The problem of sexual inversion in the minnow, Phoxinus phoxinus (L.)

The incidence of sexual inversion in Phoxinus phoxinus has been studied by examining histologically (a) the gonads of 406 adult specimens caught from the wild during a period of 16 months, (b) the gonads of 168 adults kept in captivity in groups with an experimentally altered sex-ratio, and (c) the differentiation of the gonads in the fry.
All the adults had either testes or ovaries and no case of intersexuality was observed. For both testis and ovary, we recognized two phases, depending on the seasonal cycle: an active spring-summer phase, corresponding with the period of reproduction, and a quiescent autumn-winter phase. The ovaries showed an asynchrony in oocyte development, which is typical of species that spawn many times during the breeding season.
In P. phoxinus the ovaries are easily recognizable just one month after hatching and testes are well differentiated in 2-month-old fingerlings. Differentiation is, therefore, precocious and follows a pattern typical of gonochoristic species in which hermaphroditism never occurs.     

Female reproductive fluid concentrations affect sperm performance of alternative male phenotypes in an external fertilizer

There is growing evidence that the female reproductive fluid (FRF) plays an important role in cryptic female choice through its differential effect on the performance of sperm from different males. In a natural spawning event, the male(s) may release ejaculate closer or further away from the spawning female. If the relative spatial proximity of competing males reflects the female pre-mating preference towards those males, then favoured males will encounter higher concentrations of FRF than unpreferred males. Despite this being a common situation in many external fertilizers, whether different concentrations of FRF can differentially influence the sperm performance of distinct male phenotypes (favoured and unfavoured by the female) remains to be elucidated. Here, we tested this hypothesis using the grass goby (Zosterisessor ophiocephalus), a fish with distinct territorial-sneaker reproductive tactics and female pre-mating preference towards territorial males, that consequently mate in an advantaged position and whose sperm experience higher concentrations of FRF. Our findings revealed a differential concentration-dependent effect of FRF over sneaker and territorial sperm motility only at low concentrations (i.e. at the distance where sneakers typically ejaculate), with increasing FRF concentrations (i.e. close to the eggs) similarly boosting the sperm performance of both sneaker and territorial males. The ability to release sperm close to the eggs is a prerogative of territorials, but FRF can likewise advantage the sperm of those sneakers that are able to get closer, allowing flexibility in the direction of female post-mating choice.     

Peculiarities of the male urogenital apparatus of two grunt species (Teleostei, Haemulidae)

An unusual testicular structure in the white grunt, Haemulon plumieri , and the French grunt, H. flavolineatum , and a urinary exocrine gland in H. flavolineatum are described. The testes of both species are comprised predominantly of efferent ducts, with spermatogenetic tissue restricted to the gonadal periphery. The epithelial cells of the efferent ducts produce glycogen which may serve a role in the storage and nutrition of sperm. The urinary gland is a male accessory gland thought to be associated with reproduction. The gland is mesonephric in origin and the epithelial cells of the gland produce mucins which may be involved in intraspecific chemical communication.     

From sneaker to parental male: change of reproductive traits in the black goby, Gobius niger (Teleostei, Gobiidae)

This study focuses on the consequences of the switch of tactic from parasitic to parental male in the black goby, Gobius niger (Teleostei: Gobiidae), a species showing two alternative male mating tactics. Older and larger males defend nests, court, and perform parental care on eggs, while younger and smaller ones behave as parasites, sneaking into nests while spawning occurs. Males adopting different tactics are known to present differences in primary and secondary sex traits. The social context of sneaker males was manipulated to induce a tactic switch. Sneakers were kept under two different experimental treatments with or without a female, and under exclusion of male-male competition. Males changed tactics, courting females, spawning, and performing parental care. All males showed substantial changes in primary sexual traits, such as a reduction in gonadal development and an increase in the investment in accessory structures. The experimental groups differed in the functionality of gonads and accessory organs and in the development of the secondary sex traits. These results demonstrate that the moment of switching is not genetically fixed in the black goby. Sneaker males are able to quickly reallocate energy in primary and secondary sex traits, in accordance with the adopted tactic. Several aspects of this flexible reproductive pattern resemble the socially controlled sex change found in sequential hermaphrodites.     

Mating system in a small pelagic spawner: field case study of the mandarinfish,Synchiropus splendidus

Environmental Biology of Fishes - Mating systems in fishes are extremely diverse, ranging from monogamy to multiple polygamous forms, some of which include alternative male mating tactics within...     

