Ejaculate of sneaker males is pheromonally inconspicuous in the black goby,Gobius niger (Teleostei,Gobiidae)

The black goby, Gobius niger, shows alternative male mating tactics, i.e., parental and sneaker males. Males release a sexual pheromone that attracts females and stimulates aggressive displays in males. This pheromone is produced by the mesorchial gland, a structure well developed in parental males but markedly undeveloped in sneakers. We measured the behavioral response of parental males to the ejaculates of males performing different reproductive tactics. Parental males reacted to the ejaculate of other parental males, with stereotypic aggressive behaviors, but not to the ejaculate of sneakers; consequently sneaker male ejaculate appears to be pheromonally inconspicuous.     

Sperm investment and alternative mating tactics in bluegill sunfish (Lepomis macrochirus)

Although alternative mating tactics are found in males of manyspecies, little is known about tactic-specific adaptations tosperm competition and the mechanism by which fertilization successis obtained. We now report on the sperm investment patternsof males that use alternative mating tactics in bluegill sunfish(Lepomis macrochirus). Bluegill males are characterized by threealternative mating tactics: parentals, sneakers, and satellites.Parentals delay maturation and adopt a courting and guardingtactic, whereas sneakers and satellites mature precociouslyand, respectively, use sneaking and female mimicry to stealfertilizations from parentals. We found differences among thetactics in testes weight, sperm longevity, and ejaculate spermdensity and competitiveness. Parentals had the largest testes,but the smallest relative to their body weight. Satellites hadintermediate-sized testes, and sneakers had the smallest testes,but the largest relative to their body weight. Within each tactic,there was a positive relationship between testes weight andbody weight, but the exact relationship differed among the tacticsand could not be attributed solely to allometry. Parentals hadlonger-lived sperm compared with that of both sneakers and satellites.Ejaculate sperm density was greatest in sneakers, satelliteswere intermediate, and parentals had the lowest. Competitionexperiments involving equal volumes of ejaculate showed thatfertilization success increased linearly with sperm number,consistent with a rafflelike process. However, independent ofsperm number, parental sperm were superior at fertilizing eggs.We interpret these sperm investment patterns in relation todifferences in sperm competition risk, number of mating opportunities,and alternative investment options.     

Changes along the male reproductive axis in response to social context in a gonochoristic gobiid, Zosterisessor ophiocephalus (Teleostei, Gobiidae), with alternative mating tactics

Sexual selection has given rise, in several taxa, to intrasexual variation in male phenotype. While evolutionary studies have provided explanations of the adaptive function of this dramatic male phenotypic diversity, the proximate control of its expression has still to be completely understood. Several observations, primarily from sex-changing species, indicated a major role of social interactions in reproductive axis regulation and consequently in the expression of alternative male phenotypes. Here we documented changes along the male reproductive axis in response to social context in a gonochoristic species, the grass goby Zosterisessor ophiocephalus, where fully functional alternative male mating tactics appear to be expressed as an ontogenetic gradient. In the grass goby, larger and older males dig a nest and perform parental care, while smaller males sneak fertilization during territorial male spawning. Territorial males are characterized by a higher number of gonadotropin-releasing hormone (GnRH) neurons in forebrain preoptic area, smaller testes, larger seminal vesicles, and viscous ejaculates that last longer and contain fewer sperm than those of sneakers. To experimentally investigate the role of social factors in inducing changes along the male reproductive axis, sneakers were tested in two different situations: nesting alone or with ripe females. Sneakers that mated and performed parental care showed dramatic changes in brain, reproductive apparatus morphology, and ejaculate traits. GnRH-immunoreactive cells in forebrain preoptic area increased in number, reaching values typical of wild-caught parental males. Testes size decreased while seminal vesicle size increased and ejaculates showed lower sperm densities. These results were discussed within the framework of the social transduction hypothesis, which predicts that social experience should mediate, through a cascade of internal processes, shifts between morphs throughout life.     

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.     

