Caiman latirostris (broad-snouted caiman) as a sentinel organism for genotoxic monitoring: basal values determination of micronucleus and comet assay.

Caiman latirostris is one of the two crocodilian species that inhabit Argentina. In this country, as a consequence of agricultural frontiers expansion during the last years, many areas of the geographic distribution of the broad snouted caiman overlap with regions of intensive agricultural activity. Contaminants released to the environment may induce genetic alterations in wildlife, which could lead to mutations and/or carcinogenesis. Up to the moment, no studies had been made concerning the possibbility to apply biomarkers of genotoxic evaluation in C. latirostris. The aim of this study was to adapt two widely used genotoxic techniques, the comet assay and the micronucleus test, for their application in C. latirostris and to determine the baseline values in this species, in order to establish its suitability as a sentinel organism for future genotoxic monitoring of environmental pollutants. A total of 41 juvenile caimans of 4 months old (FMO) and 10 months old (TMO) were used. Genotoxic techniques were applied on peripheral blood erythrocytes introducing the necessary modifications required by the material, which are presented here. Our results show that baseline values of DNA damage are quite stable among juvenile caimans (MN: FMO animals 0.87+/-0.74 and TMO animals 1.04+/-0.92; DI: FMO animals 103.40+/-3.36 and TMO animals 120.08+/-11.33), being independent of the nest of origin, sex and size of the animals and confirm the potential value of both short term tests as accurate screening tools for the evaluation of genotoxic agents in C. latirostris. This is the first reference to the application of genotoxic techniques on C. latirostris and the second in crocodilians. Data provided here will be useful for future studies involving the biomonitoring of natural regions where C. latirostris occurs, employing this species as a sentinel organism for genotoxic assessment of environmental pollutants.     

Seed germination and dormancy in the medicinal woodland herbs Collinsonia canadensis L. (Lamiaceae) and Dioscorea villosa L. (Dioscoreaceae)

We used a double germination phenology or “move-along” experiment (sensu Baskin and Baskin, 2003) to characterize seed dormancy in two medicinal woodland herbs, Collinsonia canadensis L. (Lamiaceae) and Dioscorea villosa L. (Dioscoreaceae). Imbibed seeds of both species were moved through the following two sequences of simulated thermoperiods: (a) 30/15 °C→20/10 °C→15/6 °C→5 °C→15/6 °C→20/10 °C→30/15 °C, and (b) 5 °C→15/6 °C→20/10 °C→30/15 °C→20/10 °C→15/6 °C→5 °C. In each sequence, seeds of both species germinated to high rates (>85%) at cool temperatures (15/6 and 20/10 °C) only if seeds were previously exposed to cold temperatures (5 °C). Seeds kept at four control thermoperiods (5, 15/6, 20/10, 30/15 °C) for 30 d showed little or no germination. Seeds of both species, therefore, have physiological dormancy that is broken by 12 weeks of cold (5 °C) stratification. Morphological studies indicated that embryos of C. canadensis have “investing” embryos at maturity (morphological dormancy absent), whereas embryos of D. villosa are undeveloped at maturity (morphological dormancy present). Because warm temperatures are required for embryo growth and cold stratification breaks physiological dormancy, D. villosa seeds have non-deep simple morphophysiological dormancy (MPD). Neither species afterripened in a 6-month dry storage treatment. Cold stratification treatments of 4 and 8 weeks alleviated dormancy in both species but C. canadensis seeds germinated at slower speeds and lower rates compared to seeds given 12 weeks of cold stratification. In their natural habitat, both species disperse seeds in mid- to late autumn and germinate in the spring after cold winter temperatures alleviate endogenous dormancy.     

