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.     

Mature males of Arctic charr,Salvelinus alpinus,release F-type prostaglandins to attract conspecific mature females and stimulate their spawning behaviour

Synopsis We examined the behavioural and biological functions of prostaglandins (PG) of F-type as a chemosensory signal during spawning in Arctic charr. Immunoassay revealed F-type PGs in water inhabited by ripe charr of both sexes performing spawning-related acts. High concentrations of immunoreactive PGFs seemed to coincide with male spawning activity. Ripe isolated males were more odorous to other charr (as assayed by EOG) than either females or immature charr. When these males received chemical cues from ovulated females, they increased their release of odorants, including F-type PGs, into the water. PGF_2α at concentrations of 0.1 nM attracted ovulated females and ripe males. It also stimulated digging behaviour in mature females. It is concluded that F-type PGs or their derivatives are released by ripe males on the spawning grounds to attract females and elicit their spawning behaviour.     

Ovarian steroid sulphate functions as priming pheromone in maleBarilius bendelisis (Ham.)

The study reveals that pre-ovulatory females of the fishBarilius bendelisis (Ham.) release sex steroids and their conjugates into the water and that a steroid sulphate of these compounds functions as a potent sex pheromone which stimulates milt production in conspecific males prior to spawning. Since males exposed to the purified sub-fraction III of the steroid sulphate fraction have increased milt volume and more spermatozoa with greater motility, the function of this priming pheromone appears to be to enhance male spawning success. High turbulence and faster water currents render the hillstream ecosystem extremely challenging for chemical communication. Therefore, ovulatory female fish secrete highly water soluble steroid sulphates for rapid pheromonal action in males. Inhibited milt volume in olfactory tract lesioned (OTL) males exposed to the steroid sulphate fraction and 17α,20β-dihydroxy-4-pregnen-3-one supports the concept that the pheromonally induced priming effect in male fish is mediated through olfactory pathways.     

The role of mounds in promoting water-exchange in the egg-tending burrows of monogamous goby, Valenciennea longipinnis (Lay et Bennett)

Valenciennea longipinnis spawns monogamously in a burrow. After spawning, the paired female constructs a conspicuous mound on the burrow by carrying and piling up substratum-derived materials while the male tends eggs in the burrow until hatching occurs. In this study, the mounds of V. longipinnis were tested in the field to confirm their function of promoting water-exchange in the burrow, and their ecological role was examined in relation to egg care by the male. The mound of V.longipinnis promoted water-exchange in the burrow, contributing to the provision of external oxygenated sea water into the burrow. Therefore, dissolved oxygen (DO) concentrations in the burrow with a mound were significantly higher than those without a mound. Although male egg-tending behaviour (e.g., fanning) may also promote water-exchange in the burrow, the water-exchange appeared to depend mainly on the hydrodynamic effect. Removals of the mound and paired female on the day of spawning led to high rates of egg-desertion by males. Since the frequency and time of fanning increase with a decrease of DO concentration in the burrow, the egg-desertion may result from an increased parental cost to males due to the decrease of water-exchange without a mound. This was supported by the fact that the DO concentrations on the day after mound removal were significantly lower in the egg-deserted burrows (measured before desertions) than in burrows not deserted by the male. Moreover, removals of paired females only also led to higher desertion rates. After removal of the female, the mound gradually collapsed by wave action and other factors, and the surface of the mound was covered with planktonic materials. Such a mound of poor quality may provide little water-exchange, which may lead to the egg-desertion by males. These results indicated that mound maintenance by females during the egg-tending period has an important role in the success of parental care by males.     

