Auditory role of the suprabranchial chamber in gourami fish

Fish hearing specialists (e.g., goldfish, holocentrids, clupeoids, mormyrids) have evolved specialized structures (e.g., Weberian ossicles, swimbladder diverticulae, gas-filled bullae) to enhance their auditory frequency range and threshold sensitivity. The inner ears of anabantoid fish are encased in membranous cranial bones and are protruded into air-filled suprabranchial chambers. This research was intended to test the hypothesis that the gas bubbles inside the suprabranchial chambers may modulate the hearing abilities of anabantoid fish because of their proximity to the membranous bone-encased inner ears. Three species of gourami (blue gourami Trichogaster trichopterus; kissing gourami Helostoma temminckii; dwarf gourami Colisa lalia) were examined. Using the auditory brainstem response recording technique, baseline audiograms tested at 300, 500, 800, 1500, 2500, 4000 Hz were obtained. The air bubbles in the suprabranchial chambers were replaced by water, and the audiograms were remeasured. Thresholds were elevated in all three species. When three blue gouramis were allowed to replenish air into the suprabranchial chambers their hearing abilities returned to baseline levels. These results support the hypothesis that air bubbles in the suprabranchial chambers can affect hearing abilities of gouramis by lowering the thresholds. Accepted: 28 May 1998     

Chorus organization and male mating behavior in the Japanese pond frog,Rana porosa brevipoda

Male mating behavior of a Japanese pond frog,Rana porosa brevipoda, was observed in an enclosed pond. Males organized chorus aggregation during the night. Within the chorus, most males defended “floating” territories. Territorial males exhibited 2 types of calls: advertisement and encounter. Mating occurred primarily in male territories with female initiation, while most spawning occurred outside of the territories. After spawning, males returned to their territories and resumed display behavior. The mating system of this frog is analogous to the typical lek system. Alternative male mating tactics, including satellite and ambush behavior, were also observed. Satellite and ambush males mated with females through forced clasping.     

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.     

Influences of establishment and maintenance of territory on reproductive activity in the male dwarf gourami Colisa lalia

We examined the importance of establishment and maintenance of territory on reproductive activity in the male dwarf gourami, Colisa lalia. After three males had been forced to fight for territory (five sets) for three weeks, social status was divided into three classes: the territorially dominant male, which guarded the territory under the floating nest; the second male which remained near the nest and occasionally attacked the dominant male; and the third male which was non-aggressive and remained at a distance from the other two males. Comparing testicular size by gonadosomatic indices (GSI) after three weeks of aggression, GSI of the dominant male (1.19 ± 0.07) was significantly larger than that of the second (0.81 ± 0.15) and the third (0.62 ± 0.08) males, as well as the initial control (not involved in any experiments: 0.85 ± 0.10, n = 5), indicating that the testes of the dominant males enlarge during territory defense. Histological observations of testes revealed that sperm production in the dominant males was more active compared to males of other classes, although spermatogenesis was confirmed in all males examined, suggesting that dominance accelerates sperm production. Social-status dependent development of testes suggests an absence of sperm competition due to the lack of sneaking by subordinate males. Since non-territorial males do not engage in alternative tactics (e.g., sneaking) leading to emission of semen, male C. lalia must obtain and defend territory if they are to increase their reproductive success.     

Observations on interbreeding between dwarf and normal arctic charr,Salvelinus alpinus,from Stora Rösjön,central Sweden

Synopsis The spawning behaviour of dwarf and normal arctic charr, Salvelinus alpinus, was studied through trough observations in October 1988. The experimental fish consisted of reared, three-summer old progeny of artificially bred dwarf and normal charr from an isolated body of water in central Sweden. The spawning behaviour of three normal female charrs was studied and video-recorded. The study showed that the arctic charr is potentially polyandric both within and between forms. The normal female was courted and mated both by normal and dwarf males. It was also noted that antagonistic behaviour on behalf of the female was much more common towards dwarf males than normal males. Guarding tactics were only observed in normal males, whereas sneaking tactics were employed both by dwarf and normal males. The dwarf as well as normal males mated the female charr either by courting the female or by joining the spawning fish at oviposition. Only dwarf males were observed resting silently on the bottom close to the redd.     

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.     

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.     