Black goby territorial males adjust their ejaculate's characteristics in response to the presence of sneakers

In many species, males can rapidly adjust their ejaculate performance in response to changing levels of sperm competition, an ability that is probably mediated by seminal fluid adaptive plasticity. In the black goby, Gobius niger, territorial males attach viscous ejaculate trails to the nest roof, from which sperm are slowly released into the water during the long-lasting spawning events. Sneaker males release their sperm in the vicinity of the nest, and territorial males try to keep them at a distance by patrolling their territory. We show here that territorial males'' ejaculate trails released a higher proportion of their sperm in the presence of a single sneaker, but this proportion decreased when there were three sneakers, an effect that is most likely mediated by a change in the seminal fluid composition. Field observations showed that when multiple sneaking attempts occurred, territorial males spent more time outside the nest, suggesting that ejaculation rate and territory defence are traded-off. Altogether, these results suggest that the adjustment of sperm release from the ejaculate may be strategic, guaranteeing a more continuous concentration of the territorial male''s sperm in the nest, although at a lower level, when he is engaged in prolonged territory defence outside the nest.     

Reproductive morphology in relation to alternative male reproductive tactics in Scartella cristata

The relationship between reproductive morphology and reproductive tactics was examined in Scartella cristata , a combtooth blenny, which exhibits three behaviourally distinct mature male types: nesters, big males that care for eggs; hole-dwellers, medium-sized, non-reproducing males that are site-attached to a hole; sneakers, small, vagrant males that release sperm in the nests of the big males. The anal fin gland was a densely folded, mucous-secreting structure probably involved in pheromone synthesis. It was relatively larger in nesters than hole-dwellers, and altogether rudimentary in sneakers. Sneakers invested more in sperm production than nesters or hole-dwellers, suggesting adaptation to sperm competition. Approximately half of the testes of nesters and hole-dwellers was comprised of a highly developed efferent duct system or 'testicular gland', but this was extremely reduced in sneakers. In nesters the gland was characterized by many large vacuoles. A pair of secretory blind pouches was present in nesters and hole-dwellers, but barely visible in sneakers. In nesters, the sperm duct walls were thickened and highly secretory containing sperm dispersed in a granular matrix. In sneakers they were thin-walled and packed with concentrated sperm. Such differences probably represent different priorities for sperm production in relation to sperm competition and sperm economy. Thus it appears the accessory structures are traits developed specifically for a nesting tactic, whereas the gonad of sneakers is simply organized to produce as much sperm as possible.     

Investment in testes,sperm‐duct glands and lipid reserves differs between male morphs but not between early and late breeding season in Pomatoschistus minutus

This study of the sand goby Pomatoschistus minutus, a nest‐holding fish with paternal care, focused on gonadal investment among males of different sizes collected early and late in the breeding season. All males caught at the nest had breeding colour, whereas trawl‐caught fish consisted of males both with and without colour. The absence or presence of breeding colour was a good predictor of testes investment. Compared to males with breeding colour, males without colour were smaller in body size but had extraordinarily large testes. In absolute terms, testes mass of males without breeding colour was on average 3·4 times greater than those of males with breeding colour. Since small colourless males are known to reproduce as sneaker males, this heavy investment in testes probably reflects that they are forced to spawn under sperm competition. Contrary to testes size, sperm‐duct glands were largest among males with breeding colour. These glands produce mucins used for making sperm‐containing mucous trails that males place in the nest before and during spawning. Since both sneakers and nest‐holders potentially could benefit from having large glands, this result is intriguing. Yet, high mucus production may be more important for nest‐holders, because it also protects developing embryos from infections. There was no significant effect of season on body size, testes or sperm‐duct glands size, but colourless males tended to be less common late in the season. Possibly this may indicate that individual small colourless males develop into their more colourful counterparts within the breeding season.     

Territorial male gobies respond aggressively to sneakers but do not adjust their sperm expenditure

We investigated whether mating behavior (sperm expenditure,courtship rate, and nest guarding) varied according to differentlevels of sperm competition in territorial males of two gobyspecies, the grass and the black gobies. We measured sperm expenditure(sperm released after 30 min from the beginning of the spawning),male courtship rate, and nest-guarding behavior in territorialmales of both species during simulated spawnings, in which wevaried the number of attending sneakers. Our results showedthat, in both species, territorial males adjusted their effortin nest guarding to the presence of rival sneakers by increasingthe time spent patrolling the territory and attacking the sneakers.In contrast, sperm expenditure and male courtship rate werenot influenced by the number of attending sneakers. These resultsare in agreement with those reported for other fish with alternativemating tactics and help to interpret previous inconsistenciesbetween theoretical predictions and measured levels of spermreleased at different levels of sperm competition by sneakersof the two gobiids studied here.     