Sperm allocation pattern during a reproductive season in the copulating marine cottoid species, <Emphasis Type="Italic">Alcichthys alcicornis</Emphasis>

The sperm allocation pattern of a copulating marine cottid fish, Alcichthys alcicornis, was investigated. A total of 86 mating events using six males were conducted in aquarium tanks over 10 days, and in 36 of them, spermatozoa were collected using a false copulation method. Males released 3–8 × 10⁸ spermatozoa in early events, with the number decreasing gradually during subsequent mating events. This sperm allocation was represented as an “early investment and tapering” pattern. It was discussed why males have significantly higher sperm release in early spawning events. The reproductive behavior consists of spawning and subsequent copulation. Spermatozoa have the ability to fertilize eggs from multiple clutches, and in earlier produced clutches the level of sperm competition should be relatively low. In addition, if early spawn happens to be the first spawn with a female, spermatozoa that are released into the water column after spawning are responsible for fertilizing the female’s first clutch. The probability of this occurring should decrease dramatically as the season progresses, due to the highly synchronous seasonal spawning of females. All of these factors should select for high sperm numbers in early ejaculates. Based on such reproductive ecology of A. alcicornis we hypothesize that this sperm allocation pattern is an adaptive reproductive strategy in response to egg availability and sperm competition occurring within the ovarian cavity.     

Non-synchronous spawning behavior in laboratory reared amphioxus Branchiostoma belcheri Gray

Spontaneous spawning in amphioxus (Branchiostoma belcheri Gray) was observed in a tank and the characteristics of spawning were analyzed by video recording under infrared light conditions during summer of 2001. Everyday when spawning was observed, without exception a male first swam up from the bottom and released sperm near the water at the surface of the tank. The initiation time of the male spawning gradually became earlier as days passed. Spawning males and females individually swam up at various intervals and released gametes. However, at the population level, the spawning pattern of amphioxus was considered to be synchronous because both males and females intensively spawned around 90 min after the spawning of the first male. The act of releasing eggs or sperms of individuals was shorter than 10 min in most of the spawning animals.     

Male moth songs tempt females to accept mating: the role of acoustic and pheromonal communication in the reproductive behaviour of Aphomia sociella

Background

Members of the subfamily Galleriinae have adapted to different selective environmental pressures by devising a unique mating process. Galleriinae males initiate mating by attracting females with either chemical or acoustic signals (or a combination of both modalities). Six compounds considered candidates for the sex pheromone have recently been identified in the wing gland extracts of Aphomia sociella males. Prior to the present study, acoustic communication had not been investigated. Signals mediating female attraction were likewise unknown.

Methodology/Principal Findings

Observations of A. sociella mating behaviour and recordings of male acoustic signals confirmed that males initiate the mating process. During calling behaviour (stationary wing fanning and pheromone release), males disperse pheromone from their wing glands. When a female approaches, males cease calling and begin to produce ultrasonic songs as part of the courtship behaviour. Replaying of recorded courting songs to virgin females and a comparison of the mating efficiency of intact males with males lacking tegullae proved that male ultrasonic signals stimulate females to accept mating. Greenhouse experiments with isolated pheromone glands confirmed that the male sex pheromone mediates long-range female attraction.

Conclusion/Significance

Female attraction in A. sociella is chemically mediated, but ultrasonic communication is also employed during courtship. Male ultrasonic songs stimulate female sexual display and significantly affect mating efficiency. Considerable inter-individual differences in song structure exist. These could play a role in female mate selection provided that the female''s ear is able to discern them. The A. sociella mating strategy described above is unique within the subfamily Galleriinae.     

The ability of the amphipod Corophium volutator (Pallas) to follow chemical signals from con-specifics

The amphipod Corophium volutator (Pallas) is a tube-dwelling species that only occasionally leaves its burrow. Animals that do crawl on the sediment are mainly males, apparently in search of females. This study was designed to determine whether C. volutator males and females release chemical signals that attract con-specifics, and if so, whether these signals are gender specific. Laboratory experiments were conducted on the over-wintering generation during their reproductive season, using a Y-maze choice test apparatus. The results show that C. volutator females release chemical signals that attract males. In the field, the attractant may guide males in search of burrowed females. In addition, male odour tends to attract males, while females do not follow chemical signals from con-specifics. We thereby show on gender-specific chemical attraction of this species.     

Evidence for sexual attraction pheromones released by male tropical donkey's ear abalone (Haliotis asinina), (L.)