Intersexual cooperation during male clasping of external female genitalia in the spider Physocyclus dugesi (Araneae, Pholcidae)

Sexual conflict may influence the shape and evolution of body structures that males use to grasp females during mating. Not only sexual coercion but also intersexual cooperation may be involved during clasping behavior. Among pholcid spiders, secondary sexual modifications of the male chelicerae, such as apophyses with spines or tooth-like processes, function to grasp the female by specific parts of her external genitalia such as grooves or apophyses of the epigynum. We analyzed how the female and the male respond when their structures for clasping are experimentally modified in the pholcid Physocyclus dugesi. We used three treatment groups for virgin females that differed in the manipulation of the epigynum apophyses (uncovered, partially covered, and fully covered by a plaster) and two groups of males (uncovered and fully covered cheliceral apophyses). We found that females are mainly cooperative to courting males not only when the female genital apophyses were experimentally covered but also when the male cheliceral apophyses were covered. The current data also indicate behavioral flexibility in males during courtship, especially when they had difficulty in genital intromission. Our experimental results, together with previous observational studies, support a modulated-cooperative scenario between the sexes for cheliceral clasping and genital intromission in pholcid spiders.     

Mating behavior ofXylotrechus pyrrhoderus Bates (Coleoptera: Cerambycidae) V. Female mounting behavior

Female mounting behavior was observed in the grape borerXylotrechus pyrrhoderus Bates (Coleoptera: Cerambycidae) under laboratory conditions. This behavior was directed towards either females (i.e., female homosexual mounting) or males. The female homosexual mounting was strongly elicited in females which had previously been allowed to fly. The frequency of this behavior was not related to the experience of mating. The investigation of the daily temporal pattern in female homosexual mounting activity indicated that the behavior most frequently occurred between 12∶00 and 16∶00, i.e., when females were searching for the pheromone-releasing males. Oviposition was also observed during this time interval. A detailed analysis revealed female mounting behaviors which are characteristic of male mounting behaviors, such as chasing conspecifics and synchronism of licking and abdominal bending. On the other hand, the frequency of male homosexual mounting was lower than that of females. Taken together with cases of other species previously reported, the expression of mounting behavior in females may be related to the evolution of the reproductive system, in which females approach their mates.     

Iridovirus disease in two ornamental tropical freshwater fishes: African lampeye and dwarf gourami

Many species of ornamental freshwater fishes are imported into Japan from all over the world. We found African lampeye Aplocheilichthys normani and dwarf gourami Colisa lalia suffering from an iridovirus infection just after being imported by tropical fish wholesalers from Singapore. African lampeye were cultured on the Indonesian Island of Sumatra and dwarf gourami were cultured in Malaysia before export. Diseased fishes displayed distinct histopathological signs of iridovirus infection: systemic appearance of inclusion body-bearing cells, and necrosis of splenocytes and hematopoietic cells. Electron microscopy revealed viral particles (African lampeye:180 to 200 nm in edge to edge diameter; dwarf gourami: 140 to 150 nm in diameter) in an inclusion body within the cytoplasm of inclusion body-bearing cells as well as in the cytoplasm of necrotized cells. Experimental infection with an iridovirus isolate from African lampeye (ALIV) revealed pathogenicity of ALIV to African lampeye and pearl gourami Trichogaster leeri. Polymerase chain reaction (PCR) products from ALIV and an iridovirus isolate from dwarf gourami (DGIV) using iridovirus-specific primers were indistinguishable. The nucleotide sequence of PCR products derived from ALIV (696 base pairs) and DGIV (701 base pairs) had 95.3% identity. These results indicate that ALIV and DGIV have a single origin.     

Mate choice in female convict cichlids (<Emphasis Type="Italic">Amatitlania nigrofasciata</Emphasis>) and the relationship between male size and dominance

We examined how male size and fighting ability influence a female’s mate assessment process and her eventual mate choice in the monogamous convict cichlid, Amatitlania nigrofasciata. Females always chose the larger of two males when they were allowed to see a larger male next to a smaller one and when a larger male defeated a smaller one in a fight. They did not differentiate between large and small males when they did not see the two males together nor did they choose a dominant over a subordinate male when both were the same size. We suggest that females select on the basis of male size because it is a better predictor of both direct and indirect benefits (i.e., future competitive interactions and foraging ability) than dominance behavior only. Despite selecting one male over the other early in the courtship period, females continued to visit both males until spawning. Our evidence suggests that this assessment behavior more closely resembles a bet-hedging tactic rather than the female’s indecision as to which male will be her mate.     

