Food preferences of adult male and female Calliphora vicina (Diptera: Calliphoridae)

Social learning is a primary mechanism for information acquisition in social species. Despite many benefits, social learning may be disadvantageous when independent learning is more efficient. For example, searching independently may be more advantageous when food sources are ephemeral and unpredictable. Individual differences in cognitive abilities can also be expected to influence social information use. Specifically, better spatial memory can make a given environment more predictable for an individual by allowing it to better track food sources. We investigated how resident food-caching chickadees discovered multiple novel food sources in both harsher, less predictable high elevation and milder, more predictable low elevation winter environments. Chickadees at high elevation were faster at discovering multiple novel food sources and discovered more food sources than birds at low elevation. While birds at both elevations used social information, the contribution of social learning to food discovery was significantly lower at high elevation. At both elevations, chickadees with better spatial cognitive flexibility were slower at discovering food sources, likely because birds with lower spatial cognitive flexibility are worse at tracking natural resources and therefore spend more time exploring. Overall, our study supported the prediction that harsh environments should favour less reliance on social learning.

Physid snails (Pulmonata: Physidae) are widespread in freshwater habitats throughout the Holartic and are generally considered to feed on periphyton. However, several studies have shown that they also consume living plant material and detritus. In streams where multiple food sources are available, snails may preferentially feed on resources based on palatability or accessibility. It is likely that snail feeding influences food availability and that, when preferable items (e.g. periphyton) are lacking, less desirable food sources can be consumed (e.g. detritus). In Florida, USA, six species of physid snails occur in low-order tributaries of the St Johns River, of which Haitia pomilia (Conrad) has been found to be abundant (M.A. Chadwick, unpublished data). The food sources available in different streams where H. pomilia have been collected vary dramatically due to the presence of a closed or open canopy. Streams with closed canopies are lined with red maple (Acer rubrum ), sweet gum (Liquidambar styraciflua ) and water oak (Quercus nigra ) trees. Streams with an open canopy (due to urbanization and stream-channel modifications) have macrophytes, particularly the invasive Hydrilla verticillata. This plant was introduced from Asia to North America in the 1960s and its role as a potential food source is not well known. The goal of this study was to assess how differences in putative detrital food sources affect H. pomilia growth. Due to their ubiquitous distribution, understanding how snails respond to changes in the availability of different food sources may yield important insights into the processing of organic matter. In June 2004, H. pomilia were collected from small tributaries of the St Johns River in the vicinity of Jacksonville, Florida and transported to the Experimental Mesocosm Facility at the University of Alabama. Snails were kept in temperature-controlled recirculation tanks (800 l, 5 m length, 0.4 m width and depth, 188C, 15 cm/s flow velocity) and provided food sources including live H. verticillata and detritus composed of air-dried red maple, sweet gum and water oak leaves (collected immediately after leaf abscission) and H. verticillata. In October 2004, feeding/growth experiments were initiated. Forty plastic Petri dishes were prepared with one of four treatments composed of detritus from H. verticillata, red maple, sweet gum or water oak (i.e. ten replicates per treatment). In order to homogenize the detritus, air-dried material of each source was conditioned in the mesocosm stream for 2 weeks, re-dried and then ground with a Wiley mill (no. 40 sieve). In each dish, 25 ml of distilled water and 75 mg of fine particulate organic matter (FPOM) were added. Snails were randomly selected from the mesocosm (total shell length 3–6 mm), photographed (RT SE digital camera, Diagnostic Instruments, Inc.), and then randomly assigned to a food source treatment. The treatments were then placed in a randomly blocked arrangement in an 188C incubator, which was used to eliminate light and the potential for periphyton growth. Digital pictures of each snail were then retaken 18 days later. Shell lengths were measured directly from each picture using image analysis software (SPOT, Diagnostic Instruments, Inc.). Snail instantaneous growth rates (g ) were calculated as g 1⁄4 ln(Wfinal/Winitial)/Dt, where W is snail mass (mg) and t is time (d). After 18 days, snails were removed from the dishes and all remaining material was dried and weighed. The remaining material was a mix of dissolved organic carbon, unconsumed FPOM and snail faeces, but this measurement was used as a proxy for food consumption. We developed a predictive model to estimate snail ash-free dry mass from shell length (Table 1). One-way ANOVA was used to assess differences among treatment for both snail growth rates and food consumption. Pair-wise comparisons among treatments were accomplished using 95% confidence intervals. Survival rates for snails among treatments ranged from 70 to 100%. Snail instantaneous growth varied significantly among treatments (F3,32 1⁄4 5.86, P 1⁄4 0.003) with theH. verticillata treatment having much higher growth rates than the other three treatments (Fig. 1). Food consumption also varied significantly among the treatments (F3,32 1⁄4 8.31, P, 0.001) with the least amount of organic matter being found in the H. verticillata treatment (Fig. 2).

