Copper uptake by two sympatric species of Killifish Fundulus heteroclitus (L.) and F. majalis (Walbaum)

Differential copper uptake within brain, visceral, gill, somatic and residual tissue was examined in the two sympatric species of killifishes Fundulus heteroclitus and F. majalis . Various salinities and copper concentrations were tested on both juvenile and adult stages to examine their effects on copper uptake. Salinity played a significant role in copper uptake in both species of killifishes. However, the effect of salinity was specific for each species and life history stage. Copper content of various tissues was directly related to the uptake pattern exhibited by whole adult fishes. Fundulus majalis brain tissue and F. heteroclitus muscle tissue were exceptions. Severe body lesions and subcutaneous haemorrhaging were observed after 2–3 day exposure to both 2 and 8 ppm copper.     

The effects of salinity on swimming performance of two estuarine fishes,Fundulus heteroclitus and Fundulus majalis

Prolonged and high‐speed swimming performance measurements were used to explore the swimming abilities of two species of estuarine fishes, the mummichog Fundulus heteroclitus and the striped killifish Fundulus majalis, under different salinities. Critical swimming performance was significantly higher for F. majalis in high salinity than in low salinity, but no difference was observed in brief constant acceleration swimming trials in this species; however, the swimming performance of F. heteroclitus was not significantly affected by salinity changes, indicating that this species is well adapted to regular estuarine salinity oscillations. Fundulus majalis displayed higher swimming speeds than F. heteroclitus in both high and low salinities, and while this cannot be explained by their respective salinity preferences, the specific habitat preferences of F. majalis for sandy subtidal habitats and F. heteroclitus for vegetated marshes could explain the better swimming performance of F. majalis.     

Morphological adaptation to thermal stress in a marine fish, Fundulus heteroclitus.

Populations of Fundulus heteroclitus (Cyprinodontidae), a coastal marine fish, were studied in control and artificially heated environments on the north shore of Long Island to determine patterns of variation in morphology and the extent to which this variation reflected adaptation to environmental characteristics. Principal components and discriminant function analyses were used to analyze variation in and among seventeen morphological characters. Fishes living in water artificially heated by a power plant exhibited marked divergence from control populations in head morphology, and convergence with a population sampled at more southern latitudes. Hence, these differences were interpreted as adaptations to warm environments. Greater morphological variation is detected at the heated locality than at control localities, and this may be partially due to a breakdown in developmental homeostasis, and partially due to selection favoring phenotypes that are rare in this environment.     

Blood cells of Fundulus heteroclitus (L.)

Much of the parenchyma of the normal pronephros of the adult Fundulus heterodilus , a euryhaline teleost, is haematopoietic tissue which was examined in cytocentrifuge preparations and plastic embedded thick sections. As we have not characterized many of the blood cells functionally, the terminology used is based on their morphological resemblance to similarly named cells in higher vertebrates. Approximately 80% of the non-erythroid elements observed in the pronephros are mature eosinophilic granulocytes (48%), immature eosinophilic granulocytes (25%), or cells likely to be their precursors [e.g. small blast cells (6%) and large blast cells (2%)]. Although there are macrophages in the pronephros that are capable of endocytotic activity, the mature and immature granulocytes are not. The granulocytes are non-specific esterase positive, PAS positive, acid phosphatase negative, and are capable of being mobilized by a RES activating agent, Ecteinascidia turbinata .     

The isozymes of glucose-phosphate isomerase (GPI-A2 and GPI-B2) from the teleost fish Fundulus heteroclitus (L.)

