Effects of courtship and relative mate size on sexual motivation in Atlantic salmon

Both sexes of Atlantic salmon Salmo salar were very sensitive to the absence of their mate on the spawning ground, particularly females during the last hour before oviposition. The improvement of behavioural chaining just before viposition might elicit the accurate timing of synchronized gamete release for successful fertilization. While the reproductive behaviour of the opposite sex could largely affect breeding activity, relative mate size appeared to be the prevailing sexual motivation factor in this species. Even in the absence of courtship, large mate size may constitute a supra-stimulus inducing an increase in spawning behaviour of the other sex. Females with smaller males delayed their first spawning activity, took longer to spawn and made more nests than those with large males. However, female egg retention was not influenced by relative male size.     

Mating patterns of female Leon Springs pupfish Cyprinodon bovinus

In a field study of Leon Springs pupfish Cyprinodon bovinus, two questions about female promiscuity were investigated. First, were females selective in the males with whom they spawned or were they unselective, spawning randomly among males? Second, how promiscuous were the females, i.e. with how many males did they spawn? If simply spawning with many males maximized a female's reproductive success, then females might be expected to spawn randomly with as many males as possible. Alternatively, if females were selective but engaged in multiple mating, they would limit their spawning to preferred males. In the only wild population of this endangered fish, breeding males defend closely associated territories in the shallow margins of a single desert pool. No territories were observed elsewhere in the pool. Therefore, all territorial males were present simultaneously and females could survey all of them, depositing any number of eggs with one, a few or many males. Rather than spawning randomly, females surveyed many males first, visited relatively few males and ultimately spawned with a small fraction of those available males. With increasing numbers of spawns, however, females increased the number of different mates with whom they spawned. Thus, females showed a bet‐hedging tactic of having a narrow mate preference while also laying eggs in the territories of other males, possibly to reduce egg predation and to avoid inbreeding.     

Spawning behavior of Arctic charr (Salvelinus alpinus): Spawning synchrony,vibrational communication,and mate guarding

A mismatch in synchrony between male and female gamete release in external fertilizers can result in reduced or failed fertilization, sperm competition, and reduced paternity. In Arctic charr (Salvelinus alpinus), males can adopt either a guard or sneak tactic resulting in both pre‐ and postcopulatory competition between males with alternative reproduction tactics. Here, spawning behavior of free‐living Arctic charr was video‐recorded, and their reproductive behavior was analyzed. From evaluating 157 spawning events, we observed that females mainly spawned with a guarding male and that the female and the guarding male synchronized timing of gamete release under sperm competition. Although sneakers spawned with higher synchrony than the guarding male in single‐male spawning events, the average sneaker released his milt less synchronized with the female than the guarding male under sperm competition. Approximately 50% of the recorded spawning events occurred under sperm competition, where each event included an average of 2.7 males. Additionally, sneakers were more exposed to sperm competition than guarding males. An influx of males, in close proximity to the female, occurred during the behavioral sequences leading up to egg release, but this influx seemed not dependent on egg release, suggesting that something else than gonadal product attracts sneaker males to the spawning female. Just before and during the actual release of gametes, the spawning couple vibrates their bodies in close contact and it seems likely that this vibrational communication between the spawning couple, which results in a larger amplitude sound wave than seen under regular courting, reveals time of gamete release to sneaker males. Thus, vibrational communication may enable synchrony between the guarding male and the female, and this might be traded against the cost of higher detectability from surrounding sneaker males, eavesdropping in close proximity.     

