Predator avoidance in mummichog larvae from a polluted habitat

Previous work has shown that adult mummichogs ( Fundulus heteroclitus ) from a polluted site (Piles Creek, PC, New Jersey) were more vulnerable to predation by blue crabs than fish from a more pristine site (Tuckerton, TK, New Jersey). The present study was conducted to compare the spontaneous activity, swimming performance and predator avoidance of fish of the two populations at early life stages. When raised in synthetic salt water, both newly hatched and 1–month-old mummichog larvae from TK had greater spontaneous activity, swimming performance, and stamina than those from PC. In comparison to TK, PC larvae were less vulnerable to predation by yearling mummichogs at 1 week old, but were more vulnerable at 1 month old. Variation in behaviour and swimming ability of TK and PC larvae accounted for the differences in vulnerability to predation. TK larvae employed greater swimming and irregular movement, which was more successful for survival of older larger larvae. In contrast, PC larvae hid, often remaining motionless, which was advantageous for survival of young smaller larvae. Contaminants had been assumed responsible for the behavioural differences in the PC population. However, since differences were seen in larvae raised in synthetic salt water, it is possible that maternally transferred neurotoxicants (possibly delayed effects) and/or inherent factors also play a role.     

First record of a population of the exotic mummichog Fundulus heteroclitus (L., 1766) in the Mediterranean Sea basin (Ebro River delta)

Until now, mummichog Fundulus heteroclitus have been recorded only from the estuaries of the southernmost river basins of the Iberian Peninsula (Guadiana and Guadalquivir Rivers). Data reported here indicate the first record of F. heteroclitus in the Ebro River delta (north-east Spain), and hence also the first citation for F. heteroclitus as an invasive species present in any estuary of the Mediterranean Sea basin.     

Hypoxia tolerance of the mummichog: the role of access to the water surface

Low dissolved oxygen (DO) had a significant effect on specific growth rate (G_S), length increment (I_L) and haematocrit (Hct) of the mummichog Fundulus heteroclitus. Regardless of access to the water surface, F. heteroclitus maintained high growth rates (G_S and I_L) at DO concentrations as low as 3 mg O₂ l^?1. With access to the water surface, both G_S and I_L of F. heteroclitus decreased by c. 60% at 1·0 mg O₂ l^?1 compared to all higher DO treatments. When denied access to the water surface, a further decrease in G_S (c. 90%) and I_L (c. 75%) was observed at 1 mg O₂ l^?1. There was no effect of diel‐cycling DO (1–11 mg O₂ l^?1) with or without surface access on G_S, I_L or Hct of F. heteroclitus. Similar trends between G_S and faecal production across DO treatments suggest that decreased feeding contributed significantly to the observed decrease in growth rate. Haematocrit was significantly elevated at 1 mg O₂ l^?1 for fish with and without access to the water surface. Increased Hct, however, was not sufficient to maintain high G_S or I_L at severely low DO. When permitted to respire in the surface layer, however, F. heteroclitus was capable of maintaining moderate growth rates at DO concentrations of 1 mg O₂ l^?1 (c. 15% saturation). Although aquatic surface respiration (ASR) was not quantified in this study, F. heteroclitus routinely swam in contact with the water surface and performed ASR at DO concentrations ≤3 mg O₂ l^?1. No hypoxia‐related mortality was observed in any DO or surface access treatment for as long as 9 days. This study demonstrates that surface access, and thus potential for ASR, plays an important role in providing F. heteroclitus substantial independence of growth rate over a wide range of low DO conditions commonly encountered in shallow estuarine environments.     

The effects of predation by the mummichog, Fundulus heteroclitus (L.), on the abundance and distribution of the salt marsh snail, Melampus bidentatus (Say)

Enclosure and exclosure experiments were conducted in Canary Creek marsh to examine how predation by a killifish, Fundulus heteroclitus (L.), affects the abundance and size distribution of the salt marsh snail, Melampus bidentatus (Say). Enclosures (7.6 × 19.7 m) were stocked with Fundulus heteroclitus at densities of one-half normal, normal, twice normal, and four times normal density. Fish exclusion pens were also built. In both years of study, the mean density of snails increased significantly in pens where fish were excluded or their density reduced. During the same period in each year, the density of snails in pens containing higher than normal fish density fell by ≈50%.

