Body Size Correlates with Fertilization Success but not Gonad Size in Grass Goby Territorial Males

In fish species with alternative male mating tactics, sperm competition typically occurs when small males that are unsuccessful in direct contests steal fertilization opportunities from large dominant males. In the grass goby Zosterisessor ophiocephalus, large territorial males defend and court females from nest sites, while small sneaker males obtain matings by sneaking into nests. Parentage assignment of 688 eggs from 8 different nests sampled in the 2003–2004 breeding season revealed a high level of sperm competition. Fertilization success of territorial males was very high but in all nests sneakers also contributed to the progeny. In territorial males, fertilization success correlated positively with male body size. Gonadal investment was explored in a sample of 126 grass gobies collected during the period 1995–1996 in the same area (61 territorial males and 65 sneakers). Correlation between body weight and testis weight was positive and significant for sneaker males, while correlation was virtually equal to zero in territorial males. That body size in territorial males is correlated with fertilization success but not gonad size suggests that males allocate much more energy into growth and relatively little into sperm production once the needed size to become territorial is attained. The increased paternity of larger territorial males might be due to a more effective defense of the nest in comparison with smaller territorial males.     

Tactic changes in dusky frillgoby Bathygobius fuscus sneaker males: effects of body size and nest availability

Field and laboratory studies were conducted to examine the effects of nest availability and body size on changes in male mating tactics from sneaking to nest‐holding in the dusky frillgoby Bathygobius fuscus. In the field, the body size of nest‐holding males decreased from early to mid‐breeding season, suggesting the possibility of a change in the tactics of sneaker males to nest‐holding. Many sneaker males did not use vacant spawning nests even when size‐matched nests were available, but they continued to reproduce as sneakers. Similarly, in aquarium experiments with available vacant nests, some sneaker males became nest‐holders irrespective of their body size, but some did not. These results showed that nest availability is not a limiting factor for changes in tactics by sneaker males in this species. Because tactic‐unchanged sneaker males were co‐housed with larger nest‐holding males in the tanks, the body size of nearby nest‐holding males may have affected the decision to change tactics for sneaker males. Moreover, smaller individuals among tactic‐changed males tended to spend more time until spawning, probably because they had relatively larger costs and smaller benefits of reproduction as nest‐holding males compared to larger males.     

The importance of sperm competition risk and nest appearance for male behavior and female choice in the sand goby, Pomatoschistus minutus

To test if an increased sperm competition risk affects malebehavior and mating decisions of both sexes, we performed twoexperiments using the sand goby, Pomatoschistus minutus, a nest-buildingfish with exclusive paternal care. In our first experiment,a nest-holding male, with a confined female, was sequentiallyexposed to a vial with a sneaker male or an empty vial. Whilemale courtship, nest building, displacement fanning, and timeoutside the nest were unaffected, individual males showed ahigher mucus preparation effort inside the nest in the presenceof a sneaker male than when alone. We found such mucus to containsperm, thus clearly suggesting an importance in sperm competition.In our second experiment, a female was free to spawn with twodifferent males, one of which was exposed to a confined sneakermale. Male mating success was not affected by the presence ofa sneaker male. However, the volume of sand the male had puton his nest was positively associated with female spawning decision,while nest-opening width was not. In a partial correlation offive traits thought to attract females (nest-opening width,sand volume, male courtship display, displacement fanning, andmale size), males that fanned well were found to also buildlarge nests or display intensely, but not both. This indicatesthat rather than being jacks-of-all-trades, individual malesfocus on a subset of traits for attracting females.     

Pre-oviposition Ejaculation in Externally Fertilizing Fish: How Sneaker Male Rose Bitterlings Contrive to Mate

Pre-oviposition ejaculation as a mating tactic of sneaker males in the rose bitterling, Rhodeus ocellatus, was studied under natural and artificial conditions. In a small pond in Yao city, Osaka, Japan, the operational sex ratio of males and females was found to be approximately 3.5:1 and the proportion of males to the mussels, which serve as spawning beds for the rose bitterling, was approximately 2:1. Competitively subordinate rose bitterling males which spawned into the mussels participated in mating by sneaking, because not all males could occupy territories around the mussels. The sneaker males often released sperm not only after but also before egg-laying (this ejaculation movement by the male before egg-laying is termed ‘pre-oviposition ejaculation’). In pair spawning with sneaker, the sneakers frequently performed pre-oviposition ejaculations, which territorial males never performed. In the field, pre-oviposition ejaculations by sneakers coincided with the leading of females by territorial males. Under artificial conditions, I demonstrated by using electrophoretic paternal analyses that the pre-oviposition ejaculations by the sneakers were more effective than the post-oviposition ejaculations by the territorial males. In addition, there were negative size-dependences in ejaculation achievement rate and fertilization success of the sneaker males.     

