Variations of opisthaptoral hard parts of Gyrodactylus salaris Malmberg, 1957 (Monogenea: Gyrodactylidae) on rainbow trout Oncorhynchus mykiss (Walbaum, 1792) in a fish farm,with comments on the spreading of the parasite in south-eastern Norway

Studies were carried out on Gyrodactylus salaris Malmberg, 1957 on rainbow trout Oncorhynchus mykiss (Walbaum, 1792) from a fish farm in Lake Tyrifjorden, south-eastern Norway. The anchors were larger, and the shape of the anchors and the ventral bar differed slightly, as compared with the same parts of G. salaris on parr of Atlantic salmon Salmo salar L. in northern and north-western Norwegian rivers. At different water temperatures (0.8°C, 10.0°C, 18.0°C), the opisthaptoral hard parts of G. salaris on rainbow trout showed considerable variation in size, but varied only slightly in shape. It was found that the total length of the anchors of G. salaris on rainbow trout may considerably exceed the previously reported maximum of 80 m for the species. The spread of G. salaris to south-eastern Norway is described and discussed.     

Temperature dependent development and survival of two sympatric species, Galerucella calmariensis and G. pusilla, on purple loosestrife

Two sympatric Europeanbeetles, Galerucella calmariensis (L.)and G. pusilla (Duft.) (Coleoptera:Chrysomelidae), have been released in NorthAmerica for biological control of purpleloosestrife, Lythrum salicaria L.(Lythraceae). Because establishment isaffected by environmental conditions, studieswere conducted at temperatures ranging from12.5 to 30 °C to determine differencesin rate of development and survival between thetwo species. No egg hatch occurred at12.5 °C for both species. Eggdevelopment was faster for G.calmariensis than for G. pusilla attemperatures 15 °C. Theminimum threshold temperature for eggdevelopment was lower for G. calmariensisthan G. pusilla. At 12.5 °C, G. calmariensis larvae developed 1.6 daysfaster than G. pusilla, but at 15, 20,25, and 27.5 °C G. pusilla developed2.9, 1.2, 1.1, and 0.6 days faster,respectively, than G. calmariensis. Nodifferences in developmental rate of pupa andtotal development time from egg to adulteclosion were observed for the two species. However, survival of G. calmariensisgenerally was higher than that of G.pusilla at lower temperatures. No differencewas observed in the preoviposition periodbetween the two species except at27.5 °C. The preoviposition period forboth species at 12.5 and 15 °C exceeded50 days and was much higher than for20 °C and above. The long preovipositionperiod suggests that temperatures below15 °C induce reproductive diapause. At15 °C, G. pusilla females livedlonger and also had a longer oviposition periodthan G. calmariensis. However, fasteregg and larval development, and higher survivalat 12.5 °C may give G. calmariensisa competitive advantage over G. pusillain cooler climates.     

Variability in the taxonomic characters of Black Sea gyrodactylids (Monogenea)

Variability of the haptoral hard parts of four Black Sea Gyrodactylus species (G. alviga Dmitrieva & Gerasev, 2000; G. crenilabri Zaika, 1966; G. flesi Malmberg, 1957; G. sphinx Dmitrieva & Gerasev, 2000) was studied in relation to season, host and geographical variability. A discriminant analysis was carried out on the measurements of 14 characters of the haptor of all four species. The haptoral hard parts of the investigated gyrodactylids decrease in size with an increase in water temperature. It is known that life-span of gyrodactylids is negatively correlated with water temperature and they exhibit peak intensities at low temperature. At the same time, life-span is considered to be a general indicator of a favourable environment. Therefore, high water temperature is not apparently advantageous for gyrodactylids. In the case of low marine salinity, in adapted species the sizes of the haptoral hard parts are larger at lower levels of salinity and vice versa for typical marine species. Lastly, in specimens parasitising the primary host, these features are larger than in those parasitising a secondary host. It is possible to say that, in general, the more favourable the environment for gyrodactylids the larger their haptoral hard parts. Unfavourable environmental conditions reduce the time of embryogenesis, which has a dual effect on gyrodactylids: positive in relation to their reproduction (by increasing the reproduction rate) and negative in relation to their development (by decreasing the size of the haptoral hard parts).     