Osmoregulation by the broad-snouted caiman, Caiman latirostris, in estuarine habitat in southern Brazil

The broad-snouted caiman Caiman latirostris, of South America mostly frequents freshwater but occurs also in estuaries. Nothing of substance is known of its osmoregulatory physiology but, in the light of accumulating evidence that alligatorids lack specialised adaptations for life in hyperosmotic waters, we anticipated its physiology would be more similar to that of Alligator mississippiensis than the euryhaline Crocodylus porosus, which has both lingual salt glands and a more complex renal:cloacal system. This proved to be the case. Caiman captured in estuaries of the Ilha do Cardoso in southern Brazil were effective hypo-osmotic osmoregulators in salinities of 0–24 ppt (seawater = 35 ppt). Plasma osmolarity, sodium and chloride were similar to those in other crocodilians and not influenced by salinity. Plasma urea was low and did not vary with salinity. We found no evidence of lingual or other salt glands. Urinary electrolyte concentrations varied considerably with salinity and in ways reminiscent of A. mississippiensis but very different from C. porosus. Ca. latirostris dehydrated in seawater more rapidly than C. porosus and had substantially higher integumental permeability to water. Caiman did not drink seawater but rehydrated rapidly when returned to freshwater (FW). We found small caiman (<500 g) only in very low salinities (<3 ppt) and larger caiman closer to the sea. We postulate that medium to large Ca. latirostris can take advantage of the feeding opportunities presented by the estuarine mangal despite lacking the physiological specialisations of crocodylids. Two individuals which we re-sighted by chance had travelled at least 600 m in 2–3 days, showing that every caiman we captured or saw was within easy reach of FW. Most likely their habitation of the estuary and its mangal is achieved through a combination of low surface area:volume ratio, relatively impermeable skin, and periodic access to FW. Accepted: 11 May 1998     

δC, δN, carbon, nitrogen and phosphorus as indicators of plant ecophysiology and organic matter pathways in Everglades deep slough, Florida, USA

Historically, the Florida Everglades was characterized by a corrugated landscape of shorter hydroperiod, elevated sawgrass (Cladium jamaicense) ridges and longer hydroperiod, deep water slough communities. Drainage and compartmentalization of the Everglades have fundamentally altered this pattern, and sawgrass ridge communities have expanded at the expense of deep water slough communities throughout much of the landscape. In this study we provide a simple isotopic and nutrient characterization of major components of the slough ecosystem to elucidate physiological and nutrient differences among species and to suggest pathways for organic matter decomposition that contribute to peat development in deep water sloughs. We examined carbon (C) and nitrogen (N) isotopes and C, N and phosphorus (P) concentrations of the floating-leaved macrophytes Nymphaea odorata and Nymphoides aquatica, the emergent macrophyte Eleocharis elongata, and the submerged species Utricularia foliosa and Utricularia purpurea, as well as soil and flocculent material from the southern Water Conservation Area 3-A. Flocculent material and soils had the highest N content (4.5 ± 0.2%) and U. foliosa and N. odorata had the highest P content (0.13 ± 0.01% to 0.12 ± 0.01%). The range for δ¹⁵N average ± SE values was 5.81 ± 0.29‰ (U. foliosa) to −1.84 ± 0.63‰ (N. odorata), while the range for δ¹³C values was −23.83 ± 0.12‰ (N. odorata) to −29.28 ± 0.34‰ (U. purpurea). Differences of up to 10‰ in C isotopic values of U. foliosa and N. odorata suggest fundamental physiological differences between these species. Along a degradation continuum, enrichment of ¹³C and ¹⁵N and extent of decomposition was negatively related to phosphorus concentrations. A two end-member ¹³C mixing model suggested that Utricularia species were the primary organic source for flocculent materials, whereas organic matter derived from root decomposition of N. odorata contributed to the progressively enriched δ¹³C values found with depth in soils. These results illustrate the fundamentally important roles of Nymphaea and Utricularia species in ecosystem dynamics of deep water sloughs.     

Growth of dinoflagellates, Ceratium furca and Ceratium fusus in Sagami Bay, Japan: The role of temperature, light intensity and photoperiod

