Induced oogenesis of the European eel (Anguilla anguilla L.) in freshwater condition

European eel is a catadromous fish species, which means that after living in freshwater premature individuals adapt to sea water, and migrate to the Sargasso Sea for spawning. Although male eel can be sexually matured even in freshwater, to date, it was believed that female eel can be matured only in seawater. Here we show that the process of sexual maturation may be induced in freshwater by treating female eels with carp pituitary (GSI = 9.87 ± 1.55%). It is thus proposed that seawater condition is not an obligatory environment for stimulating gametogenesis and for artificial maturation of the European eel in neither gender.     

Age distribution, growth, and lifetime copulation frequency of a freshwater snail, Clithon retropictus (Neritidae)

Clithon retropictus is a prosobranch snail species that reproduces in freshwater but spends its veliger period in the sea. The age distribution of this snail was investigated at three sites along Takase River in Japan by counting annual growth lines on their shells. Also, copulation performance was examined using sheaths of spermatophores stored in the bursa copulatrix of females. A mark–recapture census demonstrated that the number of growth lines was a good indicator of the age of a snail. The maximum number of growth lines was 20, suggesting that this species is one of the most long-lived freshwater gastropods. All the populations were female biased; the growth rate was higher and the life span was longer in females. Because spermatophore sheaths received by a female remained in her bursa copulatrix without being digested or discharged, the number of spermatophores implies her lifetime number of copulations. The number ranged from 0 to 91 and increased with age. Comparisons of population demonstrated that the average age was older, and the lifetime copulation number was significantly lower, at the upper stream site. These findings suggest that upstream migration had occurred only when the snails were very young and that copulation had been suppressed at the upstream site. The observed shorter longevity in males and the female-biased sex ratio are thought to be a result of the high cost paid by the male in multiple copulation. Received: February 1, 2001 / Accepted: April 12, 2001     

Mobility affects copulation and oviposition dynamics in Pieris brassicae in seminatural cages

When, how often and for how long organisms mate can have strong consequences for individual fitness and are crucial aspects of evolutionary ecology. Such determinants are likely to be of even greater importance in monandrous species and species with short adult life stages. Previous work suggests that mobility, a key dispersal? related trait, may affect the dynamics of copulations, but few studies have investigated the impact of individual mobility on mating latency, copulation duration and oviposition latency simultaneously. In this paper, we monitored the copulation dynamics of 40 males and 40 females, as well as the oviposition dynamics of the females of the Large White butterfly Pieris brassicae, a facultative long-distance disperser butterfly. Individuals from a breeding were selected to create a uniform distribution of mobility and we recorded the timing, number and duration of all copulations in a semiexperimental system. We showed that mobility, measured as the time spent in flight under stressful conditions (a proxy of dispersal tendency), correlates with all aspects of copulation dynamics: mobile males and females mated earlier and for shorter periods than less mobile individuals. In turn, late mating females increased the time between copulation and oviposition. These results feed the previously described mobility syndrome of R brassicae, involving morphological and physiological characters, with life-history traits. We suggest that the reduction of mating latency and copulation duration has an adaptive value in dispersing individuals, as their life expectancy might be shorter than that of sedentary individuals.     

Habitat Uses of Freshwater Fishes on the Scale of Reach System Provided in Small Streams

Synopsis Before we can conserve freshwater fish communities, we must first elucidate the habitat uses of each species. We investigated the relationships between the habits of freshwater fishes and environmental factors in small streams located in western Toyama Prefecture, Japan. We found 30 species – 11 fluvial, 5 brackish water, 2 anadromous, 11 amphidromous, and 1 catadromous – by a semi-quantitative collecting method. Using binary data (occurrence/non-occurrence of dominant fish), we conducted logistic regression analyses to construct predictive models. Stepwise logistic regression analyses on the basis of eight biotic and abiotic factors showed that the occurrence of dominant fish was explained by environmental conditions. The flow variation, ratio of stream bed slope to the surrounding area, distance from sea, and drift plant richness were relevant. Freshwater minnow, Phoxinus oxycephalus jouyi, preferred the gentle slopes of upstream catchments. The freshwater goby, Rhinogobius flumineus, appeared to prefer steeper slopes relative to the surrounding area. In contrast, diadromous gobies preferred reaches near the sea. These suggest a correspondence between lifestyle and preferred habitat. Consequently, the maintenance of various habitat conditions is necessary for the conservation of freshwater fishes.     

