Using polyclonal antibodies to detect predation by dogwhelks Nucella lapillus (L.)

Interactions between predators and their multiple prey species can vary greatly among locations where they coexist. As a method to assess spatial variation in predation by intertidal dogwhelks on their dominant prey, immunoassays of dogwhelk gut contents from experimental populations and field collected individuals were evaluated using polyclonal antibodies raised separately to soluble proteins from Mytilus edulis L. mussels and Semibalanus balanoides (L.) barnacles. Both antisera produced strong reactions against their homologous antigens but no cross reactions between prey species. Experimental trials tested the critical hypothesis that prey species had equal detection intervals in dogwhelk guts. Two groups of 225 dogwhelks were starved for 14 days, provided with either mussels or barnacles for five days, and then sampled over 22 days. Independent immunoassays of dogwhelk gut contents against each antibody revealed a consistent, weak cross reaction between the anti-mussel antibody and dogwhelk gut tissues. After accounting for this cross reaction, the strength of immunoassays against both prey species declined exponentially and at similar rates. The proportions of dogwhelks that tested positive for their provided prey species declined linearly through time and were not significantly influenced by prey type. Prey were detectable throughout the sampled post-feeding period and were projected to have detection limits of 24.4 days (barnacles) and 26.5 days (mussels), demonstrating that immunoassay results are not biased by dissimilar prey detection intervals. Reactions against the antibody from the non-provided prey were time invariant and occurred at relatively low frequencies. Immunoassays of dogwhelks collected from five intertidal sites on Swans Island, Maine, USA revealed patterns similar to field observations, though immunoassays classified far fewer individuals as non-feeders and more as barnacle feeders than indicated by direct field observations. Unlike single observations, immunoassays also revealed the presence of both prey in dogwhelks from four sites, though most individuals tested positive for only a single prey type. Immunoassays facilitate concurrent collections of predation data from many individuals and will enable further local- to regional-scale assessments of dogwhelk predation at additional sites around the Gulf of Maine.     

Shell form and niche occupation in Nucella lapillus (L.) (Gastropoda)

Collections of Nucella lapillus (L.) from various eastern Atlantic areas have been measured, and shell shape has been analysed by D'Arcy Thompson's method in terms of whorl ratio, apical angle, and spiral angle. In southwestern Ireland N. lapillus varies greatly from tall and narrow in sheltered situations to short and wide at very wave-exposed sites. A local population is described for a bay near Crookhaven, County Cork. In northwestern Spain the open-sea form is developed only weakly. In southwestern Ireland N. lapillus effectively populates mussel beds in the lower littoral on open coasts, whereas in Spain it is sparse or absent from such situations but plentiful high up on the shore on barnacles in places where there is some local shelter from rocks or crevices. It is suggested that failure to develop the open-sea type in Spain is responsible for this difference in niche. Both in Spain and at a site in Scotland N. lapillus feeding on mussels in sheltered situations is of the tall narrow type, so that a diet of mussels cannot alone be responsible for the development of the open sea type, although it still might be a necessary condition. It is to be expected that the genetic composition of populations will vary regionally and will contribute to variation in shell form, but the part which it plays on a purely local scale remains uncertain.     

Influence of static and fluctuating salinity on cadmium uptake and metallothionein expression by the dogwhelk Nucella lapillus (L.)

