Genetic isolation of populations of the gammaridean amphipod, Corophium volutator, in the Bay of Fundy, Canada

Selection experiments suggest that evolutionary modifications in amphipod demography can respond to local environmental changes and that local races of amphipods may be common. We tested this hypothesis in mudflat populations of Corophium volutator in the Bay of Fundy, Canada. Due to the unique topography of the Bay of Fundy, distinctive environmental conditions are prevalent in different branches of the Bay, while the impact of shorebird predation has also been shown to vary between populations. Several hypotheses have been suggested to explain ecological evidence which indicates that Corophium volutator (Pallas), a common amphipod crustacean, exhibits extensive life history variation in Bay of Fundy populations. We used RAPD-PCR techniques to examine populations of C. volutator in an investigation of genetic isolation in marine environments. Our data suggest that variation in selection pressures have played a significant role in the genetic divergence of populations of C. volutator in the Bay of Fundy.     

Parasites on an intertidal Corophium-bed: factors determining the phenology of microphallid trematodes in the intermediate host populations of the mud-snail Hydrobia ulvae and the amphipod Corophium volutator

The phenology of microphallid trematodes within their intermediate hostpopulations has been studied on an intertidal mud flat. The parasites usethe mud snail Hydrobia ulvae and the infaunal amphipod Corophium volutatoras first and secondary intermediate host, respectively. Migratory shorebirdsact as final hosts. Our results show a general trend of decline in thedensity of infected intermediate hosts during both spring and autumn, whichcould mainly be ascribed to shorebird predation. During summer the densityof both infected snails and infected amphipods increased considerably, witha culmination in June within the snail population (1000 infectedm-² and in August within the amphipod population (40 000infected m-². This time lag in parasite occurrence could berelated to (1) the development time of larval trematodes within the snails,(2) higher ambient temperatures in late summer increasing parasitetransmission between snails and amphipods during this period, and (3) ageneral increase in the Corophium population during late summer. Fromsamples collected between 1990 and 1995 it is shown that microphallidtrematodes occasionally may give rise to mass mortality in the amphipodpopulation. The prerequisites for such an event are a high parasiteprevalence within the first intermediate host population and unusually highambient temperatures, facilitating parasite transmission to the secondaryintermediate host, C. volutator.     

Evidence that the parasitic nematode Skrjabinoclava manipulates host Corophium behavior to increase transmission to the sandpiper, Calidris pusilla

We found evidence that a nematode (Skrjabinoclava morrisoni) adaptivelymanipulates the behavior of its intermediate host (the amphipod Corophiumvolutator) to increase its likelihood of transmission to itsfinal host (the semipalmated sandpiper, Calidris pusilla). We foundthat male and female amphipods parasitized by nematodes increasedtheir surface activity in the field during daytime, but notduring nighttime hours. Increased surface activity is knownto increase susceptibility of amphipods to predation by sandpipersduring the day, but not at night, when sandpipers do not feedvisually. Also, as predicted by the manipulation hypothesis,only late-stage (infective) larvae of nematodes were associatedwith behavioral changes of amphipods. We found no evidence thatparasites were associated with other amphipod behaviors in thelaboratory, such as trail complexity, distance traveled, orburrow-probing activity of crawling males as would be expectedif parasitized hosts altered their own behavior. Survivorshipof amphipods was also unaffected by parasitism, which may favorparasite transmission. Thus, behavioral changes of parasitizedhosts were simple, and their expression was context-dependentand related to likelihood of predation. We argue that maturationtimes of nematodes in relation to migration schedules of sandpipers providea narrow window of opportunity and may explain why nematodes manipulateamphipod behavior.     

The relative profitability of particulate- and filter-feeding in the herring, Clupea harengus L.

Analysis of laboratory video-recordings of herring feeding by biting and filtering on Calanus finmarchicus and three sizes of Artemia enabled the capture rates of the two methods to be estimated at different prey concentrations. At low concentrations the fish feed by selective capture of individual particles, but the capture rate achievable by this method is constrained by the maximum rate at which they can bite. Filter-feeding is not subject to this constraint because capture rate is directly proportional to prey concentration and above a critical prey concentration its capture rate exceeds that of biting. The possession of two feeding methods allows the fish to maximize prey intake over a wide range of concentrations and the phenomenon of switching between feeding methods can be explained by their relative profitabilities at different concentrations. The observation that less than 50% of fish are filtering when capture rates by the two methods are equal suggests that filtering is energetically more costly than biting. Estimates of the energy cost of filtering indicated that it may be from 1.4 to 4.6 times higher than that of biting.     