Zehnfußkrebse – Pioniere der Evolution

Decapod Crustaceans Decapod Crustaceans, which are by origin a marine group that still occurs mainly in the sea, invaded during their evolution also firm land and freshwater habitats. Stress factors associated with those non‐marine environments have successfully been countervailed by long‐lived benthic juvenile and adult life‐history stages, which were able to evolve structural and physiological adaptations. By contrast, the adaptability of the short‐lived planktonic larval stages has been much weaker, remaining physiologically fragile and mostly dependant on planktonic food sources. Terrestrial as well as limnic decapods have evolved various ”export strategies" based on extended migrations. These are performed by the adult females and/or the first larval stage, being aimed at an avoidance of stress conditions during the larval phase. In order to successfully complete the larval phase in freshwater, already the earliest developmental stages must express special structures and physiological functions aiding to the maintenance of osmotic homeostasis and to an independance from planktonic food sources.     

Reproductive behavior of females and its relation to the mating success of two male forms inMnais pruinosa (Zygoptera: Calopterygidae)

The behavior of females of the damselflyMnais pruinosa was observed in the breeding season. Males consisted of both territorial (esakii) and non-territorial (strigata) types in the study area. Females sometimes arrived at a stream for mating and oviposition. The staying time of females in the stream was 1–3 hours, while that of males was 5–8 hours. The proportion of the males that copulated with the females did not differ between the two male forms present in the stream. In the Calopterygidae, of which the females usually perform multiple copulation, oviposition without subsequent recopulation is considered to be advantageous for a mated male in order to avoid the risk of sperm displacement. From such a viewpoint, the time spent for oviposition was measured for females that arrived at the stream after copulation with different male forms. The ratio was 69.1: 11.5–30.9 betweenesakii andstrigata males. Assuming that the oviposition time is proportional to the number of fertilized eggs laid, this ratio would represent the relative reproductive success of the two male forms. In fact, the relative abundance of the two male forms was also biased in favor ofesakii males (61.7:38.3) in this population. The mechanism of coexistence of the two male forms is discussed in relation to their reproductive success.     

Abbreviation of larval development and extension of brood care as key features of the evolution of freshwater Decapoda

The transition from marine to freshwater habitats is one of the major steps in the evolution of life. In the decapod crustaceans, four groups have colonized fresh water at different geological times since the Triassic, the freshwater shrimps, freshwater crayfish, freshwater crabs and freshwater anomurans. Some families have even colonized terrestrial habitats via the freshwater route or directly via the sea shore. Since none of these taxa has ever reinvaded its environment of origin the Decapoda appear particularly suitable to investigate life‐history adaptations to fresh water. Evolutionary comparison of marine, freshwater and terrestrial decapods suggests that the reduction of egg number, abbreviation of larval development, extension of brood care and lecithotrophy of the first posthatching life stages are key adaptations to fresh water. Marine decapods usually have high numbers of small eggs and develop through a prolonged planktonic larval cycle, whereas the production of small numbers of large eggs, direct development and extended brood care until the juvenile stage is the rule in freshwater crayfish, primary freshwater crabs and aeglid anomurans. The amphidromous freshwater shrimp and freshwater crab species and all terrestrial decapods that invaded land via the sea shore have retained ocean‐type planktonic development. Abbreviation of larval development and extension of brood care are interpreted as adaptations to the particularly strong variations of hydrodynamic parameters, physico‐chemical factors and phytoplankton availability in freshwater habitats. These life‐history changes increase fitness of the offspring and are obviously favoured by natural selection, explaining their multiple origins in fresh water. There is no evidence for their early evolution in the marine ancestors of the extant freshwater groups and a preadaptive role for the conquest of fresh water. The costs of the shift from relative r‐ to K‐strategy in freshwater decapods are traded‐off against fecundity, future reproduction and growth of females and perhaps against size of species but not against longevity of species. Direct development and extension of brood care is associated with the reduction of dispersal and gene flow among populations, which may explain the high degree of speciation and endemism in directly developing freshwater decapods. Direct development and extended brood care also favour the evolution of social systems, which in freshwater decapods range from simple subsocial organization to eusociality. Hermaphroditism and parthenogenesis, which have evolved in some terrestrial crayfish burrowers and invasive open water crayfish, respectively, may enable populations to adapt to restrictive or new environments by spatio‐temporal alteration of their socio‐ecological characteristics. Under conditions of rapid habitat loss, environmental pollution and global warming, the reduced dispersal ability of direct developers may turn into a severe disadvantage, posing a higher threat of extinction to freshwater crayfish, primary freshwater crabs, aeglids and landlocked freshwater shrimps as compared to amphidromous freshwater shrimps and secondary freshwater crabs.     

