Patterns of reproductive morphology in the genus Gobiodon (Teleostei: Gobiidae)

The reproductive system of gobiid fishes (family Gobiidae), especially among hermaphroditic goby species, is morphologically diverse. Two hermaphroditic species in the genus Gobiodon, G. okinawae and G. oculolineatus, have several modifications of the gonoduct and gonad that are associated with secretion production and storage. In this study, an examination of six additional Gobiodon species, G. citrinus, G. fulvus, G. histrio, G. micropus, G. quinquestrigatus and G. rivulatus, revealed similar reproductive modifications. Among these six Gobiodon species, a number of features were found to be shared amongst each other and with G. okinawae and G. oculolineatus. All individuals had either an ovariform gonad or an ovotestis; no individuals had a purely testicular gonad. The gonadal lobes extended caudally past, rather than terminating at, their union with the gonoduct. Accessory secretory structures associated with the reproductive complex, termed accessory gonoduct structures, or AGdS, always originated from the gonoduct. The ovariform gonad was comprised entirely of ovarian tissue, while the ovotestis was divided into three morphologically distinct regions. Only one of the ovotestis regions was strictly gametogenic, consisting of both early stage oocytes and sperm-filled seminiferous lobules. The second region of the ovotestis was made up of stromal tissue surrounding some compressed lumina and a small number of early-stage oocytes. The third region was highly lobulated and acted as a storage region for eosinophilic secretions. Anteriorly, the stromal region of each of the two ovotestis lobes disappeared and the gametogenic and secretory storage regions of the ovotestis separated into two discrete lobes. In all of the examined Gobiodon species, all individuals having an ovotestis also had AGdS. However, AGdS presence among individuals having an ovariform gonad varied in a species-specific manner, with the AGdS being fully differentiated and well-developed in a number of species, and either in a very early stage of development, or absent, in others. The distribution of these AGdS states among Gobiodon species corresponds with that of several other morphological features that have been proposed by Harold et al. (Bull Mar Sci 82:119–136, 2008) as phylogenetically informative for intra-generic clade identification. Reproductive characters may prove informative in the development of hypotheses of relationships among gobiid fishes.     

Does gonad structure reflect sexual pattern in all gobiid fishes?

Synopsis In immature and adult females of protogynous gobies, small distinctive masses of cells associated with the ovarian wall develop into testis-associated glandular structures during sex change. These precursive accessory gonadal structures, or pAGS, have been found in females of known protogynous goby species, but not among gonochoric goby species, suggesting that their presence can be used as a species-specific indicator of protogyny within the family. However, a detailed examination of a developmental series of ovaries in two gonochoric species,Gobiosoma illecebrosum andG. saucrum, revealed the presence of a gonadal feature previously thought to be restricted to protogynous gobies. Among immature females of both species, pAGS-like structures having a similar appearance and placement as functional pAGS of protogynous gobies were found. In femaleG. illecebrosum, the size of these structures among immatures progressively decreased with maturation and were absent in all but the smallest adult females. A similar pattern was evident in a small sample ofG. saucrum. Population demography based on field collections showed thatG. illecebrosum exhibits sex ratios and male and female size-frequency distributions typical of gonochores and laboratory experiments indicated that final sexual identity was unaffected by social environment during the juvenile period. Thus, the presence of pAGS in juvenile femaleG. illecebrosum is not related to an ability to change sex at that ontogenic interval. Whether the transient pAGS observed here are vestiges of an ancestral protogynous condition is unknown. Based on their presence among immatures in two gonochore gobies, however, only the presence of pAGS in adult females should be used to predict protogyny among gobies.     