Seasonal changes of field populations and growth rates of two dinoflagellates, Ceratium furca and Ceratium fusus, were examined in the temperate coastal water of Sagami Bay, Japan. Weekly field sampling was conducted from August 2002 to August 2003, and laboratory experiments were also carried out to investigate effects of temperature, irradiance and photoperiod on the growth rates of these two Ceratium species. In the field, the abundances of both species increased significantly from April to August 2003, were gradually decreased from November 2002 and were not observed in January 2003. C. fusus was able to increase at lower temperatures in February 2003 compared to C. furca. In the laboratory, the two species did not grow at <10 °C or >32 °C. The highest specific growth rate of C. furca was 0.72 d⁻¹ at 24 °C and 600 μmol m⁻² s⁻¹. Optimum growth rates (>0.4 d⁻¹) of C. furca were observed at temperatures from 18 to 28 °C and at irradiances from 216 to 796 μmol m⁻² s⁻¹. The highest growth rate of C. fusus was 0.56 d⁻¹ at 26 °C and 216 μmol m⁻² s⁻¹. Optimum growth rates of C. fusus were observed at the same irradiance rage of C. furca, whereas optimum temperature range was narrower (26–28 °C). The growth curves of both species indicated saturation of the growth rates when light intensity was above 216 μmol m⁻² s⁻¹, and did not show photoinhibition at irradiances up to 796 μmol m⁻² s⁻¹. The specific growth rates of both Ceratium species were clearly decreased at L:D = 10:14 relative to those at L:D = 14:10 and L:D = 12:12. The present study indicates the two Ceratium species can adapt to a wide range of temperature and irradiance.     

The effects of heat treatments on ectomycorrhizal resistant propagules and their ability to colonize bioassay seedlings

The effect of disturbance on the resistant propagule community (RPC) of ectomycorrhizal fungi has been given relatively little attention. In this study we investigate the effects of heat, one important factor of fire disturbances, on the ability of ectomycorrhizal RPC fungi to colonize Pinus jeffreyi seedlings in greenhouse bioassays. Prior to planting the seed, soils were collected from an old growth mixed-conifer forest in the southern Sierra Nevada, California, USA and then subjected to four heat treatments of none, 45 °C, 60 °C, and 75 °C. After eight months, seedlings were harvested and the ectomycorrhizal fungi colonizing the roots were characterized by molecular methods (PCR-RFLP and DNA sequencing). Rhizopogon species increased in dominance on seedlings grown in soils receiving the 75 °C heat treatment. One species significantly increased in frequency, Rhizopogon olivaceotinctus, and two species (Cenococcum geophilum and Wilcoxina sp.) significantly decreased in frequency in the 75 °C treatment. The increase of R. olivaceotinctus, coupled with other features of its behavior, suggests that substantial heat disturbances may benefit this species in competing for roots.     

Food habits of the Broad‐snouted Caiman (Caiman latirostris: Crocodylia,Alligatoridae) in northwestern Uruguay

The food habits of the Broad‐snouted Caiman (Caiman latirostris) were studied in northwestern Uruguay. The most common prey were insects, the shrimp Pseudopalaemon bouvieri, the snail Pomacea canaliculata, fish and birds. Spiders, crabs, amphibians, snakes, turtles and mammals were consumed less frequently. Arthropods were the most frequent prey for juvenile caiman. Fish and snails were consumed by all size classes. The proportion of stomach contents with invertebrates decreased with increasing caiman size, and that with vertebrates was greater in the diet of larger caiman. Diet composition and ontogenetic shift are similar to that of other crocodilians considered as opportunistic generalist predators.

Se estudiaron los hábitos alimenticios del Yacaré (Caiman latirostris) en el noroeste de Uruguay. Las presas más comunes fueron insectos, el camarón Pseudopalaemon bouvieri, el caracol Pomacea canaliculata, peces y aves. Arañas, cangrejos, anfibios, serpientes, tortugas y mamíferos fueron consumidos menos frecuentemente. Los artrópodos fueron las presas más frecuentes de juveniles. Peces y aves fueron consumidos por todos los tamaños. La proporción de contenidos estomacales con invertebrados disminuyó al aumentar el tamaño de los caimanes, y la de vertebrados fue mayor en los individuos de mayor tamaño. La composición y cambio ontogenético en la dieta resultan similares a los de crocodilianos considerados predadores generalistas oportunistas.     

