Effects of temperature on hard clam (Mercenaria mercenaria) immunity and QPX (Quahog Parasite Unknown) disease development: I. Dynamics of QPX disease

Quahog Parasite Unknown (QPX) causes disease and mortality in hard clams, Mercenaria mercenaria. Seasonality of QPX disease prevalence in the field and changes in QPX growth and survival in vitro suggest a role of temperature in the hard clam-QPX interaction and disease development. This study specifically examined the effect of temperature on QPX disease development and dynamics. Naturally and experimentally infected clams were separately maintained in the laboratory at 13 °C, 21 °C, or 27 °C for 4 months. Following this initial treatment, temperature was adjusted to 21 °C for 5 additional months to simulate seasonal changes of temperature in the field and to investigate the effect of temperature variations on QPX disease dynamics. Mortality was continuously monitored during the experiment and clams were sampled at 2, 4 and 9 months for the assessment of QPX disease prevalence and intensity using our standard histological and quantitative PCR techniques. Results demonstrated significantly higher QPX disease prevalence and intensity, as well as higher mortality, in naturally-infected clams maintained at 13 °C as compared to those held at 21 °C or 27 °C. Similarly, disease development was significantly higher in experimentally infected clams maintained at the colder temperature (70% prevalence after 4 months) as compared to those maintained under warmer conditions (<10%). Additionally, our results demonstrated an improvement in the condition of clams initially maintained at 13 °C for 4 months after transfer to 21 °C for 5 additional months, with a significant reduction of QPX prevalence (down to 19%). Interestingly, disease development or healing in clams maintained at different temperatures exhibited a strong relationship with clam defense status (jointly submitted paper) and highlighted the impact of temperature on clam activity and QPX disease dynamics. These findings should be taken into account for the timing of activities involving the monitoring, movement (e.g. relays, transplants) or grow out (e.g. commercial culture, municipal enhancement) of hard clams in enzootic areas.     

Modulatory effects of hard clam (Mercenaria mercenaria) tissue extracts on the in vitro growth of its pathogen QPX

Quahog parasite unknown (QPX) is a fatal protistan parasite affecting cultured and wild hard clams Mercenaria mercenaria along the northeastern coasts of the USA and maritime Canada. Field investigations and laboratory transmission studies revealed some variations in the susceptibility of different hard clam stocks to QPX infection. In this study, we used in vitro QPX cultures to investigate the effect of plasma and tissue extracts from two different clam stocks on parasite survival and growth. Results demonstrated the presence of factors in clams that significantly modulate QPX growth. Extracts from gills and mantle tissues as well as plasma inhibited in vitro QPX growth, whereas foot and adductor muscle extracts enhanced parasite growth. Investigations of anti-QPX activities in plasma from two clam stocks displaying different susceptibility toward QPX disease in vivo demonstrated higher inhibition of QPX growth by plasma from New York (resistant) clams compared to Florida (susceptible) clams. Some clams appeared to be deficient in inhibitory factors, suggesting that such animals may become more easily infected by the parasite.     

Effects of salinity on hard clam (Mercenaria mercenaria) defense parameters and QPX disease dynamics

QPX (Quahog Parasite Unknown) is a protistan parasite affecting hard clams (Mercenaria mercenaria) along the Northeast coast of the United States. The fact that QPX disease epizootics are usually observed in field sites with high salinities led to the general assumption that salinity represents an important factor for disease distribution. This study was designed to investigate the effect of salinity on QPX disease development as well as constitutive and QPX-induced defense factors in M. mercenaria. Naïve and QPX-infected (both experimentally and naturally) clams were submitted to 17 and 30 psu for 4 months. Standard and QPX-specific cellular and humoral defense parameters were assessed after 2 and 4 months. These included total and differential hemocyte counts, reactive oxygen species production, phagocytic activity of hemocytes, lysozyme concentration in plasma, anti-QPX activity in plasma and resistance of hemocytes to cytotoxic QPX extracellular products. Results demonstrated higher QPX-associated mortality in naturally infected clams maintained at high salinity compared to those held at 17 psu. Our findings also showed an increase in mortality following experimental challenge with QPX in clams submitted to 30 psu but not in those held at 17 psu. Constitutive clam defense factors and the response to QPX challenge were also affected by salinity. QPX challenge caused significant but transitory changes in hemolymph parameters that were obvious at 2 months but disappeared at 4 months. Overall, our results show that salinity modulates clam immunity and the progress of QPX disease although its impact appears secondary as compared to findings we reported earlier for temperature.     

