Induction of diapause egg production in Eurytemora affinis by their own metabolites

Chemically mediated crowding effect on induction of diapause egg production in the calanoid copepod Eurytemora affinis was investigated. Two types of eggs, i.e. subitaneous and diapause eggs, produced by females that were reared in crowded culture conditions or the water from crowded culture under excess food supply were examined. 2.3% of the females that were reared at a population density of 5 or 6 animals per 10 ml of filtered lake water (FLW) produced diapause eggs. Females that were reared individually in 2-ml containers with FLW did not produce diapause eggs while 72.7% of females that were individually reared in 2-ml containers, but with water from a crowded culture (500 ind. l^–1, culture medium was changed once a week), produced diapause eggs. These results demonstrate that accumulation of their own metabolic products in the medium induces diapause egg production by E. affinis.     

The ecology of the calanoid copepod Eurytemora affinis in salt marsh tide pools

We describe selected aspects of the ecology of the copepod Eurytemora affinis in tide pools of an inland salt marsh near L'Isle-Verte, Québec along the southern shore of the St. Lawrence estuary. E. affinis performed daily horizontal migrations moving from the centers of pools to the banks and into dense algae. Male E. affinis were mainly found in the center of the pools during twilight (21 : 00 hrs) and in dense algae in daylight (12: 00 hrs) whereas most females and copepodites were found near the banks at all three sampling periods. Although these daily movements among sites may have minimized predation by diurnally foraging sticklebacks (Pisces: Gasterosteidae), other explanations for the movements can not be excluded. We also quantified the effects of fish predation upon the population structure of E. affinis. Densities of all stages (nauplius, copepodite, adult) were significantly lower in pools with fish than in pools without fish. Female E. affinis were significantly smaller (mean length) in pools with fish than in pools without fish, indicating that the sticklebacks selectively ate larger females. Male-biased sex ratios were found in both types of pools, which excluded the possibility that biased ratios in this species are caused by selective predation upon the females.     

Some reflections on the structure of the mandibleplate ofEurytemora affinis (Copepoda,Calanoida)

The mandibleplates of several specimen of the copepodEurytemora affinis collected from the Westerschelde and the Gironde estuary were studied. Using the Edge index (ITOH, 1970) this species could be classified as an omnivore. Pictures obtained by light and scanning electron microscopy reveal that the mandible teeth ofE. affinis have a molar-like structure, which likely changes in functional morphology with developmental stage, sex and age of the adults. Based on these observations, the desirability to consider the three dimensional structure of copepod mandibles for feeding mode classification is discussed.Communication no. 540 of the Delta Institute for Hydrobiological Research, Vierstraat 28, 4401 EA Yerseke, The Netherlands.     

Rapid responses to stress in Eurytemora affinis

E. affinis can adjust to temperature stress in a matter of hours. Adaptation is greater in a varying temperature than in a constant temperature, consistent with the estuarine habitat of this calanoid. The species has the capacity to adjust both in the short-term as individuals and also genetically over a number of generations. The adjustments have been examined at several levels of organization. In whole copepods the time an individual becomes comatose when exposed to a 32 °C temperature and increasing by 1/2 °C at 5 min. intervals, has been used as a repeatable assay and gives a good prediction of survival at 30 °C, the ecological limit of the species in Chesapeake bay, USA. At the molecular and cellular levels, two adaptive mechanisms which have been observed in temperature stressed copepods are the synthesis of novel proteins and phase changes in plasma membrane lipids. Both of these mechanisms have potential for further understanding the adaptation of Eurytemora to variable temperatures. They may also have application as indicators of sublethal stress.     

Salinity tolerance and osmoregulation in the freshwater crab,Barytelphusa guerini (Milne Edwards)

The freshwater crab, Barytelphusa guerini, tolerates gradual transfer to higher salinities upto seawater, regulating its blood chlorides fairly well. Its metabolic rate shows a minimum in 50% seawater and increases on either side, during dilution as well as during concentration of the medium. However, this increase is more pronounced in hypotonic than in hypertonic media.     

Surfactant-producing microorganisms isolated from the gut of a Eucalyptus-feeding sawfly,Perga affinis affinis

Summary Microorganisms which produce surfactants were isolated from the gut of a eucalypt-feeding sawfly. It is possible that surfactants in the guts of some defoliators may be microbiologically-produced.Deceased     

The ultrastructure of the eye of the mosquitofishGambusia affinis

Summary The ultrastructure of the tissue components of the eye ofGambusia affinis, excluding the sensory cells, is described. The cornea consists of two different sections of collagenous layers of different density. The choroid includes an argentea composed of- and-melanophores, lipopterinophores and a choriocapillaris associated with the rete mirabile of the choroid body. Bruch's membrane, underlying the retinal pigment layer, can develop complex associations with fibroblasts delimiting the choriocapillaris. The outer section (stroma) of the iris includes several cell types that are not found in the inner or vitread section. In adultGambusia the lens capsule is well developed, but in twoweek-oldSarotherodon larvae the lens epithelium is covered only by a glycocalyx.     

