genus Chalceus Cuvier (Teleostei: Ostariophysi: Characiformes) with the description of three new species

The Neotropical characid fishes of the genus Chalceus Cuvier, 1817, are reviewed. In total, five species are recognized (including three new species). Chalceus epakros sp. nov. is the most widespread geographically, occurring in many rivers of the Amazon basin, the Río Orinoco and in the Essequibo River drainage in Guyana. Chalceus guaporensis sp. nov. is restricted to the upper Rio Madeira, Rio Guaporé and Río Madre de Dios, of Brazil, Bolivia and Peru, respectively. Chalceus spilogyros sp. nov. occurs only in the Rio Trombetas, lower Rio Tapajós and lower Rio Madeira drainages. Chalceus macrolepidotus Cuvier occurs in the Rio Negro drainage, middle and lower Río Orinoco basin and in the rivers of the Atlantic slopes of the Guianas, and Chalceus erythrurus Cope in the Rio Amazonas and Rio Solimões to Río Ucayali drainage in Peru. Chalceus ararapeera Cuvier & Valenciennes and Creagrutus pellegrini Puyo are considered synonyms of C. macrolepidotus , and Pellegrinina heterolepis Fowler is placed into the synonymy of C. erythrurus . Characters pertaining to the monophyly of Chalceus are discussed and a key to species is presented.  © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society , 2004, 140 , 103−135.     

Structure of sperm,spermatozeugmata and ‘lateral organs’ in the bivalve Arthritica (Galeommatoidea: Leptonidae)

The position and structure of paired ‘lateral organs’ in the foot of Arthritica semen and Arthritica bifurca might indicate a chemosensory function. In both species part of the organ is also glandular. In A. semen the glandular epithelium is detached piecemeal and, probably by means of the foot, is moved to and grafted upon the gills of the same individual. The transferred epithelia appear as disk‐shaped actively secretory ‘gill bodies’ which, attached to the abfrontal side of the inner demibranch, replace the ordinary unciliated gill epithelium. The secretion is liberated into the suprabranchial chamber, which serves as a marsupium, but its function is uncertain. Arthritica semen is a protandric hermaphrodite and produces very large ova that undergo a direct development that results in a non‐planktonic lecithotrophic crawling juvenile stage. The sperm cells have filiform nuclei that are straight in the euspermatozoa and more or less helicoidal in what is considered to represent paraspermatozoa. By a process of aggregation, spermatozeugmata are formed which consist exclusively either of euspermatozoa or paraspermatozoa. Spermatozoa are stored in the oviduct in A. semen but in paired seminal receptacles in A. bifurca.     

Reproductive apparatus and male accessory structures in two batrachoid species (Teleostei, Batrachoididae)

The morphology of the genital apparatus of two batrachoid species, Opsanus tau and Porichthys notatus , was studied. The anatomical organization of the female reproductive apparatus is similar in both species but differences are observed in the rhythm of gametogenesis with individual oocyte production asynchronous in O. tau and group synchronous in P. notatus. The male reproductive apparatus is similarly organized in the two species, with both showing enlongated testes with an efferent duct system, two main testicular ducts, a common sperm duct, and a pair of multi-channel accessory structures. The sperm transport system consisting of the efferent duct system, main testicular ducts, and sperm duct is more developed in P. notatus and only in this species does it secrete sialoglycoproteins. Male accessory organs also secrete sialoglycoprotein in both species, but they appear more developed in O. tau. Intraspecific variability in development of accessory structures and mucin secretion was also observed between the two male morphs of P. notatus. Type I males, which build nests and perform parental care to eggs and fry, have larger accessory organs and more abundant secretion than type II males, which adopt opportunistic spawning tactics. The possible role played by mucins as components of the seminal fluid, in both species, and their inter-and intraspecific variability are discussed in the light of the reproductive biology and the presence of alternative male mating tactics.     