The fish, Fundulus heteroclitus (L.), like most advanced teleosts, possesses duplicate loci for the glycolytic enzyme, glucose-phosphate isomerase (D-glucose-6-phosphate ketol-isomerase, EC 5.3.1.9). The locus for the GPI-A2 (where GPI represents glucose-phosphate isomerase) isozyme is preferentially expressed in anaerobic tissues such as white skeletal muscle, while GPI-B2 predominates in aerobic tissues like liver and red muscle. We questioned whether this tissue specificity would be reflected in unique structural and functional characteristics of the respective isozymes. Consequently, an analysis of the two isozymes was undertaken. The enzymes were purified by a combination of ion-exchange chromatography and isoelectric focusing. Each isozyme was characterized as to native and subunit molecular weight, isoelectric pH, and susceptibility to thermal denaturation. Both were dimeric enzymes, with native molecular masses of 110 kDa. The isoelectric pH values for GPI-A2 and GPI-B2 were 7.9 and 6.4, respectively. Differences were apparent in thermal stability, i.e. GPI-A2 was more stable than GPI-B2. Kinetic properties were investigated as a function of both pH and temperature. The Km values for fructose 6-phosphate (Fru-6-P) differed between the isozymes at low pH, but no significant differences were observed at higher pH. The inhibition constant (Ki) for 6-phosphogluconate (6-P-gluconate) was pH dependent. GPI-A2 was slightly more sensitive to 6-P-gluconate inhibition than GPI-B2 between pH 7.0 and 8.5. The Km for Fru-6-P was temperature dependent for the GPI-B2 isozyme, but relatively temperature independent for GPI-A2 between 10 and 35 degrees C. The Ki for 6-P-gluconate was temperature dependent for both isozymes. The Ki values for GPI-A2 were consistently lower than those for GPI-B2. Energies of activation differed between the two isozymes by 4.4 kcal with GPI-A2 having the lower value. While delta G values were identical for the isozymes, their delta H and delta S values differed significantly. The structural and kinetic differences that exist between the glucose-phosphate isomerase isozymes appear to be tailored to the unique metabolic demands of the tissues in which these Gpi loci are expressed.     

Microsatellite primers for the Atlantic coastal killifish,Fundulus heteroclitus,with applicability to related Fundulus species

The mummichog (Fundulus heteroclitus), a common Atlantic coastal killifish, is a model vertebrate species for the study of molecular genetic variation in natural populations and of environmental toxicology. We report the development of a set of 20 microsatellite loci in this species. Average expected heterozygosity across all loci was 0.84 (range: 0.60–0.97), revealing a high level of variability at most loci. A survey of seven additional Fundulus species yielded one or two robust amplification products in over half (63%) of the species–primer combinations tested. Therefore, many of these loci will also prove useful in studies of other members of the genus Fundulus.     

Methylmercury teratogenesis in the killifish, Fundulus heteroclitus.

Exposure of developing eggs of the killifish, Fundulus heteroclitus, to 0.03 or 0.04 mg/l of methylmercuric chloride resulted in a variety of abnormalities. Percentage of axis formation was reduced somewhat, and many embryos developed cyclopia or intermediate conditions leading to cyclopia, reflecting interference with induction of the forebrain. Defects in the cardiovascular system also appeared in the form of failure of the heart to differentiate properly into chambers. The heart was a thin, feebly beating tube, incapable of causing the blood to circulate. Other tissues, however, continued developing fairly normally, and embryos showed spontaneous movement comparable to controls. Embryos with severe cardiovascular or optic defects did not hatch. Upon hatching, some embryos which had previously appeared normal were found to have skeletal malformations in the form of vertebral bends or the inability to uncurl from the position which they had while still inside the chorion. Exposure to the toxicant for shorter periods of time (6, 12, or 24 hours) reduced the incidence of abnormalities. The second day of development was found to be the most sensitive period.     

An immunoinhibitory substance in the serum of laboratory held killifish, Fundulus heteroclitus L.

Serum of the killifish, Fundulus heteroclitus , maintained under laboratory conditions for more than four weeks, contained a factor that depressed the immunocytoadherence response to SRBC. When serum was injected into immunocompetent fish 48 h prior to antigen stimulation it was effective; when injected simultaneously with the antigen there was no effect. Fractionation of the serum by ultracentrifugation suggests that the inhibitor is either low or very low density lipoprotein. Hypophysectomy decreased immune inhibition suggesting that the production of the inhibitor may be under the control of the pituitary.     