The aim of this study was to investigate the effect of salinity on cadmium (Cd) accumulation and metallothionein (MT) expression in the dogwhelk Nucella lapillus (L.). Adult dogwhelks (shell length: 23.4±1.3 mm) were acclimated to salinity of 33 psu (control), 22 or 11 psu under controlled laboratory conditions (9.5 °C; pH 7.9) for 10 days in a stepwise manner by reducing the salinity by 5.5 psu day⁻¹. Ten treatment groups were used and comprised five salinity regimes (three fixed salinity [33, 22 or 11 psu] and two fluctuating salinity [varied daily between 33 and 22 psu or 33 and 11 psu in a cyclic manner]) at each of two Cd concentrations (control: <0.001 μg Cd l⁻¹ or treatment: 500 μg Cd l⁻¹). After acclimation, groups of 20 dogwhelks were exposed to each of the 10 Cd/salinity combinations. All the control and Cd-exposed dogwhelks exposed to 11 psu were dead within 5 days of exposure due to hypo-osmotic stress. Twenty days after exposure to all other treatments, concentrations of Cd and MTs in the tissues of surviving dogwhelks were quantified using atomic absorption spectrophotometry and the silver saturation method, respectively. Both Cd accumulation and MT induction in control or Cd-exposed N. lapillus were significantly influenced by changes in salinity, especially at a prolonged and fixed low salinity (22 psu), although such influences of salinity on the concentration of MTs were dependent on the tissue type. The study highlights that salinity should be considered when monitoring trace metals and/or MTs in intertidal molluscs, particularly in estuarine or transplanted biomonitors.     

Enhanced condition in dogwhelks, Nucella lapillus (L.) living under mussel hummocks

Dogwhelks, Nucella lapillus eat both barnacles and mussels, Mytilus edulis. However, mussels are dangerous prey because they can snare and immobilize dogwhelks with their byssi. Despite this danger, adult dogwhelks are common inside mussel hummocks or stacks found on mature mussel beds. The whelks live in debris-filled chambers within the hummocks, unsnared by byssi. Evidence is presented to show that this is a highly favourable microhabitat for dogwhelks. Condition index (CI) measurements showed that mean CI for “hummock” dogwhelks was 20.99 in early spring, 29.65 in midsummer and 34.86 in early winter. In comparison, CI values for dogwhelks from nearby barnacle zones were 20.13, 25.03 and 24.66 respectively. The summer and winter CI values of “hummock” dogwhelks were enhanced to a highly significant extent. Data are also presented to show that shore elevation or dogwhelk shell height (over the size range of animals studied) had no confounding effect on this result. Predicted flesh and shell mass values for a standard 25 mm high whelk showed that occupation of hummocks was associated with a thin-walled shell morphology, and that the shell mass became proportionately lower in summer and early winter. A feeding experiment showed that CI rises slowly, even in dogwhelks fed to satiation on mussels. Dogwhelks were taken from the barnacle zone in March 1997 and either fed to satiation on Mytilus or starved, whilst being held in seawater at ambient seawater temperature. The CI of fed dogwhelks rose from 19.7 to 27.4 in 3 months, while that of starved Nucella fell from 19.7 to 16.3. In the meantime, the CI of dogwhelks in situ in the barnacle zone had risen from 19.7 to 23.8. Hence, 3 months' satiation ration had led to a nett 3.6 unit rise in CI; starvation to a nett 7.5 unit fall. All of the changes in CI were due to changes in flesh mass; shell mass was stable. Since “hummock” dogwhelks collected in early winter have a CI value about 10.2 units greater than barnacle zone dogwhelks, this indicates that “hummock” dogwhelks are long-term inhabitants of this microhabitat.     

Water balance and the mantle cavity fluid of Nucella lapillus(L.) (Mollusca: Prosobranchia)

When uncovered by the tide Nucella lapillus (L.) retains fluid in the mantle cavity which accounts for ≈ 39% of the total water content of the attached animal. This extra-corporeal fluid reservoir retained in the mantle cavity has been investigated in relation to desiccation. Volume changes of mantle cavity fluid (m.c.f.) and concentration changes in Cl^?, Na⁺ and total osmotic pressure of m.c.f. and blood, suggest that the m.c.f. reduces the full effects of desiccation on the animal by restricting those effects to the external compartment. The blood of Nucella living in normal sea water was found to be hypo-osmotic and an hypothesis is presented which links this to the rôle of the m.c.f. during desiccation.     