Fish density also affected the size distribution of snails within pens. In both years, mean shell length of snails in the pen with the highest density of fish was significantly greater, and mean shell length of snails within fish exclusion pens was significantly lower than in all other treatments. Gape size limitation of F. heteroclitus causes selective predation on small snails and apparently is responsible for the difference in mean shell length among treatments.

Density and size distribution measurements of the natural Melampus bidentatus population in Canary Creek marsh were also taken. Larger snails were found to occur in the low marsh zone, whereas smaller snails occurred in the high marsh zone. Since the high marsh area is flooded less often than the low marsh, and the grass types found in the high marsh zone are known to afford protection from fish predation, the distribution of snails in the marsh is consistent with the idea that fish predation is an important factor influencing the distribution of snails in Canary Creek marsh.     

Morphological changes to the gills of killifish associated with severe parasite infection

Highly significant changes were found in digenean metacercariae infected gills of killifish Fundulus heteroclitus with respect to gill abnormalities. Gills infected with >1000 metacercariae exhibited up to 42 additional gill branches per fish when compared to less parasitized conspecifics. A strong positive correlation was found between abnormal gill morphology (number of branches) and the number of endoparasites present.     

Evidence from mtDNA RFLP analysis for the introduction of Fundulus heteroclitus to southwestern Spain

Restriction analysis of mitochondrial DNA confirmed the taxonomic status of a southwestern Iberian Peninsula population of Fundulus heteroclitus and its probable origin in North America.     

Reproductive cycles in a reared strain of the mummichog, a daily spawner

Annual, lunar, and diel samplings were taken from a strain of mummichog (Arasaki strain) reared in outdoor tanks under natural conditions, to examine gonadal maturity. Gonads of yearling fish were quite immature in September. During late autumn and winter, a gradual increase in the GSI of both sexes was observed, and the growth of cortical alveolus phase oocytes in females and basal spermatogenesis in males progressed. In late February, a rapid increase in the GSI of both sexes, vitellogenesis in females, and active spermatogenesis in males, occurred. The spawning period of the yearling fish was from late March to August judging from the presence of milt-producing males and ovulated females. The spawning period of the underyearling fish started in the same month as the yearlings, but terminated 1 month earlier. Plasma levels of oestradiol-17 β (E₂) in females and testosterone in males were high during the spawning period in the yearlings. In the underyearlings, however, E₂ levels peaked in early spring, and declined in the latter part of the spawning period. Neither a lunar nor semilunar cycle was evident in the reproductive activity of this fish, which proved to be a typical daily spawner. Females showed an apparent daily reproductive cycle; oocyte maturation commenced at about 1200 hours, germinal vesicle breakdown (GVBD) occurred at about 2400 hours, and ovulation was completed by 2400 hours, 24 h after GVBD. Such clear annual and daily reproductive cycles make this strain of mummichog a suitable model for the study of environmental and endocrine regulation of reproductive cycles in marine and estuarine teleosts.     

Aspects of the life history of a freshwater population of the mummichog,Fundulus heteroclitus (Pisces: Cyprinodontidae), in the Bronx River,New York,U.S.A.

A freshwater population of the mummichog, Fundulus heteroclitus, was sampled during summer and autumn 1979, from the Bronx River, New York. Other occurrences in freshwater of this common estuarine cyprinodontid fish have been noted in Pennsylvania, New Hampshire and Canada. In the Bronx River, this species is a significant part of the fauna and is one of the few species found throughout the river system. Specimens were examined to determine the growth and diet. It appears that this freshwater population does not differ from its brackish water conspecifics with respect to age structure, growth rate and feeding behavior.     

Calcium ion regulation of muscle contraction: The regulatory role of troponin T

The relaxation and contraction in vertebrate skeletal muscle are regulated by Ca2+ through troponin and tropomyosin, which are located in the thin filament. Troponin is composed of three components, troponins C, I and T. In this review article, the Ca2+-regulatory mechanism is discussed with particular reference to the regulatory properties of troponin T.     