Gonadal morphology and difference in reproductive development of two isolated populations of Astyanax rivularis (Teleostei,Characidae)

Individuals of the same species may present different reproductive tactics depending on the environment in which they develop and mature. The present study aimed to define the gonadal development phases of males and females of Astyanax rivularis and to carry out a comparative analysis of the reproductive development of specimens captured in two isolated environments of the São Francisco River basin in Serra da Canastra, Brazil (Point 1: low vegetation and river showing calm and crystalline waters with small well formations; Point 2: current waters, and well-established areas of arboreal vegetation). Thus, the gonads of A. rivularis specimens were collected, fixed and processed with techniques for light microscopy. Five maturation phases of the females' reproductive cycle were established: immature, developing, spawning capable, regressing and regenerating. Three maturation phases of the males' reproductive cycle were observed: spawning capable, regressing, and regenerating. There are differences in the phases of gonadal development of A. rivularis between the two sampling points so that, possibly, animals upstream of the waterfall demonstrate a delay in the reproductive cycle in relation to animals downstream.     

An assessment approach for application of spermatic data in phylogenetic analyses: within the genus Moenkhausia Eigenmann, 1903 (Characiformes: Characidae)

Spermiogenesis and sperm ultrastructure from 21 species of Moenkhausia and others related genera are described. To evaluate the phylogenetic signals, 18 unordered characters were utilized in implied weighting analysis through the program TNT 1.1. Four variations of spermiogenesis were found. In the earliest spermatids, the nucleus can be positioned lateral, eccentric, strongly eccentric or nearly medial in relation to the distal centriole. The nuclear rotation can be present or absent. These spermiogenesis processes are related or intermediate to Type I and Type III. Taking into account the degrees of nuclear rotation during the spermiogenesis and other characteristics, distinct forms of spermatozoa are observed among the species analyzed. The phylogenetic analysis yielded a single most parsimonious tree with fit value 2.70000 and the topology obtained founds Moenkhausia as non‐monophyletic. However, some hypothesis of relationships previously proposed viz the clade 20, which contains the type species Moenkhausia xinguensis, is recovered herein. This clade is supported by five synapomorphies, and it allows the supposition that these species constitute a monophyletic group. The whole topology is presented and discussed.     

Reproductive morphology of the male Tuatara,Sphenodon punctatus

Over the past decade, studies on reproductive morphology in the Squamata (snakes and lizards) have expanded tremendously. With the accumulation of these studies and revisions of the terminology based on structural similarities and differences, it is imperative to review the work on tuataras to determine whether the structural organization fits the revised terminology of vertebrates. We investigated the morphology of the male reproductive system in the Tuatara, Sphenodon punctatus (Rhynchocephalia), the sister taxon to the Squamata. Previous studies on the Tuatara used a nomenclature for the testicular ducts different from the current terminology for amniotes. The reproductive system in the Tuatara is consistent with reports in the Squamata. Two rete testis tubules exit the testis within a connective tissue sheath similar to that shown in other squamate species and the protherian Echidna. Each rete testis divides into multiple ductuli efferentes that fuse with the epididymis. The epididymis transitions into the ductus deferens where the sperm become more concentrated into spherical bundles. The ductus deferens enters the cloacal urodeum separately from the ureter. An ampulla ureter or ampulla urogenital papilla was not observed, which differs from previous studies of lepidosaurians. Furthermore, a sexual segment of the kidney (SSK) was not observed, consistent with previous studies on the Tuatara.     

Spermatozoon structure of Acesta oophaga (Limidae), a cold-seep bivalve

The structure of the spermatozoon of Acesta oophaga (Bivalvia) is described by transmission electron microscopy. This cold-seep species produces ect-aquasperm, confirming that it is a broadcast spawner. The head of the sperm consists of a small, rounded, electron-dense nucleus, capped by a short conical acrosome, the contents of which are differentiated. The mid-piece contains a pair of orthogonally arranged centrioles surrounded by five spherical mitochondria. The gonad of one individual contained eggs and sperm, which supports the hypothesis that A. oophaga is a sequential hermaphrodite.     