Mate Choice and Spawning Success in the Fighting Fish Betta splendens: the Importance of Body Size, Display Behavior and Nest Size

Courtship displays should be exaggerated enough to attract mates and yet tempered so as not to deter them. We tested this hypothesis in the fighting fish Betta splendens by studying courtship displays and body size and their relationships with male parental quality and female fecundity, as well as the effects of display behavior and body size on mate choice decisions and spawning success. Because of their high degree of parental investment, males are expected to be discriminating in their choice of mates. Males who displayed more frequently built larger nests, a measure of parental quality, but larger males did not. When females were paired with males with high display rates, however, the pair had fewer eggs in their nest, even when accounting for female body mass. In a mate choice test using computer‐generated male stimuli that differed only in display behavior, females showed no preferences for displaying males vs. non‐displaying males, or for males with higher display rates vs. lower display rates. In similar tests in which the computer‐generated males differed only in size, females preferred larger males, but also preferred males that differed with respect to body size (negative assortative mating). Males preferred computer‐generated females that performed courtship displays over non‐displaying females, but showed no preferences for female body size. Neither a female's body size nor her display behavior was a significant predictor of her fecundity as estimated by the number of eggs released during spawning. Thus, our results suggest that female B. splendens must balance male parental quality (nest size) with the risk of potentially disruptive or dangerous behavior during spawning, and that females may minimize these risks through negative size‐assortative mating. Female display behavior, while unrelated to fecundity in our study, may attract males because it indicates reproductive readiness or serves a species‐recognition function.     

Sexual coercion does not exclude luring behavior in the climbing camel-spider <Emphasis Type="Italic">Oltacola chacoensis</Emphasis> (Arachnida,Solifugae, Ammotrechidae)

Sexual coercion in the form of forced copulation has been used as a typical example to illustrate the conflict of interests between females and males. Among arthropods, forced copulation has been reported for some groups of insects and crustaceans, but not for arachnids. In the present work, we analyse and describe the behavioral patterns of mating behavior of the climbing camel-spider, Oltacola chacoensis, relating it to relevant morphological features, In this species, the male forcefully clasps the female’s genital region with his chelicerae and locks her fourth pair of legs with his pedipalps. In some cases, the cuticle of the female’s abdomen was damaged by this cheliceral clasping. In contrast to other camel-spiders, the female O. chacoensis never remained motionless during mating, but continuously shook her body, opening her chelicerae notably towards the male. Despite this coercive context, males performed copulatory courtship (tapping with pedipalps) and females showed an apparent cooperative behavior (they remained still during a short period of the sperm transfer phase). These results strengthen the idea that sexual coercion (in the form of forced copulation) and luring behavior (in the form of copulatory courtship) are not two mutually-exclusive male’s strategies during a single copulation.     

Reproductive compatibility among latitudinally separated Scottolana canadensis (Willey) (Harpacticoida)

Scottolana canadensis is distributed widely along the east coast of North America. Although males exhibited mating behavior with females copepodites, copulation occurred following the female terminal molt. Crossing experiments revealed that in some cases, male mating behavior decreased with increasing latitudinal distance of male and female source locales. However, latitudinally-related differences in copepod body size most likely did not contribute to variation in male mating behavior. Survival patterns of fertilized eggs and fertility of offspring revealed postzygotic reproductive isolation of Florida populations from all others collected north to Maine.     

A test of Rensch’s rule in dwarf chameleons (Bradypodion spp.), a group with female-biased sexual size dimorphism

Rensch’s rule describes a pattern of allometry in sexual size dimorphism (SSD): when males are the larger sex (male-biased SSD), SSD increases with increasing body size, and when females are the larger sex (female-biased SSD), SSD decreases with increasing body size. While this expectation generally holds for taxa with male-biased or mixed SSD, examples of allometry for SSD consistent with Rensch’s rule in groups with primarily female-biased SSD are remarkably rare. Here, I show that the majority of dwarf chameleons (Bradypodion spp.) have female-biased SSD. In accordance with Rensch’s rule, the group exhibits an allometric slope of log(female size) on log(male size) less than one, although statistical significance is dependent on the phylogenetic comparative method used. In this system, this pattern is likely due to natural selection on both male and female body size, combined with fecundity selection on female body size. In addition to quantifying SSD and testing Rensch’s rule in dwarf chameleons, I discuss reasons why Rensch’s rule may only rarely apply to taxa with female-biased SSD.     

Hormone effects on male sex behavior in adult South African clawed frogs, Xenopus laevis

Intact, adult male Xenopus laevis were injected with human chorionic gonadotropin (HCG) and tested with intact HCG-primed females. Under these conditions, males displayed high levels of sex behavior (clasping of females). By 2 weeks after castration, these males had ceased clasping. Testosterone and dihydrotestosterone reinstated clasping in male castrates. Following removal of testosterone or dihydrotestosterone pellets, castrated males ceased to clasp. No male was ever observed to clasp following estradiol implanted in pellets or in silastic capsules. In experiments on castrated, adult, female Xenopus laevis, both testosterone and testosterone propionate pellets reliably produced male sex behavior in the form of clasping. The clasping of testosterone-implanted female and male castrates was very similar in form and duration. The behavioral effectiveness of testosterone in both sexes and the ineffectiveness of estradiol in eliciting clasping is paralleled by autoradiographic localization of sex steroids in brain where the distribution of testosterone-concentrating, cells is the same for males and females, but different from the distribution of estradiol-concentrating cells.     