Phylogeny and character evolution in the Indo-Pacific genus Ctenogobiops (Gobiiformes: Gobiidae)

Ctenogobiops is a genus of Indo-Pacific gobies that form obligate, mutualistic associations with shrimp in the genus Alpheus. This study provides a molecular phylogenetic analysis of eight Ctenogobiops species: C. aurocingulus, C. crocineus, C. feroculus, C. formosa, C. maculosus, C. mitodes, C. tangaroai, and C. tongaensis. We recover two clades within the genus, one consisting of C. feroculus and C. aurocingulus, the second including the remaining species arrayed as follows: (C. tongaensis (C. mitodes (C. formosa (C. maculosus (C. crocineus, C. tangaroai))))). Recovery of C. maculosus and C. crocineus as distinct taxa suggests that these species are not synonymous, although sampling in this study is limited. Species of Ctenogobiops are morphologically very similar to each other, with generally consistent meristic character states present throughout the genus. Recognition of species is based primarily on slight variations in color pattern, shape of the dorsal fin, and size of the gill opening. Comparison of our specimens of C. mitodes with accounts of C. pomastictus confirms that color pattern variations and lateral scale counts are more reliable indicators of species identity than relative dorsal fin spine length, particularly for smaller specimens. We evaluate the distribution of morphological characters in the context of the new phylogenetic hypothesis, and provide a summary of distinguishing characters for Ctenogobiops species. In this case, as in other instances of diverse reef-dwelling fish taxa, molecular data are ideal for inferring phylogenetic relationships, whereas morphological data remain the most expedient way to identify species.     

Patterns of gonad structure in hermaphroditic gobies (Teleostei Gobiidae)

Synopsis Hermaphroditism has been reported for a small number of gobiid fishes, but the extent of this sexual pattern within the family is not known. Gonad structure was examined in one or more species from twenty-one gobiid genera. No evidence of hermaphroditism was found in the species selected from 14 genera. Laboratory studies supported the conclusion of gonochorism for the examined species in four of them:Asterropteryx, Bathygobius, Gnatholepis, andPsilogobius. Currently, the absence of precursive testicular tissues associated with the ovary in females, in conjunction with no retained ovarian features in the testes of males, appear to be reliable indicators of a gonochoristic sexual pattern in gobiid fishes. Evidence for hermaphroditism was observed in seven genera:Eviota, Trimma, Fusigobius, Lophogobius, Priolepis, Gobiodon, andParagobiodon. Protogyny was experimentally confirmed inE. epiphanes, and the gonad structure in another nine of ten species ofEviota suggested either protogyny or protogynous tendencies. With the exception ofGobiodon andParagobiodon, which exhibited similar gonadal structure, ovarian and testicular structure varied considerably among the hermaphroditic genera examined, both with regard to the configuration and to the degree of development of ovarian and testicular tissues, or testicular tissue precursors. Findings of this study indicate that hermaphroditic gonad structure will prove to be a useful trait in determining evolutionary relationships within the Gobiidae.     

Patterns of structural change in gonads of the divine dwarfgoby Eviota epiphanes as they sexually transition

This study documents changes in gonadal structure for the serial hermaphrodite (or bidirectional sex changer) divine dwarfgoby Eviota epiphanes (family Gobiidae) as individuals transition in both directions. To evaluate transitional gonad morphology, individuals actively producing the same gamete type (oocytes or sperm) were set up into pairs and euthanised over a period of 14 days to get a time series of morphological changes during gonad transformation. Results from this study show that rapid changes in the gonad take place at a structural level as individuals change their reproductive function and gamete production. Changing from oocyte production (o-phase) to sperm production (s-phase) starts with the breakdown of vitellogenic oocytes (i.e., atresia) followed by the appearance and proliferation of spermatogenic tissue which, in most cases, was not previously visible. Changing from sperm production to oocyte production included the cessation of sperm production, a reduction in size and number of seminiferous lobules and the maturation of previtellogenic oocytes already present in the gonads. Experimental fish changed from oocyte production to sperm production more readily than from sperm production to oocyte production. The hypothesis that shifts in sexual function among serially hermaphroditic fish species have a similar cost in either direction is not supported in E. epiphanes.     

