Captive Feeding Research Articles

Mechanism of Resistance to Camptothecin, a Cytotoxic Plant Secondary Metabolite, by Lymantria sp. Larvae.

Camptothecin (CPT), a monoterpene indole alkaloid, is a potent inhibitor of eukaryotic topoisomerase I (Top 1). Because of this property, several derivatives of CPT are widely used as chemotherapeutic agents. The compound is produced by several plant species, including Nothapodytes nimmoniana (Family: Icacinaceae) presumably as a deterrent to insect pests. Here, we report, a lepidopteran larva, Lymantria sp. of Lymantriidae family which feeds voraciously on the leaves of N. nimmoniana, without any adverse consequences. Larval body weight and molting period were unaffected despite captive feeding of the larva with CPT enriched leaves. Mass spectrometric analysis indicated that nearly 46% of the ingested CPT was excreted while the rest was sequestered predominantly in the exuviae and setae (~35%). Although most of the CPT was in the parental form as found in the plant, traces of inactive, sulfated forms of CPT were recovered from the larva. Compared to that in plant, there were no critical mutations at the CPT binding domain of the insect's Top 1. The gut pH of the larva was alkaline (pH10.0). The alkaline gut environment converts CPT from its active, lactone form to inactive, carboxylate form. It is likely that such conversion might help the larva to reduce the overall burden of CPT in its gut. We discuss the results in the context of the mechanisms of resistance adapted by insects to plant toxins.

Analysis of pit and score tooth-mark sizes from bones modified by Holocene Australian terrestrial fauna in relation to body size

Carnivorous mammals, particularly the Tasmanian devil (Sarcophilus harrisii), dingo (Canis dingo), and tiger quoll (Dasyurus maculatus) have been implicated by previous research as having affected Australian faunal assemblages through deposition or modification of skeletal materials. One way of identifying such taphonomic agency is through the examination of tooth-marks left behind by modern feeding carnivores and comparing them to analogous archaeological materials. Overseas research has compared the tooth-marks of several relevant taxa through captive feeding experiments, focusing on the sizes of pits and scores and their relation to body size. Due to highly variable sampling approaches and limited reporting of mark sizes a similar multi-species comparison has not been feasible in Australia. To address this, experimental feeding trials were carried out with captive Tasmanian devils, dingoes, tiger quolls, eastern quolls, lace monitors, dogs, and one of the authors. Analysis of 2895 tooth-marks revealed that considerable overlap exists between the sizes of pits and scores from the aforementioned three species. The only species that could be consistently differentiated from the rest were the taphonomically insignificant lace monitor and eastern quoll. The ability of Tasmanian devil and tiger quoll to produce very large tooth-marks in proportion to their small body size means that Australian fauna do not conform to trends observed in overseas studies where tooth-marks separate into categories that broadly correspond with body weight. The results suggest in addition to body weight, adaptations related to osteophagy that increase jaw strength, bite force and dental robusticity can be important factors in affecting tooth-mark size.

Nutritional composition of the diet of the northern yellow-cheeked crested gibbon (Nomascus annamensis) in northeastern Cambodia.

This study measured the nutritional composition of foods consumed by the northern yellow-cheeked crested gibbon (Nomascus annamensis) in northeastern Cambodia. One group of N. annamensis was studied, and focal animal sampling was used to observe their feeding behavior. The study was conducted for 4months (January-April 2015) in the dry season and 69 foods were collected for nutritional analyses. N. annamensis fed on 37 plant species, but only seven species made up more than 80% of feeding time. N. annamensis spent the majority of their time feeding on fruit (60.36%), followed by young leaves (22.60%), flowers (13.74%), and mature leaves (3.30%). Fruit had the highest concentrations of total non-structural carbohydrates, while young leaves had the highest concentration of crude protein compared to other food items. All food items had similar concentrations of lipids, except young leaves, which had lower levels than fruit and flowers. All plant parts consumed by N. annamensis had similar amounts of neutral detergent fiber, acid detergent fiber, and acid detergent lignin. Thirty-two percent of all food items contained condensed tannins, and they had a similar level of it. All foods also had similar energy contents. This study adds to our knowledge of the feeding ecology of N. annamensis by providing baseline data on the make-up of the foods they eat and may contribute to captive feeding programs, ultimately assisting the conservation of this species.

