Selective Feeding Behaviour Research Articles

Identification of Potential Metabolites Mediating Bird's Selective Feeding on Prunus mira Flowers.

In peach orchards, birds severely damage flowers during blossom season, decreasing the fruit yield potential. However, the wild peach species Prunus mira shows intraspecific variations of bird damage, indicating that some of the wild trees have developed strategies to avert bird foraging. Motivated by this observation, we formulated the present study to identify the potential flower metabolites mediating the bird's selective feeding behavior in P. mira flowers. The birds' preferred (FG) and avoided (BFT) flowers were collected from wild P. mira trees at three different locations, and their metabolite contents were detected, quantified, and compared. The widely-targeted metabolomics approach was employed to detect a diverse set of 603 compounds, predominantly, organic acids, amino acid derivatives, nucleotide and its derivatives, and flavones. By quantitatively comparing the metabolite contents between FG and BFT, three candidate metabolites, including Eriodictiol 6-C-hexoside 8-C-hexoside-O-hexoside, Luteolin O-hexosyl-O-hexosyl-O-hexoside, and Salvianolic acid A, were differentially accumulated and showed the same pattern across the three sampling locations. Distinctly, Salvianolic acid A was abundantly accumulated in FG but absent in BFT, implying that it may be the potential metabolite attracting birds in some P. mira flowers. Overall, this study sheds light on the diversity of the floral metabolome in P. mira and suggests that the bird's selective feeding behavior may be mediated by variations in floral metabolite contents.

Trophic interactions of micro- and mesozooplankton in the Amundsen Sea polynya and adjacent sea ice zone during austral late summer

To elucidate the trophic link between micro- and mesozooplankton in the Amundsen Sea polynya (ASP) and adjacent sea ice zone, we estimated the impact of microzooplankton grazing on major phytoplankton groups, as well as the diet composition, ingestion rate, and prey selectivity of two copepods and Euphausia crystallorophias larvae on microbial communities during the late summer. Phaeocystis antarctica, which was ingested by micro- and mesozooplankton, comprised most phytoplankton biomass. Herbivorous microzooplankton consumed at least half of the phytoplankton production, but the microzooplankton grazing may not contribute strongly to the decline of the phytoplankton bloom. Three mesozooplankton species (Calanoides acutus, Metridia gerlachei, and E. crystallorophias larvae) preferentially grazed on ciliates and heterotrophic dinoflagellates (HDF) with sizes from 20 to >100 µm over phytoplankton. Although microzooplankton comprised only an average of 41.7 ± 3.2% o the total carbon available in the natural prey pool, they accounted for an average of 75.4 ± 2.9% of total carbon ingested by copepods and krill larvae. Heterotrophic food sources made up a substantial proportion of mesozooplankton diets, with strong positive selection for microzooplankton at most locations regardless of phytoplankton size and type. In particular, HDF comprised the major dietary component of mesozooplankton in the study area. The presence of mesozooplankton reduced the grazing pressure on P. antarctica and diatoms through predation on herbivorous microzooplankton. Approximately half of the primary production capacity may have indirectly reached mesozooplankton through microzooplankton consumption. Thus, strongly selective feeding behavior and higher grazing pressure on microzooplankton indicated the importance of microheterotrophic pathways through strong trophic coupling between mesozooplankton and the microbial food web during the decline of phytoplankton bloom. In the highly productive ASP system, food web structure can be classified as multivorous, whereby herbivorous and omnivorous modes both play significant roles in carbon export, enhancing the efficiency of the pelagic food web.

Foraging strategies underlying bird egg predation by macaques: A study using artificial nests.