Reproductive behavior and mate fidelity in the monogamous goby,Valenciennea longipinnis

Reproductive behavior and mate fidelity of the gobiid fish,Valenciennea longipinnis, were studied on the coral reef at Sesoko Island, Okinawa, Japan. These fish usually live in pairs, not only foraging together for benthic animals in sandy areas, but also constructing several burrows within their home range. Before spawning, both fish, although mainly the male, constructed a mound, piling up dead-coral fragments, pebbles, shells, sand and algae onto one of the burrows. After spawning an egg mass on the ceiling of the burrow, the female stayed outside and continued the construction and maintenance of the mound for 3–5 days until hatching, while the male tended the eggs inside. Mate guarding of females seemed to prevent males from monopolizing several females. Although some pairs showed mate fidelity through several spawnings, more than half of the pairs broke up after only one spawning. The pair bond was broken by mate desertion and the disappearance of each sex. Both sexes preferred larger spawning partners; larger females spawned more eggs and larger males provided better egg care. Mate desertion occurred when larger potential mates, relative to the current partner, became available. The frequency of solitary individuals was higher in males than in females, resulting in females deserting their mates more often than males. Two factors seem to have facilitated mate desertion: (1) occurrence of size mis-matched pairing and (2) overlapping home ranges.     

Female mate choice and spawning behaviour of Chinook salmon under experimental conditions

After spawning their first nest, female chinock salmon Oncorhynchus tshawytscha paired with small males ( c. 46% of female weight) spent an average of 16·2 h between spawning of successive nests compared with 9·6 h for females paired with large males ( c. 112% of female weight) ( P< 0·05). Neither frequencies of female nest construction behaviours (digging and probing) nor male courtship behaviour (crossovers and quivers) differed between large- and small-male pairs. Male quivering frequencies were correlated significantly with female digging and probing frequencies, whereas the crossover frequencies were not. It is suggested that delayed spawning by females in the presence of relatively small males is a primary mechanism by which females in the genus Oncorhynchus exhibit mate choice.     

Reproductive success in male Japanese minnows,Pseudorasbora parva: observations under experimental conditions

To evaluate the spawning success of male Japanese minnows,Pseudorasbora parva, and female mate choice, spawning behaviour was observed under both artificial and experimental conditions. Larger males had larger territories and greater reproductive success. The body weight of territorial males decreased during the maintenance of territories, while that of non-territorial males increased significantly. When the weight of non-territorial males exceeded that of territorial males, the former began to establish new territories on the substrate, suggesting a conditional strategy by non-territorial males to trade off immediate reproductive success with growth and hence improve future reproductive success. Females chose males with larger body size, probably based on dominance rank rather than the quality (or size) of territory. It was concluded that females choose males of higher dominance rank and that males compete for large territories, both of which play an important part in male reproductive success.     

Correlation of acoustic and visual signals in the cichlid fish, <Emphasis Type="Italic">Tramitichromis intermedius</Emphasis>

We investigated acoustic and visual communication concurrently in wild caught adult and captive-born, first generation offspring of the East African Rift Lake cichlid fish Tramitichromis intermedius. Only males emit sound during courtship. Sound production is always accompanied by quivering, but quiver behavior is not always accompanied by sound. This separation of quivering and sound supports the hypothesis that sound production is intentional serving a communicative role. As spawning nears, both sound production and quiver behavior increase. In terms of the ontogeny of sound production, the first observation of courtship occurs just days before the first spawning event and the first sound emission accompanies the first courtship activity. The accompaniment of quivering with sound as well as the escalation of the two behaviors with the approach of spawning follows similar patterns in wild caught and captive-born males. The tight correlation between behavior and sound production in both groups indicates their simultaneous performance plays an important role in reproduction. It is probable that the ability to produce sound and perform quiver behavior at the same time may be a measure of mate quality.     

Risk-sensitive mating decisions in a visually compromised environment

Reproductive activities are often conspicuous and can increase the risk of predation. Evidence suggests that individuals are capable of responding to predators in a risk-sensitive manner. However, most studies tend to consider only the predator-mediated responses of males and females in isolation and with little regard to differences in local environmental conditions. Here, we experimentally investigate the effects of environmental visibility (turbidity) and predation risk on reproductive decisions in the sand goby, Pomatoschistus minutus, when exposed to a visually oriented predator, the European perch, Perca fluviatilis. We found that gobies were more reluctant to spawn in the predator''s presence, although larger males spawned sooner than smaller males. Interestingly, latency to spawning was unaffected by the visual environment, suggesting that gobies may be relying on non-visual cues under turbid conditions.     

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.     