Calcium release and internal calcium regulation in acinar cells of exocrine glands

Conclusion Recent results call for a reinterpretation of the mechanisms underlying the recruitment of intracellular Ca²⁺ in exocrine glands. One new hypothesis suggested by these developments is that InsP₃-sensitive channels liberate Ca²⁺ ions from secretory vesicles, as illustrated in Fig. 5.     

Composition and abundance of resident marsh-surface nekton: comparison between tidal freshwater and salt marshes in Virginia,USA

Previous research on intertidal nekton communities has identifiedimportant determinants of community structure and distribution; however, fewstudies have compared nekton utilization of disparate marsh habitats. Inthis study, abundance and distribution patterns of resident nekton werecompared between tidal freshwater marsh and salt marsh surfaces varying inflooding depth and duration. Nekton were collected in pit traps installedalong elevational transects at four marshes in coastal Virginia (twofreshwater, two saline) from April through November 1992–1993. Thedominant fish collected at all sites was the mummichog Fundulusheteroclitus. The daggerblade grass shrimp Palaemonetes pugio was thedominant nekton species collected at salt marsh sites, and was seasonallyabundant on tidal freshwater marshes. A positive correlation betweenflooding depth and nekton abundance was observed on salt marshes; anopposite pattern was observed on tidal freshwater marshes. Tidal floodingregime influences the abundance of resident nekton, however, the effect maybe confounded by other environmental variables, including variation insurface topography and seasonal presence or absence of submerged aquaticvegetation (SAV) in adjacent subtidal areas. In mid-Atlantic tidalfreshwater wetlands, SAV provides a predation refuge and forage site forearly life stages of marsh-dependent nekton, and several species utilizethis environment extensively. Salt marshes in this region generally lackdense SAV in adjacent subtidal creeks. Consequently, between-sitedifferences in species and size-specific marsh surface utilization byresident nekton were observed. Larvae and juveniles represented 79%and 59% of total fish collected at tidal freshwater and salt marshsites, respectively. The resident nekton communities of tidal freshwater andsalt marsh surfaces are characterized by a few ubiquitous species with broadenvironmental tolerances. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of the toxic dinoflagellate, Alexandrium fundyense on three species of larval fish: a food-chain approach

Sublethal behavioural effects of exposure to paralytic shellfish toxins (PST; saxitoxin and its derivatives) from the toxic dinoflagellate Alexandrium fundyense were investigated in newly settled winter flounder Pseudopleuronectes americanus , larval sheepshead minnow Cyprinodon variegatus and larval mummichog Fundulus heteroclitus through an A. fundyense –copepod–fish food chain. Consumption of as few as six to 12 toxin-containing copepods was lethal to the fishes. After consuming fewer toxin-containing copepods, all three fish species exhibited sublethal effects from vector-mediated exposure. Prey-capture ability of mummichogs was reduced in larvae that had consumed toxic copepods, Coullana canadensis . After consuming toxic C. canadensis or mixed copepods, mummichog larvae had reduced swimming performance. Swimming activity was also significantly reduced in winter flounder after consuming toxic copepods, including time spent in motion and distance travelled. Prey capture and predator avoidance were reduced in first-feeding sheepshead minnow larvae that had consumed toxic dinoflagellate cells. Adverse effects on prey capture or predator avoidance may reduce larval survival and facilitate the transmission of PST through the food web. This study provides baseline information on sublethal effects of PST exposure on fishes using a novel food-chain approach with zooplankton as vectors.     

Calcium regulation of chloroplast protein import

The majority of chloroplast proteins is nuclear-encoded and therefore synthesized on cytosolic ribosomes. In order to enter the chloroplast, these proteins have to cross the double-membrane surrounding the organelle. This is achieved by means of two hetero-oligomeric protein complexes in the outer and inner envelope, the Toc and Tic translocon. The process of chloroplast import is highly regulated on both sides of the envelope membranes. Our studies indicate the existence of an undescribed mode of control for this process so far, at the same time providing further evidence that the chloroplast is integrated into the calcium-signalling network of the cell. In pea chloroplasts, the calmodulin inhibitor Ophiobolin A as well as the calcium ionophores A23187 and Ionomycin affect the translocation of those chloroplast proteins that are imported with an N-terminal cleavable presequence. Import of these proteins is inhibited in a concentration-dependent manner. Addition of external calmodulin or calcium can counter the effect of these inhibitors. Translocation of chloroplast proteins that do not possess a cleavable transit peptide, that is outer envelope proteins or the inner envelope protein Tic32, is not affected. These results suggest that the import of a certain subset of chloroplast proteins is regulated by calcium. Our studies furthermore indicate that this regulation occurs downstream of the Toc translocon either within the intermembrane space or at the inner envelope translocon. A potential promoter of the calcium regulation is calmodulin, a protein well known as part of the plant's calcium signalling system.     

