The nest-holding grass goby (Zosterisessor ophiocephalus) male adjusts the spawning activity in relation to parasitic nest intrusions

This study examines the temporal pattern of spawning behavior by the territorial (i.e. nest-holding) grass goby male, Zosterisessor ophiocephalus, in response to sneak intrusions by the small parasitic male under controlled laboratory conditions. The spawning activity of the territorial male consists of a sequence of upside–down movements on the ceiling of the nest accompanied by undulations of the body and sperm release. Five pairs of one territorial male and one parasitic male, each kept inside a large tank provided with an artificial buried nest (always occupied by the territorial male) and one small tunnel-shaped shelter (always occupied by the small male), were observed during one-female spawning taking place in the innermost part of the nest (i.e. the nest chamber). During the spawning, the presence of the small male nearby the nest openings elicited aggressive behavior and increased nest patrolling by the territorial male. In one spawn the small male never attempted to enter the nest. In four spawns the small male entered one to three times the nest chamber (sneaks), staying there from 2 to 203 s until the large male chased him away. The temporal patterning of the spawning activity by the territorial male (bouts of upside–down, U–D), and its changes following a sneak by the small male, were investigated using bout analysis and correlative tests. Results showed the length of bouts U–D did not change significantly after a sneak intrusion. whereas gap length (i.e. the period between subsequent bouts U–D) decreased significantly after each sneak intrusion. The mean duty cycle of bouts U–D tended to be positively correlated to the number of sneaker intrusions of each replicate. Results are discussed in the light of current knowledge on sperm competition among externally fertilizing teleosts.     

Behaviour and success of sneaker males in the sand goby, Pomatoschistus minutus

In this study we investigated in laboratory conditions the presence of alternative reproductive tactics in the sand goby and describe proximate factors affecting their expression and success. We describe the reciprocal interactions of resident males, females, and sneaking males. The pre-spawning phase proved to be important for successful nest intrusions by sneakers. The number of sneakers had no effect on the frequency of successful intrusions. When small males had exclusive access to nest sites, they built a nest and courted females, showing a full behavioural repertoire. The intensity of courtship was, however, strongly positively correlated with body size. Using microsatellite DNA markers we assessed paternity shares of territorial and sneaker males in a subset of all replicates. Following successful nest intrusion sneaker males fertilised 5–10% of the eggs. Our interpretation of the results is that sneaking in the sand goby is a conditional tactic, one that is less successful than the normal nest guarding behaviour, at least for one spawning event. Received in revised form: 9 March 2001 Electronic Publication     

Determinants of male mating success in a natural population of a stream goby of the genus Rhinogobius

The mating success of individually identified males of a stream goby, Rhinogobius sp. CB (cross‐band type), was recorded over one breeding season. One to 3 year‐old males were active in mating, but 3 year‐old males, which accounted for 36% of the population, amounted to c . 70% of the total males guarding eggs in the nest. Three quarters of the breeding males had only one brooding cycle, but the others had two or three. All the latter males changed their nest sites between cycles within a riffle. In 1 and 2 year‐old males, the number of brooding cycles contributed more to the mating success than egg mass size in one brooding cycle. For mating success of 3 year‐old males, the egg mass size in one brooding cycle, which can be enhanced by spawning with a large female or multiple females, was as important as the number of brooding cycles. These male reproductive tactics could be attributed to the age‐related ability of nest construction and mate acquisition.     