Female within-nest spawning-site preference in a paternal brooding blenny and its effect on the female mate choice

Female spawning-site preference within a nest and its effect on the female mate choice in a paternal brooding blenny Rhabdoblennius ellipes , were examined in rocky intertidal pools using artificial nests. The number of eggs deposited at the nest entrance site was lower than the number deposited at the center and at deep sites. Moreover, the within-nest difference in the egg developmental stage indicated that eggs at the nest entrance site were deposited after those at the center and deep sites. These results indicated that females prefer to spawn eggs in the center and deep sites rather than at the entrance site. Owing to the higher egg mortality rate at the entrance site, females may avoid spawning at such sites. An analysis of the nests in the study area suggested that the within-nest site preference affects female mate choice that is females avoided nests where only the entrance site was available for spawning and instead spawned in nests where the center and deep sites were available.     

Endocrine events associated with spawning behavior in the sea lamprey (Petromyzon marinus)

Levels of estradiol, progesterone, and testosterone were determined in plasma of sea lamprey (Petromyzon marinus) undergoing certain behaviors associated with spawning in natural and artificial stream environments. Significantly higher levels of estradiol, progesterone, and testosterone were found in males than in females. In the artificial spawning channel, levels of estradiol were significantly higher in females exhibiting resting and swimming behaviors than in fanning, nest building, and spawning behaviors. No significant correlation was found with either progesterone or testosterone levels and the various reproductive behaviors. The data presented are the first experimental evidence that suggest gonadal steroids may be correlated with certain reproductive behaviors in the sea lamprey.     

Geographic differences in flash intervals and pre-mating isolation between populations of the Genji firefly, Luciola cruciata

Abstract.  1. Two types of Genji firefly, Luciola cruciata , have been recognised on the basis of the inter-flash interval.
2. The fast-flash and slow-flash type fireflies, distributed in the western and eastern parts of Japan, exhibit a 2- and 4-s interval of bioluminescence flash, respectively. In addition, an intermediate-flash type is found on the boundary between these two regions.
3. The differences in the responses of the males of four field populations to different intervals of artificial flashes were examined.
4. The results revealed that in the Aomori and Sendai populations (slow-flash type), a significantly larger number of males approached the 4- and 5-s flash intervals than approached the 2- and 3-s intervals of artificial flashes. On the other hand, in the Ohtsu population (fast-flash type), a significantly larger number of males approached the 2- and 3-s flash intervals than the 4- and 5-s intervals of artificial flashes. The Inuyama population (intermediate-flash type) did not show any particular preferences to flash intervals.
5. This study shows that in firefly populations, geographic variation in flash pattern can cause some degree of pre-mating isolation between populations.     

Human-induced water turbidity alters selection on sexual displays in sticklebacks

Changes in the environment due to human activities are becomingincreasingly common. A serious problem in aquatic environmentsis increased water turbidity due to phytoplankton algal growth.This may affect the breeding system of fishes, especially thosewith a visually based mating system. Here we show that increasedturbidity affects sexual selection in the threespine stickleback(Gasterosteus aculeatus) through impaired possibility for visuallybased mate choice. In a laboratory mate preference and matechoice experiment on sticklebacks from the Baltic Sea, whichis an area suffering from increased turbidity due to human activities,we found that females spent more time with and visited moreoften males in clear water than males in turbid water. For malesin turbid water to receive the same amount of interest fromfemales as males in clear water, they needed to court significantlymore. Thus, turbid water induced selection for higher courtshipactivity. However, the final spawning decision of the femalesdid not depend on water turbidity, which suggests that nonvisualcues determined the final spawning decision. Because visualcues are important in mate attraction, increased turbidity affectsan important evolutionary force, sexual selection, which mayhave further consequences for the evolution of the sexual displaysand preferences. Differences in visual conditions could hencebe one factor that has lead to differences among sticklebackpopulation in the use of sexual signals.     

Mate choice by males of the hermit crab Pagurus filholi: Do males assess ripeness and/or fecundity of females?