Assessment of entomological indicators of Aedes aegypti (L.) from adult and egg collections in S?o Paulo, Brazil

We compared the presence and mean number of eggs from oviposition traps with the mean number of Aedes aegypti females captured by manual aspirators and by MosquiTRAPs to determine the sensitivity of each method and to standardize each indicator. The collections of adults and eggs were performed over 23 weeks in six neighborhoods of Mirassol, state of S?o Paulo, Brazil. A better assessment of indicators required larger number of MosquiTRAPs, but to quantify the number of females per house, one trap was sufficient. The sensitivities of MosquiTRAPs and manual aspirations to detect the presence of A. aegypti females were similar, but were lower compared to oviposition traps. The correlation coefficients between the number of females captured by MosquiTRAPs and manual aspirations and the number of eggs from oviposition traps were low, which may be a consequence of each method showing different stages of the mosquito life cycle.     

Time spent in distinct life history stages has sex‐specific effects on reproductive fitness in wild Atlantic salmon

In species with complex life cycles, life history theory predicts that fitness is affected by conditions encountered in previous life history stages. Here, we use a 4‐year pedigree to investigate if time spent in two distinct life history stages has sex‐specific reproductive fitness consequences in anadromous Atlantic salmon (Salmo salar). We determined the amount of years spent in fresh water as juveniles (freshwater age, FW, measured in years), and years spent in the marine environment as adults (sea age, SW, measured in sea winters) on 264 sexually mature adults collected on a river spawning ground. We then estimated reproductive fitness as the number of offspring (reproductive success) and the number of mates (mating success) using genetic parentage analysis (>5,000 offspring). Sea age is significantly and positively correlated with reproductive and mating success of both sexes whereby older and larger individuals gained the highest reproductive fitness benefits (females: 62.2% increase in offspring/SW and 34.8% increase in mate number/SW; males: 201.9% offspring/SW and 60.3% mates/SW). Younger freshwater age was significantly related to older sea age and thus increased reproductive fitness, but only among females (females: ?33.9% offspring/FW and ?32.4% mates/FW). This result implies that females can obtain higher reproductive fitness by transitioning to the marine environment earlier. In contrast, male mating and reproductive success was unaffected by freshwater age and more males returned at a younger age than females despite the reproductive fitness advantage of later sea age maturation. Our results show that the timing of transitions between juvenile and adult phases has a sex‐specific consequence on female reproductive fitness, demonstrating a life history trade‐off between maturation and reproduction in wild Atlantic salmon.     

Molecular characterisation of prolactin and analysis of extrapituitary expression in the European sea bass Dicentrarchus labrax under various salinity conditions

Although prolactin has been demonstrated to be the main hormone involved in adaptation to dilute media in several freshwater teleosts, few studies have been conducted in marine teleosts. In the Mediterranean, the sea bass Dicentrarchus labrax inhabits environments ranging from the open sea to coastal lagoons, where salinity varies greatly. We characterised the prolactin (prl) gene and analysed its expression in two organs (gill and intestine) in D. labrax acclimated to either freshwater or seawater. A 2819 bp long sequence encompassing the prl gene and a part (282 bp) of the promoter were identified, and these comprised 5 coding exons separated by 4 introns. Prolactin was similarly expressed in fresh- and seawater adapted fish, although expression in gills was significantly greater than in the intestine. Nonetheless, individuals unable to successfully regulate osmotic balance in freshwater presented overall low expression rates. Results are discussed according to the mechanism of sea bass adaptation in the wild and to their life cycle between open sea and lagoons. Finally, a phylogenetic analysis indicated that teleosts are not branched according to their life-history features (e.g. seawater vs. freshwater habitats), and no signature of positive selection was detected across the phylogeny of the prl gene in teleosts.     