Composition of phytodetrital food resources affects reproductive success in the deposit-feeding sea cucumber, Parastichopus californicus (Stimpson 1857)

Phytoplankton are important sources of dietary fatty acids (FAs) for higher trophic levels, yet FA composition varies among phytoplankton taxa, and under different growth conditions. Changes in the environment that lead to shifts in the composition of phytoplankton communities may thus alter FA supply in marine food chains. Reproductive processes in free-spawning marine invertebrates, which provision eggs with lipid to fuel early embryonic development, are particularly impacted by FA composition of the diet. In order to explore the effects of taxonomic changes in the source of phytodetrital food resources on invertebrate consumers, we conducted captive feeding experiments to examine differences in reproductive fitness of deposit-feeding sea cucumbers (Parastichopus californicus) fed two different algal diets. Body- and egg-condition variables were measured in females that were fed detritus of either the green alga Tetraselmis sp. or the diatom Thalassiosira sp., which differ in nutritional and FA composition. Subsequent timing of development and survival were recorded for pre- and post-feeding larval stages. FA analyses were conducted on feeds, spawned gonads, and eggs to identify specific FAs allocated to reproduction. Females that were fed Tetraselmis sp. had higher fecundity, but showed reduced larval survival relative to females that were fed the diatom Thalassiosira sp. Similar rates of larval development were recorded in both treatments. Significant differences were observed in the abundance of 20:5ɷ3 (EPA), 20:4ɷ4 (ARA), 22:3ɷ6 (DHA), 12:0, 16:0, and 18:0 FAs in eggs and gonads from females fed the two diets. Diet-related variation in fecundity and egg quality could directly affect recruitment success in P. californicus, and suggests that reproductive strategies may be altered under different environmental conditions. If feeding conditions are favorable to planktotrophic larvae, then producing a larger number of eggs with lower energy density (such as under Tetraselmis-fed treatments) may be acceptable, whereas different conditions may favor maternal investment in a smaller number of better-provisioned eggs (such as in Thalassiosira-fed treatments).

Do Native Rodents Prey on Land Snails? An Experimental and Quantitative Study in Hokkaido, Japan.

Predator-prey interaction is one of the most important and pervasive pressures in the ecology and evolution of prey species. However, accurate description of the food web is sometimes extremely difficult as there are many predator-prey interactions in the wild are obscure. Recent studies have reported that two closely related land snails, Karaftohelix editha and K. gainesi, on Hokkaido Island, Japan, were diversified due to predation, probably by carabid beetles. However, it is unclear 1) whether native rodents prey upon land snails on Hokkaido Island, and 2) how frequently land snails are preyed upon by rodents in this region, although it has been reported that several species of rodents are predators of land snails in many regions. Thus, we investigated these issues in this study by captive feeding trials and field observations. No rodent species other than the Siberian chipmunk, Tamias sibiricus, were found to prey upon land snails around the research site on Hokkaido Island. In addition, the population density of T. sibiricus was lower than those of other rodent species, and it has been reported that T. sibiricus is omnivorous and preys upon snails considerably less than on other food sources. Overall, these findings suggest that T. sibiricus is not an important predator of Karaftohelix land snails in Hokkaido.

Post-prandial physiology and intestinal morphology of the Pacific hagfish (Eptatretus stoutii).

Hagfishes are unique to the vertebrate lineage in that they acquire dissolved nutrients across multiple epithelia including the intestine, gill, and skin. This feat has been attributed to their immersive feeding behavior that likely simultaneously provides benefits (nutrient rich) and potentially adverse (hypercapnia, hypoxia, high environmental ammonia) physiological effects. Examinations have been conducted of the ex vivo transport capabilities of specific nutrients as well as in vivo effects of the hypothesized feeding environments, yet the physiological effects of feeding itself have never been elucidated. We examined the post-prandial physiology of Pacific hagfish (Eptatretus stoutii), identifying changes in oxygen consumption, acid-base balance, ammonia waste excretion, and intestinal morphology following feeding in captivity. Following voluntary feeding, post-prandial oxygen consumption was significantly elevated (1868 ± 272µmolkg-1h-1) 8h following feeding when compared to control resting metabolic oxygen consumption (642 ± 51µmolkg-1h-1) and resulted in a factorial metabolic scope of 2.92. Changes in acid-base status were not observed following feeding in either the excreted components or the caudal blood samples; however, a significant alkalosis was observed 8h post-feeding in the major intestinal blood vein. Significant increases (16-fold) in ammonia excretion were recorded in 36h post-fed hagfish. Finally, significant post-prandial increases in intestinal mucosal thickness and microvilli length were observed, with mucosal thickness remaining significantly increased throughout 36h and the microvilli length returning to fasted lengths by 36h. These results demonstrate the post-feeding physiology of the earliest diverging extant craniate and identify correlations between physiology and hindgut morphology 8h following feeding.