Molecular diagnostics,field validation,and phylogenetic analysis of Quahog Parasite Unknown (QPX), a pathogen of the hard clam Mercenaria mercenaria

Quahog Parasite Unknown (QPX) is a protistan parasite that causes disease and mortality in the hard clam Mercenaria mercenaria. PCR primers and DNA oligonucleotide probes were designed and evaluated for sensitivity and specificity for the QPX organism specifically and for the phylum Labyrinthulomycota in general. The best performing QPX-specific primer pair amplified a 665 bp region of the QPX small-subunit ribosomal DNA (SSU rDNA) and detected as little as 1 fg cloned QPX SSU rDNA and 20 fg QPX genomic DNA. The primers did not amplify DNA of uninfected hard clams M. mercenaria or of the thraustochytrids Schizochytrium aggregatum, Thraustochytrium aureum, and T. striatum. The general labyrinthulomycete primers, which were designed to offer broader specificity than the QPX primers, amplified a 435 bp region of SSU rDNA from QPX, and a 436 to 437 bp region of SSU rDNA from S. aggregatum, T. aureum, and T. striatum, but did not amplify that of the clam M. mercenaria. Field validation of the QPX-specific primer pair, through comparative sampling of 224 clams collected over a 16 mo period from a QPX endemic site in Virginia, USA, indicated that the PCR assay is equivalent to histological diagnosis if initially negative PCR products are reamplified. Oligonucleotide DNA probes specific for QPX and the phylum Labyrinthulomycota were evaluated for in situ hybridization assays of cell smears or paraffin-embedded tissues. Two DNA probes for QPX offered limited sensitivity when used independently; however, when used together as a probe cocktail, sensitivity was greatly enhanced. The probe cocktail hybridized to putative QPX organisms in tissues of hard clams collected from Virginia, New Jersey, Massachusetts and Canada, suggesting that the QPX organisms in these areas are either very closely related or the same species. The QPX probe cocktail did not hybridize with clam tissue or with the thraustochytrids S. aggregatum, T. aureum, and T. striatum. The labyrinthulomycete DNA probe hybridized with QPX and the 3 thraustochytrids, with no background hybridization to clam tissue. SSU rDNA sequences were obtained for the putative QPX organisms from geographically distinct sites. Phylogenetic analyses based on the QPX and Labyrinthulomycota sequences confirmed earlier reports that QPX is a member of this phylum, but could not definitively demonstrate that all of the QPX organisms were the same species.     

The influence of plankton composition and water quality on hard clam (Mercenaria mercenaria L.) populations across Long Island's south shore lagoon estuaries (New York, USA)