Febrile response to infection in the American alligator (Alligator mississippiensis)

Temperature probes were inserted into the stomachs of juvenile American alligators (Alligator mississippiensis) maintained outdoors at ambient fluctuating temperatures. Internal body temperatures (T_b) were measured every 15 min for two days, and then the alligators were injected with bacterial lipopolysaccharide (LPS), pyrogen-free saline, or left untreated. Alligators injected intraperitoneally with LPS exhibited maximum T_bs 2.6 ± 1.1 °C and 3.5 ± 1.2 °C higher than untreated control animals on days one and two after treatment, respectively. T_bs for these animals fell to within control ranges by day three postinjection. Similarly, mean preferred body temperatures (MPBTs) were significantly higher for LPS-injected alligators on days one (4.2 ± 1.8 °C) and two (3.5 ± 1.6 °C) after treatment. Intraperitoneal injection of heat-killed Aeromonas hydrophila, a gram-negative bacterium known to infect crocodilians, resulted in a fever while injection of Staphylococcus aureus (gram positive) did not elicit a febrile response. Injection of LPS in alligators maintained indoors in a constant temperature environment resulted in no increase in internal T_b. These results indicate that alligators did not exhibit a febrile response in the absence of a thermal gradient, and suggest that febrile responses observed are probably behavioral in nature.     

Horizontal transmission of a microsporidium from the convergent lady beetle, Hippodamia convergens Guérin-Méneville (Coleoptera: Coccinellidae), to three coccinellid species of Nova Scotia

Convergent lady beetles, Hippodamia convergens Guérin-Méneville, are a popular choice for aphid control in North America. An unidentified microsporidium was found in H. convergens adults that were purchased from a commercial insectary in 2004. This study examined egg cannibalism and egg predation as a means of horizontal transmission of the unidentified microsporidium among H. convergens larvae and three coccinellid species found in Nova Scotia: Coccinella septempunctata (seven-spotted lady beetle), C. trifasciata perplexa (three-banded lady beetle), and Harmonia axyridis (multicolored Asian lady beetle). The microsporidium was transmitted with 100% efficiency when first instars fed on microsporidia-infected eggs. Mean spore count data from smear preparations of infected beetles suggest that the infection was as heavy in C. trifasciata perplexa (a native coccinellid) (11.2 ± 0.96 spores/100 μm²) as it was in H. convergens (the natural host) (12.8 ± 1.16) but lighter in the introduced species C. septempunctata (7.5 ± 0.65) and H. axyridis (0.8 ± 0.11). For all of the beetle species examined, larval development was significantly longer for microsporidia-infected individuals than for their uninfected cohorts. The microsporidium had no effect on larval mortality. Based on the results of this study, field-collected H. convergens should be examined for microsporidia and uninfected individuals should be used to rear individuals for release in biological control programs. However, this is unlikely to happen because H. convergens are relatively easy and inexpensive to collect from their overwintering sites for redistribution.     

Effects of temperature on development, survival, longevity, and fecundity of the Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) predator, Axinoscymnus cardilobus (Coleoptera: Coccinellidae)

Axinoscymnus cardilobus (Homoptera: Aleyrodidae) is an important predator of Bemisia tabaci (Coleoptera: Coccinellidae) that occurs in high population density of B. tabaci. Temperature among other factors is observed to play an important role in the development of arthropods. The effect of temperature on the development of A. cardilobus was studied at seven constant temperature regimes (14, 17, 20, 23, 26, 29, 32 °C). The results indicated that the duration of egg, larval and pupal stages were significantly influenced by increased temperature. The rate of development gradually increased with increase in temperature from 14 °C to 26 °C, but declined from 26 °C to 32 °C. The survival rates of different insect stages were stable at temperatures between 20 °C and 26 °C, but at extreme temperatures of 32 °C and 14 °C, a sharp decrease was evident. Ovipositional period of the female decreased when temperatures were increased from 17 °C to 32 °C. The highest fecundity of the female (225.7 eggs per female) was recorded at 23 °C. Life tables of A. cardilobus were constructed based on the experimental results at temperatures of 14–32 °C. The reproductive rate (R₀), the innate capacity for increase (r_m) and the finite rate of increase (λ) reached the maximum values at 23 °C, of 70.7, 0.059 and 1.062, respectively. The mean generation time (T) decreased with increased temperature from 17 °C to 32 °C, the highest and least values recorded at 17 °C and 32 °C were 112.7 and 38.7, respectively. These results offer valuable insight on the importation and establishment of A. cardilobus into new environments with diverse temperature regimes.     