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.     

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.     

Sexually selected nest-building--Pomatoschistus minutus males build smaller nest-openings in the presence of sneaker males

Both natural selection and sexual selection may act on nest-building. We tested experimentally how different regimes of egg-predation and male-male competition influence nest-building before mating, using the marine fish sand goby, Pomatoschistus minutus. Males with sneaker males present built the smallest nest-openings, smaller than males held alone or with Pomatoschistus microps males (which may predate eggs and compete over nest-sites but not compete over fertilizations). Males with visual access to other nest-building males tended also to build smaller openings than males held alone or with P. microps. Males with egg-predators present built nests with openings not differing significantly from any other treatment. Our results indicate that the small nest-openings found in the sneaker male treatment are sexually selected through protection against sneaking or by female choice. Across treatments, time span before a male started to build his nest also explained variation in nest-opening width; males starting late built larger nest-openings.     

Male traits associated with alternative reproductive tactics in Gobius niger

Male black goby Gobius niger , adopting parental or sneaking tactics, differed in secondary sex traits (elongation of the 4th ray of the first dorsal fin and black nuptial colouration) thus allowing the classification of wild-caught males. Parental males were larger and older than sneaker males, suggesting that the mating tactic is an expression of an ontogenetic gradient. Males adopting alternative tactics differed also in primary sex traits, including their testes and their two pairs of accessory structures: the seminal vesicles and mesorchial glands. Sneaker males had a higher investment in testes, while parental males showed larger seminal vesicles and more developed mesorchial glands. Histological analyses also showed that seminal vesicles from parental males presented some functional differences from those of sneakers. In the former these organs were devoted solely to mucin secretion, while in the latter they stored sperm and had a lower activity of secretion. Seminal vesicle features influenced ejaculate (sperm trail) characteristics and performance. Parental male trails were richer in mucins, but poorer in sperm than trails deposited by sneakers. As a consequence, while sneakers produced trails that released a large amount of immediately active sperm, trails laid by parental males released less sperm more constantly over a long time.     

Alternative reproductive tactics and courtship in the common goby

In the marine common goby Pomatoschistus microps , males either build nests and attract females to spawn or act as sneakers, forcing themselves into other males' nests during mating, to fertilize some of the eggs in the clutch. The reproductive tactics of small males were studied in the presence of surplus nest material and an excess of gravid females, while a larger, nestholding male spawned with a female. Of 24 small males, 13 only attempted to sneak, seven only courted females and/or spawned in their own nest, and four performed both behaviours. The small males who attracted females successfully were significantly larger than the ones who failed to do so. Females had been courting the small male more often when he subsequently spawned in his own nest, than when he did not get a female. The small males did not court the females very frequently, and their courtship rate did not depend on whether or not they attracted females. Instead, female courtship behaviour may be a cue for a male either to spawn as a nest holder or become a sneaker. The study pointed out the importance of female behaviour for male reproductive tactics, which could be more important in fish than is known currently.     

Parasitic spawning in sand gobies: an experimental assessment of nest-opening size, sneaker male cues, paternity, and filial cannibalism

Sneaking is common in nest-building fish with paternal care,but the role of nest-opening size in protecting against entryby sneaker males has never been tested before. Using the sandgoby (Pomatoschistus minutus), a fish with exclusive paternalcare, experimental manipulations of nest openings provided nosupport for the hypothesis that nest openings serve as physicalor visual defense or that sneaker males prefer to parasitizenests with wide openings. Female mating preference was alsonot influenced by nest-opening size. However, female courtshipbehavior and visibility were important cues for sneaker males.Most sneak entries occurred when the nest holder was occupiedwith courtship, chasing another sneaker male or nest building.In half the cases of observed sneak entry, the sneaker malefertilized eggs, also when sneaking only occurred before spawning.Sneak entry and its duration were good estimates of stolen paternity,but neither sneak entries nor degree of fertilizations werecorrelated with filial cannibalistic behavior. Testes size didnot explain parasitic spawning success in replicates with geneticallydetermined sneaking. However, all sneaker males without breedingcoloration had huge testes and small sperm duct glands, whereasnest-holding males had small testes and large sperm duct glands,and sneaker males with breeding coloration were intermediate.     