Energetics of osmoregulation: II. Water flux and osmoregulatory work in the euryhaline fish, Fundulus heteroclitus

Teleost fish experience passive osmotic water influx in fresh water (FW) and water outflux in salt water, which is normally compensated by water flow driven by active ion transport mechanisms. Euryhaline fish may also minimize osmotic energy demand by "behavioral osmoregulation", seeking a medium isotonic with their body fluids. Our goal was to evaluate the energy requirement for osmoregulation by the euryhaline fish Fundulus heteroclitus, to determine whether it is of sufficient magnitude to favor behavioral osmoregulation. We have developed a method of weighing small fish repetitively for long periods without apparent damage, which was used to assess changes in water content following changes in external salinity. We found that cold (4 degrees C) inhibits osmoregulatory active transport mechanisms in fish acclimated to warmer temperatures, leading to a net passive water flux which is reversed by rewarming the fish. A sudden change of salinity at room temperature triggers a transient change in water content and the initial slope can be used to measure the minimum passive flux at that temperature. With some reasonable assumptions as to the stoichiometry of the ion transport and ATP-generating processes, we can calculate the amount of respiration required for ion transport and compare it to the oxygen uptake measured previously under the same conditions. We conclude that osmoregulation in sea water requires from 6% to 10% of the total energy budget in sea water, with smaller percentages in FW, and that this fraction is probably sufficient to be a significant selective driving force favoring behavioral osmoregulation under some circumstances.     

The effect of captivity on the immune response of the killifish, Fundulus heteroclitus L.

Fundulus heteroclitus maintained under laboratory for more than four weeks showed a significantly lower immunocytoadherence (rosette) response to thymus-dependent antigens (SRBC and DNP-BSA) than newly captured fish. There was no comparable effect on scale allograft rejection nor in the response to a thymus-independent antigen (DNP-Ficoll) as measured by the rosette response. This suggests that captivity has a differential effect on a sub-population of lymphocytes analogous to the T-helper cells of mammals.     

Asexual and sexual hybrids between Fundulus diaphanus and F. heteroclitus in the Canadian Atlantic region

Levels and origins of clonal diversity in asexual hybrid animals are critical to understanding how they can coexist with their sexual progenitor species. In this study, asexual gynogenetic hybrids between Fundulus diaphanus and Fundulus heteroclitus known from two sites in Nova Scotia (Canada) were characterized using discriminant morphological traits, eight microsatellite loci, and mitochondrial DNA. Fifteen clonal genotypes were uncovered, all bearing the same F. diaphanus maternal haplotye. Each site harboured a different dominant clone along with several rarer clones that all appear to be of recent origin. Unexpectedly, highly introgressed sexually reproducing hybrids (0.25 > q > 0.75) were also detected. Sexual hybrids with maternal ascendance in either species were also found at three other sites in the Atlantic region. Based on a single meristic trait (scale counts), it is shown that asexual clones can be significantly more variable than populations of sexual parental species. Also, species are morphologically more alike when living in sympatry, suggesting that introgression may occur via sexual hybrids. Altogether, these results confirm and refine the available knowledge on this hybrid system, and indicate that hybridization is probably a more widespread phenomenon than suspected, with implications for the phenotypic variability of a widely used model species, F. heteroclitus.     

Karyotypic analysis of Cajanus,Atylosia, and Rhynchosia species

Summary Somatic chromosomes of two cultivais of Cajanus cajan, eight species of Atylosia (A. albicans, A. cajanifolia, A. lineata, A. platycarpa, A. scarabaeoides, A. serica, A. trinervia and A. volubilis), and of Rhynchosia rothii were analysed. All species had 2n=22. Eight of the 10 species studied had two pairs of satchromosomes while A. scarabaeoides and A. sericea had only one sat-chromosome pair. Based on relative chromosome length (L%), arm ratio (pa-value) and presence or absence of secondary constriction, a karyotype formula for each species was formulated. Based on these parameters the chromosome pairs could also be assigned to groups ranging from 8 to 10 in different species. Except for the asymmetrical karyotype of A. albicans, the other species had rather moderately symmetrical karyotypes.     