Long-term changes in the population of Eurytemora affinis (Copepoda,Calanoida) in the Gironde estuary (1978–1992)

Long-term changes in the population of Eurytemora affinis were investigated during 15 years (1978–1992) at a fixed station in the Gironde estuary (South West France). Total numbers, sex-ratio, % ovigerous females, proportion of copepodites and clutch-size were taken into account and their long-term distribution was related to temperature, river flow, salinity, suspended matter and chlorophyll a concentrations after the seasonal effect was removed for all variables.There was a great decrease of the river flow during the period of investigation, due to a general deficit in pluviosity. On the contrary, the general trend for salinity was an increase from 1978 to 1992. The same pattern was observed for chlorophyll, indicating an intrusion of marine phytoplankton. Water temperature increased significantly during the study period, following the general increase in air temperature observed in the area. For the suspended particulate matter (SPM), an increase was observed between 1978 and 1981–1982, then a very sharp decrease occurred from 1984 onwards.Numbers of E. affinis were inversely correlated with temperature and salinity, and positively correlated with the river flow. E. affinis was negatively correlated with chlorophyll concentration because of the covariation with salinity. No clear long-term trend was observed for the sex-ratio. A significant correlation was found between females carrying egg-sacs and SPM concentration, probably due to a decrease of the predation pressure in very turbid waters. The percentages of copepodites tended to decrease with time and were inversely correlated with temperature. Clutch-size significantly decreased during the 15-year period. This trend was mainly explained by temperature and salinity.It is concluded that, in the absence of strong human alteration in the Gironde estuary the long-term distribution of zooplankton can be explained by the natural environmental variability. The dominant factors are the river flow which governs the movement of the populations along the estuary and the temperature which influences the reproductive processes. Any change in climate will have consequences on the pelagic community.     

Salinity and temperature tolerance of juvenileMesopodopsis orientalis: laboratory studies

Separate and combined effects of changes in salinity and water temperature on the survival of laboratory hatched juvenileMesopodsis orientalis were investifated. Full strength seawater (35) was not favorable to juvenile survival. Salinities down to 10% seawater were tolerated when subjected to sudden exposure, but salinity acclimation increased juvenile ability to tolerate even fresh water. Water temperatures tolerated by the animals ranged from 12°C to 33°C. Salinities of 30% to 60% seawater and water temperatures of 22°C to 28°C were most favorable to the juveniles. Experimental results were compared with field observations and a relationship between the salinity and temperature of seawater and abundance of juveniles in May to June, and November to January in Bombay coastal waters (west coast of India) was established. Seawater of reduced salinity was found to be a major factor for occurrence of juvenileM. orientalis in abundance.     

Salinity tolerance of Mytilocypris henricae (Chapman) (Crustacea,Ostracoda)

Salinity tolerance, and the effects of temperature upon it, of the Australian ostracod Mytilocypris henricae (Chapman) was determined in direct transfer experiments using adults. Animals were subjected to a combination of 11 salinities (ranging between 0.0 g · 1^–1 and 45.0 g · 1^–1) and 4 temperatures (10, 15, 20 and 25 °C). Survival was analysed using two statistical techniques: the logit linear model and the proportional hazards model. Results show that both salinity and temperature have a significant effect on survival, but there is no significant interaction between temperature and salinity.     

Salinity Tolerance of Some Teleost Fishes of Peter the Great Bay, Sea of Japan

Salinity tolerance in some marine teleost fishes was studied. Based on a comparison of sexually mature specimens in the summer season, the investigated species can be arranged in the order of decreasing capability for hyperosmoregulation into the following series: the Far Eastern dace Trybolodon brandti, the haarder Mugil soiuy > the frog sculpin Myoxocephalus stelleri > the snowy sculpin M. brandti > the plain sculpin M. jaok > the masked greenling Hexagrammos octogrammus > the pipefish Syngnathus acusimilis. The adult Far Eastern dace and the haarder showed high salinity tolerance and fully adapted to fresh water. Sculpins and the masked greenling usually occur only in seas or brackish water, but they were capable of enduring fresh water for a long time. Unlike them, the pipefish, which is also a euryhaline fish and occurs in river estuaries and brackish bays, perished in fresh water within 1 h. Representatives of the genus Myoxocephalus show between-species differences in salinity tolerance, which allows them to colonize extensive near-shore areas of the sea and to occupy specific ecological niches.     