Anatomy and histology of the male reproductive system of the fire ant,Solenopsis invicta Buren (Hymenoptera : Formicidae)

The male reproductive system of the fire ant, Solenopsis invicta Buren (Hymenoptera : Formicidae), consists of the testes, vasa efferentia, vasa deferentia, seminal vesicles, accessory glands, ejaculatory duct, wedge, aedeagal bladder, and external genitalia. The testes in newly eclosed males appear as 4 large white lobes filled with packets of sperm. Each lobe of the testes contains only one follicle. As the testes degenerate, the maturing sperm migrate through the vasa efferentia and vasa deferentia into the seminal vesicles. The seminal vesicles attach to the accessory glands, which are lined with secretory columnar epithelium. The posterior ends of the accessory glands taper and unite to form the ejaculatory duct. A sclerotized wedge is found at the junction of the accessory glands and the ejaculatory duct. An aedeagal bladder, joining the ejaculatory duct posterior to the wedge, is lined with squamous epithelium enveloped by heavy musculature. The ejaculatory duct continues posteriorly to form a distal aedeagus surrounded by 3 pairs of valves, comprising the external genitalia.     

On the mechanism of sperm release in three gobiid fishes (Teleostei: Gobiidae)

Synopsis In fish, gamete release is commonly assumed to be synchronous in externally inseminating fishes. By collecting and counting the number of sperm and eggs released during separate matings in three demersal spawners, the mediterranean gobies, Zosterisessor ophiocephalus, Gobius niger, and Knipowitschia panizzae, we observed that gametes are released asynchronously. Males release sperm before females start laying their eggs. Sperm is released in the form of sperm trails laid on the nest surface; subsequently active spermatozoa leave the trails and move in the water for several minutes. Sperm trails consist of bands of viscous material in which sperm is embedded. In most cases eggs are not laid directly over the sperm trail, suggesting that sperm may contact the eggs after the latter are released in the water. Male sperm duct glands, seminal vesicles, known to secrete mucosubstances, are likely involved in the production of sperm trails. The possible influence of this mode of insemination on the mating style of marine gobies is discussed.     

Variations of sperm release in three batches of zebrafish

By collecting and counting the number of sperm released during separate matings in three batches of zebrafish Danio rerio , aged 3–4, 4–5 and 5–6 months, males were observed to release sperm before the female started laying their eggs. After the female left the nest, the number and motility of sperm and life span of sperm of younger fish were higher than those of older fish in water samples collected under the nest and at the surface of the tank. Sperm were released in the form of sperm trails laid on the nest surface, subsequently active spermatozoa left the trails and moved in the water for several minutes. Sperm trails consisted of bands of viscous material in which the sperm were embedded. In most cases eggs were not laid directly over the sperm trail, suggesting that sperm may contact the eggs after the latter are released into the water. In all the three tested groups there was no significant difference ( P  > 0·05) between the number of sperm collected on some portions of the acetate sheets which lined the nest ceiling. This result demonstrated that the greater activity of younger fish accelerated the sperm dispersal in water. Male sperm duct glands, seminal vesicles, known to secrete mucosubstances are probably involved in the production of sperm trails. The possible influence of insemination on the mating style of zebrafish is discussed.     

Reproductive-tactic-specific variation in sperm swimming speeds in a shell-brooding cichlid

Theory predicts that males experiencing elevated levels of sperm competition will invest more in gonads and produce faster-swimming sperm. Although there is ample evidence in support of the first prediction, few studies have examined sperm swimming speed in relation to sperm competition. In this study, we tested these predictions from sperm competition theory by examining sperm characteristics in Telmatochromis vittatus, a small shell-brooding cichlid fish endemic to Lake Tanganyika. Males exhibit four different reproductive tactics: pirate, territorial, satellite, and sneaker. Pirate males temporarily displace all other competing males from a shell nest, whereas sneaker males always release sperm in the presence of territorial and satellite males. Due to the fact that sneakers spawn in the presence of another male, sneakers face the highest levels of sperm competition and pirates the lowest, whereas satellites and territorials experience intermediate levels. In accordance with predictions, sperm from sneakers swam faster than sperm from males adopting the other reproductive tactics, whereas sperm from pirates was slowest. Interestingly, we were unable to detect any variation in sperm tail length among these reproductive tactics. Thus, sperm competition appears to have influenced sperm energetics in this species without having any influence on sperm size.     