The timing of gonadal development and moult in three raptors with different breeding seasons: effects of gender, age and body condition

Differences between species in breeding seasons are thought to be mediated through differences in their reproductive physiology. Little is known about how the timing and duration of gonadal maturation varies between raptor species, how the timing of moult relates to the gonadal cycle, whether the timing and degree of sexual maturation varies between juveniles and adults or whether body condition has a significant effect. To address these questions, data on gonadal size and moult for adults and juveniles of both sexes of three raptor species were extracted from the Predatory Bird Monitoring Scheme (based on birds found dead by members of the public). The three species, Sparrowhawk Accipiter nisus, Kestrel Falco tinnunculus and Barn Owl Tyto alba, have different ecologies – diurnal bird predator, diurnal mammal predator and nocturnal mammal predator, respectively. All are single‐brooded but have different breeding seasons. The duration of gonadal maturation was markedly different between the species. Barn Owls showed the earliest maturation and the latest gonad regression, and Sparrowhawks the latest maturation and earliest gonad regression. Kestrels were intermediate. In males of all species, the testes remained fully mature throughout their respective breeding seasons. In females, the ovaries remained partially mature throughout the breeding season. Moult started slightly earlier in Sparrowhawks than in Kestrels and coincided with gonadal regression in the two species. Although females of the two species started to moult earlier than males, moult duration was similar between the sexes. Barn Owls showed no distinct annual pattern of moult. In juveniles of all three species, the gonads were smaller than in adults throughout spring and started to mature later. Gonad size in birds that had starved tended to be smaller than in birds dying from other causes, but did not influence the difference in gonad mass between adults and juveniles and between seasons. Body condition had no effect on moult. Whilst ecology has led to the evolution of different breeding seasons, differences between species, and between adults and juveniles, are mediated through adaptive differences in their reproductive physiology.     

Variation in reproductive success and gonadal allocation in the simultaneous hermaphrodite,Serranus fasciatus

Summary This paper examines the correlates of individual size, reproductive success, gonadal allocation, and growth in a hermaphroditic reef fish. Individuals in S. fasciatus mature as simultaneous hermaphrodites; large individuals subsequently lose female function and become functional males. Daily female reproductive success was highly correlated with both hermaphrodite size and amount of female gonadal tissue. Three separate comparisons gave a positive correlation between male reproductive success and male gonadal allocation: (1) Males had higher levels of male gonadal allocation and male reproductive success than hermaphrodites. (2) The percent of gonad allocated to male tissue in hermaphrodites was higher in the year they had higher male mating success. (3) Male gonadal tissue of hermaphrodites was positively correlated with male reproductive success in the year that male reproductive success by hermaphrodites was higher and more variable. There was no evidence for a trade-off between male function, female function, and growth among hermaphrodites. Many of these patterns have also been observed in plants, but the selective pressures leading to these patterns in S. fasciatus and plants are probably quite different.     

Reproductive cycle by histological characterization of the ovary in the butterfly goodeid Ameca splendens from the upper Río Ameca Basin, Mexico

The ovarian cycle was studied in Ameca splendens, a viviparous fish native to western Mexico. Two wild populations living in environments with differential conditions (a small pond adjacent to a reservoir and a spring) were examined to determine whether the conditions these populations are exposed to can elicit differences in the reproductive cycle. The two sites differ from each other with respect to several environmental factors: the spring has clear, oxygen‐rich water while the pond has higher levels of conductivity, hardness and inorganic nitrogen. Six stages of gonadal maturation were identified in A. splendens, based on histological and macroscopic characteristics of the gonad. The relative frequency of gonadic stages at both sites showed two reproductive peaks during the year: from March to May and from September to November. Histologically, ovaries exhibit an asynchronous development in both populations, revealing the existence of a multiple reproductive cycle. Relative mean condition shows organisms are in peak condition (K > 1) at age class 1+ as they recruit to reproduction; K was <1 following the onset of multiple reproduction. The Fulton condition factor shows that the mean condition is slightly higher in the spring population. The relative frequency of gonadal maturation differed between the study sites and is indicative of the plasticity of A. splendens in facing different conditions within the environments it inhabits.     