Chew, shake, and tear: Prey processing in Australian sea lions (Neophoca cinerea)

AbstractPinnipeds generally target relatively small prey that can be swallowed whole, yet often include larger prey in their diet. To eat large prey, they must first process it into pieces small enough to swallow. In this study we explored the range of prey‐processing behaviors used by Australian sea lions (Neophoca cinerea) when presented with large prey during captive feeding trials. The most common methods were chewing using the teeth, shaking prey at the surface, and tearing prey held between the teeth and forelimbs. Although pinnipeds do not masticate their food, we found that sea lions used chewing to create weak points in large prey to aid further processing and to prepare secured pieces of prey for swallowing. Shake feeding matches the processing behaviors observed in fur seals, but use of forelimbs for “hold and tear” feeding has not been previously reported for other otariids. When performing this processing method, prey was torn by being stretched between the teeth and forelimbs, where it was secured by being squeezed between the palms of their flippers. These results show that Australian sea lions use a broad repertoire of behaviors for prey processing, which matches the wide range of prey species in their diet.

Discrimination Factors and Incorporation Rates for Organic Matrix in Shark Teeth Based on a Captive Feeding Study.

Sharks migrate annually over large distances and occupy a wide variety of habitats, complicating analysis of lifestyle and diet. A biogeochemical technique often used to reconstruct shark diet and environment preferences is stable isotope analysis, which is minimally invasive and integrates through time and space. There are previous studies that focus on isotopic analysis of shark soft tissues, but there are limited applications to shark teeth. However, shark teeth offer an advantage of multiple ecological snapshots and minimum invasiveness during removal because of their distinct conveyor belt tooth replacement system. In this study, we analyze δ13C and δ15N values of the organic matrix in leopard shark teeth (Triakis semifasciata) from a captive experiment and report discrimination factors as well as incorporation rates. We found differences in tooth discrimination factors for individuals fed different prey sources (mean ± SD; Δ13Csquid = 4.7‰ ± 0.5‰, Δ13Ctilapia = 3.1‰ ± 1.0‰, Δ15Nsquid = 2.0‰ ± 0.7‰, Δ15Ntilapia = 2.8‰ ± 0.6‰). In addition, these values differed from previously published discrimination factors for plasma, red blood cells, and muscle of the same leopard sharks. Incorporation rates of shark teeth were similar for carbon and nitrogen (mean ± SE; λC = 0.021 ± 0.009, λN = 0.024 ± 0.007) and comparable to those of plasma. We emphasize the difference in biological parameters on the basis of tissue substrate and diet items to interpret stable isotope data and apply our results to stable isotope values from blue shark (Prionace glauca) teeth to illustrate the importance of biological parameters to interpret the complex ecology of a migratory shark.

Maternal investment and delayed feeding in neonatal Lake Erie watersnakes: a life‐history strategy