Sperm maturation and male tactic-specific differences in ejaculates in the plainfin midshipman fish Porichthys notatus

Using the plainfin midshipman fish Porichthys notatus, a species with alternative reproductive tactics (ARTs), we investigated how sperm maturation shapes sperm competitive abilities. We compared sperm performance and morphology before and after final sperm maturation by sampling sperm from the testes and stripped ejaculates of guarders and sneakers. In accordance with sperm competition risk theory, ejaculates from sneaker males had three times as much sperm as ejaculates from guarder males and sneaker males produced faster swimming sperm than guarder males, but this was only the case after final sperm maturation had occurred. Additionally, fully mature sperm found in ejaculates had larger heads and midpieces than sperm found in the testes. These results emphasize the important role played by non-sperm components of an ejaculate in mediating sperm performance and potentially also morphology.     

Sperm release behaviour and fertilization in the grass goby

Nesting males of the grass goby Zosterisessor ophiocephalus showed bouts, with intervals of c. 30 min duration, of upside-down movements while rubbing its genital papilla onto the ceiling of its burrow. Such behaviour was shown during female courting and spawning, and even after female removal. Observations showed that this behaviour was associated with the release of a sperm trail on the substratum and clumped spermatozoa in water, agglutinated with a mercury-bromophenol blue and PAS positive glycoprotein secretion of the sperm duct glands. Agglutination in the secretion delayed the activation of spermatozoa and contributed a steady supply, for up to 40 min, of motile spermatozoa during prolonged egg laying by the female. Sperm released before egg laying achieved c. 50% fertilization success compared with nearly 100% obtained if the sperm was released during egg laying. The sperm release behaviour may improve the nest owner's reproductive success against intruders or sneakers. It also allows defence of the nest while the female is spawning and may allow the male to court other females in the proximity.     

Androgens and Immune Function in Male Alternative Reproductive Morphotypes of the Peacock Blenny Salaria pavo

Species with alternative reproductive tactics offer the opportunity to analyse how behavioural and morphological traits are tuned to produce successfully competing phenotypes within one sex. In the teleost fish Salaria pavo , alternative reproductive tactics are sequential. The older ornamented males compete for access to females by guarding a cavity to which they attract females to spawn. Ornamented males that are found without a nest are called 'floaters'. Younger mature males which are too small to compete with nest-holders attempt to 'sneak' as female mimics into successful nests and release their sperm to fertilize freshly spawned eggs. The alternative tactics in S. pavo are associated with different levels of the androgens testosterone and 11-ketotestosterone, which have been found to suppress immune function in several teleost fish. A field study was carried out to analyse the relationship between these reproductive tactics, androgens and blood levels of lymphocytes as a monitoring method of immune function. We expected highest investment in the immune system in sneakers because these have the lowest androgen levels and functionally because investing in self-maintenance increases their future prospect to switch tactic and to reproduce as a nest-holder. Indeed, the relative count of lymphocytes correlated negatively with body size and thus was highest in sneakers and lowest in nest-holders. In concordance, 11-ketotestosterone and testosterone levels were found to be higher in floaters and nest-holders than in sneakers. However, no correlation was found between individual levels of testosterone or 11-ketotestosterone and lymphocytes. Thus, a trade-off between reproductive traits associated with high androgen levels and immunocompetence might exist at the level of alternative tactics but this might not be explained by acute immunosuppressive effects of circulating androgens.     