基于耳石微化学的乌苏里白鲑生境履历分析

为了分析乌苏里白鲑(Coregonus ussuriensis Berg)的洄游生态类型及生境履历, 采用X射线电子探针微区分析技术(EPMA)研究了2013年12月、2014年1月黑龙江干流2尾和松花江干流2尾乌苏里白鲑矢耳石的锶(Sr)、钙(Ca)元素微化学特征。定量线分析结果显示, 乌苏里白鲑耳石锶钙比值(Sr/Ca×103)波动显著, 具有对应淡水生活的低值区(小于5), 而且还有对应咸水生活的高值区(大于10), 显示了乌苏里白鲑的溯河洄游履历; 耳石元素面分析结果也显示乌苏里白鲑的淡水-咸水洄游的特征。结合耳石年轮特征分析, 乌苏里白鲑具有年度(季节)洄游特征, 部分群体有规律在淡水-咸水中季节洄游, 不同个体在淡水、咸水之间停留时间存在较大差异。研究表明, 乌苏里白鲑伴随着季节性洄游特征, 具有江海或者淡水-河口之间洄游的履历。     

实验室条件下长角血蜱的生物学特性研究

实验室条件[(27±1)℃;75%RH;6L：18D]下,长角血蜱完成其生活史需135.8d：卵的孵化期为38.5d：幼虫吸血前期、吸血期和蜕皮前期分别为5.3d,3.8d和13.9d;若虫吸血前期、吸血期和蜕皮前期分别为7.2d,5.4d和16.9d;成虫吸血前期、吸血期、产卵前期和产卵期分别为7.6d,9.4d,7.8d和20.0d。雌虫饱食体重与产卵量之间存在非常显著的正相关(r＝0.9496,P<0.001)。雌虫的生殖效率指数REI＝11.06,生殖适合度指 数RFI＝7.19。生活周期在不同季节无明显变化。雄虫吸血期受雌虫吸引而成功地交配,这一过程是在吸引性信息素的作用下完成的。     

Function and genetics of long versus short copulations in the cactophilic fruit fly,drosophila mojavensis (diptera: drosophilidae)

Variation in copulation duration of Drosophila mojavensisstrains was influenced by both sexes. Males maintained predominant control, as copulation duration of pairs from different strains was more similar to that of the strain from which the male was derived, but female origin also contributed significantly to the duration of copulation. Variation among strains was controlled by genes acting additively in both sexes. The size of both males and females also affected copulation duration. Small males copulated longer on average than large males, while males paired with large females copulated longer than those paired with small females. The importance of copulation duration to fitness was tested by correlation analyses with male size, female size, female remating latency, and number of eggs laid prior to female remating. Longer copulations stimulated earlier oviposition, possibly by increasing accessory gland secretions that are passed by males during copulation.     

Diverse migration strategy between freshwater and seawater habitats in the freshwater eel genus Anguilla

The freshwater eels of the genus Anguilla, which are catadromous, migrate between freshwater growth habitats and offshore spawning areas. A number of recent studies, however, found examples of the temperate species Anguilla anguilla, Anguilla rostrata, Anguilla japonica, Anguilla australis and Anguilla dieffenbachii that have never migrated into fresh water, spending their entire life history in the ocean. Furthermore, those studies found an intermediate type between marine and freshwater residents, which appear to frequently move between different environments during their growth phase. The discovery of marine and brackish-water residents Anguilla spp. suggests that they do not all have to be catadromous, and it calls into question the generalized classification of diadromous fishes. There has been little available information, however, concerning migration in tropical Anguilla spp. Anguilla marmorata, shows three fluctuation patterns: (1) continuous residence in fresh water, (2) continuous residence in brackish water and (3) residence in fresh water after recruitment, while returning to brackish water. Such migratory patterns were found in other tropical species, Anguilla bicolor bicolor and Anguilla bicolor pacifica. In A. b. bicolor collected in a coastal lagoon of Indonesia, two further patterns of habitat use were found: (1) constantly living in either brackish water or sea water with no freshwater life and (2) habitat shift from fresh water to brackish water or sea water. The wide range of environmental habitat use indicates that migratory behaviour of tropical Anguilla spp. is facultative among fresh, brackish and marine waters during their growth phases after recruitment to the coastal areas. Further, the migratory behaviours of tropical Anguilla spp. appear to differ in each habitat in response to inter and intra-specific competition. The results suggest that tropical Anguilla spp. have a flexible pattern of migration, with an ability to adapt to various habitats and salinities. The ability of anguillids to reside in environments of various salinities would be a common feature between tropical and temperate species without a latitudinal cline. Thus, the migration of Anguilla spp. into fresh water is clearly not an obligatory behaviour. This evidence of geographical variability among Anguilla spp. suggests that habitat use is determined by environmental conditions in each site.     