AbstractNeonatal growth can have lasting consequences on survival and reproduction. In many taxa, larger, faster growing neonates experience higher survival, reach sexual maturity more rapidly, and achieve higher lifetime fecundity. In contrast to their closest relatives, Lake Erie watersnakes grow slower, mature later, and may delay feeding until after their first hibernation. To determine if Lake Erie watersnakes do indeed delay feeding until after their first hibernation, we compared age class 0 (between birth and first hibernation) and age class 1 (emergence from hibernation and through the first full season) snakes in the field and in the laboratory. In the field, only 0.6% of pre‐hibernation neonates were found to contain prey, while 11.9% of post‐hibernation neonates contained prey. During captive feeding experiments, the probability of eating was positively correlated with age (binary logistic regression, Wald = 25.354, P < 0.001). To clarify the underlying mechanism for delayed feeding, we compared neonatal yolk and fat reserves among species with delayed feeding (Lake Erie watersnakes, Graham's crayfish‐eating snakes), species that commence feeding immediately after birth (common gartersnakes, Dekay's brown snakes) and a species falling between these extremes (queen snakes). Like Lake Erie watersnakes, Graham's crayfish‐eating snakes contained large energy reserves (yolk + fat body mass to carcass mass ratio = 0.39 and 0.24, respectively), common gartersnakes and Dekay's brown snakes lacked measurable reserves (0.00), and queen snakes contained intermediate reserves (0.17). Taken together, this evidence suggests that neonatal Lake Erie watersnakes do delay feeding until after their first hibernation and contain large energy reserves at birth to facilitate this behavior. While most snake life‐history studies have focused on the trade‐off between offspring size and number, Lake Erie watersnake females invest large amounts of energy in offspring condition.

A taphonomic signature for quolls in the Australian archaeological record

Australian archaeofaunal assemblages are often heavily fragmented by taphonomic agents whose identity or origins are frequently difficult to discern. This study explores whether the fragmentation and accumulation of bone by carnivorous marsupial quolls may be distinguished from that produced by humans. Analyses of 140 scats obtained from captive feeding trials and wild populations of three quoll species (Dasyurus maculatus, Dasyurus viverrinus and Dasyurus hallucatus) indicates that damage to bones by quolls may be identified through a combination of the median length of bone specimens and observations of specific types of damage to the bone surface. Our results demonstrate that bone consumed by D. viverrinus and D. hallucatus is highly unlikely to be confused with human-accumulated assemblages due to low dietary overlap and the very small bone fragment size produced by both quoll species. Bone accumulations of the larger D. maculatus species, however, may be incorrectly attributed to humans due to the consumption of medium-large mammals by both humans and quolls, and the larger size of bone fragments produced by D. maculatus. Although fragments as large as 25mm were recovered from wild D. maculatus scats, the median length of scat-bone fragments for D. maculatus falls between ~8.30–10.40mm. This is significantly different statistically to the median fragment length (11.90mm) of bone in scats of the Tasmanian devil, Sarcophilus harrisii, as reported by Caroline Northwood (1990). Scats from wild D. maculatus indicate that polish and pitting are the most common forms of surface damage to bone, with more than 25% of specimens displaying these marks. Punctures and tooth drag marks are far rarer, with only 5% of bone specimens exhibiting this kind of damage. In light of these results, we advocate for detailed observation of the surface of bone specimens, along with obtaining specimen lengths, in order to distinguish quoll accumulated bone in archaeofaunal assemblages.

Lifelong and carry-over effects of early captive exposure in a recovery program for Atlantic salmon (Salmo salar)

A full life cycle understanding of how different captive rearing strategies affect wild fitness is needed for many species of conservation concern. Over the life cycle of endangered Atlantic salmon, we measured effects on wild fitness resulting from two widely applied conservation captive rearing strategies. One strategy releases juveniles before the onset of feeding (reduced exposure) and the other after 5 months of captive feeding (extended exposure). Fish were released into the wild and monitored 1–3 years later as seaward migrating juveniles. A sample of migrating fish from both rearing strategies was held captive in the ocean until mature, and artificially bred to monitor offspring viability. Extended early captive exposure resulted in smaller size-at-stage throughout life, shorter generation time and reduced offspring viability. Altering early captive exposure by 5 months generated long-term and transgenerational effects on fitness and life history traits that likely accelerate domestication effects and hence provide insight into effective recovery strategy design.

Prey capture and processing behaviors vary with prey size and shape in Australian and subantarctic fur seals

AbstractWhen hunting at sea, pinnipeds should adapt their foraging behaviors to suit the prey they are targeting. We performed captive feeding trials with two species of otariid seal, Australian fur seals (Arctocephalus pusillus doriferus) and subantarctic fur seals (Arctocephalus tropicalis). This allowed us to record detailed observations of how their foraging behaviors vary when presented with prey items that cover the full range of body shapes and sizes encountered in the wild. Small prey were captured using suction alone, while larger prey items were caught in the teeth using raptorial biting. Small fish and long skinny prey items could then be swallowed whole or processed by shaking, while all prey items with body depths greater than 7.5 cm were processed by shaking at the water's surface. This matched opportunistic observations of feeding in wild Australian fur seals. Use of “shake feeding” as the main prey processing tactic also matches predictions that this method would be one of the only tactics available to aquatic tetrapods that are unable to secure prey using their forelimbs.