An analysis of the pattern of feeding in the Costa Rican weevil, Exopthalmus jekelianus, on the tropical tree, Cedrela odorata

Feeding patterns were recorded and analysed for adult female weevils, Exopthalmus jekelianus (White) (Coleoptera: Curculionidae), feeding on Central American mahogany, Cedrela odorata L., in the field in Costa Rica. The study forms part of an investigation into the relationship between feeding patterns and the fine-scale variation in leaf chemistry occurring within the host plant. The weevils’ feeding patterns were the simplest in temporal structure of any reported to date for an insect herbivore. Weevils spent an average of only 3% of their time feeding during the 10-h observation periods. Meals lasted an average of 2.8 min and occurred at a mean intermeal interval of 84 min. The feeding patterns gave the appearance of a short-term rhythm underlying the onset of feeding (as has been found in locusts and caterpillars), although there were insufficient meals taken by individuals over the 10-h period to test this suggestion. Meals were notable in apparently lacking intrameal pauses and also commencing without preliminary sampling behaviours, such as palpating or biting. Whether the combination of short, infrequent meals, ingested without pauses and not preceded by sampling behaviour, represents an adaptation reducing apparency to natural enemies, or else simply reflects low nutritional needs, is discussed. Correlations between meal durations and following and preceding intermeal intervals suggested that variation in intermeal intervals stemmed largely from variation in meal duration, not vice versa, with variation in meal duration resulting from an external influence such as leaf nutritional and/or allelo-chemistry. The latter suggestion is currently being tested.     

The zooplankton: its community structure,food and feeding,and role in the ecosystem of Lake Vechten

The structure, feeding and metabolism of the filterfeeders community of Lake Vechten (The Netherlands) were investigated for seven years in relation to the functioning of the lake's ecosystem. The ¹⁴C-technique used in the grazing and assimilation study is discussed in detail with a critical analysis of the methodological errors.The three major species which contributed to the annual density, biomass and grazing maxima in spring are: Bosmina longirostris, Daphnia spp. and Eudiaptomus gracilis. The rise in grazing pressure in recent years, particularly in May, was accompanied by a corresponding decrease in the seston (<33 µm) biomass, and in increase of inedible algae, especially Ceratium hirudinella, in late summer. The means of daily grazing ranged from 3% in March to 34% in June. The mean annual ratio ingestion: phytoplankton production varied from 70 to 230%. The specific filtering rate, SFR (ml · day^–1 · mg^–1 · zoop · C), was related directly to water temperature but inversely to the food concentrations.The main errors in the ingestion and assimilation rates were related to the leaching of the isotope from the animals in the preservation fluid. The loss of tracer was 42 and 26%, respectively, for the two rates.In spring, the food removed by the grazers per day was equivalent to 125–400% of the daily primary production. This caused a sharp decrease in the seston concentrations and a recurring clear water phase because of a sharp increase in the Secchi depth. The zooplankton assimilatory removal of carbon and the sedimentation loss rates to the hypolimnion exceeded the primary production rates. The inconsistencies in the carbon budget are possibly due to our lack of knowledge of the horizontal transport of material from the littoral, bacteria as an alternative food source for zooplankton, and the DOC dynamics.The grazers' activity as SFR in deep, stratifying lakes like Vechten is 3 to 4 times that in the shallow, mixed and more eutrophic Dutch lakes. In the former category of lakes the crustacean herbivores serve as an important link in the food chain in the limnetic region.     

Thermoregulatory use of heat increment of feeding in the tawny owl (Strix aluco)

The heat increment of feeding (HIF) was investigated in the tawny owl (Strix aluco) in central Norway (63°N, 10°E), close to the northern limit of its distribution. HIF was measured as the increase in heat production (measured as oxygen consumption) after force-feeding the owls with laboratory mice at thermoneutral conditions (20 °C) and during cold-exposure (5 °C and −5 °C). The basal metabolic rate of the owls (mean mass 419 g) was 4.39 kJ h⁻¹ and the lower critical temperature was approximately 16 °C. During cold conditions, HIF substituted for thermogenesis, and at an ambient temperature of −5 °C the substitution was complete. Calculations indicate that the substitution by HIF may save the owls as much as 60% of their daily thermoregulatory costs. This corresponds to about 10% of their total daily energy budget.     