Type and nature of cues used by Nucella lapillus to evaluate predation risk

The ability of prey to detect and adequately respond to predation risk influences immediate survival and overall fitness. Chemical cues are commonly used by prey to evaluate risk, and the purpose of this study was to elicit the nature of cues used by prey hunted by generalist predators. Nucella lapillus are common, predatory, intertidal snails that evaluate predatory risk using chemical cues. Using Nucella and a suite of its potential predators as a model system, we explored how (1) predator type, (2) predator diet, and (3) injured conspecifics and heterospecifics influence Nucella behavior. Using laboratory flumes, we determined that Nucella responded only to the invasive green crab (Carcinus maenas), the predator it most frequently encounters. Nucella did not respond to rock crabs (Cancer irroratus) or Jonah crabs (Cancer borealis), which are sympatric predators but do not frequently encounter Nucella because these crabs are primarily subtidal. Predator diet did not affect Nucella responses to risk, although starved predator response was not significantly different from controls. Since green crabs are generalist predators, diet cues do not reflect predation risk, and thus altering behavior as a function of predator diet would not likely benefit Nucella. Nucella did, however, react to injured conspecifics, a strategy that may allow them to recognize threats when predators are difficult to detect. Nucella did not react to injured heterospecifics including mussels (Mytilus edulis) and herbivorous snails Littorina littorea, suggesting that they are responding to chemical cues unique to their species. The nature of cues used by Nucella allows them to minimize costs associated with predator avoidance.     

The feeding, growth, and energetics of two rocky intertidal predators (Pisaster ochraceus and Nucella canaliculata) under water temperatures simulating episodic upwelling

Although most upwelling regions are marked by strong fluctuations in water temperature, few studies have examined how episodic cold-water events affect the physiology and ecology of benthic marine invertebrates. I tested the hypothesis that upwelling-related variation in water temperature regulates the feeding, growth, and energetics of two rocky intertidal predators, the sea star Pisaster ochraceus (Brandt, 1835) and the whelk Nucella canaliculata (Duclos, 1832). Sea stars and whelks were maintained in laboratory tanks at a constant 9 °C, a constant 12 °C, and a treatment that simulated the Oregon coast upwelling regime by cycling between 14-day periods of 12 and 9 °C. Early in the experiments, sea stars and whelks held at 9 °C consumed about 30% fewer mussels (Mytilus trossulus) than those in warmer tanks. Despite lower consumption by whelks in colder tanks, 9 and 12 °C individuals attained the same final size. Similarly, sea stars in 9 °C tanks showed greater growth per gram of mussel tissue consumed than individuals held at 12 °C. These results suggest that reduced consumption under colder conditions was balanced by reduced metabolic costs. Moreover, there appeared to be an energetic advantage to living in the temperature regime characteristic of intermittent upwelling. Sea stars alternately exposed to 12 and 9 °C had a significantly higher growth rate, conversion efficiency, and storage of reserves in the pyloric caeca than individuals in the constant 12 °C tanks. Whelks maintained under fluctuating temperatures tended to grow faster than those held at constant 12 or 9 °C, although this trend was not statistically significant (p=0.069). These results suggest that benthic consumers experiencing cyclic temperatures may feed intensely during periods of warmer water while benefiting from reduced metabolic costs during cold-water intrusions. Because the fecundity of Pisaster and Nucella is a function of energy stored during the upwelling season, interannual variability in upwelling patterns could alter the reproductive output of these species.     

Behavioural aspects of predation by juvenile Atlantic salmon (Salmo salar L.) on particulate,drifting prey

A recirculatory flume tank simulating a simplified stream environment was used to study the feeding behaviour of juvenile Atlantic salmon (Salmo salar L.), 5.1 to 9.4 cm in fork length (from tip of snout to fork of tail), on artificial particulate prey passively drifting in the water current. Changes in feeding behaviour at two different times of the year and when fish were presented with prey of different sizes are described and quantified. Responsiveness to food was greatly reduced in autumn as compared to summer. The maximum distances at which prey elicited a response decreased in autumn to 40% of the summer value, and the maximum distances which fish traversed in order to capture prey decreased by 80% over the same period. During the peak growing season, the response to a range of prey sizes from 0.013 to 0.102 × fish fork length was directly related to prey size and could be accounted for on the basis of visual theory alone. Capture distances were closely related to fixation distances. Maximum capture distance increased to a peak value for prey of between 0.025 and 0.069 × fork length, while larger prey were never captured and the smallest prey rarely evoked a response. Prey size selectivity also operated after capture, through rejection versus retention of the prey.     