The annual reproductive cycle of the freshwater mussel Dreissena polymorpha Pallas in lakes

Summary The annual development of the gonads of Dreissena polymorpha was studied at three sampling sites in two lakes over 3 and 1 1/2 years, respectively. A resting stage occurred after the last spawning in summer/autumn. Oogenesis (accompanied by multiplying segmentation of the oogonia and early growth processes of its oocytes) restarted in specimens at least 1 year old at low temperatures (below 10° C) during winter and early spring. At one location (Fühlinger See) the onset of the spawning season was correlated with an increase of water temperatures above 12° C. At 2 m depth, two main spawning periods in May and August were normally recognized, the first at temperatures of 12–16° C, the second at 16–21° C. It was clearly demonstrated for the first time in Dreissena polymorpha that the oocytes became mature in successive cohorts within one gonad. A female mussel may spawn several times during the reproductive season. At 9 m depth, the onset of spawning also started at about 12° C; this occurred in late summer, with two spawning periods within 1 month at a temperature range of 12–16° C. At another location (Heider Bergsee) the size of the gonads and the oocytes was reduced during April of both years studied, when food supply was low simultaneously with rapidly rising water temperatures in this shallow lake. There was no spawning period during spring. The major spawning period was delayed until July (temperatures 19–22°C). This shows (1) the synchronizing influence of low winter temperatures on the annual reproductive cycle and (2) a temperature threshold of at least 12° C for the start of the spawning processes. The results are discussed with regard to the geographical limits of further spread of Dreissena polymorpha.     

Life Tables of Phytoseiulus Macropilis (Banks) (Gamasida: Phytoseiidae) at Different Temperatures

The biology of Phytoseiulus macropilis (Banks) fed on Tetranychus urticae Koch was studied at different temperatures. The total development times averaged 7.5, 5.7, 4.2, 4.2 and 5.6 days at 20, 25, 28, 30 and 32°C, respectively at 78 ± 2% RH and 16 h photoperiod daily. The intrinsic rate of natural increase (r _m) and the net reproduction (R _o) reached maximum values 0.47 and 88.9, respectively, at 28°C. The mean generation time decreased (20.0-8.8 days) with increasing temperature 20-28°C.     

Low Temperature Stimulates Cell Enlargement and Intracellular Calcification of Coccolithophorids

Temperature effect on growth, cell size, calcium uptake activity, coccolith production was studied in coccolith-producing haptophytes, Emiliania huxleyi (Lohmann) Hay & Mohler (strain EH2) and Gephyrocapsa oceanica Kamptner (strain GO1) (Coccolithophorales, Prymnesiophyceae). E. huxleyi grew at a wider temperature range (10°–25°C), while G. oceanica growth was limited to warmer temperatures (20°–25°C). Cell size was inversely correlated with temperature. At low temperature, the enlargement of chloroplasts and cells and the stimulation of coccolith production were morphologically confirmed under fluorescent and polarization microscopes, respectively. ⁴⁵ Ca uptake by E. huxleyi at 10°C was greatly increased after a 5-day lag and exceeded that at 20°C. These results clearly showed that low temperature suppressed coccolithophorid growth but induced cell enlargement and as stimulated the intracellular calcification that produces coccoliths.     

Adaptations to terrestrial overwintering of hatchling northern map turtles,<Emphasis Type="Italic"> Graptemys geographica</Emphasis>

We conducted a 3-year field and laboratory study of winter biology in hatchlings of the northern map turtle (Graptemys geographica). At our study area in northern Indiana, hatchlings routinely overwintered in their natal nests, emerging after the weather warmed in spring. Winter survival was excellent despite the fact that hatchlings were exposed frequently to subfreezing temperatures (to –5.4 °C). In the laboratory, cold-acclimated hatchlings exhibited low rates of evaporative water loss (mean=2.0 mg g^–1 day^–1), which would enable them to conserve body water during winter. Laboratory-reared hatchlings were intolerant of freezing at –2.5 °C for 24 h, conditions that are readily survived by freeze-tolerant species of turtles. Winter survival of hatchling G. geographica probably depended on their extensive capacity for supercooling (to –14.8 °C) and their well-developed resistance to inoculative freezing, which may occur when hatchlings contact ice and ice-nucleating agents present in nesting soil. Supercooled hatchlings survived a brief exposure to –8 °C. Others, held at –6 °C for 5 days, maintained ATP concentrations at control levels, although they did accumulate lactate and glucose, probably in response to tissue hypoxia. Therefore, anoxia tolerance, as evidenced by the viability of hatchlings exposed to N₂ gas for 8 days, may promote survival during exposure to subfreezing temperatures.Abbreviations EWL evaporative water loss - FP_eq equilibrium freezing point - INA ice-nucleating agents - T_c temperature of crystallizationCommunicated by L.C.-H. Wang     