Seasonal variation in male alternative reproductive tactics

Genetic parentage analyses reveal considerable diversity in alternative reproductive behaviours (e.g. sneaking) in many taxa. However, little is known about whether these behaviours vary seasonally and between populations. Here, we investigate seasonal variation in male reproductive behaviours in a population of two‐spotted gobies (Gobiusculus flavescens) in Norway. Male two‐spotted gobies guard nests, attract females and care for fertilized eggs. We collected clutches and nest‐guarding males early and late in the breeding season in artificial nests and used microsatellite markers to reconstruct parentage from a subset of offspring from each nest. We hypothesized that mating, reproductive success and sneaking should be more prevalent early in the breeding season when competition for mates among males is predicted to be higher. However, parentage analyses revealed similar values of mating, reproductive success and high frequencies of successful sneaking early (30% of nests) and late (27% of nests) in the season. We also found that multiple females with eggs in the same nest were fertilized by one or more sneaker males, indicating that some males in this population engage in a satellite strategy. We contrast our results to previous work that demonstrates low levels of cuckoldry in a population in Sweden. Our results demonstrate marked stability in both the genetic mating system and male alternative reproductive tactics over the breeding season. However, sneaking rates may vary geographically within a species, likely due to local selection influencing ecological factors encountered at different locations.     

Reproductive behaviour of sneaker males of the peacock blenny

In the peacock blenny Salaria pavo small sneaker males tried to steal 'fertilizations' at most in two different nests of large nesting males throughout the breeding season and spent most of their time associated with a particular nest. Sneakers did not associate with ripe females. As nesting males were the limiting reproductive resource in this population due to the scarcity of appropriate nest sites, sneakers were likely to maximize their chances of achieving parasitic fertilization of eggs by associating with successful nests.     

Melanin‐based coloration of sneaker male Atlantic salmon is linked to viability and emergence timing of their offspring

The ‘good genes’ hypothesis of sexual selection predicts that male ornaments are favoured by female mate choice because male ornament reveals genetic quality. In species with different male reproductive tactics, variation in genetic quality among ‘sneaking’ males has rarely been investigated, as usually ‘sneakers’ are thought not to be chosen by females. Here we focused on the alternative reproductive tactic in Atlantic salmon (Salmo salar Linnaeus, 1758) to test whether the skin colour of sneakers may reveal the performance traits of their offspring. A fully factorial breeding design was realized between 20 sneakers and two females using in vitro fertilization. We quantified the red and dark colorations of males and measured the survival of their progeny under semi‐natural conditions. In addition, the size of offspring and their emergence timing from the gravel nest were monitored in the laboratory. We found that darker males sired more viable offspring, whereas red coloration was negatively correlated with offspring survival. Nevertheless, darker and redder male pigmentations were linked to a delay in offspring emergence. These results demonstrate that colours can reveal individual genetic quality in an alternative male reproductive tactic, with male melanin‐based coloration being linked to both beneficial and detrimental effects for the offspring. Our results imply that sneaker ornaments may potentially play a role in both intra‐ and intersexual selection. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 126–135.     

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.     

Females solicit sneakers to improve fertilization success in the bitterling fish (Rhodeus sericeus)

In most species there is greater variance in reproductive fitness among males than females. A consequence is the evolution of alternative male mating tactics, including sneaking behaviour whereby males attempt to mate with females courted by other males, which could undermine female choice. In bitterling (Rhodeus sericeus), fish that lay their eggs on the gills of living freshwater mussels, sneaking is common and successful. Here we show that female bitterling can significantly improve their fertility with an increase in the number of spawning partners. Females perform conspicuous behaviours associated with spawning more frequently close to sneakers, and spawn more eggs close to high-quality sneakers. This is the first time that females have been shown to engage in behaviour that increases the probability of sneaking, and raises the possibility of a sexual conflict over the number and source of ejaculates during spawning in this species.     

Alternative male mating tactics in Gobius niger

In the field, parental males of the black goby Gobius niger were always >9 cm L _T, showed a conspicuous elongation of the first dorsal fin, and were darkly coloured. Larger parental males did not occupy larger nests or obtain more eggs, suggesting that over a threshold size reproductive success was not correlated with male size. The mating system was polygynous with different egg clutches simultaneously present in a nest. Smaller sexually mature males were observed around and inside nests in which spawning was occurring. These opportunistic males ranged in body size between 6 to 8 cm L _T. In contrast to parental males, they did not show an exaggeration of the first dorsal fin and were cryptically coloured, thus resembling small females in their external morphology. Aquarium experiments confirmed that smaller males perform a sneaking behaviour, releasing sperm when parental males spawn. As a consequence, it is possible to define three male types: type I are small, without an elongated dorsal fin and adopt a sneaking mating tactic; type III are large, have a pronounced elongation of the dorsal fin and perform parental behaviour; type II are intermediate both in size and elongation of the first dorsal fin and behave as either as sneakers or, possibly, as parental males according to nest availability and male competition.     

Bourgeois Males of the Peacock Blenny,Salaria pavo,Discriminate Female Mimics from Females?