Size-Dependent Male Alternative Reproductive Tactics in the Shell-Brooding Cichlid Fish Lamprologus callipterus in Lake Tanganyika

Reproductive parasitism among males is prevalent in fishes. Typically, small ripe males parasitize the reproductive effort of large bourgeois males by using various behavioural tactics. We examined the size‐dependent advantages of parasitic behavioural tactics in a shell‐brooding cichlid fish of Lake Tanganyika with three male types (large bourgeois males and medium–dwarf parasitic males). The extremely small ‘dwarf males’ weighing only 2.5% on average of large males, perform a specialized tactic in which they avoid attacks by the resident large males by entering the inner part of the whorl of the shell where a female is spawning. Field observations and a manipulation experiment revealed that the very small size of dwarf males is essential for utilizing this positional advantage. Larger dwarf males and medium males opportunistically adopt darting and sneaking which likely result in very low reproductive outcomes. The size associated advantage and disadvantage of parasitic tactics are the major factors shaping the size distribution of ripe males in this species. The success of parasitic spawning by dwarf males is determined not only by body size of the males, but also by the relative sizes of females and shells in which they spawn. These factors would affect the choice of different tactics among dwarf males. The analyses of body condition among ripe and unripe males across a wide range of body sizes suggested that onset of sexual activities at very small body sizes in dwarf males may be associated with higher condition factors that is a pre‐requisite for maintaining investment in testes and intense reproductive activities.     

Paternal inheritance of growth in fish pursuing alternative reproductive tactics

In species with indeterminate growth, age‐related size variation of reproductive competitors within each sex is often high. This selects for divergence in reproductive tactics of same‐sex competitors, particularly in males. Where alternative tactics are fixed for life, the causality of tactic choice is often unclear. In the African cichlid Lamprologus callipterus, large nest males collect and present empty snail shells to females that use these shells for egg deposition and brood care. Small dwarf males attempt to fertilize eggs by entering shells in which females are spawning. The bourgeois nest males exceed parasitic dwarf males in size by nearly two orders of magnitude, which is likely to result from greatly diverging growth patterns. Here, we ask whether growth patterns are heritable in this species, or whether and to which extent they are determined by environmental factors. Standardized breeding experiments using unrelated offspring and maternal half‐sibs revealed highly divergent growth patterns of male young sired by nest or dwarf males, whereas the growth of female offspring of both male types did not differ. As expected, food had a significant modifying effect on growth, but neither the quantity of breeding substrate in the environment nor ambient temperature affected growth. None of the environmental factors tested influenced the choice of male life histories. We conclude that in L. callipterus growth rates of bourgeois and parasitic males are paternally inherited, and that male and female growth is phenotypically plastic to only a small degree.     

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.     

Reproductive success in male sunbleak, a recent invasive fish species in the U.K.

The spawning behaviour of male nest guarding sunbleak Leucaspius delineatus , a recent invasive species in southern England, was studied and quantified for the first time. In the absence of physical differences between territorial and non‐territorial males ( i.e . colour, size, etc .), the reproductive behaviour of territorial males was analysed and related to reproductive success. The results showed that females preferred high‐courting and highly aggressive males. The initial cue in female mate choice, however, was based on courtship, while aggression was the decisive behavioural trait in influencing mate choice, providing a direct signal of physical condition and 'paternal competence'. Some males picked nest sites which were subsequently preferred by other males taking over the nest of a previous male ('communal nest'), with the new territorial male adopting the eggs already present at the nest. It appears that either due to female preference for nests already containing eggs or lower rates of sired egg predation by dilution among unrelated eggs, sunbleak males have adopted the mating strategy of allopaternal care.     

Variability of GnRH secretion in two goby species with socially controlled alternative male mating tactics

Male reproductive phenotypic plasticity related to environmental-social conditions is common among teleost fish. In several species, males adopt different mating tactics depending on their size, monopolizing mates when larger, while parasitizing dominant male spawns when smaller. Males performing alternative mating tactics are often characterized by a strong dimorphism in both primary and secondary reproductive traits. According to studies on sex-changing species and on species where only one male morph is reproductively active, male alternative phenotypes are expected to vary also in gonadotropin-releasing hormone (GnRH) neurons in forebrain preoptic area (POA). Here, we compared the intra- and inter-sexual variations in number and size of GnRH neurons, along with gonads and male accessory structure investment, in two goby species, the grass goby, Zosterisessor ophiocephalus, and the black goby, Gobius niger, characterized by male alternative mating phenotypes. In both species, older and larger males defend nests, court and perform parental care, while younger and smaller ones try to sneak territorial male spawning. We found that grass goby and black goby have different patterns of GnRH expression. Grass goby presents a clear intra-sexual dimorphism in GnRH expression, related to the occurrence of alternative mating tactics, while in the black goby, only inter-sexual differences are observed. The inter- and intra-specific variability in the GnRH neurons in these two goby species is discussed in light of the differences in migratory behavior, nest type, and mating system.     