Spatial distribution of resting stages,rate of emergence from diapause and times to adulthood and to the appearance of the first clutch in 3 species of cyclopoid copepods

The spatial distribution of dormant copepodids of 3 species of cyclopoid copepods — Cyclops vicinus, Mesocyclops leuckarti and Thermocyclops crassus — was studied in 4 small lakes in South Germany. The rate of emergence from diapause and times from the resting stage to adulthood and from adulthood to the appearance of the first clutch was studied at 4 constant temperatures (5, 10, 15, 20 °C) in the laboratory. Resting stages of C. vicinus were always concentrated in the deepest parts of the lakes and were found relatively deep in the mud. M. leuckarti- and T. crassus-copepodids preferred shallow areas in deep lakes but were concentrated in the deep areas in shallow lakes. Copepodids of both species were always concentrated in the uppermost mud layers.Rate of emergence from diapause was strongly temperature-dependent. At high temperatures (20 °C) copepodids of all species under study emerged within 2 weeks. At lower temperatures C. vicinus copepodids showed the highest rate of emergence. At 5 to 10 °C only few M. leuckarti- and T. crassus-copepodids had emerged after the investigation period (7 weeks). Both C. vicinus and T. crassus showed the highest rate of emergence at the natural end of diapause but even at that time only few T. crassus-copepodids emerged at 5 °C. Times to adulthood at 5 °C were shortest in C. vicinus. At higher temperatures this species was passed by M. leuckarti. Times from adulthood to the appearance of the first clutch at 5–15 °C were shortest in C. vicinus. T. crassus produced no clutch at 5 and 10 °C.     

Reef coral survival and mortality at low temperatures in the Arabian Gulf: new species-specific lower temperature limits

A series of cold fronts passing over the western Arabian Gulf from December 1988 to March 1989 produced the longest period of sustained low water temperatures ever recorded in a coral reef area. Sea water temperatures recorded on two reefs during this period provide new estimates of lower thermal limits for reef coral survival. Severe mortality of the corals Acropora pharaonis and Platygyra daedalea occurred at the northern site where minimum temperatures fell below 11.5°C on four consecutive days and mean daily temperatures were 13°C or less for more than 30 days. However, Porites compressa, the principal reef-former in this area, and various faviid corals initially showed only sub-lethal effects and appeared normal after six months. Corals were not damaged at the southern site, where minimum water temperature fell below 12.5°C for two consecutive days, but mean temperatures were 14°C or less for only 5 non-consecutive days.     

Effect of acute pH depression on the survival of the freshwater amphipod Hyalella azteca at variable temperatures: field and laboratory studies

Field observations on temperature and pH of a small pond showed that a amphipod population of Hyalella azteca was exposed to variable seasonal pH between 5.10–5.85, and water temperatures between 2–21 °C. Laboratory experiments were designed to simulate seasonal temperatures and field pHs of a small pond habitat. Laboratory bioassay experiments were conducted to determine the survival of Hyalella azteca at pHs 4, 5, 6 and 7, and varying temperatures of 5°, 10°, 15°, 20° and 25 °C.The LT₁₀₀ at pH 4 and 25 °C was 5.7 ± 0.47 days, compared to 47.3 ± 2.49 days at 5 °C. An Analysis of Variance (ANOVA) showed temperature was a significant (p > 0.0001) source of variation in the acute lethality of pH to H. azteca. A Duncans Multiple Range Test (DMRT) further showed that in laboratory experiments at pH 4, there was a significant difference ( = 0.01) between the LT_100s at 5°, 10°, 15° and 20 °C, but not between temperatures 20° and 25 °C.     