Changes in the size and number of secretion granules in the rat exocrine pancreas induced by feeding or stimulation in vitro

Summary The size, number and volume per cell of secretion granules in rat exocrine pancreas have been measured using stereological techniques. The changes which occur as a result of feeding starved animals (90 min) or stimulating lobular fragments in vitro with carbachol are documented. In fasted animals mean acinar cell volume was estimated as 1670 m³ and the cells contained an average of around 450 secretion granules with a corrected mean diameter of 0.70 m. They occupied around 7% of cell volume. After feeding mean cell volume was about 1300 m³ and the cells contained an average of about 190 granules per cell with a mean diameter of 0.58 m. They occupied 3% of cell volume. A shift in the size frequency distribution of granule diameters occurred as a result of feeding. In vitro experiments in which lobules were induced to secrete with carbachol (10M, 3 h, 37° C) had a similar effect. Mean cell volume was reduced from around 1760 m³ to 1360 m³, mean granule number from around 420 per cell to 180 per cell and the volume density of granules was reduced from about 8% to 3% of cell volume. There was no significant change in mean granule diameter or shift in the size-frequency distribution of granule diameters. Incubation of tissues with cycloheximide (1 mM, 3 h, 37° C) did not prevent secretion by carbachol but it prevented replacement of granules. As a consequence, depletion by carbachol was greater in the presence of cycloheximide, the granules being reduced to around 110 per cell and to only 2.5% of cell volume. We conclude that feeding causes a preferential loss of larger granules and that during secretion replacement of granules occurs. Some of these granules are smaller than those evident in the glands of starved animals.     

Clonidine, octopaminergic receptor agonist, reduces protein feeding in the blow fly, Phormia regina (Meigen)

Results in this study are consistent with those of Murdock and his colleagues who clearly demonstrated that clonidine, an agonist of octopaminergic receptors in some insects, significantly increases sucrose feeding. Their studies, however, did not examine the effect of clonidine on protein feeding. Injection of a 20 microg/microl/fly dose of clonidine significantly reduces protein feeding in both sexes of Phormia regina, instead of stimulating feeding as is observed with carbohydrate feeding. The manner in which the flies are fed prior to starvation and the method of testing influences the amounts of diet consumed. It is proposed that the biogenic amines influence the state of hunger (i.e., protein versus carbohydrates) while other chemicals and neural mechanisms (i.e., such as sulfakinins and stretch receptors, respectively) affect satiety.     

Particle size selection in individuals from epifaunal versus infaunal populations of the nereidid polychaete Neanthes succinea(Polychaeta: Nereididae)

Neanthes succinea (Frey & Leuckart, 1847) is a common nereidid polychaete of both epifaunal and infaunal estuarine habitats. The gut contents of individuals collected from two epifaunal and two infaunal habitats are compared. Our a priori expectation was that individuals from epifaunal habitats would be classified as macrophagous with guts indicating carnivory and/or macroalgal herbivory, while individuals from infaunal habitats would be classified as microphagous with guts indicating deposit feeding. At all four locations gut contents indicated deposit feeding with little indication of macrophagous feeding. Average particle sizes for mineral grains did not differ between the four collection sites. For the two infaunal locations mean size of the mineral grains in gut contents was significantly smaller than ambient sediments. In addition to mineral grains, guts contained diatoms, dinoflagellates, macrophytic detritus, protozoan tests, and a variety of metazoans. Our study demonstrates that caution is necessary when inferring feeding type from morphology and that population and habitat specific differences in diet can occur within the same species.     

The plastic reproductive allocation of the cruciferous perennialRorippa indica in response to different degrees of feeding damage

The degree of feeding damage in the wild to the cruciferous perennial Rorippa indica (L.) Hieron ranged from 0% (not damaged) to 100% (heavily damaged). However, “not damaged” and “heavily damaged” individuals did not differ in the relative suitability of their intrinsic traits for P. rapae, which caused the heaviest damage on the plant. Therefore, the different degrees of feeding damage may be due to variability in the extrinsic traits of the plant, that is, it may be determined by the habitat conditions where individual plants exist. Furthermore, R. indica allocated more resource to seed production at the expense of the roots when it was experimentally subjected to heavy leaf damage. The result suggested that R. indica individuals may escape, by means of seed dispersal and seed dormancy, from unfavorable habitats where they are heavily damaged by herbivores.     