Abstract

The tropical donkey's ear abalone (Haliotis asinina) is routinely collected in many parts of the Indo-Pacific and has significant potential for commercial aquaculture. Although its reproductive cycle has been investigated, no studies have reported the use of chemical signals to coordinate reproduction and spawning. Using a bioassay designed with one caged individual, whilst the other is free to roam, we investigated the presence of attraction pheromones released from mature individuals. Only mature females were attracted to caged mature males with all other treatments showing no significant attraction. Those mature females also took significantly less time to reach the mature males than other pairings. Temperature influenced the response with the maximum number of positives occurring between 25 and 31°C, which coincides with the optimum physiological temperatures and the spawning times for this species. We have also shown that the attraction pheromone is present in mature male testes and induces stereotypical pre-spawning behaviours (sweeping epipodial and cephalic tentacles) as well as attracting females. Some individuals also moved towards the surface of the water, this may also be a pre-spawning behaviour. This is the first time that a sexual attraction pheromone has been reported for any haliotid species and is likely to have a critical function in the synchronization of spawning in the wild between sexes.     

Scatter-spawning of the catfish,Silurus asotus

Reproductive behaviour of the catfish,Silurus asotus was studied in temporary waters around paddy fields. Spawning occurred nocturnally during the first week from the initiation of irrigation. In reproductive activities, a male first energetically pursued a female with its head near to the female’s belly (chasing) and then began to cling to the female’s body from the side, bending its tail or head (clinging). Finally the male enfolded the female’s body, with its anus near to the female’s (enfolding). In some cases, 2–4 males pursued a single female and two males enfolded a female at the same time. Although no aggressive behaviour was evident between males, it was always the largest male that could most frequently approach and enfold the female. The mating pair moved a long distance in a ditch, paddy field and/or creek, performing reproductive activities. It is thought that the spawning site and period of spawning of the fish enable the larvae to avoid the danger of predation and to efficiently feed, firstly on plankton and later on larvae of other fishes which become abundant during the irrigation period. Although some eggs and larvae may die due to the drying out or high water temperatures of such unstable temporary waters, scattering eggs may reduce the incidence of the annihilation of the young.     

Male reproductive cycle of the Siberian salamander Salamandrella keyserlingii (Caudata: Hynobiidae) in coastal tundra of the Sea of Okhotsk

The adaptations which allowed the Siberian salamander (Salamandrella keyserlingii Dybowski, 1870) to form its exceptionally large, polyzonal range (forest-steppe, forests, and southern tundras of Siberia and part of European Russia) remain insufficiently studied. We checked the hypothesis that S. keyserlingii was able to colonize the northern territories, characterized by a short and cold summer and therefore unsuitable for other amphibians, due to multiyear maturation of its spermatozoa and eggs which was described in the southern part of Western Siberia. For this purpose, the male reproductive cycle of S. keyserlingii was studied during the entire 4-month active season in the Sea of Okhotsk coastal tundras. The complete development of gametes there took only 3 months: proliferation of spermatogonia started already in the spawning pond soon after spermiation in May and ended by the time the males left the water; spermatocytes were formed at the end of June, and spermatozoa, by the second half of August. Spermatogenesis occurred synchronously in all the maturing lobules along the entire length of the testis. Mature spermatozoa were stored in the testes until spring when external fertilization took place in the pond. Morphological and histological changes in the testes and vasa deferentia, the mode of fertilization, and annual reproduction of S. keyserlingii were similar to those of other studied species of the family. Our data disprove the previous conclusion about multiyear spermatogenesis of S. keyserlingii, which, therefore, cannot be considered among the possible adaptations which facilitated colonization of the northern territories by this species.     

Size-dependent Mating Behaviours of Male Sand-bubbler Crab,Scopimera globosa: Alternative Tactics in the Life History