Mating senescence and male reproductive organ size in the Mexican fruit fly

Ageing can reduce the probability that individuals reproduce. The present study investigates whether ageing influences the mating frequency of mass‐reared fertile and sterile Mexican fruit flies Anastrepha ludens (Loew). The ability of males of different ages to inhibit female remating is also determined, and the growth of male reproductive organs is measured as they age. Young males (6 days old) have a lower mating frequency than older males, and also have a lower capacity to inhibit female remating than older males. However, 7‐day‐old males are as likely to inhibit female remating as older males. Young males also have smaller reproductive organs than middle‐aged (21‐day‐old) or senescent males (57‐day‐old). These results have implications for the sterile insect technique because sterilized males of A. ludens are released in the field 6 days after emergence. The highest mating frequency, the lowest mating latency and the largest size of testes are observed at 21 days of age. Older males (57 days old) have more sperm in their seminal vesicles than young males (6 and 9 days old). Accessory glands take longer to grow to their complete size compared with testes, and mating frequency is more closely associated with accessory gland size than testes size. Furthermore, there are more sperm in the seminal vesicles during the afternoon period of peak sexual activity than during the morning when sexual activity is absent. These results indicate that, even at the onset of reproductive senescence, mass‐reared males of A. ludens are still capable of mating, as well as inhibiting remating in females.     

Ultrastructure and function of the seminal vesicle of Bittacidae (Insecta: Mecoptera)

The fine structure of the seminal vesicle and reproductive accessory glands was investigated in Bittacidae of Mecoptera using light and transmission electron microscopy. The male reproductive system of Bittacidae mainly consists of a pair of testes, a pair of vasa deferentia, and an ejaculatory sac. The vas deferens is greatly expanded for its middle and medio-posterior parts to form a well-developed seminal vesicle. The seminal vesicle is composed of layers of developed muscles and a mono-layered epithelium surrounding the small central lumen. The epithelium is rich in rough endoplasmic reticulum and mitochondria, and secretes vesicles and granules into the central lumen by merocrine mechanisms. A pair of elongate mesodermal accessory glands opens into the lateral side of the seminal vesicles. The accessory glands are similar to the seminal vesicle in structure, also consisting of layers of muscle fibres and a mono-layered elongated epithelium, the cells of which contain numerous cisterns of rough endoplasmic reticulum and mitochondria, and a few Golgi complexes. The epithelial cells of accessory glands extrude secretions via apocrine and merocrine processes. The seminal vesicles mainly serve the function of secretion rather than temporarily storing spermatozoa. The sperm instead are temporarily stored in the epididymis, the greatly coiled distal portion of the vas deferens.     

Morphology of the male system and spermatophores of the arrowworm Ferosagitta hispida (Chaetognatha)

Transmission electron microscopy reveals that the somatic testicular tissues and sperm ducts are elaborations of the epithelial lining of the tail coelom. The testes consist of closely packed spermatogonia embedded between specialized lateral field cells. These cells contain few organelles and appear to function mainly as a compartment boundary. Masses of spermatogenic cells are released into the tail coelom from the anterior end of the testes. The sperm ducts, lined by simple cuboidal ciliated epithelium, collect mature spermatozoa from the tail coelom and convey them to the blindly ending seminal vesicles. The sperm ducts also modify coelomic fluid entering them along with the spermatozoa. The seminal vesicles consist of a simple glandular lining epithelium embedded in the stratified epidermis. Secretions of the lining epithelium surround the enclosed sperm mass and correspond in position to a noncellular spermatophore coat visible by light microscopy around released sperm masses. Spermatophores leave the seminal vesicles through a temporary split that forms between microfilament-containing suture cells. Maturation of spermatozoa and filling of the seminal vesicles is cyclical, occurring late each day. © 1994 Wiley-Liss, Inc.     

Sexual selection affects the sizes of the mammalian prostate gland and seminal vesicles

The accessory reproductive glands of male mammals contribute the bulk of the secretions in which spermatozoa are transported to the female tract during copulation. Despite their morphological diversity,and the chemical complexity of their products,little is known about the possible effects of sexual selection upon these glands in mammals. Here we consider the seminal vesicles and prostate glands in a sample of 89 species and 60 genera representing 8 Orders of mammals. The sizes of the accessory glands are analysed in relation to body weight and testes weight. Both the seminal vesicles size and prostate size (corrected for body weight) correlate positively with relative testes size in this sample; this finding remains highly significant after application of procedures to correct for possible phylogenetic biases in the data set. The accessory reproductive glands are also significantly larger in those mammals which have large relative testes sizes,and in which the likelihood of sperm competition is greatest. These results support the hypothesis that sexual selection has played an important role in the evolution of the mammalian prostate gland and seminal vesicles.