Bird egg predation is widespread in non-human primates. Although nest predation is often described as opportunistic, little is known about foraging strategies and nest detection in primates. Since it is the prevalent cause of nest failure in the tropics, birds select nest sites within specific microhabitats and use different nest types to increase nesting success. Identifying the nests targeted by the northern pigtailed macaques (Macaca leonina), an omnivorous cercopithecine species, and known nest predator, will shine light on nest foraging strategies in primates. The aim of this research was to reveal if nest predation is a selective or opportunistic feeding behavior. We studied, using artificial nests and camera traps, the influence of nest type (open-cup vs. cavity), microhabitat (i.e., understory density, canopy cover, canopy height, ground cover, and presence vs. absence of thorns and lianas), and nest height, on nest predation by a troop of northern pigtailed macaques in the Sakaerat Biosphere Reserve (Thailand), a degraded environment. In our study, macaque predation on artificial nests was high; out of the 200 nests that were set up, 112 were plundered by macaques. Although predation rates decreased with nest height, nest type, and microhabitat had no significant effect on predation by macaques. Nest detectability and accessibility did not affect predation rates. Macaques actively searched for nests in different microhabitats, suggesting that nest predation by this primate might be considered a selective feeding behavior in this degraded habitat. Consequently, nest predation by this primate might have important conservation implications on the population dynamics of forest-dwelling bird species. Behavior observation methods, such as instantaneous scan sampling, may underestimate nest predation by primates, a furtive and cryptic behavior.

Terrestrial support of zooplankton biomass in northern rivers

AbstractThe contribution of terrestrially derived carbon to micro‐crustacean zooplankton biomass (i.e., allochthony) has been previously studied in lakes, reservoirs, and estuaries, but little is known about zooplankton allochthony in rivers. In lacustrine environments, allochthony is regulated by distinct selective feeding behavior of different taxa. However, we hypothesized that restricted possibility for selective grazing in turbulent environments such as rivers would decouple zooplankton from specific microbial and algal food resources, such that their allochthony would mirror the terrestrial contribution to the surrounding bulk particle pool. We tested this idea by analyzing allochthony in 13 widely distributed Swedish rivers, using a dual‐isotope mixing model. Zooplankton biomasses were generally low, and allochthony in different micro‐crustacean groups (Cladocera, Cyclopoida, Calanoida) varied from 2% to 77%. As predicted, there were no correlations between allochthony and variables indicating the supply of algal and microbial food resources, such as chlorophyll a and bacterial production. Instead, the allochthony was generally similar to the share allochthonous contribution in bulk particulate organic matter, with relationships close to the 1 : 1 line. The zooplankton community allochthony was strongly regulated by the ecosystem metabolic balance between production and respiration, which in turn was dependent upon the ratio between total autochthonous organic carbon concentrations and water color. Our study for the first time shows that micro‐crustacean allochthony is regulated differently in rivers compared to in lacustrine systems, and points to inefficient support of zooplankton biomass by algal resources in turbulent waters.

A method for Rearing Perch, Perca fluviatilis, Larvae Using Paramecium caudatum, Followed by Wild Zooplankton and Formulated Dry Feed in Combination With Adequate Tank Systems

The present study investigates methods for larviculture and fingerling production in the European perch, Perca fluviatilis. Perch larvae in the stage of first feeding were sensitive to many manipulations necessary in fish culture. Lowering and increasing the tank water level as required for cleaning and water renewal, water flow and aeration led to disturbed buoyancy or mortality in a distinct percentage of larvae. Paramecium caudatum, wild zooplankton containing > 70% copeopds, and formulated dry feed were used for first feeding in combination with flow through tanks or static tanks. For first feeding Paramecium caudatum in combination with a static tank system was optimal resulting in survival rates of circa 90% at 15 days post hatch (dph). Wild zooplankton was no optimal starter feed as perch fed non-selectively on any feed particle available. This resulted in moderate survival rates of circa 50% at 15 dph. First feeding with formulated dry feed caused malformations (enlargement of swimbladders) and a high mortality of > 80%. Weaning from Paramecium caudatum to formulated dry feed and to zooplankton was tested on 8-16 dph larvae. Perch accepted the new food type within 3 days. The optimal time point for zooplankton weaning was 12 dph. In this age larvae had developed a selective feeding behaviour, and fed mainly on nauplii and copepodites. Weaning to formulated dry feed was impossible as larvae developed malformations resulting in high mortality as described above. Weaning from wild zooplankton to formulated dry feed was possible for larvae ≥ 29 dph. No cannibalism was observed in the experiments. The method was also tested in large scale experiments resulting in a survival rate of 65±4%, a total length of 45.0±7.2 mm, and a body weight of 1097±293 mg at 75 dph.