Seasonal dynamics and persistence of Gyrodactylus salaris in two riverine anadromous Arctic charr populations

The seasonal occurrence of the monogenean ectoparasite Gyrodactylus salaris Malmberg infecting Arctic charr, Salvelinus alpinus (L.) in the two rivers Skibotnelva and Signaldalselva in northern Norway was studied in the period from autumn 2003 to autumn 2005. Skibotnelva has been infected with the parasite since 1979, and treated with rotenone twice. Most likely resident Arctic charr avoided the rotenone treatment in small tributary streams, and thus was the source of the repeated re-infection of this river. G. salaris was first recorded in Signaldalselva in the year 2000 and it is still untreated. Unlike Atlantic salmon, which is highly susceptible to G. salaris, Arctic charr can display a wide range of host-responses to G. salaris infections. Arctic charr were sampled by electro fishing with a total sample of 681 Arctic charr. The results from this study demonstrate an evident seasonal dynamic in G. salaris infection in charr in both rivers. Parasite intensities fluctuated with the rise and fall in temperature through the year, with an autumn high and spring low. There was a significantly lower prevalence and mean intensity of G. salaris in Skibotnelva than in Signaldalselva. There were also a lower prevalence and intensity of G. salaris in the older than in the youngest charr. The different history of infection and treatment in the two rivers might be the underlying cause of these observed dissimilarities. The current study indicates that Arctic charr is a good natural host for G. salaris.     

Seasonal variations of opisthaptoral hard parts of Gyrodactylus salaris Malmberg, 1957 (Monogenea: Gyrodactylidae) on parr of Atlantic salmon Salmo salar L. in the River Batnfjordselva,Norway

Seasonal variations in size and shape of the marginal hooks, the anchors and the ventral bar of the opisthaptor of Gyrodactylus salaris Malmberg, 1957 were studied. The G. salaris specimens were collected from parr of Atlantic salmon Salmo salar L. in the River Batnfjordselva, north-western Norway. Samples were taken at roughly monthly intervals during a two-year period. The marginal hooks, the anchors and the ventral bar showed considerable seasonal variation in size, but varied only slightly in shape. The variation in 12 of the 14 characters measured showed a significant regression to the variation in the water temperature. The total length of the marginal hooks of G. salaris can be considerably longer than the previously reported maximum of 40 m for the species.     

Mycorrhiza does not alter low temperature impact on <Emphasis Type="Italic">Gnaphalium norvegicum</Emphasis>

Extreme arctic-alpine vegetation has relatively low affinity to form mycorrhizal symbiosis. We asked whether the mycorrhizal growth benefit for the host plant is lower at low temperatures. We investigated the role of two root-associated fungi and temperature in growth, carbon–nitrogen relations and germination of an arctic-alpine herb. Seeds of Gnaphalium norvegicum were germinated at 8° or 15°C with or without arbuscular mycorrhizal (AM, Glomus claroideum) and dark septate endophytic (DSE, Phialocephala fortinii) inocula in a climate chamber. We found that germination percentage, shoot and root biomass, shoot N% and root AM colonization were lower at 8°C than at 15°C. P. fortinii inoculation had a positive impact on germination at both temperatures, whereas G. claroideum produced no effect. N% was lower in AM plants at both temperatures. Plant biomass and shoot N content were higher in AM plants than in control plants at 15°C, but not at 8°C. DSE inoculation tended also to have positive effects on plant biomass and N content at 15°C. At 15°C, rate of photosynthesis, photosynthetic nutrient use efficiency and specific leaf area were positively affected by G. claroideum, which suggests that G. claroideum formed a carbon sink and possibly enhanced the seedling water economy. The positive effects of P. fortinii were probably due to its saprotrophic function in the substrate because it did not colonize the roots. These results suggest that the effects of AM and DSE on plant growth are affected by temperature and that the mycorrhizal benefit for the host plant was lower at the lower temperature. Low saprotrophic activity and decreased mycorrhiza-mediated nutrient acquisition may thus constrain plant nutrient acquisition in cold environments. Decreased mycorrhizal benefit may be related to the comparatively low mycotrophy of cold environment vegetation.     