Characterization of microsatellite loci for the Amazonian rummy‐nose tetra,Hemigrammus bleheri (Teleostei,Characidae)

The rummy‐nose tetra, Hemigrammus bleheri, is a small fish found in forest streams of the Rio Negro floodplain, central Amazonia. This species is popular in aquaria and used as an ornamental fishery resource by the riverine people from middle Rio Negro. Here we describe eight microsatellite DNA loci for rummy‐nose tetras. Number of alleles and heterozygosity per locus in a sample of 30 fish ranged from five to 22 and from 0.52 to 0.96, respectively. These highly variable genetic markers provide important tools for investigating population history and identifying conservation units in rummy‐nose tetras.     

Comparative morphology of the gonadal structure related to reproductive strategies in six species of neotropical catfishes (Teleostei: Siluriformes)

We studied the relationship between the morphology of the reproductive system and the reproductive strategies of six neotropical catfishes using macroscopic and microscopic analyses. The reproductive system of the examined Siluriformes showed diversified characteristics, but permitted their being grouped according to three reproductive strategies: pelagic spawning, demersal spawning, and internally fertilizing. The pelagic spawners Pseudoplatystoma corruscans and Conorhynchos conirostris have testes that are characterized by filiform lobes, absence of testicular secretion, full‐grown oocytes of small diameter, thin zona radiata, and cuboidal follicular cells. Pimelodus maculatus is morphologically distinct from the other two pelagic spawners catfishes due to the presence of testicular secretion. The demersal spawners Lophiosilurus alexandri and Rhinelepis aspera possess homogeneous testicular secretion, large mature oocytes, and columnar follicular cells. The most specialized reproductive system was observed in the internally fertilizing Trachelyopterus galeatus, which possesses a seminal vesicle accessory to the testes, spermatozoa with elongated nuclei that form spermatozeugmata, and a secretory ovarian lamellar epithelium that is associated with sperm storage. The reproductive system observed in Neotropical catfishes showed a relationship associated with the type of fertilization and the reproductive strategies of the six species studied. © 2011 Wiley‐Liss, Inc.     

Reproductive biology of the Panama graysby Cephalopholis panamensis (Teleostei: Epinephelidae)

The reproductive biology of the Panama graysby Cephalopholis panamensis was studied from collections and behavioural observations made in the Gulf of California from 2001 to 2006. Histological examinations, particularly the identification of gonads undergoing sexual transition, confirmed a protogynous hermaphroditic sexual pattern. The population structure and mating behaviour provided further support for protogyny. Size and age distributions by sex were bimodal, with males larger and older than females and sex ratios biased towards females. Mating groups consisted of a large male and several smaller females, and courtship occurred in pairs during the evening. Results on spawning periodicity and seasonality were incomplete, but histological data, monthly gonado‐somatic indices (I_G) and behavioural observations suggest that adults spawned around the full moon from May to September. Certain aspects of their reproductive biology (e.g. protogyny and low egg production) indicate that C. panamensis is particularly vulnerable to fishing and would benefit from a management policy in Mexico.     

A systematic review of the species of the genus Bryconamericus (Teleostei: Characidae) from Central America

A systematic revision of the fish genus Bryconamericus from Central America was done based in museum collections (UCR, STRI, BMNH, USNM, UMMZ) and samples collected by the author in Panama. Five valid species are recognized: B. bayano, B. emperador, B. gonzalezoi sp. nov. B. scleroparius and B. terrabensis: B. ricae is synonyms of B. scleroparius. Moreover, B. scleroparius and B. terrabensis were redescribed with fresh material and the lectotype of B. scleroparius was designated. Bryconamericus baudoensis, B. ortholepis, B. scopiferus (from western of Colombia), B. cascajalensis and B. zeteki (from Central America) are synonyms of B. emperador.