Digesta kinetics in two arvicoline rodents, the field vole (Microtus agrestis) and the steppe lemming (Lagurus lagurus)

A large number of small mammals practice cecotrophy, i.e. ingesting a certain fraction of their own faeces typically termed ‘cecotrophs’. This behaviour is generally thought to limit metabolic losses of nitrogen, because a colonic separation mechanism (CSM) selectively accretes fine, nitrogen-rich particles (such as microbes) in the cecotrophs. Two types of CSM have been described, a wash-back CSM (in lagomorphs) where fluids wash through the colonic digesta in a retrograde manner into the caecum, resulting in a selectively prolonged solute marker retention in passage studies; and a mucus-trap CSM (in hystricomorph rodents) where microbes are trapped in mucus-filled anatomical structures in the colon mucosa (grooves/furrows/folds). In the mucus-trap CSM, no selective retention of any passage marker occurs. How the CSM operates in muroid rodents is not well explored, but both mucus-filled anatomical structures and a moderate degree of selective solute marker retention have been reported in the literature. Here we demonstrate selective solute marker retention in two muroid, arvicoline rodent species (field voles Microtus agrestis, body mass 28.6 ± 7.4 g, and steppe lemming Lagurus lagurus, 19.8 ± 2.0 g) on a pelleted high-fibre diet, where a solute marker was retained 20–55% longer than a particle marker (with mean retention times of 5.6 ± 0.5 vs. 4.8 ± 0.9 and 5.0 ± 1.5 vs. 3.3 ± 0.9 h, respectively). The animals achieved an apparent organic matter digestibility similar to that of much larger herbivores on diets of similar fibre content. In addition to a selective feeding behaviour and a high relative food intake, a digestive physiology that includes coprophagy, and a CSM using both mucus-trap and wash-back effects, are characteristic for herbivorous arvicoline rodents. The relative contributions of the two CSM components – whether they have additive or complementary effects – remain to be explored.

What you need is what you eat? Prey selection by the bat Myotis daubentonii.

Optimal foraging theory predicts that predators are selective when faced with abundant prey, but become less picky when prey gets sparse. Insectivorous bats in temperate regions are faced with the challenge of building up fat reserves vital for hibernation during a period of decreasing arthropod abundances. According to optimal foraging theory, prehibernating bats should adopt a less selective feeding behavior--yet empirical studies have revealed many apparently generalized species to be composed of specialist individuals. Targeting the diet of the bat Myotis daubentonii, we used a combination of molecular techniques to test for seasonal changes in prey selectivity and individual-level variation in prey preferences. DNA metabarcoding was used to characterize both the prey contents of bat droppings and the insect community available as prey. To test for dietary differences among M. daubentonii individuals, we used ten microsatellite loci to assign droppings to individual bats. The comparison between consumed and available prey revealed a preference for certain prey items regardless of availability. Nonbiting midges (Chironomidae) remained the most highly consumed prey at all times, despite a significant increase in the availability of black flies (Simuliidae) towards the end of the season. The bats sampled showed no evidence of individual specialization in dietary preferences. Overall, our approach offers little support for optimal foraging theory. Thus, it shows how novel combinations of genetic markers can be used to test general theory, targeting patterns at both the level of prey communities and individual predators.

Host-Related Olfactory Behavior in a Fruit-Piercing Moth (Lepidoptera: Erebidae) in Far Eastern Russia.

The host preference of the economically important fruit piercing moth, Calyptra lata (Butler 1881), was studied when exposed to different fruits and the odors of those fruits in enclosed feeding assays and in a two-choice olfactometer. The fruits consisted of three ripe and locally available types: raspberries, cherries and plums. Moths were released in cages with the ripened fruit and observed for any feeding events, which were then documented. Moths fed on both raspberries and cherries, but not on plums. To test the role of olfactory cues in fruit preference, male moths were released singly in the two choice olfactometer, with one type of fruit odor released in one arm and background control air in the other. The behavior of the moths was recorded on video. Parameters scored were 1) time to take off, 2) flight duration and 3) total time to source contact. The moths showed a significant preference for raspberry odor, exhibited a neutral response to cherry odor and significantly avoided the odor of plums. These results indicate that Calyptra lata demonstrates selective polyphagic feeding behavior and uses olfactory cues from both preferred and non-preferred fruits to detect and locate potential food sources. The possible implications for pest control are discussed.