Acceptance and suitability of different host stages of Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) and seven other tephritid fruit fly species to Tetrastichus giffardii Silvestri (Hymenoptera: Eulophidae)

Tetrastichus giffardii Silvestri is a gregarious eulophid endoparasitoid of several tephritid fruit fly species. Host stage suitability was studied using nine age groups of Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), namely, eggs less than 24 h and between 24 and 48 h old, and 1- to 7-day-old larvae. Life table studies for T. giffardii using C. capitata as host were done at 26 ± 5 °C and 55–60% RH. Egg load in relation to age of the female parasitoid was also assessed as was the effect of host deprivation on adult longevity. Host acceptance and suitability were examined with respect to eight species of tephritids. Potential hosts so tested were five Ceratitis species, the Medfly, C. capitata, the mango fruit fly, Ceratitis cosyra (Walker), the Natal fruit fly, Ceratitis rosa Karsch, Ceratitis fasciventris (Bezzi), and Ceratitis anonae Graham; two Bactrocera species, the melon fruit fly, Bactrocera cucurbitae (Coquillett) and the newly invasive Bactrocera invadens Drew, Tsuruta, and White; and one Dacus species, the lesser pumpkin fly, Dacus ciliatus Loew. No parasitoids were obtained from eggs while all larval stages were suitable though at varying degrees. Parasitism and number of progeny was related to host age in a curvilinear manner with maxima at 4- to 5-day-old larvae. By contrast, development time decreased with age of host larvae while sex ratio was not affected. The intrinsic rate of increase was 0.17 ± 0.01; gross and net reproductive rates were 64.9 ± 4.3 and 44.9 ± 3.8, respectively. Non-ovipositing females lived significantly longer than ovipositing ones. The females accepted all host species tested, but only C. capitata, D. ciliatus and, to a much lesser extent, C. cosyra were suitable. In the remaining host species, most eggs were encapsulated. In C. capitata and D. ciliatus, percent parasitism was similar, but number of progeny was lower and the sex ratio, as the proportion of females, was higher when the parasitoid was reared on D. ciliatus. Progeny per puparium were also similar for the two hosts. In the light of these results it can be concluded that T. giffardii has a narrow host range, but it attacks and successfully develops in larvae representing a wide range of ages.     

Characterization of biocontrol traits in the entomopathogenic nematode Heterorhabditis georgiana (Kesha strain), and phylogenetic analysis of the nematode’s symbiotic bacteria

Our objective was to estimate the biocontrol potential of the recently discovered entomopathogenic nematode species Heterorhabditis georgiana (Kesha strain). Additionally, we conducted a phylogenetic characterization of the nematode’s symbiotic bacterium. In laboratory experiments, we compared H. georgiana to other entomopathogenic nematodes for virulence, environmental tolerance (to heat, desiccation, and cold), and host seeking ability. Virulence assays targeted Acheta domesticus, Agrotis ipsilon, Diaprepes abbreviatus, Musca domestica, Plodia interpunctella, Solenopsis invicta, and Tenebrio molitor. Each assay included H. georgiana and five or six of the following species: Heterorhabditis floridensis, Heterorhabditis indica, Heterorhabditis mexicana, Steinernema carpocapsae, Steinernema feltiae, Steinernema rarum, and Steinernema riobrave. Environmental tolerance assays included Heterorhabditis bacteriophora, H. georgiana, H. indica, S. carpocapsae, S. feltiae, and S. riobrave (except cold tolerance did not include S. carpocapsae or S. riobrave). Host seeking ability was assessed in H. bacteriophora, H. georgiana, S. carpocapsae, and Steinernema glaseri, all of which showed positive orientation to the host with S. glaseri having greater movement toward the host than S. carpocapsae (and the heterorhabditids being intermediate). Temperature range data (tested at 10, 13, 17, 25, 30 and 35 °C) indicated that H. georgiana can infect Galleria mellonella between 13 and 35 °C (with higher infection at 17–30 °C), and could reproduce between 17 and 30 °C (with higher nematode yields at 25 °C). Compared with other nematode species, H. georgiana expressed low or intermediate capabilities in all virulence and environmental tolerance assays indicating a relatively low biocontrol potential. Some novel observations resulted from comparisons among other species tested. In virulence assays, H. indica caused the highest mortality in P. interpunctella followed by S. riobrave; S. carpocapsae caused the highest mortality in A. domesticus followed by H. indica; and S. riobrave was the most virulent nematode to S. invicta. In cold tolerance, S. feltiae exhibited superior ability to cause mortality in G. mellonella (100%) at 10 °C, yet H. bacteriophora and H. georgiana exhibited the ability to produce attenuated infections at 10 °C, i.e., the infections resumed and produced mortality at 25 °C. In contrast, H. indica did not show an ability to cause attenuated infections. Based on the phylogenetic analysis, the bacterium associated with H. georgiana was identified as Photorhabdus luminescens akhurstii.     