The survival and development of the shrimp Crangon crangon (L.), reared in the laboratory under non-circadian light-dark cycles

The shrimp, Crangon crangon (L.), has been reared from hatching to the late juvenile phase, under a circadian (LD 12 : 12) and two non-circadian (LD 8 : 8 and LD random) light-dark cycles. During the zoeal phase, survival in the non-circadian regimes was markedly lower than in the control circadian treatments. This effect supports the hypothesis that the entraining influence of daily environmental cycles is important in coordinating the various physiological processes within the animal. There was no evidence, however, that growth and morphological development were affected in the non-circadian regimes.     

Effects of temperature,salinity and aerial exposure on predation and lysosomal stability of the dogwhelk Thais (Nucella) lapillus (L.)

The ingestion and absorption rate of standard length Thais lapillus (L.) stepwise-acclimated to constant temperature-salinity conditions and preying on Mytilus edulis (L.) varied directly with environmental salinity at 10, 15 and 20°C. Dogwhelk ingestion and absorption rates indicate that cold torpor existed at 5°C and heat stress was evident at 20°C. The feeding cycle duration was significantly longer for dogwhelks acclimated to 20%. S than in those acclimated to 30%. S at 10°C even though no significant difference existed between the two groups of snails in the drilling and ingestion or postfeeding phases of the cycle. Ingestive conditioning of dogwhelks to mussels occurred; the duration of the drilling and ingestion and total feeding cycle declined as a function of the number of mussels consumed by a snail. Dogwhelks of all sizes prey on a wide length range of mussels and there is also a high degree of variability in the ingestion rate of snails as a function of their size. A prominent feature of the lack of a relationship between dogwhelk ingestion rate and snail size was that the percentage of nonfeeding snails increased at low salinity and temperature extremes. Digestive-tubule cell lysosomal stability was tested as an index of digestive capability and animal condition; in stepwise-acclimated dogwhelks, it correlated well with their ingestion and absorption rates. The ingestion rate of dogwhelks acclimated to 30%. S and subjected to a 30?17.5?30%. S semidiurnal pattern of fluctuating salinity for 21 days was significantly lower than for snails maintained at 30%. S; however, snails acclimated to 17.5%. S and exposed to the same pattern of fluctuating salinity fed at a higher rate than snails maintained at 17.5%. S. Aerial exposure of snails maintained at 30%. S and 10°C water temperature resulted in an ingestion rate 2.1 times faster than for snails constantly submerged suggesting that tidal emersion is not always stressful to intertidal carnivores. The postfeeding phase of the feeding cycle was shortened in dogwhelks subjected to aerial exposure. Although significant variation occurred in digestive-tubule cell lysosomal stability during the first cycle of fluctuating salinity, the variability had declined significantly by Day 21. This observation suggests that digestive tubule lysosomal stability becomes adapted to a fluctuating osmotic environment, although the initial changes in lysosomal stability are probably related to intralysosomal protein catabolism and production of amino acids for intracellular osmoregulation. Variations in the osmotic environment of T. lapillus have resulted in unexpected outcomes with respect to their ingestion rate under conditions of fluctuating salinity and aerial exposure.     

Biochemical stimuli for feeding in Acanthaster planci (L.)

The typical feeding response of the Crown of Thorns Starfish Acanthaster planci (L.) can be induced by mucoproteins of molecular weight greater than 200,000 daltons found in mucus obtained from corals of the genera Acropora and Fungia.     