Deep-ocean origin of the freshwater eels

Of more than 800 species of eels of the order Anguilliformes, only freshwater eels (genus Anguilla with 16 species plus three subspecies) spend most of their lives in freshwater during their catadromous life cycle. Nevertheless, because their spawning areas are located offshore in the open ocean, they migrate back to their specific breeding places in the ocean, often located thousands of kilometres away. The evolutionary origin of such enigmatic behaviour, however, remains elusive because of the uncertain phylogenetic position of freshwater eels within the principally marine anguilliforms. Here, we show strong evidence for a deep oceanic origin of the freshwater eels, based on the phylogenetic analysis of whole mitochondrial genome sequences from 56 species representing all of the 19 anguilliform families. The freshwater eels occupy an apical position within the anguilliforms, forming a highly supported monophyletic group with various oceanic midwater eel species. Moreover, reconstruction of the growth habitats on the resulting tree unequivocally indicates an origination of the freshwater eels from the midwater of the deep ocean. This shows significant concordance with the recent collection of mature adults of the Japanese eel in the upper midwater of the Pacific, suggesting that they have retained their evolutionary origin as a behavioural trait in their spawning areas.     

A part of the Japan Sea form of the threespine stickleback, Gasterosteus aculeatus, spawns in the seawater tidal pools of western Hokkaido Island, Japan

The Japan sea form of the threespine stickleback, Gasterosteus aculeatus, was found to spawn in the seawater tidal pool of the Cape Benkei, western Hokkaido Island, Japan, in 2001 and 2003. Nest-guarding males, adult females and juveniles of this form were also observed in four tidal pools of the Capes Benkei, Kabuto and Kamui, in 2001–2003. Otolith Sr:Ca ratios in sticklebacks collected from these tidal pools were relative high from the core to the edge, suggesting they lived in seawater environments throughout its life cycle. These findings suggest that a part of the Japan Sea formȁ9s individuals in western Hokkaido Island have the potential to breed in the coastal sea and the life history style has evolved in dependence on the seawater environment.     

Prior oviposition, female receptivity and last-male sperm precedence in the cosmopolitan pest Callosobruchus maculatus (Coleoptera: Bruchidae)

Sperm competition studies have shown that P₂ (the proportion of ova fertilized by the last male to mate) increases as the interval between inseminations is experimentally increased. Variation in the number of sperm in storage is associated with sperm use (or loss) from the female's sperm stores between copulations (fewer sperm from previous mates at the time of the last copulation) and with the extent of prior oviposition and female receptivity to further copulation: females that lay many eggs tend to have few remaining sperm in storage and to be more receptive to further copulation. Using the bruchid beetle Callosobruchus maculatus, we examined the effect of prior oviposition and female receptivity to further copulation on the extent of last-male sperm precedence (measured as P₂). Extent of prior oviposition was experimentally manipulated independently of the intermating interval by altering the availability of oviposition sites between inseminations. Females given few or no oviposition sites laid fewer eggs, were less receptive and had a lower P₂ than females given abundant oviposition sites. To examine the effect of female receptivity on P₂ independently of prior oviposition, we examined the outcome of sperm competition experiments using (1) females from lines that had been selected for different latencies to copulation and (2) natural variation in female latency to receptivity. Female receptivity to further copulation had no detectable effect on P₂. When oviposition resource is abundant, female receptivity may be a poor predictor of current sperm load.     