Males of the hermit crab, Pagurusfilholi, often grasp the edges of shells occupied by females and drag them during the mating season. This behavior was experimentally confirmed to be a precopulatory guarding behavior displayed by males for ripe females, and males were found to recognize females which were within about 5 days of spawning. Most theoretical models for mating preference assume the choosing sex (the male in the present case) has complete reproductive information about potential mates, and predict that males will preferably choose more fecund females and/or females that will require less guarding time (i.e. that will spawn sooner) as partners. Several male-choice experiments between two ripe females, both previously guarded by other males, were carried out to examine the above predictions. Males did not prefer females of larger size, higher fecundity or with less time remaining until spawning. These results suggest that males may not have complete information about potential partners, rather that male hermit crabs may adopt a mating strategy of pairing with the first ripe female they encounter. Even with such incomplete mate assessment, males may enhance their reproductive success by recognizing ripe females that will spawn within a given time (about 5 days in the present case).     

Indirect mate choice, direct mate choice and species recognition in a bower-building cichlid fish lek

Sexual selection arising through female mate choice typically favours males with larger, brighter and louder signals. A critical challenge in sexual selection research is to determine the degree to which this pattern results from direct mate choice, where females select individual males based on variation in signalling traits, or indirect mate choice, where male competition governs access to reproductively active females. We investigated female mate choice in a lekking Lake Malawi cichlid fish, Hemitilapia oxyrhynchus, in which males build and aggressively defend sand 'bowers'. Similar to previous studies, we found that male reproductive success was positively associated with bower height and centrality on the lek. However, this pattern resulted from males holding these territories encountering more females, and thus their greater success was due to indirect mate choice. Following initial male courtship, an increase in the relative mating success of some males was observed, but this relative increase was unrelated to bower size or position. Crucially, experimentally manipulating bowers to resemble those of a co-occurring species had no appreciable effect on direct choice by females or male spawning success. Together, these results suggest indirect mate choice is the dominant force determining male-mating success in this species, and that bowers are not signals used in direct mate choice by females. We propose that, in this species, bowers have a primary function in intraspecific male competition, with the most competitive males maintaining larger and more central bowers that are favoured by sexual selection due to higher female encounter rates.     

Nonindependent mating in a coral reef damselfish: evidence of mate choice copying in the wild

Theoretical and experimental studies have shown that mate choicecopying is a viable mating strategy under certain conditions.Copying experiments in fish have been conducted primarily inthe laboratory, except for one study conducted in the fieldunder artificial conditions. We investigated whether in a wildpopulation of the coral reef whitebelly damselfish (Amblyglyphidodonleucogaster) females copy the choice of other females. Femalespreferentially spawn with males that have recently mated. Todetermine if the presence of new eggs in the nest was the reasonfemales chose mates or whether females were mate choice copying,we conducted egg-switching experiments. Eggs from males thatrecently mated were donated to males that had no eggs. If femalesare mate choice copying, then donor males with no eggs in thenest should continue to receive additional eggs. If femalesare using the presence of new eggs as the criterion for matechoice, then foster males with new eggs should receive additionaleggs. We found that donor males received new eggs significantlymore often than expected. More females mated with donor malesthan foster males. Furthermore, females preferentially choseto mate with males whom they had seen mating with another female.Females appear to remember the mate choice of other femalesand choose to mate with those same males even after 1 day. Theseresults suggest that females may be copying the mating decisionof other females rather than choosing males based on the presenceof new eggs in the nest.     

Mate sampling and choosiness in the sand goby

To date, mate choice studies have mostly focused on establishing which mates are chosen or how the choices are performed. Here, we combined these two approaches by empirically testing how latency to mate is affected by various search costs, variation in mate quality and female quality in the sand goby (Pomatoschistus minutus). Our results show that females adjust their mating behaviour according to the costs and benefits of the choice situation. Specifically, they mated sooner when access to males was delayed and when the presence of other females presented a mate sampling cost. We also found a positive link between size variation among potential mating partners and spawning delay in some (but not all) experimental conditions. By contrast, we did not find the number of available males or the females'' own body size (‘quality’) to affect mating latency. Finally, female mating behaviour varied significantly between years. These findings are notable for demonstrating that (i) mate sampling time is particularly sensitive to costs and, to a lesser degree, to variation among mate candidates, (ii) females'' mating behaviour is sensitive to qualitative rather than to quantitative variation in their environment, and (iii) a snapshot view may describe mate sampling behaviour unreliably.     