Reproduction and sexual dimorphism in two populations of the polymorphic spiny lizard Sceloporus minor from Hidalgo,México

Male‐biased sexual dimorphism is extensive in New World spiny lizards (Sceloporus: Phrynosomatidae) and is particularly prominent in the polymorphic minor lizard Sceloporus minor. However, the possible relationship between patterns of sexual dimorphism and gonadal development is little known for most species. In this study, we explored aspects of sexual dimorphism in noncolor morphological traits in S. minor and characterized the gonadal cycle in males and females from each of two sites (El Enzuelado and La Manzana) in Hidalgo, México, differing in key ecological aspects linked to life‐history trait expression in other lizards. Males were generally larger than females in each population and expressed larger forms of several other morphological traits, although not all comparisons attained statistical significance. Both sexes attained reproductive maturity at a larger size in El Enzuelado relative to La Manzana, and females from El Enzuelado had larger litters. Gonadal cycles differed substantially between the two populations and suggest that reproductive activity of males and females was synchronous at El Enzuelado and asynchronous at La Manzana, an unusual pattern. Geographic variation in sex‐specific responses to environmental variables may be at least partly responsible for the exceptional species diversity of spiny lizards in México.     

In search of determinants: gene expression during gonadal sex differentiation

The diversity of inputs that guide sexual fate during development is both intriguing and daunting. In the field of fish biology, the study of sex determination is of great importance. For example, in aquaculture, sexually dimorphic growth rates and overall size leads to one sex being more marketable than the other. Moreover, for breeding purposes it is important to maintain balanced sex ratios. Furthermore, sex determination is sensitive to environmental factors, such as temperature and contaminants, which can lead to skewed sex ratios, intersexes and sterility in wild or farmed fish. The gonad is typically the first organ to exhibit morphological signs of sexual dimorphism and therefore is likely to be the primary organ system whose fate is controlled by the sex determination cues in many fish species. Additionally, the sexual fate of the gonad has been shown to fully or partially control organismal sex differentiation. Thus, understanding the genetic regulation of gonadal sex differentiation is critical in studies of fish sex determination. This review summarizes recent knowledge of genes expressed during gonadal sex differentiation in gonochoristic teleost fish. Three species are discussed, which serve as excellent model systems for probing teleost sex differentiation: the Oreochromis niloticus, Oryzias latipes and Danio rerio. The similarities and differences between gonadal gene expression in these three species and in comparison to mammals suggest conserved roles during vertebrate gonadal sex differentiation. In the future, it will be essential to develop tools to assay the function of genes expressed during gonadal sex differentiation in fish.     

Comparative morphology of the reproductive system of seven species of ostariophysan fishes from the upper Das Velhas River,Brazil

The success of fishes in different environments is related with the variation of reproductive strategies developed by the systematic group, which is reflected in the morphology of the reproductive system and can have ecological and evolutionary implications. This study comparatively analyzed the morphological characteristics of the male and female reproductive systems of ostariophysan fish species from the upper Das Velhas River in the São Francisco River basin, Brazil. In order to accomplish this, 393 specimens belonging to seven fish species were sampled between April 2010 and June 2015 for histological, ultrastructural, histochemical, and morphometric analyses. All the species examined have anastomosing tubular testes with unrestricted distribution of spermatogonia. Astyanax bimaculatus , A. fasciatus , A. scabripinnis , and Harttia torrenticola had their spermatozoa embedded in a glycoprotein secretion within the tubule lumen. Most species had type I spermiogenesis, whereas Rhamdia quelen had type III spermiogenesis. While all females examined had asynchronous oocyte development, there were remarkable morphological, histochemical, and morphometric differences in the ovarian follicles and enveloping layers. Hoplias malabaricus and H. torrenticola , which exhibit parental care behaviour, had a significantly larger diameter of vitellogenic oocytes and larger spermatozoa nuclei. Apareiodon ibitiensis , H. torrenticola , and A. scabripinnis , species that have rheophilic preferences, exhibited a thicker zona radiata than the other species examined. The follicular cells of R. quelen and H. torrenticola were columnar and produced a jelly coat and mucosubstances, respectively. The females of the seven fish species studied show a correlation of the reproductive strategies with the reproductive system morphology, while males retained more similar morphological characteristics between species. J. Morphol. 278:170–181, 2017. © 2016 Wiley Periodicals,Inc.     