Freshwater habitat use by a moray eel species,Gymnothorax polyuranodon,in Fiji shown by otolith microchemistry

Freshwater eels of the Anguillidae are diadromous because they migrate between ocean and freshwater environments, but other anguilliform fishes are generally considered to be strictly marine species. A few marine eels of the Muraenidae and Ophichthidae have occasionally been found in freshwater or estuaries, indicating that anguillids are not the only anguilliform eels that can use freshwater in some parts of the world. The moray eel Gymnothorax polyuranodon is one species that is known to be present in freshwater in the Indo-Pacific, but its life history is unknown. One way to evaluate what types of habitats are used by fishes is to determine the ratio of strontium (Sr) to calcium (Ca) in their otoliths, because this can show if they have used freshwater or saltwater environments. To evaluate the patterns of freshwater use by this unusual species of marine eel, the otolith Sr/Ca ratios of four G. polyuranodon (275–344 mm) caught in a freshwater stream of Fiji were analyzed. The consistently low Sr/Ca values (0–4) indicated upstream movement after settlement and freshwater or estuarine residence of all four individuals. These eels did not appear to have entered freshwater just for a short time period, which is consistent with other reports that this species is present in estuarine and freshwater habitats. This suggests that G. polyuranodon may be a catadromous species of marine eel. The similarities and differences between the life histories of anguillid eels and the few marine eels that have evolved the ability to invade freshwater habitats is discussed in relation to the evolutionary origin of diadromy in anguilliform fishes that originated in the marine environment.     

Mortality of the terrestrial adult and aquatic nymphal life stages of Baetis vernus and Baetis rhodani in the Breitenbach, Germany (Insecta: Ephemeroptera)

1. The mortality of Baetis vernus Curtis and Baetis rhodani Pictet during the terrestrial-aerial and aquatic life stages was studied at the Breitenbach near Schlitz, Hesse, Germany. The number of females emerging from the stream was recorded with emergence traps. To estimate mortality of females of both species during terrestrial life, numbers of emerging females were compared with numbers of females returning to the stream for oviposition, as shown by numbers of egg masses found in the stream. 2. Mortality of female B. vernus during their terrestrial life stage was 98.8%. It was 91.2 and 96.6%, respectively, during the first and second generations of B. rhodani. 3. To estimate the mortality of both sexes of B. rhodani during the aquatic life stage, the number of eggs laid by the first generation was compared with the number of adults emerging during the second generation. 4. Mortality during the aquatic phase (both sexes combined) of B. rhodani was 91.1%. 5. Mortality during the terrestrial life stages was at least as high, if not higher than during the aquatic stages. Evidently, there is a considerable export of organic material into the terrestrial environment around the stream. Mortality during terrestrial life may be an important regulator of population size.     

Pre-oviposition mate-guarding and mating behaviour of Argia vivida (Odonata: Coenagrionidae)

Abstract. 1. At Halcyon Hotsprings, British Columbia, Canada, male and female Argia vivida Hagen encountered to mate in two different ways.
2. In the morning (before 12.30 hours solar time), males basked at sunspots in the forest and darted out at passing females, attempting to take them in tandem (the first method of encounter).
3. If a male was successful, the pair engaged in a 31.3±4.8 min copulation followed by an hour of tandem flight before beginning oviposition.
4. As the day progressed, unmated males moved slowly toward the water and arrived at the water at about the same time as the earliest ovipositing pairs (1131±27.5 min solar time).
5. Males retained their grasp on their mates during oviposition (contact-guarding) but since some tandems separated during oviposition, non-tandem males at the water could capture recently released, gravid females (the second method of encounter).
6. The new pairs performed a brief copulation (10.2±3.38 min) and began ovipositing immediately thereafter.
7. Some females that avoided recapture attempted to oviposit unguarded.
8. We believe the long duration of morning copulations and period of tandem constitute a male strategy, which we call 'pre-oviposition guarding', to guard females until it is warm enough at the oviposition site for the females to begin ovipositing.
9. Separation of tandems during oviposition may be initiated by either member of the pair and we suggest that one benefit to a female of leaving a guarding mate is increased efficiency of oviposition when the intensity of male harassment is low.
10. The mating system of A. vivida thus comprises a series of complementary male and female mating behaviours.