Factors leading to the separation of mating behaviours were investigated in the sand-bubbler crab, Scopimera globosa. The crabs mated on the surface (surface copulation, SC) and underground (UC). UC males were large (old) whilst SC males were small (young). Burrowless females bred in the UC males' burrows. These females accepted UC in exchange for access to a burrow. UC occurred much more frequently than SC in the burrow area in which females oviposited. Most SC occurred in the water-saturated area affording a rich diet. SC was accepted by most large and small females in both areas and most UC by small females in the burrow area. SC was an alternative to UC for males in that there was a size dependence between types of copulation. These two mating behaviours involved different degrees of interaction with neighbouring males. Males attempting to carry a female to their burrows for UC were more often disturbed by other males than were males attempting SC. In the interaction for both UC and SC, larger males were likely to resist the disturbances. UC males needed their own burrows, but these burrows were not enlarged before mating. UC males have a higher paternity of eggs than SC males, because SC males' sperm is often displaced by other males. Thus, UC was a behaviour with relatively higher costs and benefits for male crabs than SC behaviour. Alternative mating behaviours in male S. globosa are conditional, and explained by intrasexual interactions and a male life history strategy with a trade-off between growth and reproduction. It is not likely that the size dependence of male mating behaviour is caused by mate preference of females for UC males in the burrow area.     

Burrow ventilation and associated porewater irrigation by the polychaete Marenzelleria viridis

Burrow ventilation of benthic infauna generates water currents that irrigate the interstices of the sediments surrounding the burrow walls. Such activities have associated effects on biogeochemical processes affecting ultimately important ecosystem processes. In this study, the ventilation and irrigation behavior of Marenzelleria viridis, an invasive polychaete species in Europe, was analyzed using different approaches. M. viridis showed to perform two types of ventilation: (1) muscular pumping of water out of the burrow and (2) cilia pumping of water into the burrow. Flowmeter measurements presented muscular pumping in time averaged rates of 0.15 ml min⁻¹. Oxygen needle electrodes positioned above the burrow openings revealed that muscular undulation of the worm body pumps anoxic water out of the burrow. On the other hand, microscope observations of the animal showed that ventilation of oxygen-rich water in the burrow occurs by ciliary action. The volume of water irrigated by M. viridis appears to vary linearly within the first 24 h incubation, with rates ranging from 0.003 to 0.01 ml min⁻¹. From those rates we could estimate that the time averaged rate of cilia ventilation should be about 0.16 ml min⁻¹. Since the cilia pumping into the burrow occurs in periods of 24 ± 12 min and at 50-70% of the measured time, considerable amounts of water from deeper sediments may percolate upwards to the sediment surface. This water is rich in reduced compounds and nutrients and may have important associated ecological implications in the ecosystem (e.g. affecting redox conditions, organic matter degradation, benthic recruitment and primary production).     

Environmental factors affecting the spawning burrow selection by the gobiid Valenciennea longipinnis

Spawning burrow selection by the longfinned goby Valenciennea longipinnis was studied in the near-shore moat on coral reefs, Okinawa, Japan. The gobies make several burrows within their home range, and spawn in one of them. To examine the factors important for spawning burrow selection three characteristics were investigated: current strength, burrow length and effect of underground water on the burrow. Among the burrows, pairs tended to spawn in a larger burrow irrespective of their body sizes. Most of the other non-spawning burrows were too small for a pair to stay together, because hard substrata may prevent the fish from excavating and shaping the burrow as they like. Moreover, pairs preferred to spawn in burrows where the underground water was oozing out, probably because the male's parental burden will decrease due to the higher dissolved oxygen concentration in such burrows. Although current strength may affect a water-exchange in a V. longipinnis burrow in relation to water-exchange function of a mound, it did not affect the spawning burrow selection because of the smaller velocity difference among the burrows relative to the daily fluctuation of tidal current.     

Biogeochemical responses following coral mass spawning on the Great Barrier Reef: pelagic–benthic coupling

This study quantified how the pulse of organic matter from the release of coral gametes triggered a chain of pelagic and benthic processes during an annual mass spawning event on the Australian Great Barrier Reef. Particulate organic matter (POM) concentrations in reef waters increased by threefold to 11-fold the day after spawning and resulted in a stimulation of pelagic oxygen consumption rates that lasted for at least 1 week. Water column microbial communities degraded the organic carbon of gametes of the broadcast-spawning coral Acropora millepora at a rate of >15% h⁻¹, which is about three times faster than the degradation rate measured for larvae of the brooding coral Stylophora pistillata. Stable isotope signatures of POM in the water column reflected the fast transfer of organic matter from coral gametes into higher levels of the food chain, and the amount of POM reaching the seafloor immediately increased after coral spawning and then tailed-off in the next 2 weeks. Short-lasting phytoplankton blooms developed within a few days after the spawning event, indicating a prompt recycling of nutrients released through the degradation of spawning products. These data show the profound effects of coral mass spawning on the reef community and demonstrate the tight recycling of nutrients in this oligotrophic ecosystem.     