An autecological study of the potentially toxic dinoflagellate Alexandrium affine isolated from Vietnamese waters

The potentially toxic dinoflagellate species Alexandrium affine isolated from Ha Long Bay (Tonkin Gulf), Vietnam was cultured and maintained for morphological, physiological and toxicological studies. Classical morphological examinations including plate pattern were in good agreement with the international nomenclature of the species. The fine structure of A. affine, including morphology of its developmental stages during vegetative and sexual reproduction was found to be typical of other species in the genus. Two general trends in growth of A. Affine from Vietnamese waters were apparent: (1) growth rates were low at low salinities (10 and 15 psu) in all experimental temperatures (21–27 °C); (2) growth rates were high at salinities 25, 30, and 35 psu in all temperatures. There were no significant differences in growth rates at different salinities at low temperature (21 °C), and the most significant difference in growth rate was between high temperature–high salinity and high temperature–low salinity. The optimum temperature and salinity for growth were 24 °C and 30 psu. Maximum division rates per day (0.5–0.7) were at salinities 30 and 35 psu and at temperatures 24 and 27 °C. But the best conditions for division rate were 21 and 24 °C at salinities 30 and 35 psu. Toxicity analyses indicated A. affine to be both toxic and non-toxic at certain times. In the former case, toxicity was very low, 2.28 fmol  per cell; the toxicity component of A. affine was compared with that of A. leei and the mussel Perna viridis including neoSTX, STX, and GTX₁–GTX₄.     

Effect of temperature on survival, development and reproduction of the predatory lacewing Dichochrysa prasina (Neuroptera: Chrysopidae) reared on Ephestia kuehniella eggs (Lepidoptera: Pyralidae)

Preimaginal development and adult longevity and reproduction of Dichochrysa prasina Burmeister were studied at six constant temperatures (15, 20, 25, 27, 30 and 33 °C) and a photoperiod of 16:8 (L:D). Eggs of the flour moth Ephestia kuehniella (Zeller) were used as food throughout preimaginal development, whereas the adults of D. prasina fed on a liquid diet of water, yeast hydrolysate, sugar and honey. At the highest tested temperature of 33 °C no larvae completed their development. At the rest of the tested temperatures the egg to adult developmental period ranged from approximately 92 days at 15 °C to 25 days at 30 °C. Percentages of adult emergence ranged from 36% at 15 °C to 84% at 30 °C. Both adult longevity and fecundity were significantly affected by temperature and the intrinsic rate of increase (r_m) reached its maximum value at 27 °C. These results could be useful for the establishment of a small scale rearing and mass production of D. prasina.     

A preliminary study on the seasonal body temperature rhythms of the captive mountain hare (Lepus timidus)

The mountain hare (Lepus timidus) is a year-round active herbivore adapted to survive the boreal winter. Captive mountain hares (N = 4) were implanted with intraabdominal thermosensitive loggers to record their core body temperature (T_b) for a year and during food deprivation (8–48 h) in summer and winter. The average T_b was 38.7 ± 0.01 °C in summer and 38.3 ± 0.01 °C in winter. The yearly T_b correlated positively with the ambient temperature. The 24-h T_b was the highest from late scotophase to early photophase in summer and winter and the lowest during middle-late photophase in summer or during early-middle scotophase in winter. The range of the 24-h oscillations in T_b increased in three animals in winter. Food deprivation did not induce hypothermia in summer or winter. These preliminary data suggest that the mountain hare can spare a modest amount of energy with the wintertime reduction in T_b.     