We conducted a two-year study to assess how plankton composition and water quality impacts the distribution, densities, condition, growth, biochemical composition and reproductive success of juvenile and adult Mercenaria mercenaria (L.) in Long Island's south shore estuaries (LISSE). Juvenile and adult hard clams were placed in suspended cages at 10 locations ranging from the ocean inlets to locations furthest from inlets in Shinnecock Bay (SB), the eastern-most barrier island estuary of LISSE, and Great South Bay (GSB), the western-most barrier island estuary of LISSE. Phytoplankton community composition, temperature, salinity, dissolved oxygen, and clam growth and condition were monitored bi-weekly. A benthic survey of M. mercenaria densities in both estuaries was also conducted. In both 2004 and 2005, juveniles in central bay locations had significantly faster growth rates, lower mortality rates, and higher lipid content relative to sites closest to the inlets. Adult hard clams closest to the Fire Island inlet also had significantly lower condition indexes compared to mid-bay stations and densities of wild M. mercenaria populations in both estuaries were lower near inlets compared to locations further from inlets. In addition to substantial spatial differences within each estuary, differences were also observed between the embayments as juvenile clams in SB grew approximately twice as fast as those in GSB and adults in SB had significantly greater condition indexes than clams in GSB. Instantaneous juvenile growth rates were highly correlated to temperatures below 24 °C (p < 0.0001) and were also significantly correlated with several indicators of suspended food quantity and food quality (centric diatoms, phytoplankton cells > 5 μm, and dinoflagellates (inverse correlation)) which co-varied independently of temperature. In sum, these results suggest tidal exchange in LISSE promotes a water quality regime (cold water, with low food concentration) which would reduce the growth of juvenile clams and the overall reproductive success of adult hard clams located near newly-formed ocean inlets. However, increased exchange for regions furthest from inlets could enhance juvenile clam growth rates by reducing summer peak temperatures (> 24 °C) and densities of poor food sources (dinoflagellates).     

Effect of environmental factors on survival and growth of quahog parasite unknown (QPX) in vitro

Quahog parasite unknown (QPX) is a protistan microorganism associated with mass mortalities of hard clams (Mercenaria mercenaria) along the northeastern coasts of the United States and maritime Canada. Because several studies indicate modulatory effects of prevailing environmental parameters on disease outbreaks, this study tested the effect of major environmental parameters (temperature, salinity and oxygen concentration; individually or combined) on QPX survival in artificial seawater and parasite growth in culture media in vitro. Three QPX isolates from two different geographic locations were compared. Results indicated that in vitro growth of QPX was optimal in standard culture medium at 34 ppt between 20 °C and 23 °C. Additionally, significant differences in temperature optima were observed for geographically distinct QPX isolates (p < 0.001) confirming previous studies suggesting the existence of different QPX strains (or ecotypes). When tested in seawater, QPX exhibited opposite trends with higher survival at 15 °C and 15 ppt. Results also demonstrated limited survival and growth of QPX under anoxic conditions. Additionally, results showed that the parasite is able to survive extreme temperatures (−12 °C to 32 °C) suggesting that QPX could overcome short periods of extreme conditions in the field. These results contribute to a better understanding of interactions between QPX and its environment, but potential impacts of environmental conditions on QPX disease development need further work as it also involves clam response to these factors.     

Recognizing biotic breakage of the hard clam, Mercenaria mercenaria caused by the stone crab, Menippe mercenaria: An experimental taphonomic approach

The ability to assign lethal traces left on prey to particular durophagous predators enhances our understanding of predation pressure in the fossil record. To determine whether stone crabs (Menippe mercenaria Say 1818) leave diagnostic traces in the act of feeding on hard clams (Mercenaria mercenaria Linnaeus 1758), live clams were offered to crabs in laboratory aquaria over several months and the fragments produced during predation were examined for diagnostic breakage patterns. These fragments were then compared both macroscopically and using scanning electron microscopy to the fracture patterns produced by tumbling clams in a rock tumbler which simulated breakage during transport in the surf zone, and crushing clams using an Instron which simulated breakage resulting from sediment compaction. Fossil specimens of Mercenaria mercenaria were also examined to determine whether the criteria for recognizing predation traces generated experimentally could be recognized. While not all acts of predation produce diagnostic traces, when larger fragments (greater than 50% shell remaining) are produced during feeding, predatory-diagnostic breakage ranges from 70 to 80%. Macroscopic breakage patterns generated during the predation experiments were also present in fossil specimens. Damage caused by abiotic mechanisms (tumbling and crushing) is highly unlikely to be confused with damage produced by this predator.     