Factors affecting female parental investment in the monogamous goby, Valenciennea longipinnis

Female Valenciennea longipinnis construct a conspicuous rubble mound on a burrow after spawning while the paired male tends eggs in the burrow until hatching occurs. The mound has a function of promoting water-exchange in the burrow through hydrodynamic effects, contributing to prevention of the male egg-desertion by reducing his parental costs. Although higher mounds are more effective in water exchange, they cost females much work after spawning. In this study, I investigated effects of six ecological and environmental factors on the mound height, i.e., female parental investment. Multiple regression analysis indicated that only female body size could explain the female parental investment: larger females tended to construct higher mounds. The size-assortative mound building suggests that the females strive to construct mounds as high as they can irrespective of the other ecological and environmental factors. Because current strength and oozing of underground water fluctuated even in a day, females may be obliged to construct high mounds on the basis of the worst condition.     

Reproductive system of the Schrenckii salamander (Salamandrella schrenckii, Amphibia, Caudata, Hynobiidae) in spring and fall

The reproductive system of 319 individuals of the Schrenckii salamander (Salamandrella schrenckii Strauch 1870) (synonym S. tridactyla sensu (Kuz’min et al., 2008) from a Khabarovsk population has been studied before wintering and during the spawning of animals. In the fall, all adult males had enlarged testes filled with bundles of spermatozoa and no spermatozoa in the spermaducts. Females had large pigmented ova in the ovaries and empty expanded oviducts. In the spring, only mature S. schrenckii individuals were found in the water; the entire spectrum of physiological states from the preparation for breeding to its end was noted in them. The preovulatory stage, ovulation, pregnancy, and spawning were registered in females; the predominance of spermatozoa in the testes or in spermaducts, or almost complete absence of them in the reproductive system, and different degrees of hypertrophy of spermaducts were noted in males. These differences are related to the different times of arrival of individuals to the spawning pond. The material analyzed evidences the yearly breeding of S. schrenckii. S. schrenckii differs from S. keyserlingii in the type and duration of the reproductive cycle, sizes and morphology of spermatozoa, and structure and functioning of ovaries (Saveliev et al., 1993; Kuranova and Saveliev, 2006). The majority of the reviewed characteristics of S. schrenckii are similar to those of the allied genus representatives: Hynobius nigrescens and H. retardatus (Hasumi et al., 1990; Iwasawa et al., 1992; Hasumi, 1996a).     

The role of chemical signals in the spawning induction of polychaete worms and other marine invertebrates

Extracts of gonad, body fluid and spawning water (into which gametes have been released by the process of spawning) were tested for the presence of spawning-inducing activity (SIA) on both sexes of the polychaetes Nereis succinea (Frey and Leuckhart) and Platynereis dumerilii (Audouin and Milne-Edwards). Gonadal and body fluid extracts from Asterias rubens (L.) and Echinus esculentus (L.) (echinoderms), Arenicola marina (L.) (polychaete), Clupea harengus (L.) (teleost) and body fluid and spawning water of Nereis virens (Sars) (polychaete) all exhibit SIA on male N. succinea. C. harengus extract from male gonads also had SIA on male P. dumerilii. Phytoplankton monoculture extracts were also tested. The cryptomonad (Rhodomonas baltica) (Karsten) had SIA on male P. dumerilii, and the diatom Phaeodactylum tricornutum (Bohlin) had some activity on Mytilus edulis (L.). The active fraction of R. baltica is chromatographically similar to uric acid (the natural sperm-release pheromone produced by females of P. dumerilii) [Nature 382 (1996) 214], but has a different retention time and UV absorbance spectra on reverse phase HPLC. Conspecific extracts of spawning water and gonadal material did not have SIA on the same and opposite sex in A. marina and N. virens. The role of chemical signals in marine invertebrates is discussed in relation to their mode of spawning.