Juvenile bisexuality in the red sea bream,Pagrus major

The histology of the gonad of the red sea bream,Pagrus major, was examined in order to study the early gonadal development, sexual maturation and sex ratio in a natural population. A total of 1,117 fish between the ages of 4 months and 8 years were examined. Gonads of 4-month-old fish were either sexually undifferentiated with a central cavity, or ovarian in form. Gonads of 12- and 18-month-old fish were ovaries or bisexual gonads, while those of 2-year-old fish were ovaries, bisexual gonads or testes. Fish aged between 3 and 8 years had ovaries or testes, except for a few bisexual gonads found in 3- and 4-year-old fish. The chronological appearance of females, hermaphrodites and males in that order, and histological evidence, suggested that the testis originates from the ovary via a bisexual gonad in the juvenile stage. The sex ratio of females to males at the age of 2 years and over was about 1:1, suggesting that hermaphroditic red sea bream appear in about 50% of the juvenile population. The sexual pattern in this species, therefore, is concluded to be gonochorism with a bisexual juvenile stage.     

Comparison of quantitative gonad maturation scales in a temperate oyster (Crassostrea gigas) and a sub-tropical oyster (Crassostrea corteziensis)

Quantitative scales to evaluate maturity of female gonads were compared for a temperate oyster, Crassostrea gigas and a tropical oyster, Crassostrea corteziensis grown in the same locality. C. gigas had well-defined maturation and spawning periods and a resting phase in winter; in C. corteziensis mature individuals occurred most of the year and there were several spawning peaks. Of the quantitative scales used here, average oocyte diameter and gonad coverage area, much used for C. gigas, and ovary maturity index, less used, were inadequate to distinguish the reproductive pattern of C. corteziensis, since they both skewed the degree of maturation in vitellogenic stages in favor of C. gigas. Maximum oocyte diameter and maximum cytoplasm area were different among species at vitellogenic stages and also in previtellogenic stages. Nucleus:cytoplasm ratio was significantly different in previtellogenic and spawned stages between C. gigas and C. corteziensis. The Index of gonadal development was skewed in favor of C. gigas in postvitellogenic stage. The only scale that was comparable between species was reproductive potential, but it also was one of the most laborious. Other ordinal scales commonly used, such as a visual external evaluation of the gonad, only classified correctly a quarter of the stages.     

Taxonomic Study of Korean <Emphasis Type="Italic">Scirpus</Emphasis> L. s.l. (Cyperaceae) II: Pattern of Phenotypic Evolution Inferred from Molecular Phylogeny

Scirpus L. s.l. is well known as one of the polyphyletic groups in Cyperaceae. Recent molecular phylogenetic studies clearly suggested that Scirpus s.l. should be separated into several independent genera. In this study, we intend to present the morphological variations and patterns of phenotypic evolution based on molecular phylogeny of Korean Scirpus s.l. Five genera, including 21 taxa from Korean Scirpus s.l., were examined: three species of Bolboschoenus, three species of Schoenoplectus, eight species of Schoenoplectiella including one hybrid, five species of Scirpus, and two species of Trichophorum. For morphological analyses, 23 and 48 characters were selected from vegetative and reproductive organs, respectively. Molecular phylogeny was inferred from a nuclear ribosomal internal transcribed spacer, the chloroplast rbcL gene, and the chloroplast trnL-F region. Distinct characteristics and quantitative variation was presented for identification of the five genera and their species. A pronounced pattern of morphological character change was reduction, although many other character states seem to be homoplastic. We suggest that the reduction of phenotypic characteristics has been expressed in terms of condensation of internodes, reduction of leaf blade, and simplification of inflorescence among five genera of Korean Scirpus s.l.     

Inhibition of primordial germ cell proliferation by the medaka male determining gene Dmrt1bY

Background  

Dmrt1 is a highly conserved gene involved in the determination and early differentiation phase of the primordial gonad in vertebrates. In the fish medaka dmrt1bY, a functional duplicate of the autosomal dmrt1a gene on the Y-chromosome, has been shown to be the master regulator of male gonadal development, comparable to Sry in mammals. In males mRNA and protein expression was observed before morphological sex differentiation in the somatic cells surrounding primordial germ cells (PGCs) of the gonadal anlage and later on exclusively in Sertoli cells. This suggested a role for dmrt1bY during male gonad and germ cell development.     