Musculoskeletal anatomy and feeding performance of pre‐feeding engyodontic larvae of the European eel (Anguilla anguilla)

Being part of the elopomorph group of fishes, Anguillidae species show a leptocephalus larval stage. However, due to largely unknown spawning locations and habitats of their earliest life stages, as well as their transparency, these Anguilla larvae are rarely encountered in nature. Therefore, information regarding the early life history of these larvae, including their exogenous feeding strategy and feeding performance, is rather scarce. To better understand the structural basis and functional performance of larval feeding in captivity, the functional morphology of the cranial musculoskeletal system in pre- and first-feeding engyodontic leptocephali of the European eel (Anguilla anguilla) was studied. A 3D reconstruction of the feeding apparatus (head of the leptocephali < 1 mm) was used to visualize and describe the musculoskeletal changes throughout these stages. To analyze the ontogenetic changes in the functionality of the feeding apparatus towards the active feeding phase, 3D data of joints, levers and muscles derived from the reconstructions were used to estimate bite and joint reaction forces (JRFs). Observing a maximum estimated bite force of about 65 μN (and corresponding JRFs of 260 μN), it can be hypothesized that leptocephalus larvae are functionally constrained to feed only on soft food particles. Additionally, potential prey items are size delimited, based on the theoretically estimated average gape of these larvae of about 100 μm. This hypothesis appears to be in line with recent observations of a diet consisting of small and/or gelatinous prey items (Hydrozoa, Thaliacea, Ctenophora, Polycystenia) found in the guts of euryodontic leptocephalus larvae.

Experimentally derived δ¹³C and δ¹⁵N discrimination factors for gray wolves and the impact of prior information in Bayesian mixing models.

Stable isotope analysis of diet has become a common tool in conservation research. However, the multiple sources of uncertainty inherent in this analysis framework involve consequences that have not been thoroughly addressed. Uncertainty arises from the choice of trophic discrimination factors, and for Bayesian stable isotope mixing models (SIMMs), the specification of prior information; the combined effect of these aspects has not been explicitly tested. We used a captive feeding study of gray wolves (Canis lupus) to determine the first experimentally-derived trophic discrimination factors of C and N for this large carnivore of broad conservation interest. Using the estimated diet in our controlled system and data from a published study on wild wolves and their prey in Montana, USA, we then investigated the simultaneous effect of discrimination factors and prior information on diet reconstruction with Bayesian SIMMs. Discrimination factors for gray wolves and their prey were 1.97‰ for δ13C and 3.04‰ for δ15N. Specifying wolf discrimination factors, as opposed to the commonly used red fox (Vulpes vulpes) factors, made little practical difference to estimates of wolf diet, but prior information had a strong effect on bias, precision, and accuracy of posterior estimates. Without specifying prior information in our Bayesian SIMM, it was not possible to produce SIMM posteriors statistically similar to the estimated diet in our controlled study or the diet of wild wolves. Our study demonstrates the critical effect of prior information on estimates of animal diets using Bayesian SIMMs, and suggests species-specific trophic discrimination factors are of secondary importance. When using stable isotope analysis to inform conservation decisions researchers should understand the limits of their data. It may be difficult to obtain useful information from SIMMs if informative priors are omitted and species-specific discrimination factors are unavailable.