Impact of zooplankton food selectivity on plankton dynamics and nutrient cycling

Within models, zooplankton grazing is typically defined as being dependent on total prey concentration, with feeding selectivity expressed only as a function of prey size. This behavior ignores taxonomic preferences shown by the predators and the capacity of some zooplankton to actively select or reject individual prey items from mixtures. We carried out two model experiments comparing impacts of zooplankton displaying passive and active selection, which resulted in contrasting dynamics for the pelagic system. Passive selection by the grazer resulted in a top down control on the prey with a fast turn-over of nutrients. Active selection, on the other hand led to a bottom-up control, with slower nutrient turnover constraining primary production by changing the system toward export of particulate matter. Our results suggest that selective feeding behavior is an important trait, and should be considered alongside size and taxonomy when studying the role of zooplankton impact in the ecosystem.

A FEAST FOR CROWS: BIRD PREDATION ON IRREGULAR ECHINOIDS FROM BRITTANY, FRANCE

Selective feeding behavior of birds on burrowing irregular spatangoid sea urchins, normally out of reach for such predators, is described. Behavioral observations were made on Carrion Crows (Corvus corone) feeding on spatangoid sea urchins (Echinocardium cordatum) during low tide on two different beaches in Brittany, France. The on-site searching behavior of individuals and flocks of crows on the surf line was observed together with characteristic feeding traces on the sediment. Wound morphologies on collected tests were documented with respect to possible preservation potential and recognition in the fossil record. Documented traces on feeding sites allow for clear identification of predator species and can be linked to observed bird behavior. The two sites differ in sea urchin size and the resulting predation traces on the echinoid tests. Predation on smaller specimens fragments the test, whereas predation on larger specimens leaves a characteristic wound morphology that is mainly restricted to the aboral side of the test. The wound morphology resulting from test puncturing involves both extensive inter- and intraplate fragmentation but does not completely destroy the tests. These predation traces are compared to other observed records of bird predation on echinoids. The potential for recognition and preservation in the rock record is then discussed.

Does body mass convey a digestive advantage for large herbivores?

Summary A key concept of body mass (BM) in niche separation of large herbivores assumes that the decrease in diet quality inherent to increasing BM (due to less selective feeding behaviour) is balanced by a simultaneous increase in digestive ability (due to longer retention times), resulting in no or less‐than‐expected reduction in digestibility (as measured in the animal as a result of diet quality and digestive ability). However, the second part of this concept has been challenged recently due to theoretical problems and mismatch with empirical data. A proxy for digestibility, such as metabolic faecal nitrogen (MFN), will comprise both information on diet quality and digestive ability in free‐ranging animals. In captive animals, if diet is kept constant, such a proxy can exclusively indicate digestive ability. Comparing free‐ranging and captive animals under such conditions, one would expect an increase in MFN with BM in captive animals and no relationship between these measures in free‐ranging animals if BM was related to digestive ability. We compared captive ungulates on a consistent grass hay diet (17 species; 30–4000 kg BM) to a sample of free‐ranging East African ungulates (19 species; 12–4000 kg BM). MFN was used as the major proxy for digestibility. In captive animals, there was no influence of BM on MFN (P = 0·466); for free‐ranging animals, a significant decreasing effect of body mass on MFN (P = 0·002) and therefore diet quality was found at a scaling of BM−0·15. In conclusion, scenarios that assume a compensation of the evident decrease in diet quality with BM via an increased digestive ability are not supported by this study. This does not rule out other feeding‐related factors in facilitating large BM, such as compensation by an increased diet intake.

Exclusion Performance in Dwarf Goats (Capra aegagrus hircus) and Sheep (Ovis orientalis aries)

Using a comparative approach, we investigated the ability of dwarf goats and sheep to use direct and indirect information about the location of a food reward in an object-choice task. Subjects had to choose between two cups with only one covering a reward. Before making a choice, subjects received information about the baited (direct information) or non-baited cup (indirect information). Both goats and sheep were able to use direct information (presence of food) in the object choice task. After controlling for local enhancement, we found that goats rather than sheep were able to use indirect information (i.e., the absence of food) to find a reward. The actual test setup could not clarify whether individual goats were able to inferentially reason about the content of the baited cup when only shown the content of the non-baited cup or if they simply avoided the empty cup in that situation. As browsing species, feral and wild goats exhibit highly selective feeding behaviour compared to the rather unselective grazing sheep. The potential influence of this species-specific foraging flexibility of goats and sheep for using direct and indirect information to find a food reward is discussed in relation to a higher aversion to losses in food acquisition in goats compared to sheep.