Gradients of salinity stress, environmental stability and water chemistry as a templet for defining habitat types and physiological strategies in inland salt waters

The search for pattern in the geographic occurrence of salt lake flora and fauna often reveals strong associations of specific taxa with certain types of water chemistry. Solute composition, along with salinity and habitat stability, may provide a templet shaping the distribution of many organisms inhabiting saline lakes. A review of studies demonstrating habitat associations, specific solute tolerance, and ionic and osmotic adaptations provide evidence of fidelity to particular conditions of environmental chemistry across a wide taxonomic spectrum. Under low salinity conditions, some species show osmoregulatory adaptability to varied solute composition but the capacity for such flexibility is reduced with increased salinity and only certain taxa are found in hypersaline waters dominated by a particular solute. Anionic ratios of chloride, bicarbonate–carbonate, and sulfate appear to be especially important determinants of distribution. Specific solute tolerance presents an alternative explanation to disrupted hydrographic connections in describing how biogeographic distributions may be restricted to certain aquatic habitats in arid regions. Physiological adaptations to chemistry, exemplified in the brine fly genus Ephydra, may be an integral part of the evolution, ecology and diversification of saline water organisms.     

Aspects of habitat selection in the mosquitofish gambusia affinis

Laboratory experiments were performed to determine behavioral preferences of Gambusia affinis for habitat variables in partitioned aquaria. The fish preferred calm water, dark-colored substrates and subsurface vegetation providing lateral concealment. Floating cover, which obstructed access to the surface, was avoided. Lack of preference for real over plastic plant cover indicates that visual rather than chemical cues are involved. These laboratory preferences correspond to the reported microhabitat distribution of G. affinis in nature and indicate the presence of an active habitat preference, as opposed to passive habitat correlation, in this species. Species-specific habitat preferences, which may be narrower where a species occurs sympatrically with its congeners, probably form part of a reproductive isolating mechanism.     

Salinity tolerance and morphology of the osmoregulation organs in Cladocera with special reference to Cladocera from the Aral sea

The hyperosmotic regulation of adult Cladocera is determined mainly by the amount of salts consumed with the food and by reabsorption of salts in cells of the nuchal (neck) organ. The hypoosmotic regulation both in adults and embryos is determined mainly by excretion of salts in special epipodite cells or in cells of the nuchal (neck) organ. The salinity of the Aral sea for the last 30 years increased from 8–10 to 26–28, which led to changes in the Cladocera fauna. At present only 4 species of Cladocera inhabit the Aral sea instead of 14 species that were previously found. These changes are in agreement with osmoregulation capacities of Cladocera. Note added in proof. Since this paper was accepted for publication, all Cladocera have disappeared from the Aral Sea. This happened when salinity reached 30–32. This disappearance was predicted by and agrees with earlier laboratory experiments with Aral Sea Cladocera (Aladin, 1982b).     

Development of 19 polymorphic microsatellite loci for the intermediate horseshoe bat, Rhinolophus affinis (Rhinolophidae, Chiroptera)

The intermediate horseshoe bat (Rhinolophus affinis) is a widespread species in Southeast Asia. We developed 19 novel microsatellite loci from an enriched genomic library of the bat, and tested their polymorphism using a single population from Guangdong province, southern China. The number of alleles ranged from 3 to 15 per locus with the expected and observed heterozygosity ranging from 0.397 to 0.920 and 0.280–0.926, respectively. Three markers significantly deviated from the Hardy-Weinberg expectations after Bonferroni correction and no linkage disequilibrium was detected in any of loci. These microsatellite loci will be useful in studying the phylogeography of this species.     

Salinity tolerance of the barbel,Barbus callensis Valenciennes, 1842 (Pisces,Cyprinidae) and its ecological significance

The lethal salinity limits (LC₅₀ and mean survival times) of two populations of barbel, Barbus callensis, were determined. Conditions in Lake Ichkeul, Tunisia, are lethal for the fish in summer; this explains their seasonal migrations into Oued Sejnane and the other tributaries. Tolerance increased between 1984 and 1985 from LC₅₀ = 15.6 to LC₅₀ = 17.2 in a population from Oued Mejerdah; this may be connected with the dissolution of rock salt in the new Sidi Salem reservoir.

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Résumé Les limites létales de salinité (CL₅₀ et durée moyenne de survie) de deux populations de barbeaux tunisiens ont été déterminées. Nous avons montré que les conditions de salinité dans le lac Ichkeul sont létales pour ces poissons en été, ce qui explique leurs migrations saisonnières vers l'oued Sejnane et les autres affluents. Nous avons aussi constaté une élévation récente de la tolérance de la population de la Mejerdah, qui peut être en relation avec la dissolution des roches salines dans le nouveau réservoir de Sidi Salem.