Reputation and emotion: How the mind drives our food preferences and choices

Caenorhabditis elegans is commonly used as an infection model for pathogenesis studies in Pseudomonas aeruginosa. The standard virulence assays rely on the slow and fast killing or paralysis of nematodes but here we developed a behaviour assay to monitor the preferred bacterial food sources of C. elegans. We monitored the food preferences of nematodes fed the wild type PAO1 and mutants in the type III secretion (T3S) system, which is a conserved mechanism to inject secreted effectors into the host cell cytosol. A ΔexsEΔpscD mutant defective for type III secretion served as a preferred food source, while an ΔexsE mutant that overexpresses the T3S effectors was avoided. Both food sources were ingested and observed in the gastrointestinal tract. Using the slow killing assay, we showed that the ΔexsEΔpscD had reduced virulence and thus confirmed that preferred food sources are less virulent than the wild type. Next we developed a high throughput feeding behaviour assay with 48 possible food colonies in order to screen a transposon mutant library and identify potential virulence genes. C. elegans identified and consumed preferred food colonies from a grid of 48 choices. The mutants identified as preferred food sources included known virulence genes, as well as novel genes not identified in previous C. elegans infection studies. Slow killing assays were performed and confirmed that several preferred food sources also showed reduced virulence. We propose that C. elegans feeding behaviour can be used as a sensitive indicator of virulence for P. aeruginosa PAO1.

The effective and quick assessment of food preference is important when attempting to identify foods that might function as effective reinforcers in dogs. In the current experiment a food preference assessment was conducted where more highly preferred foods were expected to be associated with faster approaches in a subsequent runway task. Eight dogs were tested in a paired preference assessment offering combinations of two of six types of raw food, including the dog’s staple diet, to identify a rank order of preference for the foods. A different raw food was offered as the staple in two preference tests. The results showed that the staple foods were not preferred as highly as the other foods and that each dog displayed unique and stable preferences for the different foods. In the runway task the dogs were required to walk five metres to obtain a small amount of their most preferred, least preferred or staple foods and latency of approach to the foods was recorded. The approach latencies were faster for their most preferred food compared to their least preferred and the staple foods. The use of a runway to assess reinforcer effectiveness combined an effortful behaviour to obtain food while also requiring the dogs to make a choice, thus precluding the need for more complicated and time-consuming methods of preference assessment. The application of this method for fast and effective identification of preferred reinforcers is currently being investigating further to inform pet owners of simple methods to increase their training successes. Owners of raw food fed dogs are advised to conduct a preference assessment to identify their dogs most preferred food for use as a reinforcer during training.

Many free-living animal species, including the majority of fish, insects, and amphibians, change their food and habitat during their life. Even though these ontogenetic changes in niche are common, it is not well understood which ecological conditions have favored the evolution of these shifts. Using an adaptive dynamics approach, we show that it is evolutionarily advantageous to switch to an alternative food source in the course of ontogeny when this results in a higher intake rate for the switching consumers. Individuals are, however, not able to specialize on this new food source when this negatively affects the performance early in life on the original food source. Selection on these early life stages is so strong that in species with a complete diet shift, evolution results in large juveniles and adults that are maladapted to the alternative food source while their offspring are specialized on the original food source when young. These outcomes suggest strong selection to decouple the different life stages, such that they can maximize their performance on different food sources independently from each other. Metamorphosis could be a way to decouple the different life stages and therefore evolve in species that feed on multiple food sources during their life.

The obesogenic food environment facilitates access to multiple palatable foods. Exendin-4 (EX4) is a glucagon-like peptide 1 receptor (GLP1R) agonist that inhibits food intake and has been proposed as an obesity therapy. This study tested whether the composition of the food environment and experience with palatable foods modulate the effects of EX4 on food intake and reward. Mice fed a cafeteria (CAF) or control diet were tested for the anorectic effects of EX4 when simultaneously offered foods of varying individual preference and in a conditioned place preference (CPP) test for chocolate. Plasma glucagon-like peptide 1 (GLP1) and hypothalamic GLP1R mRNA were analyzed post mortem. Mice fed a CAF diet developed individual food preference patterns. Offering mice either novel or highly preferred foods decreased the potency of EX4 to inhibit food intake compared to low preference foods or chow. Compared to the control diet, CAF diet intake blocked the decrease in chocolate CPP caused by EX4 and decreased the expression of hypothalamic GLP1R mRNA without altering the plasma GLP1 concentration. The composition of the food environment, food preference, and experience modulate the ability of EX4 to inhibit food intake and reward. These data highlight the significance of modeling the complexity of the human food environment in preclinical obesity studies.