Tetraploid Induction by Inhibiting Mitosis I with Heat Shock, Cold Shock, and Nocodazole in the Hard Clam Mercenaria mercenaria (Linnaeus, 1758)

Tetraploid induction by inhibiting mitosis I with heat shock (32, 35, and 38°C), cold shock (1, 4, and 7°C), and nocodazole (0.02 to 1.6 mg/L) was investigated in the hard clam Mercenaria mercenaria. All treatments were applied to fertilized eggs about 5 min before the first cell division at 22 to 23°C, and lasted for 10, 15, and 20 min. Three replicates were produced for each treatment with different parents. The ploidy of resultant larvae and juveniles was determined with flow cytometry. Heat shock of 35 and 38°C was effective in inhibiting mitosis I, producing 54% to 89% tetraploid larvae. Heat shock of 32°C accelerated embryonic development without inhibiting mitosis or producing tetraploids. In all heat-shock groups, the survival to D-stage larvae was lower than in controls, suggesting that heat-shock treatments and tetraploidy were detrimental to larval development. At the juvenile stage, survivors from heat-shock groups contained no tetraploids. Cold shocks suspended the first cell division during the treatment, but produced no tetraploids in the 4°C and 7°C treatment groups. Cold shock of 1°C produced 31% tetraploid larvae in one replicate, with none surviving to juvenile stage. Nocodazole inhibited mitosis I at concentrations of 0.04 mg/L or higher, but did not produce tetraploids. This study indicates that heat shock is most effective in inducing tetraploids through mitosis I inhibition, although none of the induced tetraploids survived to juvenile stage.     

Effects of water temperature change on immune function in surf clams, Mactra veneriformis (Bivalvia: Mactridae)

Surf clam, Mactra veneriformis is one of the crucial fishery resources in Korea. This study was performed to examine the immune functions of the surf clam under the stress of water temperature changes at 10 °C, 20 °C or 30 °C for 24 h. Viable bacterial counts (VBC), total haemocyte count (THC), phagocytic activity, lysozyme activity, NRR times and SOD activity were assessed in three different water temperature groups. Clams held at 10 °C decreased in THC, lysozyme activity and NRR times, but phagocytic activity was increased. The highest temperature (30 °C) significantly increased in THC, whereas it decreased in phagocytic activity, lysozyme activity and NRR times. In clams maintained at 20 °C, phagocytic activity, lysozyme activity and NRR times were increased whereas THC was somewhat decreased with respect to clams held at 30 °C. However, water temperature changes did not elicit any alteration of VBC and SOD activity. The present study demonstrates that acute water temperature change affects the haemocytic and haemolymphatic functions, reducing immunosurveillance in stressed surf clam, M. veneriformis.     

Potential impacts of brown tide, Aureococcus anophagefferens, on juvenile hard clams, Mercenaria mercenaria, in the Coastal Bays of Maryland, USA

The rate of growth of juvenile hard clams, Mercenaria mercenaria, was studied in the Coastal Bays of Maryland during an outbreak of the brown tide, Aureococcus anophagefferens. Brown tide dominated the plankton community during the month of June 2002, with cell densities at several sites reaching category 3 (>200,000 cells ml⁻¹) levels. Temperatures during the bloom were 18.6–27.5 °C. Nutrient conditions preceding and during the bloom were conducive for the proliferation of A. anophagefferens: while inorganic nitrogen and phosphorus were <1 μg at N or P l⁻¹, urea was elevated during bloom development. Organic nitrogen, phosphorus and carbon were in the range of levels observed in previous brown tide blooms and increased following the collapse of the bloom. Growth rates of juvenile clams were significantly lower during the period of the brown tide bloom than following its collapse. Growth rates of M. mercenaria were found to be negatively impacted at brown tide densities as low as 20,000 cells ml⁻¹, or category 1 levels. The low growth rates of M. mercenaria could not be explained by temperature, as the lowest growth rates were found when water temperatures were at levels previously found to be optimal for growth.     