Survival, growth and feeding of vendace, Coregonus albula (L.), larvae in net enclosures

Vendace, Coregonus albula (L.), larvae reared in net enclosures anchored in the littoral zone of Lake Ylä-Enonvesi, eastern Finland, were observed for a period of 44 days in order to determine the effects of density on mortality, growth and feeding of the larvae. The ratio of newly-hatched fish to their food was regulated by controlling the number of fish stocked into the enclosures. Prey animals were expected to move freely in and out of the enclosures. The effect of nylon mesh (500 μm) on the penetration of zooplankters into the enclosures was negligible. The influence of possible starvation was determined by analysing the growth of the larvae, their Fulton condition factor, the instantaneous amount of food ingested, and the food composition in their guts. All these indicators were inversely correlated with larval density. Vendace larvae were found to be resistant to mortality from direct starvation. At all densities the survival rate was over 60%. At the time of complete yolk absorption, there was no increase in mortality.     

Fatty acid composition of canola (Brassica napus L.), as affected by agronomical,genotypic and environmental parameters

Vegetable oils with a high relative amount of unsaturated fatty acids are of great significance for human health. There is not any data on the effects of tillage practices on fatty acid composition of canola (Brassica napus L.). Hence, in a 2-year split plot experiment, the effects of different tillage systems (no (NT), minimum (MT) and conventional tillage (CT)), canola genotypes (Hyola 401 (V1) and PF (V2)) and sowing dates (including Sep. 8, 23 and Oct. 7) on the fatty acid composition of canola were evaluated. Tillage practices and the combination of canola genotypes and sowing dates were randomized to the main and sub-plots, respectively. The highest oleic acid content was the result of combining NT, V1 and Sep. 23, and the lowest was related to the combination of CT, V2 and Oct. 7. While the combination of NT, V1 and D1 resulted in the highest amount of unsaturated fatty acids, this amount was the lowest for the combination of CT, V2 and Sep. 23. For the selection of an appropriate canola producing strategy, all these parameters must be taken into account. The combination of NT, V1 and Sep. 23 may be the most favorable cropping strategy for canola production under a Mediterranean climate.     

Flock feeding and time budgets in the house sparrow (Passer domesticus L.)

A winter population of house sparrows at a farm fed on barley seed in two distinct types of habitat: cattlesheds and open fields. The risk of predation was apparently higher in the fields where birds scanned more frequently than in the cattlesheds and where scanning was negatively influenced by flock size but positively influenced by distance from cover. Individual time budgets were more influenced by flock size than by seed density in the fields but more influenced by seed density than by flock size in the cattlesheds. Higher rates of scanning resulted in greater flock vigilance and longer flight distances in the fields but flight distance was negatively influenced by the density of seeds on which birds were feeding.     

Behavioural responses to visual stimuli by the snails Tectarius muricatus,Turbo castanea, and Helix aspersa

The visual responses of three gastropods were studied for comparison with data previously obtained for the marsh periwinkle, Littorina irrorata. Turbo castanea, an archeogastropod inhabiting subtidal grass beds, had the lowest response thresholds for bar width (0.3–1.4⁰) and shape reflectance (83%), and showed significant preferences in two binary-choice tests. Tectarius muricatus, a littorinid inhabiting hard substrate in the supratidal zone, had slightly higher response thresholds (1.4–6.5^o; 75%) than T. castanea, and showed a significant preference in only one binary-choice test. Helix aspersa, a terrestrial pulmonate primarily active e at night, had much higher response thresholds (14.5–24.6°; 19%) than T. castanea and T. muricatus, and showed no significant preferences in binarychoice tests. Assuming that these response threshold estimates approximate actual sensory thresholds, then T. castanea can see slightly better than T. muricatus, and both species can see much better than H. aspersa. This conclusion coincides with expectations based on the light intensities and complexity of visual stimuli present in the habitats of these snails.     

Behavioural studies on the green turtle (Chelonia mydas) in the sea

Underwater observations of green turtles near Fairfax Island, Bunker Group, Australia, disclosed female behaviour patterns to avoid copulation, including a striking adpressed hind limb position; resting in a female sanctuary area; avoidance swimming; face-to-face confrontation, followed or accompanied by biting; and a ‘refusal’ position, with the female assuming a vertical position, her limbs widely outspread and plastron facing the male. Copulation activity precedes egg laying on Fairfax. Copulation lasts as long as 6 hr. Females outnumber males, who engage in multiple copulations. The ‘escort’ is a group of one to five males attendant upon mated pairs. Hatchlings feed on various invertebrates. Cleaner fishes groom adult female turtles.     