A Review of Feeding Behavior, Growth, Reproduction and Aquaculture Site Selection for Green-Lipped Mussel, <i>Perna viridis</i>

Green-lipped mussel, Perna viridis is a warm water mussel species that is distributed widely in the Indo-Pacific regions. It is a commercially important species and has demonstrated a great culture potential in tropical countries. The feeding behavior of P. viridis is influenced by both seston concentration and its nutritional values. It is shown the mussels exhibit higher ingestion rate when the organic content of the seston is higher. Interestingly, several studies have reported that P. viridis can demonstrate selective feeding behavior towards phytoplankton. Short term studies have shown that the P. viridis exhibits preferentially ingestion of dinoflagellates, while long term studies show that the P. viridis has a higher growth rate during diatom blooms. Nevertheless, spawning of P. viridis is induced by high primary productivity at relatively high sea water temperature. In the temperate countries, spawning is seasonal but normally occurs in summer. In the tropical countries, however, the P. viridis has been shown to spawn all year-round with two peaks which coincide with monsoon seasons. The site selection is critically important when considering the green mussel culture. Feasibility study for P. viridis farming is normally carried out first in order to evaluate the environmental conditions of the site. This paper attempts to review the current knowledge of biology, selective feeding behaviour, growth, reproductive and the aquaculture site selection methods for green-lipped mussel.

Effect of Different Bacterial-Feeding Nematode Species on Soil Bacterial Numbers, Activity, and Community Composition

The effects of bacterial-feeding nematodes on bacterial number, activity, and community composition were studied through a microcosm experiment using sterilized soil inoculated with soil bacteria (soil suspension) and with bacteria and three species of bacterial-feeding nematodes (Cephalobus persegnis, Protorhabditis filiformis, and Caenorhabditis elegans). Catalyzed reporter deposition-fluorescence in situ hybridization, CO2 evolution, and denaturing gradient gel electrophoresis (DGGE) of PCR amplified 16S rRNA gene fragments were used to investigate bacterial numbers, activity, and community composition, respectively. Our results showed that bacterial numbers and activity significantly increased in the presence of bacterial-feeding nematodes, which indicated that bacterial-feeding nematodes had a significant positive effect on soil bacteria. The different nematode species had different effects on bacterial numbers and activity. C. persegnis and P. filiformis, isolated from native soil, increased the bacterial number and activity more than C. elegans. The DGGE analysis results showed that dominant bacterial species significantly differed among the treatments, which suggested that bacterial-feeding nematode species modified the bacterial community composition in soil. Further gene sequence analysis results showed that the dominant bacterial species in this study were gram-negative bacteria. Given the completely same conditions except nematode species, the varied selective feeding behavior of different nematode species was the most likely reason for the altered bacterial community composition. Overall, the alteration of bacterial numbers, activity and community composition resulting from the bacterial-feeding nematodes may ultimately affect soil ecological functioning and processes.

Copepod Foraging on the Basis of Food Nutritional Quality: Can Copepods Really Choose?

Copepods have been considered capable of selective feeding based on several factors (i.e., prey size, toxicity, and motility). However, their selective feeding behaviour as a function of food quality remains poorly understood, despite the potential impact of such a process on copepod fitness and trophodynamics. In this study, we aimed to evaluate the ability of copepods to feed selectively according to the nutritional value of the prey. We investigated the feeding performance of the calanoid copepod Acartia grani under nutritionally distinct diets of the dinoflagellate Heterocapsa sp. (nutrient-replete, N-depleted and P-depleted) using unialgal suspensions and mixtures of prey (nutrient-replete vs. nutrient-depleted). Despite the distinct cell elemental composition among algal treatments (e.g., C:N:P molar ratios) and the clear dietary impact on egg production rates (generally higher number of eggs under a nutrient-replete diet), no impact on copepod feeding rates was observed. All unialgal suspensions were cleared at similar rates, and this pattern was independent of food concentration. When the prey were offered as mixtures, we did not detect selective behaviour in either the N-limitation (nutrient-replete vs. N-depleted Heterocapsa cells) or P-limitation (nutrient-replete vs. P-depleted Heterocapsa cells) experiments. The lack of selectivity observed in the current study contrasts with previous observations, in which stronger nutritional differences were tested. Under normal natural circumstances, nutritional differences in natural prey assemblages might not be sufficiently strong to trigger a selective response in copepods based on that factor alone. In addition, our results suggest that nutritional quality might depend not only on the growing conditions but also on the inherent taxonomical properties of the prey.