Synchronous female spawning and male mating behavior in a land-locked population of Japanese charr, Salvelinus leucomaenis japonicus

In resource-based promiscuous mating systems, synchronous spawning of females affects competition among males and variation in the reproductive success of males. We documented the mating behavior of Japanese charr (Salvelinus leucomaenis japonicus) through an annual breeding season to examine the relationship between female spawning synchrony and male mating behavior. Females spawned highly synchronously in the population studied, i.e., approximately half the spawning was finished within the first three days of the entire spawning season (11 days). The daily operational sex ratio (OSR) was nearly 1:1 through the spawning period. The number of males around a spawning female was very small (1.21+/-0.49 males per female) over the spawning ground and period, suggesting that a competitive male could effectively chase subordinate males away from a spawning female. A few males attempted to sneak near the oviposition site of females (16%; 9 of 57 breeding groups), while some males adopted sneaking tactics in the initial phase of females' spawning (24%). We did not observe any males to succeed in sneak fertilizations. We conclude that in this Japanese charr population, the synchronous spawning of females was related to the unbiased daily OSR, male aggregation around females, and consequently whether and how efficiently males engaged in sneak mating behavior.     

Reproductive success of a marine teleost was correlated with proactive and reactive stress-coping styles

The present study investigated the relationship between reproductive success and stress-coping styles in gilthead seabream Sparus aurata in captivity. To characterise stress-coping styles, a total of 22 breeders were submitted to three different individual-based tests, one group-based test and post-handling glucocorticoid quantification. To assess spawning participation, a microsatellite analysis was performed on a total of 2698 larvae, which allowed each offspring to be assigned unambiguously to a single parental couple. Overall, S. aurata showed defined proactive and reactive behavioural traits. Proactive breeders exhibited higher levels of activity and risk taking and lower glucocorticoid blood levels than reactive breeders. The stress-coping style traits were consistent over time and context (different tests). Breeders that contributed to a higher number of progeny exhibited proactive behaviours, while those showing low progeny contribution exhibited reactive behaviour. Therefore, breeders with a high proportion of progeny (> 20%) had significantly higher activity and risk taking and lower cortisol than breeders with low progeny contribution (< 20%). In addition, males were more proactive than females and males exhibited significantly higher activity, risk taking and lower cortisol than females. This study is the first to establish in S. aurata breeders: (a) a relationship between stress-coping styles and spawning success; (b) a relationship between stress-coping styles and gender; and (c) the existence of proactive and reactive traits at the adult stage.     

Competitor intrusions and mate-search tactics in a territorial marine fish

Recent theoretical studies have drawn attention to the importanceof understanding the costs females experience during mate choiceand mating and how females resolve the trade-offs presentedby such costs. In garibaldi damselfish (Hypsypops rubicundus)females defend permanent feeding and shelter territories andmust leave their territories to search for and spawn with nestingmales. Both mate searching and spawning occur in bouts, separatedby returns to the territory. I used focal female observationsto test predictions of the hypothesis that such behavior isa means of minimizing the amount of food lost to competitorsthat enter the female's territory while she is searching foror spawning with males. Consistent with this hypothesis, therewas a strong likelihood that the number of intruders enteringthe territory would increase linearly, and hence their totalimpact exponentially, with time away. In addition, the averageduration of searching bouts and the duration of a spawning boutwere significantly inversely related to a measure of territorialintruder pressure. Most intruders were heterospecific food competitors;incidence of intrusion by conspecifics was rare, and intrudingconspeciflcs did not contest the owner upon her return. In addition,the time females spent in their territories before beginninganother bout of searching was not positively related to theduration of the previous bout. Thus, there, is no support forthe alternative hypotheses that returning to the territory isa means of preventing takeover of the territory by conspedflcsor is the result of fatigue.