In a Portuguese population of Salaria pavo, two types of reproductively active males occur: large bourgeois males that defend nests and have fully developed secondary sex characters (SSC) and small sneaker males that mimic the females’ morphology and behaviour to approach nests and parasitize fertilizations. These two alternative reproductive tactics are sequential, as sneakers develop into bourgeois males. We investigated whether bourgeois males were able to discriminate between sneakers and females of different sizes. In a laboratory experiment bourgeois males were sequentially presented with a female and a sneaker matched for size. Complementary field observations were conducted on the interactions between females and sneakers with bourgeois males. If bourgeois males discriminated females from sneakers, we predicted that they should direct more aggressive behaviours towards sneakers and more courtship acts towards females. In general, bourgeois males courted and attacked small females and sneakers equally. However, large sneakers were courted less and attacked more than large females. Larger sneakers, beginning to develop SSC, were attacked more and courted less by the bourgeois male than smaller sneakers, and larger females were attacked less and courted more than smaller females. These results strongly suggest that only small female‐mimicking males were able to deceive bourgeois males. In S. pavo, if the sneakers’ fertilization success correlates with their female‐mimicking ability, a fitness decrease with an increasing body size can be predicted.     

Alternative mating tactics of the gobiid fish <Emphasis Type="Italic">Bathygobius</Emphasis><Emphasis Type="Italic">fuscus</Emphasis>

The reproductive ecology of the gobiid fish Bathygobius fuscus was studied at Nobeoka, Miyazaki, Japan. Males of this species maintain small rock holes as a nest and females spawn an egg mass on the wall of the nest. The males employed two forms of mating tactic: nest holding and sneaking. A nest holder stayed in the nest and waited for a female to visit, whereas a sneaker intruded into a nest while a pair was engaged in reproduction. Males larger than 55 mm standard length were always nest holders; those of smaller size employed both tactics. As the larger males excluded the smaller males, the latter did not occupy a nest hole. With a decrease in the number of larger males, smaller males changed their mating tactic from sneaking to nest holding. The results suggest that male Bathygobius fuscus adopt a conditional strategy whereby they change their tactic depending on their social status. Electronic Publication     

A MICROSATELLITE ASSESSMENT OF SNEAKED FERTILIZATIONS AND EGG THIEVERY IN THE FIFTEENSPINE STICKLEBACK

Attempts by males to steal fertilizations from other males are common in many species. In some sticklebacks, males also are known to steal eggs from the nests of rivals and to carry them back to their own nests. However the genetic consequences of these nest-raiding behaviors seldom have been investigated. Here we assess genetically the prevalence of sneaked fertilizations and egg stealing, and we describe the mating system in a natural population of the fifteenspine stickleback. Six microsatellite markers were developed and employed to assay a total of 1307 embryos from 28 nests. Guardian males and all nest-holding males in the local area also were genotyped for two to six loci Analysis of male genotypes and those of embryos revealed that five of the 28 nests (18%) contained progeny from sneaked fertilizations, and that four of the 24 nests (17%) with resident males contained stolen egg clutches Comparisons of the composite DNA genotypes of nest-holding males against those of inferred sneakers implicated one nest holder as the sneaker of a nest seven meters from his own. Also, the genetic data demonstrated that nests of males frequently contain eggs from multiple females. The multilocus genotypes of inferred mothers indicated that females mate with multiple males, sometimes over distances greater than one kilometer.     

A trade-off generated by sexual conflict: Mediterranean wrasse males refuse present mates to increase future success

A variety of mechanisms, including intrasexual competition,intersexual conflict, and physiological constraints, can explainpatterns of reproduction and the adaptive value of specificbehaviors. In a Mediterranean wrasse, Symphodus ocellatus (Labridae),large, nesting males occasionally refuse to spawn with willingfemales in the presence of small, sneaker males. We exploredthe possible adaptive significance of this behavior. Nestingmales refuse females despite the fact that it reduces theirimmediate mating success. This nesting-male behavior also decreasesfemale and sneaker mating success and occurs when sneaker malessurround the nest. Experiments that decreased the number ofsneakers around nests showed that nesting males respond immediatelyto mating opportunities when fewer sneakers are present, andthus they are not simply constrained by a lack of energy orlack of sperm. Experiments that increased the number of sneakersat the nest caused nesting males initially to refuse spawningopportunities, followed by a subsequent decrease in sneakerpresence and an increase in mating rate. We propose that thisbehavior is the result of a trade-off between immediate matingsuccess and future reproduction created by competition betweenmales and conflict between the sexes. Males reduce their immediatemating success by reducing spawning at the nest; sneaker malessubsequently leave, and this decreases mate competition forthe nesting male. Unresponsiveness of nesting males also causessexual conflict between females and nesting males over mating.We argue that this behavior and the existence of a trade-offcan only be understood by examining intersexual conflict andintrasexual competition simultaneously.