Competitive ability of the antagonists Ulocladium atrum and Gliocladium roseum at temperatures favourable for Botrytis spp. development

Ulocladium atrum and Gliocladium roseum are fungal antagonists capable of suppressing sporulation of Botrytis spp. on dead plant parts. The effect of temperature (3 to 36 °C) on antagonist conidial germination and mycelial growth was assessed on agar. In addition conidial germination of U. atrum was measured on dead lily leaves. The optimum temperature of both antagonists for both conidial germination and mycelial growth was between 27 and 30 °C. U. atrum was less affected by lower temperatures than G. roseum. At optimum temperature, 50% of conidia of U. atrum and G. roseum germinated within 2.6 and 10.0 hrs, respectively. At low sub-optimal temperatures (6 °C), 50% of conidia germinated within 18 and 96 hours, respectively.In bioassays on dead onion leaves, U. atrum suppressed sporulation of B. cinerea and B. aclada at all temperatures tested (6 to 24 °C) by more than 85%. On dead cyclamen leaves, G. roseum was more efficient than U. atrum at 21 and 24 °C but, in contrast to U. atrum, showed no antagonistic activity at temperatures below 21 °C. On dead hydrangea leaves, U. atrum significantly reduced sporulation of B. cinerea at temperatures as low as 3 and 1 °C. Under Dutch growing conditions, the mean air temperature during leaf wetness periods in onion and lily fields was 15 °C with temperatures only occasionally above 20 °C. In greenhouse crops of cyclamen, the mean temperature during high humidity periods was 17 °C. It is therefore concluded that U. atrum is better adapted than G. roseum to temperatures which occur in the field, in greenhouse crops such as cyclamen, or during cold storage of plant stocks.     

Developmental rates of heterozygous and homozygous rainbow trout reared at three temperatures

The hatching distributions of rainbow trout (Salmo gairdneri) with different genotypes at eight loci are compared in two experiments with the same strain. Embryos were incubated at temperatures colder (5 and 8°C) and warmer (12°C) than normally experienced by these fish (9.5°C). At hatching, embryos were separated into five hatching groups representing the chronological order of hatching. There is no significant correlation between multilocus heterozygosity and hatching time at any temperature in either experiment. Fish in the middle of the hatching distribution had the highest average heterozygosity. In both experiments, heterozygotes at the majority of loci examined tended to hatch relatively later within the hatching distribution at 12°C than at both 5 and 8°C. Fish with different genotypes atPgm2 andCk1 showed significant differences in hatching time that were consistent between experiments.Ck1 heterozygotes hatched sooner than homozygotes at 8°C but later at 12°C.Pgm2 heterozygotes hatched later than homozygotes at all temperatures and significantly later in four of five cases. At the other loci examined, however, the relative hatching distributions of fish with particular genotypes were not significantly different or repeatable between experiments.This research was supported by National Science Foundation Grant BSR-8300039 awarded to Dr. Fred W. Allendorf. Moira M. Ferguson was supported by a postgraduate scholarship from the Natural Sciences and Engineering Research Council of Canada.     

Variability of the opisthaptoral hard parts ofGyrodactylus callariatis Malmberg, 1957 (Monogenea: Gyrodactylidae) from Atlantic codGadus morhua L. in the Oslo Fjord,Norway

The present study describes the variability of the opisthaptoral hard parts ofGyrodactylus callariatis Malmberg, 1957 infesting juvenile Atlantic codGadus morhua L. in the Oslo Fjord, Norway. Samples were taken monthly or bimonthly from January 1993 to July 1994. The length of the 14 characters measured varied considerably throughout the period, and showed a significant regression on the water temperature: as the water temperature increased the length of the hard parts decreased andvice versa. There were no significant differences in the size of the hard parts between young worms (without penis) and older worms (with penis). Some of the characters (especially the anchor shaft) from parasites located on the skin and fins were significantly longer than those of parasites located in the oral cavity, pharynx and gills. Generally, the variation in the shape of the hard parts was small; the anchor root, ventral bar membrane and ventral bar processes were the most variable parts. The shape of the hard parts did not vary as a consequence of seasonal changes in the water temperature, age of the worms or site on the host.     