Thermal sensitivity of escape response performance by the scallop Placopecten magellanicus: Impact of environmental history

To examine the impact of environmental history on the thermal sensitivity of escape response performance in juvenile giant scallops, Placopecten magellanicus, we compared animals sampled in late May, when water temperatures and day length were increasing, to animals sampled in late September, when water temperature and day length were decreasing. Habitat temperature was approximately 12 °C at both sampling times. For May scallops, performance was better at 6 than at 12 or 18 °C whereas September scallops performed better at 6 and 12 °C than at 19 °C. Regardless of environmental history, the rate of phasic contractions consistently declined at 18–19 °C, due to a decrease in the number of phasic contractions. Force measurements during escape responses of May scallops showed that phasic force production and the minimal interval between contractions changed little with temperature, whereas the minimum and mean durations of phasic contractions decreased as temperature rose. Phasic contraction rate in the first series increased with temperature. Reliance upon tonic contractions was higher in scallops tested at 18 °C than in those tested at 6 °C. Environmental history, more than habitat temperature at the time of sampling, seems to set the thermal sensitivity of phasic contraction rate in P. magellanicus. Phasic force production did not change within the thermal range tested.     

Growth and protein synthesis of barramundi, Lates calcarifer, fed lupin as a partial protein replacement

Protein synthesis is an essential growth process in all animals. Little information is available on post-prandial protein synthesis and even less where different protein sources are compared. Protein synthesis was measured at 4 and 24 h after feeding juvenile barramundi in order to determine the effect of using lupin as a partial protein replacement for fish meal on the post-prandial protein metabolism. Juvenile barramundi (4.3 ±0.6 g) were held in a recirculation system (27 °C, salinity 10‰ and 24 h light) for 15 days. Fish were fed one of two isonitrogenous isoenergetic diets (40% crude protein, 16% lipid and 18.5 GE MJ kg^− 1). One diet was formulated with 100% fish meal as the protein source while the other had 45% of the protein replaced with lupin ingredients (lupin kernel meal (Lupinus angustifolius) and lupin protein concentrate). All fish were fed a ration of 6%·d^− 1 and feed intake was not significantly different between the two diets. Specific growth rate (SGR) and growth efficiency (in relation to protein (PPV) and energy (PEV)) were 6.5 ± 0.14%·d^− 1, 43.8 ± 2.72% and 38.31 ± 1.56%, respectively, and were not significantly different between the two diets. There was no significant difference in protein synthesis between the two diets at 4 and 24 h after feeding, however protein synthesis was significantly higher 4 h after feeding than at 24 h (p = 0.02). Neither growth performance nor protein metabolism was altered by replacing 45% of the protein with lupin protein and indicated this to be a suitable protein source for barramundi feeds.     

Phenology of first and peak emergence of Aphthona lacertosa and A. nigriscutis: Two flea beetles introduced for biological control of leafy spurge, Euphorbia esula L.

Nonlinear models were used to estimate first emergence and peak abundance dates for Aphthona lacertosa Rosenhauer and A. nigriscutis Foudras, two flea beetles introduced to control leafy spurge, Euphorbia esula L., in North America. For model development, 26 field sites were sampled for flea beetle abundance at weekly intervals for eight weeks in three western Minnesota counties in 2000, 2001, and 2002. A three-parameter Weibull function, fit to observed cumulative probability distributions, were used to predict accumulated degree-days (ADD) to first emergence. Bias testing indicated the Weibull function provided a useful estimate of first emergence for A. lacertosa (304 ADD, lower developmental threshold 7.5 °C), but failed to produce a useful estimate for A. nigriscutis. A third-order polynomial was used to approximate seasonal abundance and predict peak abundance for each species. Estimated ADD to peak abundance of A. lacertosa was 594 ± 24 (DD > 7.5 °C) and 670 ± 15 (DD > 9.3 °C) for A. nigriscutis. Models were validated with additional data sets from Minnesota, Montana, and North Dakota. Estimated date of peak emergence provided useful predictions of peak emergence for Minnesota and North Dakota, but failed to predict peak emergence in Montana. We speculate that variation in climate and environmental conditions between Midwestern states and Montana were responsible for differing emergence patterns. We conclude that phenology models should be developed regionally to provide useful predictions of peak emergence for land managers. Maps were developed for Minnesota to spatially display predicted dates of peak abundance for A. lacertosa and A. nigriscutis.     