啃食性端足类强壮藻钩虾对筼筜湖三种大型海藻的摄食选择性

Marine algae vary considerably in their nutritional,chemical,and structural composition,thus providing a heterogeneous and variable food resource for marine herbivores. However,Due to seasonal fluctuation in species composition and abundance of marine algae,herbivores usually encounter the environments with little tasty,highly nutritional food. Because herbivores eat foods that are much lower in nutrients than their own tissues,they display a diversity of behavioral and physiological adaptations to cope with the low nutritional value of their foods. Selective feeding on more nutritious plants,increasing consumption of lower quality foods( compensatory feeding) have all been proposed as important behaviors allowing herbivores to obtain adequate nourishment.Amphipods were common benthic species in macroalgal-based communities. They may regulate the macroalgal community structure by their selective feeding behavior. This study investigated the feeding of amphipod Ampithoe valida on three dominant macroalgae( Ulva lactuca,Gracilaria tenuistipitata var. liui and Rhizoclonium sp.) of Yundang Lagoon, and analyzed how the nutritional quality in terms of dry mass / wet mass( DM / FM),total organic carbon( TOC),total nitrogen( TN),C / N ratio and protein level may affect the food selectivity in the amphipod. The results showed that there was negative correlation between the feeding rates and the DM / FM,or TOC / FM of the macroalgae when macroalgae was separately offered to A. valida,indicating compensatory feeding behavior in the amphipod,that is,A. valida can use quantity to compensate quality when nutritional value of macroalgae was low. A. valida preferentially fed on U. lactuca and Rhizoclonium sp.,and their feeding rates negatively correlated to the TOC concentrations or protein levels in the macroalgae. However,no relationship was found between the feeding rates and TN. These results suggest there are no predictable effects of the nutritional quality on the feeding selectivity of amphipods. However,although A. valida have strong preference to green algae,Yundang Lagoon doesn' t structure a macroalgal community dominated by red algae G. tenuistipitata var. liui.

Size selective predation on an invasive bivalve, Limnoperna fortunei (Mytilidae), by a freshwater crab, Zilchiopsis collastinensis (Trichodactylidae)

Limnoperna fortunei, or the golden mussel, invaded South America through the Rio de la Plata estuary in 1991. The size-selective predation on this bivalve by freshwater decapods crustaceans could be an important part of selective trophic behavior because shell sizes are correlated with the flesh contents and their resistance to being broken. The aim of the paper was analyze the size selective predation by the freshwater crab Zilchiopsis collastinensis Pretzmann, 1968 on different sizes of the invasive bivalve L. fortunei. We considered three combinations (AC, AD and BD) of equal numbers of three different shell lengths of mussels: A (small) = 7 to 10.99 mm, B (medium) = 11 to 14.99 mm and C = 15 to 18.99 mm and D = 19 to 22.99 mm (large). These combinations were offered to each adult female intermolt crab individually, and the number of mussels remaining was registered after one, two and 24 hours to evaluate prey-size selection. After this trial, ten female crabs were recorded preying on two different sizes of mussels (A and C) in combination (AC), and we registered the selective feeding behavior (feeding methods and time of predation) with each size of mussel. The results indicated that female crabs ate different sizes of golden mussels, showing an increased consumption of large mollusks after 24 hours, although these sizes demanded higher predation times. Large mussels were encountered at the first time (one and two hours) by the crabs, and these mussels were consumed successfully in the combination AD. These female crabs showed several alternative strategies to access the flesh and were efficient in handling large mussels, presenting an advantageous degree of plasticity for their predatory responses. L. fortunei could be a new food resource for adult Z. collastinensis females, and it could be responsible for a new interaction “native predator-invasive prey” in the system.