Rapid identification of the north-western Pacific billfish species using quantitative real-time polymerase chain reaction techniques

Billfishes are important fishery resources traded and consumed worldwide. As morphological traits are usually removed during processing, molecular methods are applied to identify billfish products. In this study, the approaches of quantitative real-time PCR were developed to identify the six billfish species (Istiompax indica, Istiophorus platypterus, Kajikia audax, Makaira nigricans, Tetrapturus angustirostris and Xiphias gladius) widely distributed in the north-western Pacific Ocean. The developed singleplex systems showed high fidelities to each of the six species via either examining the ΔCt values or melting curve patterns. For samples containing multiple species, individual species are identifiable by a quantitative real-time PCR assay that includes all the singleplex systems. A multiplex system was also developed to identify unknown samples composed of a single species. The methods developed in this study provide a fast and high-throughput manner to identify the north-western Pacific billfish species when morphological traits are unavailable, such as in processed products.     

Observation and establishment of gonad development stages in polyplacophorans (Mollusca): Chiton (Chiton) articulatus a case study

Gonad development stages (GDS) and, subsequently, the reproductive cycle are described by performing histology of some gonad portions. In polyplacophorans, gametogenesis is not enough to define GDS; further anatomical gonad features are relevant. In most adult polyplacophorans, the gonad is a simple anatomical structure that resembles and operates as one single gonadal acinus without glandular structure. These features have gone unnoticed causing inaccurate GDS assignment and, consequently, imprecise reproductive season in polyplacophorans. Here, dissection protocols that allow extracting a compact gonad are established. Emphasizing the anatomical structure of the whole gonad and the displacement of gametes, five GDS were assigned to both sexes of Chiton (Chiton) articulatus: I‐goniogenesis, II‐development, III‐ripe, IV‐spawning, V‐rest. Tissue platelets contribute importantly to GDS assignment and even help distinguishing between males and females. Neither a randomly selected portion of gonad nor a longitudinal section are recommended because it leads to misinterpretation higher than 50% in determining GDS and besides ignores displacement of gametes. A panoramic sweep across a complete transverse‐section of each gonad was validated as the best option for establishing GDS. This new methodology was tested on several polyplacophorans species, and seems generally applicable for histological assessment of reproductive cycle and reproductive season in polyplacophorans.     

Photoperiodic activation of brains in castrates and the role of the gonad in reproductive maturation ofLimax maximus

Summary Results obtained with castration and gonad implantation verify that a factor(s) from the gonad is required for development of the female accessory sex organs (ASO) inLimax maximus. In addition, they show that a gonadal factor promotes rapid gonadal growth and sperm production, and gradual or incomplete development of the penis. Although an immature slug that is castrated and then switched to inductive photoperiods fails to exhibit reproductive tract maturation, in two differently designed experimental tests, the brains of such animals were able to promote sexual maturation when subsequently paired with an immature gonad. We interpret the results of these experiments as evidence for photoperiodic induction of secretion of maturation-inducing factor (MH) by the brain in the absence of the gonad. One or more gonadal hormones appear to be both necessary and sufficient for production of sperm and for development of ASO, but they are not required for the photoperiodic stimulation of MH release.Abbreviations ASO accessory sex organs - MH maturation hormone     

Male display characters, gonadal maturation and androgens in the cichlid fish Oreochromis mossambicus

  The relationships between gonadal maturation and the expression of behavioral and morphological display characters in O. mossambicus was investigated and the possible role of androgens in the coordination of this process was evaluated using genital papilla size as a bioassay for androgen levels. Morphological and behavioral displaying characters were found to be correlated among themselves. The sexually dimorphic characters were correlated with gonad maturation and androgen levels, but not with the gonado-somatic index. Gonad maturation and androgen levels were closely related. Territoriality and other behavioral variables involved in reproduction were also correlated with gonad maturation and androgen levels. These data suggest that in O. mossambicus androgens play a mediating role between gonadal maturation and the expression of display characters, both morphological and behavioral. Received: 23 February 1999 / Received in revised form: 3 May 1999 / Accepted: 10 May 1999