Relationship between temperature optima and secreted protease activities of three Pythium species and pathogenicity toward plant and animal hosts

The in vitro physiological characteristics of three species of Pythium (oomycetes) that utilize different food sources were compared with their ecological activities: P. insidiosum is a pathogen of mammals (including humans), P. graminicola infects the roots of graminaceous hosts, and P. grandisporangium is an enigmatic water mold isolated from mangrove leaves and marine algae. P. insidiosum and P. graminicola showed peak growth rates at 37 °C before complete inhibition of growth at 40 °C; P. grandisporangium grew fastest at 22 °C. Differences between the invasive pressures exerted by the hyphae of these microorganisms were not considered significant in relation to the substrates colonized by these water molds. All three species showed substantial secreted protease activity, producing three or more serine proteases with weights ranging from 24-38 kDa. Fastest growth rates were supported when collagen was supplied as the sole carbon source, and none of the species were able to grow on purified plant cell wall polysaccharides. The growth and nutritional characteristics of P. graminicola and P. grandisporangium bear little obvious relationship to the ecological niches that they inhabit. This highlights the caution necessary in extrapolating from laboratory analyses to the natural environment, and points to the potential importance of ecological opportunity in determining the host range and food source of certain microorganisms.     

Effects of the estuarine dinoflagellate Pfiesteria shumwayae (Dinophyceae) on survival and grazing activity of several shellfish species

A series of experiments was conducted to examine effects of four strains of the estuarine dinoflagellate, Pfiesteria shumwayae, on the behavior and survival of larval and adult shellfish (bay scallop, Argopecten irradians; eastern oyster, Crassostrea virginica; northern quahogs, Mercenaria mercenaria; green mussels, Perna viridis [adults only]). In separate trials with larvae of A. irradians, C. virginica, and M. mercenaria, an aggressive predatory response of three strains of algal- and fish-fed P. shumwayae was observed (exception, algal-fed strain 1024C). Larval mortality resulted primarily from damage inflicted by physical attack of the flagellated cells, and secondarily from Pfiesteria toxin, as demonstrated in larval C. virginica exposed to P. shumwayae with versus without direct physical contact. Survival of adult shellfish and grazing activity depended upon the species and the cell density, strain, and nutritional history of P. shumwayae. No mortality of the four shellfish species was noted after 24 h of exposure to algal- or fish-fed P. shumwayae (strains 1024C, 1048C, and CCMP2089) in separate trials at ≤5 × 10³ cells ml⁻¹, whereas higher densities of fish-fed, but not algal-fed, populations (>7–8 × 10³ cells ml⁻¹) induced low (≤15%) but significant mortality. Adults of all four shellfish species sustained >90% mortality when exposed to fish-fed strain 270A1 (8 × 10³ cells ml⁻¹). In contrast, adult M. mercenaria and P. viridis exposed to a similar density of fish-fed strain 2172C sustained <15% mortality, and there was no mortality of A. irradians and C. virginica exposed to that strain. In mouse bioassays with tissue homogenates (adductor muscle, mantle, and whole animals) of A. irradians and M. mercenaria that had been exposed to P. shumwayae (three strains, separate trials), mice experienced several minutes of disorientation followed by recovery. Mice injected with tissue extracts from control animals fed cryptomonads showed no response. Grazing rates of adult shellfish on P. shumwayae (mean cell length ±1 standard error [S.E.], 9 ± 1 μm) generally were significantly lower when fed fish-fed (toxic) populations than when fed populations that previously had been maintained on algal prey, and grazing rates were highest with the nontoxic cryptomonad, Storeatula major (cell length 7 ± 1 μm). Abundant cysts of P. shumwayae were found in fecal strands of all shellfish species tested, and ≤45% of the feces produced viable flagellated cells when placed into favorable culture conditions. These findings were supported by a field study wherein fecal strands collected from field-collected adult shellfish (C. virginica, M. mercenaria, and ribbed mussels, Geukensia demissa) were confirmed to contain cysts of P. shumwayae, and these cysts produced fish-killing flagellated populations in standardized fish bioassays. Thus, predatory feeding by flagellated cells of P. shumwayae can adversely affect survival of larval bivalve molluscs, and grazing can be depressed when adult shellfish are fed P. shumwayae. The data suggest that P. shumwayae could affect recruitment of larval shellfish in estuaries and aquaculture facilities; shellfish can be adversely affected via reduced filtration rates; and adult shellfish may be vectors of toxic P. shumwayae when shellfish are transported from one geographic location to another.