Pyrosequencing of prey DNA in faeces of carnivorous land snails to facilitate ecological restoration and relocation programmes

Identifying and understanding predator diets is of high importance in biological conservation. This is particularly true for the introduction, establishment and maintenance of predator populations in newly created or modified ecological communities, such as translocation sites or restored habitats. Conservation status of predators may not permit captive feeding trials or intrusive gut-content methods, so non-intrusive diet assessment is required, such as faecal analysis. However, prey such as earthworms leave no morphological clues suitable for accurately discriminating between species consumed through visual faecal analysis. This study uses non-intrusive molecular methods on earthworm DNA extracted from the faeces of the carnivorous land snail Powelliphanta patrickensis to identify its earthworm diet and any seasonal trends. Data from 454-pyrosequencing revealed earthworm DNA in all samples (n = 60). Sequences were compared to a DNA library created from published and unpublished studies of New Zealand's endemic earthworms and online databases. Unidentified earthworm sequences were clustered into molecular operational taxonomic units (MOTUs). Twenty-six MOTUs were identified, 17 of which matched the library, whereas nine did not. Similarity indices indicate that there were seasonal differences (P < 0.05) in the earthworm communities represented in the summer and the winter diets. This study highlights the importance of utilising the vast body of data generated by pyrosequencing to investigate potential temporal diet shifts in protected species. The method described here is widely applicable to a wide range of predatory species of conservation interest and can further inform habitat restoration and relocation programmes to optimize the long-term survival of the target species.

Songbird dispersal of American ginseng (Panax quinquefolius)

American ginseng (Panax quinquefolius) is an uncommon perennial understory herb found in eastern deciduous forest. The species is harvested for the international medicinal plant trade. While previous research has inferred that seed dispersal is limited, the production of bright red, fleshy berries suggests long-distance dispersal may be facilitated by songbirds. The objective of this study was to determine how songbirds interacted with ginseng and whether they dispersed or predated ginseng seeds. We used infrared, motion-activated cameras to observe animal—ginseng interactions in the field. To determine the disperser potential of songbirds observed visiting ginseng in the field, we conducted a captive feeding study at the Tennessee Aquarium. Thrushes removed berries from ginseng infructescences more frequently, compared to other potential dispersers, and regurgitated viable seeds 5–37 minutes after ingestion in feeding trials. By dispersing ginseng seeds, thrushes provide a mechanism for ginseng to improve its probability of persistence in the face of 3 primary threats to populations: deer browse, harvest, and climate change.

Improving accuracy of DNA diet estimates using food tissue control materials and an evaluation of proxies for digestion bias

Ecologists are increasingly interested in quantifying consumer diets based on food DNA in dietary samples and high-throughput sequencing of marker genes. It is tempting to assume that food DNA sequence proportions recovered from diet samples are representative of consumer's diet proportions, despite the fact that captive feeding studies do not support that assumption. Here, we examine the idea of sequencing control materials of known composition along with dietary samples in order to correct for technical biases introduced during amplicon sequencing and biological biases such as variable gene copy number. Using the Ion Torrent PGM(©) , we sequenced prey DNA amplified from scats of captive harbour seals (Phoca vitulina) fed a constant diet including three fish species in known proportions. Alongside, we sequenced a prey tissue mix matching the seals' diet to generate tissue correction factors (TCFs). TCFs improved the diet estimates (based on sequence proportions) for all species and reduced the average estimate error from 28±15% (uncorrected) to 14±9% (TCF-corrected). The experimental design also allowed us to infer the magnitude of prey-specific digestion biases and calculate digestion correction factors (DCFs). The DCFs were compared with possible proxies for differential digestion (e.g. fish protein%, fish lipid%) revealing a strong relationship between the DCFs and percent lipid of the fish prey, suggesting prey-specific corrections based on lipid content would produce accurate diet estimates in this study system. These findings demonstrate the value of parallel sequencing of food tissue mixtures in diet studies and offer new directions for future research in quantitative DNA diet analysis.

Do measures of plant intake and digestibility from captive feeding trials align with foraging patterns of free-ranging snowshoe hares?