Single versus combined exposure of Hyalella azteca to zinc contaminated sediment and food

The amphipod Hyalella azteca was exposed for 28d to different combinations of Zn contaminated sediment and food. Sediment exposure (+clean food) resulted in increased Zn body burdens, increased mortality and decreased body mass when the molar concentrations of simultaneously extracted Zn were greater than the molar concentration of Acid Volatile Sulfide (SEMZn–AVS>0), suggesting that dissolved Zn was a dominant route of exposure. No adverse effect was noted in the foodexposure (+clean sediment), suggesting selective feeding or regulation. Combined exposure (sediment+food) significantly increased adverse effects in comparison with sediment exposure, indicating contribution of dietary Zn to toxicity and bioaccumulation. The observed enhanced toxicity also supports the assumption on the presence of an avoidance/selective feeding reaction of the amphipods in the single sediment or food exposures. During 14d post-exposure in clean medium, the organisms from the same combined exposure history received two feeding regimes, i.e. clean food and Zn spiked food. Elevated Zn bioaccumulation and reduced reproduction were noted in amphipods that were offered Zn spiked food compared to the respective organisms that were fed clean food. This was explained by the failure of avoidance/selective feeding behavior in the absence of an alternative food source (sediment), forcing the amphipods to take up Zn while feeding. Increasing Zn body burdens rejected the assumption that Zn uptake from food was regulated by H. azteca. Our results show that the selective feeding behavior should be accounted for when assessing ecological effects of Zn or other contaminants, especially when contaminated food is a potential exposure route.

Intraspecific selectivity, compensatory feeding and flexible homeostasis in the phagotrophic flagellate Oxyrrhis marina: three ways to handle food quality fluctuations

The phagotrophic flagellate Oxyrrhis marina shows a strong stoichiometric plasticity when fed differently grown Rhodomonas salina. We tested whether differently pre-conditioned O. marina displayed selective feeding behaviour from a mixture of nitrogen and phosphorus depleted R. salina. We observed selective feeding of O. marina, always selecting phosphorus rich R. salina independent of the pre-conditioning of the protists. In a second experiment, O. marina was again pre-conditioned either with nitrogen- or phosphorus-depleted R. salina and was refed with either of the differently limited R. salina in single food treatments (not in a mixture). The phagotrophic flagellate displayed compensatory feeding which means that O. marina feed more on the food source which they were not given before. Due to its stoichiometric plasticity, O. marina might handle bad quality food by following the stoichiometry of its prey and additionally by active selective feeding towards P-rich algae to enhance growth. Post-ingestion selection might as well be an important feature which means that ingested elements in excess are quickly excreted and scarce elements are ingested through accelerated food uptake.

EVALUATING HABITATS AND FEEDING HABITS THROUGH ECOMORPHOLOGICAL FEATURES IN GLYPTODONTS (MAMMALIA, XENARTHRA)

The goal of this study is to evaluate ecomorphological variables in glyptodonts from different ages (Miocene to early Holocene), clades, and sizes, with the purpose of inferring their habitats and feeding habits. The analyses included estimation of body masses and three variables: relative muzzle width (RMW), hypsodonty index (HI), and dental occlusal surface area (OSA). RMW allows the distinction of two main groups: the small-sized early Miocene propalaehoplophorids were selective feeders, while the larger post-Miocene forms were more bulk feeders. The Pleistocene Glyptodon appears as an exception, implying a reversion to a selective feeding behavior. The relation between RMW and HI allows discriminating feeding niche partitioning in glyptodonts. Among the early Miocene propalaehoplophorids, Eucinepeltus would have been a highly selective feeder in relatively closed environments, Propalaehoplophorus a highly selective feeder in moderately open habitats, and Cochlops a less selective feeder in moderately open habitats. Among the large Pliocene and Pleistocene taxa, cf. Neuryurus and Neosclerocalyptus were probably bulk feeders in relatively open environments, while Panochthus and Doedicurus were bulk feeders in open environments. Alternative interpretations can be assessed for Glyptodon: it was a more selective feeder in closer habitats, or had a different feeding behavior, browsing on specific plants at higher levels from the ground, and/or a specialized physiology. The late Miocene and Pliocene forms (Hoplophractus, Eosclerocalyptus, and Urotherium) were probably intermediate between the Miocene and the Pleistocene ones.