The effect of high temperature and fallow period on infection of mung bean and cashew roots by the vesicular-arbuscular mycorrhizal fungus Glomus intraradices

The experiments described were designed to investigate the way in which high temperatures (30°C and above) affected the survival and infectivity of spores of Glomus intraradices formulated as the commercial inoculum NutriLink^TM. Infection of mung bean (Vigna radiata) occurred most rapidly at 30°C compared with either 22° or 38°C, although the final percentage of the root length infected (6 weeks) was similar at all three temperatures. Early rapid infection led to greater plant growth of this species at 30°. In cashew (Anacardium occidentale) no infection occurred at 38°C and this was associated with low plant growth, compared with the other temperatures at which infection reached 40–60% after 4 months. In both species differences in root temperature were associated with marked differences in the morphology and growth of the root systems, with poor root growth at 38°C. Spores of G. intraradices retained infectivity with respect to mung bean for up to 6 weeks in moist fallow soil, although maximum infectivity was observed in soil without a fallow period. The effects of temperature on germination of spores buried in filter paper sandwiches in soil were consistent with the data for infection and growth. Germination was most rapid and reached the highest percentage at 3 weeks at 30°C. Lowest germination was attained at 38°C. We conclude that G. intraradices can retain its infectivity in moist soil at high temperatures, but that the extent to which the plants become infected and hence their response, depends not only on this but also on host factors such as root growth.     

The effect of temperature on maturation threshold body-length in Daphnia magna

Aquatic invertebrates are usually larger at maturity when water temperatures are lower. For the freshwater cladoceran Daphnia, it has been suggested that a threshold size must be attained to initiate maturation, which results two instars later in the deposition of eggs into the brood chamber. This threshold size is believed to temperature on maturation threshold body-length in Daphnia magna. Daphnids were raised from birth to maturity under three constant-temperature regimes (12°C, 16°C, 22°C), and two food-level conditions. Animals were measured daily, and a body-length based maturation threshold determined for each individual. We demonstrate that mean maturation threshold length is negatively correlated with ambient water temperature. Further, daphnids with a larger threshold length tended to be larger at maturity. A maturation threshold linked to body length suggests that reduced variation in size at maturity is adaptive, even at the cost of additional variation in instar number or age at maturity.     

Effect of rearing temperature and larval density on larval survival, age at pupation and adult size of Anopheles gambiae

The effects of temperature and larval density on survival of larvae, growth rate, age at pupation, and adult size (measured as wing length and dry weight) of laboratory-reared Anopheles gambiae (Diptera: Culicidae) were studied. Larvae were reared at three temperatures (24, 27 and 30°C) and three densities (0.5, 1 and 2 larvae/cm²). The effects of density and temperature strongly interacted to determine the mosquitoes' life-history parameters. Survival was highest at the intermediate temperature of 27°C. The differences between the temperatures increased with increasing density. At 30°C survival decreased as density increased, but at 27°C increasing density led to higher survival. Age at pupation increased as temperature decreased from 30°C to 24°C and as density decreased from 2 to 0.5 larvae/cm². Adult size also increased as temperature decreased, but showed a negative correlation with density only at 27°C. In contrast, at 24°C and 30°C a decrease in density led to a decrease in adult size. Growth rate showed a similar pattern. At 27°C growth rate decreased as density increased, but at other temperatures the opposite trend was observed.     

Ventilation rate and behavioural responses of two species of intertidal goby (Pisces: Gobiidae) at extremes of environmental temperature

We investigated the behavioural responses of two gobiid fish species to temperature to determine if differences in behaviour and ventilation rate might explain any apparent vertical zonation. A survey of the shore at Manly, Moreton Bay revealed Favonigobius exquisitus to dominate the lower shore and Pseudogobius sp.4 the upper shore. These species were exposed to a range of temperatures (15–40°C) in aquaria for up to 6 h. At 20 °C F. exquisitus exhibited a mean gill ventilation rate of 26 ± 1.4 bpm (beats per minute) differing significantly from Pseudogobius, which ventilated at a fivefold greater rate of 143 ± 6 bpm. The ventilation rate in F. exquisitus underwent a fivefold increase from normal local water temperature (20 °C) to high temperature (35 °C) conditions, whereas that of Pseudogobius did not even double, suggesting that Pseudogobius sp. is a better thermal regulator than F. exquisitus.While both species emerged from the water at high temperatures (>30 °C) the behaviours they exhibited while immersed at high temperature were quite different. F. exquisitus undertook vertical displacement movements we interpret as an avoidance response, whereas Pseudogobius sp. appeared to use a coping strategy involving movements that might renew the water mass adjacent to its body. The thermal tolerances and behaviours of F. exquisitus and Pseudogobius sp. are in broad agreement with their vertical distribution on the shore.