The aim of this work was to assess the specific food type (high carbohydrate, high fat, high protein) preference profiles of individuals with Prader-Willi syndrome (PWS), obese controls and normal weight individuals. Subjects tasted a food predominantly high in carbohydrate, a food predominantly high in protein and a food predominantly high in fat over repeated trials and indicated their most preferred, second preferred and least preferred foods. Specific items tested on a given trial were counterbalanced in a block randomized fashion. These were 12 individuals with Prader-Willi syndrome, 12 matched obese controls (obese, but otherwise normal) and 14 normal weight subjects. The basic data were expressed as a proportion of each food type selected as most preferred over the total 27 trials. PWS subjects preferred high carbohydrate foods over high protein foods and high protein foods over high fat foods. These subjects demonstrated a statistically reliable difference in preference for high carbohydrate foods over high fat foods. However, normal weight and obese control subjects demonstrated no difference in food preferences. The only significant between-group comparisons were between PWS subjects and obese controls, with the PWS group showing a significantly greater preference for high carbohydrate foods than obese controls. The obesity of PWS was shown to have a significant and distinctly different food preference profile from normal weight and obese controls. The differences in food preference between the obese PWS and non-PWS subjects is in accord with the growing recognition of functional subgroups within the obese population, that may have not only differing underlying etiologies, but also distinct behavioral profiles of ingestion.

Dietary habits and social interactions affect choice of feeding location by sheep

To evaluate performance in a complex survival task, we studied the morphology of the Physarum plasmodium transportation network when presented with multiple separate food sources. The plasmodium comprises a network of tubular elements through which chemical nutrient, intracellular signals and the viscous body are transported and circulated. When three separate food sources were presented, located at the vertices of a triangle, the tubular network connected them via a short pathway, which was often analogous to the mathematically shortest route known as Steiner's minimum tree (SMT). The other common network shape had high fault tolerance against accidental disconnection of the tubes and was known as cycle (CYC). Pattern selection appeared to be a bistable system involving SMT and CYC. When more than three food sources were presented, the network pattern tended to be a patchwork of SMT and CYC. We therefore concluded that the plasmodium tube network is a well designed and intelligent system.

As human DNA profiles can be obtained from blow fly artifacts, this study aimed to establish the feeding preferences of Lucilia cuprina (Wiedemann) blow flies when offered human biological fluids and nonhuman food sources. One-day-old and 3-day-old blow flies of both sexes were simultaneously offered human blood, semen and saliva, pet food, canned tuna and honey, and the number and length of visits documented over 6 h. One-day-old flies visited pet food and honey most often, but stayed longest on honey and semen. Three-day-old flies visited semen and pet food most often, and stayed longest on these food sources. Blood and saliva were the least preferred options for all flies. Overall, flies preferred dry blood and semen to the wet forms. These findings demonstrate that even when other food sources are available, flies at a crime scene may feed on human biological fluids if present, potentially transferring human DNA.