Effects of temperature on two Mediterranean population of Dinophilus gyrociliatus (Polychaeta: Dinophilidae): II. Effects on demographic parameters

The effects of temperature on demographic characteristics of two populations from Ravenna and Genoa of the polychaete Dinophilus gyrociliatus were investigated. Temperature affects age-specific survival and fecundity and all the demographic parameters often to a different degree in the two populations. Individuals from Ravenna survive longer than those from Genoa. The most evident differences in the age-specific fecundity curves of the experimental groups are related to age at maturity and the duration of the reproductive period that are in inverse proportion to temperature. In both populations of D. gyrociliatus, the maximum daily fecundity is observed at intermediate temperatures. In all cases, the Genoa females mature earlier, attain their maximum fecundity more quickly and have a shorter reproductive period than their Ravenna counterparts.Age at maturity, fecundity during the first reproductive events and juvenile survival are by far the most important characteristics in determining the fitness of the two populations at the tested temperatures. Even though the greatest net growth rates and highest expectation of life were recorded at 12 °C in the Ravenna population, the delay in the attainment of sexual maturity means that, at this temperature, the population growth rate is lowest. The higher juvenile survivorship and the greater fecundity observed at 24 °C is counter-balanced by the early attainment of sexual maturity induced at 30 °C. The comparison of the population growth rate calculated in laboratory with field data suggests that temperature is one of the main environmental parameters determining the fitness of D. gyrociliatus.     

Effects of temperature on fecundity in vitro, egg hatching and reproductive development of Benedenia seriolae and Zeuxapta seriolae (Monogenea) parasitic on yellowtail kingfish Seriola lalandi

Globally, aquaculture industries involved with commercial culture of kingfish (Seriola spp.) experience outbreaks of monogenean parasites, which can cause heavy stock losses. In Australia and New Zealand, aquaculturists of kingfish Seriola lalandi incur financial losses caused by two monogenean species: Benedenia seriolae and Zeuxapta seriolae which parasitise the skin and gills, respectively. This study provides information on some basic temperature-dependent life-cycle parameters of these problematic monogeneans on S. lalandi. Hatching times and age at maturity were inversely related to water temperature within the range experienced by wild kingfish in New Zealand (13-21 degrees C). Mature B. seriolae in vitro laid on average 37 eggs/day that hatched over approximately 4 days; peak hatching occurred 9, 11 and 22 days post-deposition at temperatures of 21, 17.5 and 13+/-1.0 degrees C, respectively. Z. seriolae in vitro laid on average 246 eggs/day that hatched over 2 days; peak hatching occurred 7, 9 and 15 days post-deposition at these respective temperatures. B. seriolae matured within 20, 25 and 48 days p.i. at 21, 18 and 13 degrees C. Z. seriolae matured within 25, 37 and >52 days p.i. at the same temperatures. This research describes stages in the reproductive development of B. seriolae and Z. seriolae and discusses the inclusion of basic parasitic life-cycle parameters into management strategies designed to maximise treatment efficacy and limit monogenean epizootics in sea-cage kingfish culture.     

Effects of temperature, pH and salinity on the infection of Leptolegnia chapmanii Seymour (Peronosporomycetes) in mosquito larvae

The effects of temperature, pH, and NaCl concentrations on the infectivity of zoospores of Leptolegnia chapmanii (Argentine isolate) were determined for Aedes aegypti and Culex pipiens under laboratory conditions. Zoospores of L. chapmanii were infectious at temperatures between 10 and 35 degrees C but not at 5 or 40 degrees C. At the permissive temperatures, mortality rates in young instars were much higher than in older instars and larvae of Ae. aegypti were more susceptible to L. chapmanii than larvae of Cx. pipiens. At 25 degrees C, Ae. aegypti larvae challenged with L. chapmanii zoospores resulted in 100% infection at pH levels ranging from 4 to 10. Larvae of Cx. pipiens exposed to similar pH and zoospore concentrations resulted in increasing mortality rates from 62% to 99% at pH 4 to 7, respectively, and then decreased to 71% at pH 10. Aedes aegypti larvae exposed to L. chapmanii zoospores in NaCl concentrations ranging from 0 to 7 parts per thousand (ppt) at 25 degrees C resulted in 100% mortality while mortality rates for Cx. pipiens decreases from 96% in distilled water to 31.5% in water with 6 ppt NaCl. Control Cx. pipiens larvae died when exposed at a NaCl concentration of 7 ppt. Vegetative growth of L. chapmanii was negatively affected by NaCl concentrations. These results have demonstrated that the Argentinean isolate of L. chapmanii tolerated a wide range of temperatures, pH, and salinity, suggesting that it has the potential to adapt to a wide variety of mosquito habitats.     