     

Hydration-state-responsive proteins link cold and drought stress in spinach

Spinach (Spinacia oleracea L.) seedlings exposed to low nonfreezing temperatures (0–10° C) that promote cold acclimation, synthesize a variety cold-acclimation proteins and at the same time acquire a greater ability to withstand cellular dehydration imposed by the freezing of tissue water. Two of these proteins (160 and 85 kDa) become more abundant over time at low temperature. In addition, a small decline in tissue water status from a maximally hydrated state also appears to be associated with an initiation of the accumulation of these proteins at a noninductive temperature. Imposing a severe water stress on young seedlings grown at 25° C by withholding water leads to substantial accumulation of the 160- and 85-kDa proteins, and maximal induction of freezing tolerance. This evidence implies that responses to cold acclimation and water stress involve common mechanisms, and further establishes the linkage of these two proteins with stresses having an osmotic component.Abbreviations ABA abscisic acid - CAP cold-acclimation protein - kDa kilodaltons We thank T. Sinclair and K. Cline for critical reading and discussions, N. Denslow for assistance with protein sequencing methods, and L. Greene, S. Henry for preparing the monoclonal antibodies. The work was made possible by support from the USDA Competitive Grants Program No. 90-37280-5527, the Institute for Food and Agricultural Sciences, and through access to the protein sequencing and hybridoma facilities of the Interdisciplinary Center for Biotechnology Research at the University of Florida. Florida Agricultural Experiment Station Journal Series R-02399.     

Proline Metabolism and Cross-Tolerance to Salinity and Heat Stress in Germinating Wheat Seeds

Germination/growth of wheat (Triticum aestivum L., cv. Zimai 1) seeds and changes in the levels of proline and protein as well as in activities of key enzymes involved in proline metabolism in response to salinity-, heat-stresses and their cross-stress were studied. With decreasing water potential caused by increasing concentrations of NaCl, germination percentage, fresh weight of seedlings and protein amount markedly decreased, whereas proline amount slightly increased. The activities of pyrroline-5-carboxylate synthetase (P5CS), ornithine aminotransferase (OAT), and proline dehydrogenase (PDH) peaked at ?0.2 MPa water potential. Germination percentage and amounts of proline and protein increased as germination temperature elevated to 25°C from 15°C, and decreased above 25°C; fresh weight of seedlings increased to 30°C from 15°C, and decreased above 30°C. However, the activities of P5CS, OAT and PDH gradually decreased with elevaing temperature. Seeds pretreated at 33°C or in ?0.8 MPa NaCl solution for various time length increased tolerance to subsequent salt + water stress or heat stress, as measured by germination percentage and fresh weight of seedlings 5 days after beginning of experiment. The acquisition of cross-tolerance resulting in limitation of negative stress effects does not relate directly to proline level and activities of P5CS, OAT and PDH involved in proline metabolism. Proline amount as measured four days or later after stress imposition cannot be considered a symptom of salt-, water- and heat-stress injury or an indicator of the resistance.     

Multiple density dependence in two sub-populations of the amphipod Monoporeia affinis: a potential for alternative equilibria

Possible mechanisms for differences in population densities and dynamics were investigated in the amphipod Monoporeia affinis at two deep sites in the northern Bothnian Sea. The two sites were sampled yearly for 10 years. Average sizes, growth and mortality of the different age-classes were estimated from the cohort structure of the two populations. Laboratory experiments also investigated the ability of the common predatory isopod Saduria entomon to cause densitydependent (DD) mortality of the prey M. affinis. At site A, 43 m depth, the average density of M. affinis was twice as high as at site B, 81 m depth. The fluctuations in density were asynchronous between the two sites. Recruitment and subadult sizes of Monoporeia affinis were density dependent at both sites. The main functional difference between the two populations seemed to be the DD mortality of the 1 + cohort that occurred only at the low-density site B. A corresponding DD mortality was found in the predation experiments at densities of 1 + m. affinis corresponding to those found at site B. The potential importance of the predator was also indicated by a significant negative correlation between the biomass of S. entomon and the rate of change in M. affinis density in the field. The similarities in the abiotic factors between the two sites suggested that differences in carrying capacity should be small. The results could be explained by the predation regulation hypothesis for the low-density population at site B, while at site A M. affinis seemed to be regulated by intra-specific competition and limited by predation. It is suggested that in this simple predator-prey system there is potential for the existence of alternative equilibria.