Influence of egg size on embryos and larvae of Fundulus heteroclitus (L.)

Egg size for Fundulus heteroclitus (L.) populations is concordant with the distribution of the two F . heteroclitus subspecies, i.e. F. h. heteroclitus eggs are considerably larger than F. h. macrolepidotus eggs. The influence of egg size on survival of embryos during incubation and survival and growth of newly-hatched larvae was estimated for four populations representing both subspecies along the Atlantic coast of the United States and in Delaware Bay. Survival of embryos was determined for incubation periods of 14, 21 and 28 days. Greatest differences in survival were detected following the longest incubation period where less than 50 per cent of the smaller F. h. macrolepidotus eggs survived while little or no mortality was detected among the larger F. h. heteroclitus eggs . Influence of egg size on larval survival was also greatest among those larvae hatched after 28 days where F. h. macrolepidotus larvae survived without food, for an average of 6 days, while F. h. heteroclitus larvae survived 11–12 days. F. h. heteroclitus larvae were significantly larger at hatching than F. h. macrolepidotus larvae. Larval growth rates were the same (0.4 mm day⁻¹) in both subspecies. As a result, size differences at hatching were still maintained after 42 days of growth. The differences in egg size along with other morphological and reproductive characteristics of F. heteroclitus populations probably represent genetically based adaptations to environmental conditions, of which the length of the spawning season is one of the major components stimulating the coevolution of these traits.     

Stress and interpopulation variation in glycolytic enzyme activity and expression in a teleost fish Fundulus heteroclitus

Northern populations of Fundulus heteroclitus have twofold greater activity of lactate dehydrogenase-B (LDH-B) than southern populations, but exposure to stress increases LDH-B in southern populations, abolishing this difference. To test whether differences in the activity of other hepatic glycolytic enzymes between populations are sensitive to stress, we injected fish with a pharmacological dose of cortisol in coconut oil (400 microg g(-1)) or exposed them to handling stress and measured the activities of all the glycolytic enzymes. At rest, liver phosphofructokinase (PFK) and aldolase (ALD) activities were greater in southern fish, whereas LDH-B activity was greater in northern fish. No other glycolytic enzymes differed in activity between populations in control fish. Cortisol injection and handling stress decreased PFK and ALD and increased LDH activities in the southern but not the northern population, such that the populations no longer differed in the activity of any enzyme following treatment. Unlike Ldh-B mRNA, Pfk and Ald mRNA levels did not parallel enzyme activity, suggesting complex kinetics or regulation at multiple levels. Plasma cortisol did not differ between populations at rest but was significantly different between populations in treated fish. These data suggest that differences in liver enzyme activity may be related to differences in stress hormone physiology between populations.     

The vitelline envelope,chorion, and micropyle of Fundulus heteroclitus eggs

The architecture and transformation of the vitelline envelope of the developing oocyte into the chorion of the mature egg of Fundulus heteroclitus have been examined by scanning and transmission electron microscopy. The mature vitelline envelope is structurally complex and consists of about nine strata. The envelope is penetrated by pore canals that contain microvilli arising from the oocyte and macrovilli from follicle cells. During the envelope's transformation into the chorion, the pore canals are lost and the envelope becomes more fibrous and compact and its stratified nature less apparent. The micropyle, of pore, through which the sperm gains access to the enclosed egg is located at the bottom of a small funnel-shaped depression in the envelope. Internally, the micropyle opens on the apex of a cone-like elevation of the chorion. During the development of the envelope, structured chorionic fibrils, the components of which are presumed to be synthesized by the follicle cells, become attached to its surface. These chorionic fibrils are though to aid in the attachment of the egg to the substratum and perhaps to help prevent water loss during low tides when the egg may be exposed.