The significance of sound interception to males of the bicolor damselfish,Pomacentrus partitus,during courtship

Synopsis Playback experiments conducted in the field and the laboratory demonstrated the use of sound interception in bicolor damselfish,Pomacentrus partitus. Two courtship sounds produced by male bicolors: the ‘chirp’ which occurs at the initiation of courting and the ‘grunt’ which occurs near the termination, just prior to spawning, were found to hold different meanings to intercepting male competitors. Males responded to grunt playback with directional swimming towards the sound source and increased courtship behavior. No directional response was observed during chirp playback. The grunt sound appears to indicate that a spawn-ready female is present near the sound source. Males therefore move towards it, likely to interfere with the imminent spawning or to gain a possible spawning partner. Such is not observed in response to chirps, as little advantage would be gained by moving to the source of a sound which is known to serve as an ‘advertisement’ or ‘territorial keep-out’ signal. Thus, upon intercepting a neighbor's chirps, males exhibit courting within their own territory, or directly court a nearby female.     

Androgens and male mating behavior in rough-skinned newts, Taricha granulosa

Cyproterone acetate was administered either orally or intraperitoneally to intact, adult male newts, Taricha granulosa. The number of males that exhibited the courtship behavior of clasping when tested with nuptial females was not altered by the antiandrogen treatments. In males which were unresponsive to nuptial females, the occurrence of clasping was not evoked by injections for 4 days of testosterone, dihydrotestosterone, or 11-ketotestosterone. Further, the incidence of clasping was not significantly elevated by injections of prolactin and/or testosterone for 30 days. The effect of sexual activity on testosterone and dihydrotestosterone levels in male newts was determined by radioimmunoassay of plasma collected from males which were: (1) isolated from females; (2) allowed to clasp a female for 2 min; or (3) allowed to clasp a female for 1 hr. The testosterone and dihydrotestosterone levels were unchanged during this period of clasping. In February and again in June, plasma androgen concentrations were measured in males which differed in their propensity to initiate courtship when paired with females. Androgen levels were similar for males that clasped a female and males that never attempted to clasp a female. Plasma androgen levels in the male newt are apparently not correlated with sexual responsiveness.     

Cytomorphology of female and male gonads in Antarctic toothfish <Emphasis Type="Italic">Dissosctichus mawsoni</Emphasis> (Nototheniidae) from the Ross Sea in the summer period

Results of histological analysis of gonads of female and male Antarctic toothfish Dissostichus mawsoni caught in the Ross Sea of the Pacific sector in the period of Antarctic summer (December–February) 2004–2005 are presented. Morphological indices and index of gonad maturity are described and ecological criteria of assessment of maturity stages of ovaries, cytological indices of oocytes, and the type of toothfish oogenesis are determined. It was established that in the period of fishing Antarctic toothfish, females and males with gonads at maturity stage III dominate. Ovaries contain two groups of oocytes of the period of trophoplasmatic growth and large oocytes of the nearest spawning season that comprise the smallest proportion of total sex cells. In the testes of two male toothfish, the primary fusion of renal and generative tissues was revealed. It is suggested that the termination of gonad maturity of toothfish takes place from March to April, and spawning takes place from June to August.     

Formation and structural organization of the egg�Csperm bundle of the scleractinian coral Montipora capitata

The majority of scleractinian corals are hermaphrodites that broadcast spawn their gametes separately or packaged as egg–sperm bundles during spawning events that are timed to the lunar cycle. The egg–sperm bundle is an efficient way of transporting gametes to the ocean surface where fertilization takes place, while minimizing sperm dilution and maximizing the opportunity for gamete encounters during a spawning event. To date, there are few studies that focus on the formation and structure of egg–sperm bundle. This study explores formation, ultrastructure, and longevity of the egg–sperm bundle in Montipora capitata, a major reef building coral in Hawai‘i. Our results show that the egg–sperm bundle is formed by a mucus layer secreted by the oocytes. The sperm package is located at the center of each bundle, possibly reflecting the development of male and female gametes in different mesenteries. Once the egg–sperm bundle has reached the ocean surface, it breaks open within 10–35 min, depending on the environmental conditions (i.e., wind, water turbulence). Although the bundle has an ephemeral life span, the formation of an egg–sperm bundle is a fundamental part of the reproductive process that could be strongly influenced by climate change and deterioration of water quality (due to anthropogenic effects) and thus requires further investigation.