Mate availability affects female choice in a fish with paternal care: female counterstrategies against male filial cannibalism

Theory predicts that individuals should adopt counterstrategies against intersexual conflict with their mating partners if the counterstrategies are effective and cost-efficient. In fishes, males with parental care often cannibalize their own offspring, which reduces the female’s fitness and creates intersexual conflicts. Males of the goby Rhinogobius flumineus cannibalize more eggs in the nest when they have access to additional females prior to spawning. Thus, it is predicted that females will strategically avoid spawning with males that have high mate availability. In the present study, we experimentally tested this prediction. When sexual pairs were placed in tanks, most females (control females; 21/22) successfully spawned inside the nest. In contrast, when a gravid female (stimulus female) that was housed in a small transparent cage was shown to the experiment pairs prior to spawning, only about half of the females (experiment females; 16/29) spawned inside the nest; the remaining females released unfertilized eggs outside of the nest. Moreover, experiment females infrequently accepted and followed males into nests, and delayed spawning more often than control females. R. flumineus females prefer males that court frequently. Indeed, experiment females that infrequently received courtship tended to spawn outside of the nest. However, infrequent courtship alone could not explain outside-nest spawning, delay in spawning, or the shorter stay of females in nests. These results imply that the presence of a stimulus female dampens female spawning with males. We suggest that R. flumineus females may strategically reject or hesitate to spawn with males that have high mate availability, and that this spawning avoidance may be a counterstrategy against male filial cannibalism.     

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.     

Colonial Nesting and the Importance of the Brood Size in Male Parasitic Reproduction of the Mediterranean Damselfish Chromis chromis (Pisces: Pomacentridae)

We investigated male parasitic spawning in a protected natural population of Mediterranean damselfish. Chromis chromis nested in colonies, inside which males showed a high variability in mating success. Our field observations indicate that the egg batches obtained by the most successful fish were five times bigger than the ones obtained by the less successful fish and many males never received ovipositions. On the other hand, reproductive parasitism was a common tactic within the colony. Successful nesting males sneaked into their neighbours' nests depending on the amount of eggs in their nest, with small clutch size inducing the males to parasitic reproduction. Males failing to receive egg depositions on their nests showed a significantly higher parasitism rate than successful males. Non-territorial males occupied stations in the water column above the breeding grounds and whenever the opportunity arose, they disrupted spawning in progress, stealing copulation with females. We observed that the likelihood of males being parasitized by sneakers was not correlated with the size of their own clutch; on the contrary, it depended both on the number of neighbouring nests and on the number of neighbouring males with barren nests (i.e. unsuccessful males). No correlation was found between parasitic behaviour and male size, suggesting males may switch between spawning in their own and in their neighbour's nests depending on mating opportunity. The hypothesis that colonial nesting facilitates parasitic reproduction is here discussed.     

Alternative reproductive tactics in snail shell‐brooding cichlids diverge in energy reserve allocation