Context Measures of intake and digestibility from captive feeding experiments are often used to evaluate the nutritional value of plant species to herbivores; however, there is question about how well plant-quality rankings from these trials predict foraging patterns of free-ranging animals. Studies addressing the alignment of results from feeding trials and herbivory in the field using captive and free-roaming conspecifics are needed. Aims Our goal was to compare the feeding patterns of snowshoe hares in captive intake and digestion trials with those of free-living conspecifics in the species’ south-western range. Methods We conducted in vivo intake and digestion trials using captive hares to determine quality and consumption levels of the predominant conifer species in our study system. In the field, we quantified browsing intensity and over-winter depletion patterns of these conifers. We then compared voluntary intake and nutritional quality measured in captivity to consumption in the field. Key results Digestible energy (DE, kJ g–1) of conifers ranged from 11.0 (Pinus contorta) to 13.8 (Pseudotsuga menziesii) among six conifers, and digestible protein (DP, g protein per 100 g feed) from 1.2 (Thuja plicata) to 2.7 (P. contorta). During digestion trials, single-species intake was correlated with the content of digestible protein (DP) and digestible energy (DE). Hares maintained energy balance when fed two single-species diets (Pinus contorta, Pseudotsuga menziesii) and a mixed-species diet. Conifer species on which hares were able to maintain body mass (Pinus contorta, Picea engelmannii, Pseudotsuga menziesii) also tended to be the most heavily exploited by free-living hares. DP content of browse species predicted both browsing intensity and overwinter depletion of conifer species. Conclusions Voluntary intake and nutritional quality of browse, especially DP, successfully predicted foraging patterns of free-ranging conspecifics. Implications Intake and digestion trials can be a useful tool for better understanding patterns of herbivory in the field, and winter habitat quality for populations in this region is likely to be influenced by access to the most energy- and protein-rich conifers.

Ontogenetic and Among-Individual Variation in Foraging Strategies of Northeast Pacific White Sharks Based on Stable Isotope Analysis

There is growing evidence for individuality in dietary preferences and foraging behaviors within populations of various species. This is especially important for apex predators, since they can potentially have wide dietary niches and a large impact on trophic dynamics within ecosystems. We evaluate the diet of an apex predator, the white shark (Carcharodon carcharias), by measuring the stable carbon and nitrogen isotope composition of vertebral growth bands to create lifetime records for 15 individuals from California. Isotopic variations in white shark diets can reflect within-region differences among prey (most importantly related to trophic level), as well as differences in baseline values among the regions in which sharks forage, and both prey and habitat preferences may shift with age. The magnitude of isotopic variation among sharks in our study (>5‰ for both elements) is too great to be explained solely by geographic differences, and so must reflect differences in prey choice that may vary with sex, size, age and location. Ontogenetic patterns in δ15N values vary considerably among individuals, and one third of the population fit each of these descriptions: 1) δ15N values increased throughout life, 2) δ15N values increased to a plateau at ∼5 years of age, and 3) δ15N values remained roughly constant values throughout life. Isotopic data for the population span more than one trophic level, and we offer a qualitative evaluation of diet using shark-specific collagen discrimination factors estimated from a 3+ year captive feeding experiment (Δ13Cshark-diet and Δ15Nshark-diet equal 4.2‰ and 2.5‰, respectively). We assess the degree of individuality with a proportional similarity index that distinguishes specialists and generalists. The isotopic variance is partitioned among differences between-individual (48%), within-individuals (40%), and by calendar year of sub-adulthood (12%). Our data reveal substantial ontogenetic and individual dietary variation within a white shark population.

Morphology of the tongue dorsal surface of gilthead seabream (Sparus aurata)

The gilthead seabream is a food fish, one of the most frequently used in aquaculture. In the species of commercial interest, feeding in captivity is very important and this process is strictly related to the morphological characteristics of the oral cavity. The aim of this study is, using the standard procedures for light and scanning electron microscopy, to analyze the morphology of the tongue dorsal surface to show if relationships are present between the tongue morphology and the nutritional habits and choices of this farmed species. The main characteristic of the gilthead seabream oral cavity floor is the presence of an apical pouch, with, probably, a protective role mainly for the apical, free part of the tongue. Three zones, like in other teleosts, an apex, a body and a root, can be clearly distinguished. In the pouch foliate-like papillae were observed, while the whole tongue is characterized by the presence of two types of papillae, respectively with a fungiform and cylindroid aspect, both randomly distributed throughout the whole dorsal surface of the tongue. Scattered and numerous taste buds, with the typical pear-onion shape, together with small and numerous taste pores are also present, distributed throughout the tongue surface. Our results demonstrate that in the gilthead seabream important mechanic and sensory roles are carried out by specific anatomical structures. Our anatomical data could give, together with further biochemical and physiological data, an important support with the aim of improving the nutrition of aquaculture species.