Fluo-3检测细胞内钙离子的条件优化

目的:优化用于检测细胞内钙离子的Fluo-3浓度条件和羧苯磺胺浓度条件,以得到最适的检测用浓度组合。方法:应用析因实验设计方法,选择32种不同的Fluo-3和羧苯磺胺浓度组合孵育CHO-K1细胞,通过FlexStation检测平台检测细胞内的钙离子浓度。结果与结论:检测信号随着Fluo-3浓度的升高而增强,同时随着羧苯磺胺浓度的升高而减弱。4μmol/L的Fluo-3和1mmol/L的羧苯磺胺浓度组合是最适用的检测条件。     

Piscivory by the mummichog (Fundulus heteroclitus): Evidence from the laboratory and salt marshes

While piscivory is common in many fishes, there are few accounts for the fundulid, Fundulus heteroclitus (mummichog). We suspected that this species might be involved in several forms of piscivory including predation, cannibalism and scavenging. To evaluate these possibilities we conducted several laboratory experiments and field observations in its primary habitat, salt marshes. We found that digestion of larvae and small juveniles of F. heteroclitus was fast (< 1 h) and this makes detection of small fish prey difficult for any form of piscivory. In addition, laboratory experiments (one-on-one encounters, feeding on dead prey) indicated that both cannibalism and scavenging of conspecific prey were possible. Field observations (n = 2449 stomachs from fish 12-106 mm TL over four years at two salt marshes) also suggested that piscivory occurred frequently (4.3-24.7% of stomachs examined) based on the detection of numerous fish hard parts, especially pharyngeal jaws. These structures allowed us to determine that most prey were F. heteroclitus and to back-calculate the size of the prey and thus the piscivore/prey size relationship. As a result, it appears that both cannibalism (0.2-9.1% of stomachs) and scavenging (0.5-9.9%) are common feeding modes of F. heteroclitus in salt marshes and, subsequently, modes of energy transfer for salt marshes in general. We suggest that future studies of fish feeding consider that cannibalism and scavenging may be frequent possibilities when fish remains are detected in stomach contents.     

Calcium cyclotron resonance and diatom mobility

The hypothesis that movement of biological ions may be predicted by cyclotron resonance theory applied to cell membranes is tested in these experiments. Diatoms (Amphora coffeaeformis) were chosen as the biosystem since they move or don't move, depending on how much calcium is transported across the membrane. The experiments demonstrate that a particular ion (calcium) is apparently moved across the cell membrane in response to the DC and AC values of magnetic flux densities (B) and the frequency derived from the cyclotron resonance theory. A clear resonance is shown and a rather sharp frequency response curve is demonstrated. The experiments also show a dose response as the AC value of the flux density is varied, and that odd harmonics of the basic cyclotron frequency are also effective.     

Calcium regulation of nucleocytoplasmic transport

Bidirectional trafficking of macromolecules between the cytoplasm and the nucleus is mediated by the nuclear pore complexes (NPCs) embedded in the nuclear envelope (NE) of eukaryotic cell. The NPC functions as the sole pathway to allow for the passive diffusion of small molecules and the facilitated translocation of larger molecules. Evidence shows that these two transport modes and the conformation of NPC can be regulated by calcium stored in the lumen of nuclear envelope and endoplasmic reticulum. However, the mechanism of calcium regulation remains poorly understood. In this review, we integrate data on the observations of calcium-regulated structure and function of the NPC over the past years. Furthermore, we highlight challenges in the measurements of dynamic conformational changes and transient transport kinetics in the NPC. Finally, an innovative imaging approach, single-molecule super-resolution fluorescence microscopy, is introduced and expected to provide more insights into the mechanism of calcium-regulated nucleocytoplasmic transport.