The effect of feeding on the metabolic rate in harbour seals (Phoca vitulina)

The heat increment of feeding was estimated in harbour seals (Phoca vitulina). Seals were given different amounts of herring, ranging from 0.8 to 2.65 kg. The caloric content of the herring ranged from 6575 to 12560 kJ·kg^-1 depending on time of year. Metabolic rate increased within 30 min after feeding, and the magnitude and duration of heat increment of feeding depended on the size of the meal and the caloric content of the herring. Measured heat increment of feeding was up to 14.9% of gross energy intake and metabolic rate increased as much as 46% above resting, postabsorptive metabolic rate for 15 h duration in a harbour seal with a body weight of approximately 40 kg.     

Foodplant selection and induction of feeding preference among host and non-host plants in larvae of the tobacco hornworm Manduca sexta

Ten host plant (Solanaceae) and twelve non-host plant species were tested as foodplants for first instar larvae of the tobacco hornworm, Manduca sexta. Only nine host and three non-host plant species elicited feeding and supported growth up to fifth instar. The range of acceptability suggested that plants be divided into hosts, acceptable non-hosts, and unacceptable non-hosts. Using the two-choice feeding preference test we found that the initial preference for hosts was preserved when larvae were reared on hosts, but was less strong or absent for larvae reared on acceptable non-hosts. Thus oligophagy in the tobacco hornworm is not induced, but must be inherited.Newly-hatched first instar larvae and fifth instar larvae showed a preference hierarchy among both hosts and non-hosts. Fifth instar larvae reared separately on two different host species showed slightly different preference hierarchies among hosts. The preference for the rearing plant was increased and also two other host species changed positions in hierarchies.Feeding preferences of larvae reared on hosts or acceptable non-hosts were determined using plant combinations of host vs. host, host vs. acceptable non-host, and acceptable non-host vs. acceptable non-host. Induction of feeding preference was found in all three of these categories. This shows that induction of feeding preference in the tobacco hornworm is not restricted to host plant species.The degree to which feeding preferences were induced ranged from very strong to undetectable and dependend on the plant species paired. The strength of induction in the tobacco hornworm was found to correlate inversely with taxonomic relatedness of the plant species paired. Analysis of induction data from the literature revealed a similar correlation for other lepidopteran species.

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Résumé Vingt-deux espèces de plantes, dont 10 planteshôtes (Solanées), ont été testés comme plantes alimentaires pour des chenilles de ler stade de Manduca sexta. Sur cet ensemble, seulement 12 plantes (dont 9 plantes hôtes) induisaient la prise de nourriture et permettaient la croissance jusqu'au 5ème stade. La diversité des résultats suggère que les plantes pouvaient être classées en hôtes, non-hôtes acceptables et non-hôtes refusés. En utilisant le test du choix alimentaire préférentiel entre deux rondelles de feuilles, les chenilles néonates de ler stade ont préféré nettement les plantes-hôtes aux autres. Cette préférence initiale pour les plantes-hôtes était préservée quand les cheniles étaient élevées sur plantes-hôtes, mais devenait moins nette ou disparaissait pour des chenilles élevées sur d'autres plantes acceptées. Ainsi l'oligophagie ches M. sexta n'est pas induite, mais doit être héritée.Les chenilles néonates, aussi bien que celles de 5ème stade, présentent des préférences hiérarchisées parmi les plantes hôtes ou non. La seule frontiere nette observée était entre espèces de plantes acceptables ou non. Les hiérarchies préférentielles des chenilles du 5ème stade différaient légèrement lors-qu'elles avaient été élevées sur deux plantes-hôtes différentes. La différence essentielle était l'observation d'une préférence accrue pour l'espèce ayant servi à l'élevage, mais deux autres plantes-hôtes changaient aussi de position hiérarchique.La cause de ces changements de préférence a été approfondie, les chenilles étant élevées sur des feuilles de chaque espèce acceptable (hôte ou non). Leurs préférences alimentaires ont été définies en utilisant des combinaisons diverses (hôte x hôte, hôte x non-hôte acceptable, non-hôte acceptable x non-hôte acceptable). L'induction de la préférence alimentaires a été obtenue dans ces trois associations. Ceci montre que l'induction des choix alimentaires chez M. sexta n'est pas limitée aux plantes-hôtes. Le degré d'induction de la préférence alimentaire variait de très fort à indécelable; il dépendait de l'association examinée. La source de la variabilité de cette induction a été examinée en fonction de la relation entre la force de l'induction et les rapports taxonomiques des plantes associées. La relation obervée était inversée pour M. sexta. L'examen des données de la littérature ont révélé une relation du même type pour les autres espèces de Lépidoptères.