Life history theory predicts that the amount of resources allocated to reproduction should maximize an individual's lifetime reproductive success. So far, resource allocation in reproduction has been studied mainly in females. Intraspecific variation of endogenous energy storage and utilization patterns of males has received little attention, although these patterns may vary greatly between individuals pursuing alternative reproductive tactics (ARTs). ARTs are characterized by systematic variation of behavioral, physiological, and often morphological traits among same‐sex conspecifics. Some individuals may rely on previously accumulated reserves, because of limited foraging opportunities during reproduction. Others may be able to continue foraging during reproduction, thus relying on reserves to a lesser extent. We therefore predicted that, if male tactics involve such divergent limitations and trade‐offs within a species, ARTs should correspondingly differ in energy reserve allocation and utilization. To test this prediction, we studied short‐term and long‐term reserve storage patterns of males in the shell‐brooding cichlid Lamprologus callipterus. In this species, bourgeois males investing in territory defense, courtship, and guarding of broods coexist with two distinct parasitic male tactics: (1) opportunistic sneaker males attempting to fertilize eggs by releasing sperm into the shell opening when a female is spawning; and (2) specialized dwarf males attempting to enter the shell past the spawning female to fertilize eggs from inside the shell. Sneaker males differed from other male types by showing the highest amount of accumulated short‐term and long‐term fat stores, apparently anticipating their upcoming adoption of the nest male status. In contrast, nest males depleted previously accumulated energy reserves with increasing nest holding period, as they invest heavily into costly reproductive behaviors while not taking up any food. This conforms to a capital breeder strategy. Dwarf males did not accumulate long‐term fat stores at all, which they can afford due to their small behavioral effort during reproduction and their continued feeding activity, conforming to an income breeder strategy. Our data confirm that the resource storage patterns of males pursuing ARTs can diverge substantially, which adds to our understanding of the coexistence and maintenance of alternative reproductive patterns within species.     

Big is better: the importance of size for reproductive success in male Pomatoschistus minutus (Pallas) (Pisces, Gobiidae)

The sand goby, Pomatoschistus minutus , was used in aquarium experiments to study the importance of body size for the ability of males to gain access to nest sites and mates. When several male and female P. minutus were allowed to reproduce together, on average, half of the males built nests, and half of those males obtained eggs in their nests. Males with nests were significantly larger than males without nests, and nests with eggs belonged to males larger than the males with empty nests. In another experiment, when two males were competing for one nest, the largest male occupied the nest when both fish were put into the aquarium simultaneously. However, when the smaller male had been allowed to establish a nest before the larger male was introduced, the small male could usually retain the nest. Males with a body length < 50 mm did not build nests at all in the early part of the breeding season. In female choice experiments, no preference for larger males was found. Thus, male-male competition for nest sites and behavioural differences between different sized males seem to be the main factors influencing the non-random mating success in male P. minutus.     

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.     

Simultaneous spawning by female stream goby Rhinogobius sp. and the association with brood cannibalism by nesting males

A laboratory experiment was conducted by varying the undersurface area of nesting substratum and the number of females in an experimental tank to elucidate the determinants of the mating pattern in the stream goby, Rhinogobius sp. cross‐band type. Males with larger nests tended to attract two or more females to their nest in a tank. Moreover, males spawned simultaneously with multiple females and entire brood cannibalism by males was rarely observed under a female‐biased sex ratio. When males spawned with a single female with low fecundity, however, entire brood cannibalism occurred at a high frequency, suggesting that a male guarding a nest with fewer eggs consumes the brood. Therefore, spawning behaviour of females that leads to a large egg mass would decrease the risk of entire brood cannibalism. In this species, simultaneous spawning by multiple females in a nest serves as a female counter‐measure against entire brood cannibalism. These results suggest that a conflict of interest between the sexes through brood cannibalism is a major determinant of simultaneous spawning.     

Breeding sounds of male Padogobius nigricans with suggestions for further evolutionary study of vocal behaviour in gobioid fishes

The male Arno goby Padogobius nigricans courts ripe females by emitting sounds at a high rate, mainly from the nest hollow. Laboratory observations revealed that each sound is an almost pure tone wave showing marked amplitude modulation and decrease of frequency throughout its length. The mean tone frequency averaged 79.4 Hz and the sound duration averaged 327 ms. Both these sound parameters were significantly affected by the temperature of the water. Acoustic behaviour during sexual interactions was compared for tank-confined males and males from a community group. The fact that acoustic activity of the male peaked when the female stayed motionless at the nest entrance suggested that the sound emitted by the male P. nigricans has a role as an advertising signal. Observation of spawning behaviour showed the emission of sounds by the male rapidly diminished and eventually ceased shortly after the beginning of oviposition. Thus, the male sound seems not to be a functional component of the spawning behaviour. Finally, data on vocal behaviour of this species were examined within a comparative framework, also taking into consideration phylogenetic relationships between Italian freshwater gobies.     