Growth,reproduction, and feeding oF Fundulus heteroclitus (L.) on a North Carolina salt marsh

Fundulus heteroclitus (L.) from a North Carolina Spartina marsh teed largely on small crustaceans (amphipods, tanaids and copepods) and polychaetes. Fish longer than 30 mm standard length also ingested considerable amounts of living plant material. Smaller individuals were distinctly carnivorous. Recognizable particles of Spartina detritus occurred in less than 15% of the guts examined. The relationship of weight to length changed significantly during the year. Although females were larger than males of the same age. males were heavier than females of the same length, except for a brief period at the peak of the spawning season in the early spring. An average second season fish may lay up to 512 eggs from March through August, but first season fish did not reach reproductive size by the end of the spawning season. Growth of first season fish in mid-summer averaged 5% of their total weight per day. These significant seasonal changes in ecological properties of killifish populations are important in any estimates of growth, reproduction, and production.     

Trophallaxis in honeybees, Apis mellifera (L.), as related to their past experience at the food source

Forager honeybees returning to the hive after a successful foraging trip unload the collected liquid to recipient hivemates through mouth-to-mouth food exchange contacts (trophallaxis). The speed at which the liquid is transferred (unloading rate) from donor to recipient is related to the profitability offered by the recently visited food source. However, because a forager's evaluation of the profitability of a food source, as measured by dancing behaviour, is influenced by previous foraging experience, we investigated whether trophallaxis might also be influenced by previous foraging experience. We measured unloading rate for a given profitability condition at the food source (in terms of solution flow rate) in three groups of foragers that differed in their previous experience at the source. One group experienced the same flow rate of solution in five successive visits (control group), another group experienced a lower flow rate in the first four visits and the third group experienced a higher flow rate in the first four visits. The results of the present study show that animals trained to a lower flow rate increased their unloading rate compared with the control group, indicating an influence of past foraging experience on their evaluation of food source profitability. This influence was not observed in the group trained to a higher flow rate, which responded as the control group. Additional experiments indicated that foragers appear to evaluate the profitability of the source by integrating an overall flow rate throughout the entire visit, instead of measuring only the current flow rate delivered by the feeder. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.      

Behavioral plasticity of the soft-shell clam, Mya arenaria (L.), in the presence of predators increases survival in the field

Soft-shell clams, Mya arenaria, are sessile, suspension-feeding bivalves that are preyed upon by the exotic green crab, Carcinus maenas. Clams evade crab consumers by burrowing deeper into the sediment after perceiving a threat from a nearby predator. The purpose of this study was to determine the types of signals that M. arenaria use to detect predators and the types of behaviors clams use to avoid being eaten. In a field study, clams increased their burial depth in the presence of green crab predators consuming conspecifics that were caged nearby, and also increased burial depth after artificial tactile stimulation in the laboratory assay. These results indicate that clams can use chemical and mechanical cues to detect potential predatory threats. We performed a field study to examine the difference in survivability of clams that had burrowed deeper into the sediment in response to predators vs. control clams that were burrowed less deeply. Significantly higher survival rates were observed in clams that had initially burrowed more deeply, suggesting that increasing burial depth is a valid predator avoidance strategy. Some bivalves also alter their pumping rates in the presence of predators, making them less apparent and providing more structural defense by covering soft tissue, and we measured pumping time of soft-shell clams in the presence and absence of predators, when burrowing was not an option for escape. Soft-shell clams did not alter their pumping time in the presence of green crab predators, possibly because they employ a burrowing method called “hydraulic” or “jet-propelled” burrowing, where it is necessary for the clam to pump in order to burrow. Chemical signals and tactile cues instigated behavioral changes in M. arenaria, and this change in behavior (increasing burial depth) increased clam survival in the field.