Effects of temperature on the establishment potential of the predatory mite Amblyseius californicus McGregor (Acari: Phytoseiidae) in the UK

Amblyseius californicus was introduced into the UK in the early 1990s as a biocontrol agent against glasshouse red spider mite Tetranychus urticae. This study investigated the effects of temperature on the establishment potential of A. californicus in the UK in the light of recent reports of their successful overwintering outside of glasshouse environments. The developmental thresholds were 9.9 and 8.6 °C respectively using simple and weighted linear regression. Using the day-degree requirement per generation calculated by weighted regression (143 day-degrees) in combination with climate data, it was estimated that up to seven generations would be possible annually outdoors in the UK. Non-diapausing adult females froze at −22 °C, with 100% mortality after reaching their freezing temperature. Up to 90% of mites died before freezing after short exposures to low temperatures. Significant acclimation responses occurred; 90% of acclimated individuals survived 26 days exposure at 0 °C and 11 days at −5 °C (acclimated mites were reared at 19 °C, 6L:18D followed by 1 week at 10 °C, 12L:12D). Non-diapausing adult females survived over 3 months outdoors in winter under sheltered conditions and oviposition was observed. The experimental protocol used in this study is discussed as a pre-release screen for the establishment potential of other Amblyseius species, and similar non-native biocontrol agents.     

Effects of temperature on two Mediterranean populations of Dinophilus gyrociliatus (Polychaeta: Dinophilidae): I. Effects on life history and sex ratio

The effects of temperature on the life history characteristics of two populations of the polychaete Dinophilus gyrociliatus, one from Ravenna (northern Adriatic Sea) and the other from Genoa (Ligurian Sea), were investigated. The temperatures tested (6, 12, 18, 24 and 30 °C) cover a wider range than those prevailing in the natural environment. In the populations studied there are broad differences in timing of development and reproduction. At 6 °C, the adults of both populations survive for a long time but they are unable to reproduce. At 12 °C, only the animals from Ravenna manage to reproduce. At the higher temperatures (18, 24 and 30 °C), the development of the animals belonging to the Genoa strain is faster than that of the Ravenna strain. The duration of the various phases of the biological cycle is very similar in both populations, but that from Ravenna exhibits greater tolerance of low temperatures, slower development rate and lower development threshold temperature than does the Genoa population. Temperature and geographical origin also have strong effects on reproductive characteristics. The highest fecundity values were observed at 12 °C in the Ravenna strain, the lowest at 30 °C in both groups. At 18 °C, the Genoa population is more fecund than the Ravenna one, while the situation is reversed at 12 °C. The smallest ovigerous capsules are produced at 30 °C, the biggest at 12 °C, and the Genoa females produce larger capsules than do the females from Ravenna, except at 12 °C. The size of both male and female eggs varies in relation to temperature, the smallest female eggs generally being laid at the higher temperatures. At all the temperatures tested, the sex ratio of the Ravenna population is higher than that of the Genoa population. In the Ravenna strain, temperature has no effect on the sex ratio, while in the Genoa strain the sex ratio at 24 °C is lower than at 18 and 30 °C. Comparison of the two populations at the same temperature reveals considerable differences in the characteristics of their respective life histories and sex ratios. It is very likely that the extreme selectivity of the harbor environments has favored the fragmentation of the species into differentiated populations that have adapted to the conditions prevailing in the different localities.     