Ejaculate traits in relation to male body size in the eastern mosquitofish Gambusia holbrooki

In the present study, the correlation between sperm number, sperm quality (speed, viability, longevity and length), sperm bundles quality (size and dissolving rate) and male body size has been tested in the eastern mosquitofish Gambusia holbrooki a poecilid species characterized by coercive mating tactics where males do not possess obvious ornaments, and the body size is the key determinant of pre‐copulatory male mating success. The results do not tally with theoretical predictions. Indeed, no correlation between male body size and either sperm or sperm‐bundle traits has been found, evidencing the lack of the theoretically expected trade‐off between the investment in characters involved in mate acquisition and the investment in ejaculate quality. An explanation for the observed pattern comes from the extremely dynamic mating system of G. holbrooki, characterized by variable size‐related male mating success and strong post‐copulatory selective pressure, with all males facing a similar high level of sperm competition. In this situation, a higher investment in growth and maintenance at the expense of ejaculate quality is not expected. These results underscore the necessity to comprehend detailed information on species’ reproductive biology and reproductive environment to understand both the evolution of ejaculate characteristics and possible deviations from theoretical predictions.     

Ultrastructure and histochemistry of the testicular efferent duct system and spermiogenesis in Opistognathus whitehurstii (Teleostei, Trachinoidei)

 Testis organization and spermatogenesis, with the emphasis on spermiogenesis, in Opistognathus whitehurstii are described by ultrastructural and histochemical methods. The germinal epithelium is extremely reduced and restricted to the periphery of the testis, while most of the organ is occupied by a highly developed system of testicular efferent ducts. A semicystic type of spermatogenesis is observed and in the germinal epithelium spermatogenesis occurs only until the spermatidal stage. Young spermatids are released into the lumen of the testicular lobules and mature to sperm within the efferent duct system. The epithelial cells of these ducts are involved in protein and glycogen secretion and in phagocytosis of degenerating germ cells and residual bodies cast off by developing spermatids. On the basis of these functions, the testicular efferent duct system cells are considered to be homologous to the Sertoli cells. A correlation between a highly developed testicular efferent duct system and semicystic spermatogenesis is examined and a possible functional meaning of this apparently unusual mode of sperm production is proposed. Accepted: 18 March 1997     

Variation of male reproductive apparatus in relation to fertilization modalities in the catfish families Auchenipteridae and Callichthyidae (Teleostei: Siluriformes)

To investigate the relationship between fertilization modalities and the morphology of male reproductive apparatus, two species of Auchenipteridae, Auchenipterus nuchalis and Tatia intermedia , and six species of Callichthyidae, Callichthys callichthys , Corydoras aeneus , Corydoras bondi , Corydoras ehrhardti , Corydoras potaroensis and Hoplosternum littorale were studied. The species analysed show either internal or external fertilization, the latter including the so called 'sperm drinking' type of mating. An anal fin modified as an intromittent organ, a pair of seminal vesicles, and the release of sperm in the form of discrete bundles (spermatozeugmata) characterize the male reproductive apparatus of the internal fertilizer A. nuchalis . Seminal vesicles are present also in C. aeneus , C. bondi , C. ehrhardti , C. potaroensis and H. littorale , species performing 'sperm drinking' spawning. In contrast, regardless of the family, species showing the more classic type of external fertilization lack specialized accessory organs. Where occurring, the major function of seminal vesicles is the secretion of mucins. The role of these mucosubstances, in relation to spermatozeugmata formation, in internal fertilizers, or the protection of sperm passing through the female gut, in the 'sperm-drinking' species, is discussed. Variation, between families, in the shape of testis and accessory structures, as well as in the type of spermatogenesis was found. Neither the reproductive modalities nor the phylogenetic relationships, however, appear to fully account for these differences.     

Unexpected female preference for smaller males in the marbled goby Pomatoschistus marmoratus

The study tested the role of body size and of nest size in female mate choice in the marbled goby, Pomatoschistus marmoratus. The results show a female preference for smaller males, supporting the idea that smaller males may be preferred to larger ones in the absence of male–male competition. No effect of nest size was detected, suggesting that other nest characteristics, beyond nest size, may be implicated.     

An insight into the reproductive biology of the bearded goby Sufflogobius bibarbatus

Preliminary results obtained from histological analyses of the male reproductive organs, supplemented with field and behavioural data, indicate that Sufflogobius bibarbatus, a small, slow growing gobiid exhibiting low fecundity, which plays an important role in the food web off Namibia, where large areas of the shelf are hypoxic, spawns demersally. Large males defend benthic nests, possibly at the edge of the hypoxic shelf. Male reproductive strategy appears to be flexible, and tentative evidence to suggest that polygyny and sneaking may also occur is presented.