Mate Choice and Mating Pattern in a Stream Goby of the Genus Rhinogobius

The mate choice and mating pattern of a benthic goby Rhinogobius sp. CB (cross band type) were investigated in the Kamo River, Shikoku, Japan. During the breeding season, gravid females assumed a nuptial color and either males or females initiated a courtship display. Males preferentially courted a female of similar size to lead her to his nest, whereas females courted more frequently when they encountered a large male. Eggs in any one nest were always at the same developmental stage. Sampling data of nesting males and females indicated that, in more than half the nests, males gathered more than one female before spawning. In some nests with eggs, two or three females had spent ovaries, indicating that the eggs were laid by multiple females within a short span of time. However, a comparison between the total number of eggs which females would spawn in one nest and the number of eggs actually deposited suggested that eggs were contributed by one female in most nests. This low level of polygyny in spite of multiple female availability is attributed to a limited available spawning area of the nest.     

Breeding pattern and nest guarding in Sicyopterus lagocephalus, a widespread amphidromous Gobiidae

Amphidromous gobies are usually nest spawners. Females lay a large number of small eggs under stones or onto plant stems, leaves or roots while males take care of the clutch until hatching. This study investigates the breeding pattern and paternal investment of Sicyopterus lagocephalus in a stream on Reunion Island. In February 2007 and January 2010, a total of 170 nests were found and the presence of a goby was recorded at 61 of them. The number of eggs in the nests ranged from 5,424 to 112,000 with an average number of 28,629. We showed that males accepted a single female spawning in the nest and cared for the eggs until hatching. The probability for a nest to be guarded increased with the number of eggs within it, suggesting that paternal investment depends on a trade-off between the reproductive value of the current reproduction and future nesting events. We showed that large nest stones were occupied by large males (TL >80 mm), whereas smaller males (TL <50 mm) were found under smaller cobbles, probably because of male–male competition for available nests. Our results suggest that the male’s choice relies upon a similarity to the female size, while the female’s choice was based on both body and nest stone sizes.     

Effects of androgens on social behavior and morphology of alternative reproductive males of the Azorean rock-pool blenny

In the Azorean rock-pool blenny Parablennius sanguinolentus parvicornis two sequential reproductive tactics occur. Larger and older males establish breeding territories, while some of the smaller males become attached to nest-holder territories, acting as satellites on these territories, which they help to defend while trying parasitic fertilizations when females go in the nests to spawn. In the present paper we tested the effects of the androgens 17alpha-methyltestosterone (MT) and 11-ketotestosterone (KT) in the expression of male secondary sex characters and bourgeois behavior in satellite males. One week after satellites were implanted with Silastic tubes containing MT, KT, or castor oil (control), androgen-treated satellites had developed male secondary sex traits such as longer and wider male-type genital papilla and anal glands that secrete a sex pheromone, both traits being less expressed or absent, respectively, in satellite males. Androgen treatment had no effect on the gonadosomatic index or on the development of the testicular gland. KT treatment had a positive effect on relative liver weight. In terms of behavior, androgen-implanted individuals were less aggressive both in a mirror test and toward females when these were introduced into their tanks. MT-treated individuals spend more time inside the provided nests. Only androgen-implanted satellites managed to have the females entering their nests. When given a chance in a group tank either to try to attract females to their own nest or to act as satellites of an already established nest-holder's nest, MT-implanted males spent significantly more time in their own nest than near the nest-holder nest. These data suggest that androgens, particularly testosterone, may be involved in mating tactic switching in this species.     

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.