First report of three protozoan parasites (a haplosporidian, Marteilia sp. and Marteilioides sp.) from the Manila clam, Venerupis (=Ruditapes) philippinarum in Japan

Recently, natural stocks of the Manila clam, Venerupis (=Ruditapes) philippinarum, have been drastically reduced in Japan. To clarify the reason for this decline in number, clams were sampled monthly from Yamaguchi and processed for histological observations, during which three protozoan parasites were discovered. Transmission electron microscopy revealed that these parasites were unidentified haplosporidian in the connective tissues, Marteilia sp. in the digestive gland and Marteilioides sp. in the oocytes. Histopathological observations suggest that Marteilia sp. and Marteilioides sp. were not pathogenic to the host. However, infection with a haplosporidian may have a negative impact on the clams. The prevalence of these parasites was low and further investigations should be undertaken to clarify their taxonomic status and establish any pathogenicity to clams.     

Giardia duodenalis: Kinetics of cyst elimination and the systemic humoral and intestinal secretory immune responses in gerbils (Meriones unguiculatus) experimentally infected

This study aimed to determine the pre-patent period and to evaluate the kinetics of cyst elimination and the systemic humoral (IgA, IgG₁, IgG_2a, IgM, IgE) and intestinal secretory (IgA) immune responses in gerbils (Meriones unguiculatus) experimentally innoculated with different doses of Giardia duodenalis trophozoites. Forty-eight animals aged 6-8 weeks were used, equally distributed among six groups, five groups innoculated with different doses of trophozoites (10¹, 10², 10³, 10⁴, 10⁵) and one control (non-infected) group. Coproparasitological examinations were carried out daily up to 91 days after inoculation (d.a.i.) to determine the pre-patent period and the kinetics of cyst elimination. Blood and stool samples were weekly collected for antibody assays. The pre-patent period was observed from the 9 d.a.i. onwards, with intermittent elimination of variable quantities of cysts up to 27 d.a.i.. All infected gerbils, irrespective of the dose received, were able to mount systemic humoral immune responses as evidenced by specific IgM titers from 7 to 28 d.a.i., corresponding to the peak of cyst elimination, followed by high and persistent IgG1 titers. Intestinal secretory responses were also seen with two peaks of fecal IgA titers, corresponding to IgM and IgG1response peaks, respectively. In conclusion, systemic and intestinal humoral immune responses were related to the control of giardiasis in this experimental model.     

Effect of storage temperature on survival and infectivity of Steinernema rarum (OLI strain) (Rhabditida: Steinernematidae)

Nematode strains of the entomopathogenic family Steinernematidae differ in their ability to infect insects at different temperatures. Survival and infectivity of infective juveniles (IJs) of Steinernema rarum (OLI) were studied after their storage at 23 ± 2 °C and at 5 ± 1 °C. Survival at 23 ± 2 °C was always above 95%. At 5 ± 1 °C, survival decreased at week 5, but infectivity did the same after week 2. Unlike other steinernematids, both infectivity and survival of IJs would be higher for S. rarum (OLI) when stored at 23 ± 2 °C.     

Temperature impact on reproduction and development of congener copepod populations

The goal of this study was to relate the temperature response of all developmental stages and reproductive biology of two congener copepod pairs inhabiting different biogeographic regions to their geographic distribution patterns. Survival of adult females and egg production, embryonic development and hatching success of the genera Centropages and Temora from two stations, in the North Sea and the Mediterranean, were studied in laboratory experiments in a temperature range from 2 to 35 °C. Postembryonic development was determined from cohorts raised at temperatures between 10 and 20 °C with surplus food. Tolerance limits and optima of female survival, reproduction and development distinguished the northern species Centropages hamatus and Temora longicornis from the southern T. stylifera, while C. typicus, which is found in both regions, was intermediate. Thus, thermal preferences could in part explain distribution patterns of these species. While C. hamatus and the two Temora species showed distinct temperature ranges, C. typicus was able to tolerate different temperature conditions, resulting in its wide distribution range from the subarctic to the tropics. However, the thermal range of a species did not necessarily correlate with the optimal temperatures in the experiments. Optima of egg production and stage development were surprisingly low in T. stylifera, which has a mere southern distribution.