Distinct habitats are often linked through fluxes of matter and migration of organisms. In particular, intertidal ecotones are prone to being influenced from both the marine and the terrestrial realms, but whether or not small-scale migration for feeding, sheltering or reproducing is detectable may depend on the parameter studied. Within the ecotone of an upper saltmarsh in the United States, we investigated the sex-specific movement of the semi-terrestrial crab Armases cinereum using an approach of determining multiple measures of across-ecotone migration. To this end, we determined food preference, digestive abilities (enzyme activities), bacterial hindgut communities (genetic fingerprint), and the trophic position of Armases and potential food sources (stable isotopes) of males versus females of different sub-habitats, namely high saltmarsh and coastal forest. Daily observations showed that Armases moved frequently between high-intertidal (saltmarsh) and terrestrial (forest) habitats. Males were encountered more often in the forest habitat, whilst gravid females tended to be more abundant in the marsh habitat but moved more frequently. Food preference was driven by both sex and habitat. The needlerush Juncus was preferred over three other high-marsh detrital food sources, and the periwinkle Littoraria was the preferred prey of male (but not female) crabs from the forest habitats; both male and female crabs from marsh habitat preferred the fiddler crab Uca over three other prey items. In the field, the major food sources were clearly vegetal, but males have a higher trophic position than females. In contrast to food preference, isotope data excluded Uca and Littoraria as major food sources, except for males from the forest, and suggested that Armases consumes a mix of C4 and C3 plants along with animal prey. Digestive enzyme activities differed significantly between sexes and habitats and were higher in females and in marsh crabs. The bacterial hindgut community differed significantly between sexes, but habitat effects were greater than sex effects. By combining multiple measures of feeding ecology, we demonstrate that Armases exhibits sex-specific habitat choice and food preference. By using both coastal forest and saltmarsh habitats, but feeding predominantly in the latter, they possibly act as a key biotic vector of spatial subsidies across habitat borders. The degree of contributing to fluxes of matter, nutrients and energy, however, depends on their sex, indicating that changes in population structure would likely have profound effects on ecosystem connectivity and functioning.

Social foraging is thought to provide the possibility of information transmission between individuals, but this advantage has been proved only in a handful of species and contexts. We investigated how social connections in captive flocks of house sparrows (Passer domesticus) affected the discovery of (i.e. feeding for the first time from) two hidden food patches in the presence of informed flock-mates. At the first-discovered and most-exploited food patch social connections between birds affected the order of discovery and presumably contributed to a greater exploitation of this patch. However, social connections did not affect discovery at the second food patch despite its close spatial proximity. Males discovered the food sources sooner than females, while feeding activity was negatively related to patch discovery. Age had no effect on the order of discovery. Birds that first discovered and fed at the food patches were characterized by higher level of social indifference, i.e. followed others less frequently than other birds in an independent context. Our findings provide experimental evidence for the importance of variable social connections during social foraging in house sparrow flocks, and suggest that social attraction can contribute differently to the exploitation of different patches when multiple food sources are present.

Dietary reconstruction of an early to middle Holocene human population from the central California coast: insights from advanced stable isotope mixing models

Summary1. I tested the hypothesis that the potential for non‐lethal effects of predators are more important for overall performance of the fast‐growing exotic signal crayfish (Pacifastacus leniusculus Dana) than for the slower growing native noble crayfish (Astacus astacus L.). I further tested if omnivorous crayfish switched to feed on less risky food sources in the presence of predators, a behaviour that could reduce the feeding costs associated with predator avoidance.2. In a 2 month long outdoor pool experiment, I measured behaviour, survival, cheliped loss, growth, and food consumption in juvenile noble or signal crayfish in pools with either a caged predatory dragonfly larvae (Aeshna sp.), a planktivorous fish that do not feed on crayfish (sunbleak, Leucaspius delineatus Heckel), or predator‐free controls. Crayfish had access to multiple food sources: live zooplankton, detritus and periphyton. Frozen chironomid larvae were also supplied ad libitum outside crayfish refuges, simulating food in a risky habitat.3. Crayfish were mainly active during hours of darkness, with signal crayfish spending significantly more time outside refuges than noble crayfish. The proportion of crayfish outside refuges varied between crayfish species, time and predator treatment, with signal crayfish spending more time in refuges at night in the presence of fish.4. Survival in noble crayfish was higher than in signal crayfish, and signal crayfish had a higher frequency of lost chelipeds, indicating a high level of intraspecific interactions. Crayfish survival was not affected by the presence of predators.5. Gut‐contents analysis and stable isotope values of carbon (δ13C) and nitrogen (δ15N) indicated that the two crayfish species had similar food preferences, and that crayfish received most of their energy from feeding on invertebrates (e.g. chironomid larvae), although detritus was the most frequent food item in their guts. Signal crayfish guts were more full than those of noble crayfish, but signal crayfish in pools with fish contained significantly less food and fewer had consumed chironomids compared with predator‐free controls. Length increase of signal crayfish (35%) was significantly higher than of noble crayfish (20%), but signal crayfish in pools with fish grew less than in control pools.6. This short‐term study indicates that fish species that do not pose a lethal threat to an organism may indirectly cause reductions in growth by affecting behaviour and feeding. This may occur even though prey are omnivorous and have access to and consume multiple food sources. These non‐lethal effects of predators are expected to be particularly important in exotic crayfish species that show a general response to fish, have high individual growth rates, and when their feeding on the most profitable food source is reduced.