Feeding preference and deterrence in rabbitfish Siganus fuscescens for the cyanobacterium Lyngbya majuscula in Moreton Bay, south‐east Queensland, Australia

Rabbitfish Siganus fuscescens preferences for Lyngbya majuscula collected from three bloom locations in Moreton Bay, Queensland, Australia, were tested along with a range of local plant species in the laboratory. Consumption of L. majuscula by fish did not differ between wild and captive‐bred fish ( P  = 0·152) but did differ between bloom location ( P  = 0·039). No relationship was found between consumption rates and lyngbyatoxin‐a concentration ( r ² = 0·035, P  = 0·814). No correlation existed between C : N and proportion of food consumed when all food types were analysed statistically, whereas a clear correlation was observed when L. majuscula was removed from the calculations. In simulated bloom conditions, fish avoided ingestion of L. majuscula by feeding through gaps in the L. majuscula coverage. Both wild and captive‐bred S. fuscescens showed a distinct feeding pattern in 10 day no‐choice feeding assays, with less L. majuscula being consumed than the preferred red alga Acanthophora spicifera . Lyngbya majuscula however, was consumed in equal quantities to A. spicifera by wild S. fuscescens when lyngbyatoxin‐a was not detectable. Wild fish probably do not preferentially feed on L. majuscula when secondary metabolites are present and are not severely impacted by large L. majuscula blooms in Moreton Bay. Furthermore, poor feeding performance in both captive‐bred and wild S. fuscescens suggests that they would exert little pressure as a top‐down control agent of toxic L. majuscula blooms within Moreton Bay.     

Identification of seagrasses in the gut of a marine herbivorous fish using DNA barcoding and visual inspection techniques

Traditional visual diet analysis techniques were compared with DNA barcoding in juvenile herbivorous rabbitfish Siganus fuscescens collected in Moreton Bay, Australia, where at least six species of seagrass occur. The intergenic spacer trnH-psbA, suggested as the optimal gene for barcoding angiosperms, was used for the first time to identify the seagrass in fish guts. Four seagrass species and one alga were identified visually from gut contents; however, there was considerable uncertainty in visual identification with 38 of 40 fish having unidentifiable plant fragments in their gut. PCR and single-strand conformational polymorphism (SSCP) were able to discriminate three seagrass families from visually cryptic gut contents. While effective in identifying cryptic gut content to family level, this novel method is likely to be most efficient when paired with visual identification techniques.     

Complete mitochondrial genome of the rabbitfish Siganus fuscescens (Perciformes, Siganidae).

We determined the complete nucleotide sequence of the mitochondrial genome for the rabbitfish Siganus fuscescens (Perciformes, Siganidae). This mitochondrial genome, consisting of 16,491 base pairs (bp), included 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs, and a noncoding control region similar those found in other vertebrates; the gene order was identical to that of typical vertebrates. Most of the genes of S. fuscescens were encoded on the H-strand, while the ND6 and eight tRNA (Gln, Ala, Asn, Cys, Tyr, Ser [UCN], Glu, and Pro) genes were encoded on the L-strand. The reading frames of ATPase 8 and 6 and those of ND4L and ND4 overlapped by ten and seven nucleotides, respectively. All mitochondrial protein-coding genes began with an ATG start codon, except for CO1, which started with GTG. Open reading frames of S. fuscescens ended with TAA (ND1, CO1, ATPase 8, ND4L, ND5 and ND6), and the remainder had incomplete stop codons, either TA (ATPase 6 and CO3) or T (ND2, CO2, ND3, ND4, and Cytb). The origin of L-strand replication in S. fuscescens was located in a cluster of five tRNA genes (WANCY) and was 34 nucleotides in length. A major noncoding region between the tRNA-Pro and tRNA-Phe genes (828 bp) was considered to be the control region (D-loop). Within this sequence, we identified a conserved sequence block characteristic of this region. The rabbitfish was grouped with Siganus canaliculatus in most parsimony analyses, which showed 100% bootstrap support for their divergence. These findings are useful for inferring phylogenetic relationships and identification within the suborder Acanthuroidei.     

Multiplex PCR and RFLP approaches for identification of rabbitfish (Siganus) species using mitochondrial gene regions

Molecular assays are described for the identification of six rabbitfish (Siganus) species. A multiplex PCR assay using primers targeting the mitochondrial cytochrome b region simultaneously identifies four species: Siganus canaliculatus, S. fuscescens, S. javus, and S. spinus. Subsequent RFLP assays of multiplex amplicons differentiate between S. virgatus and S. corallinus based on diagnostic fragments from the mitochondrial cytochrome oxidase I region. Assays were validated with known specimens demonstrating accuracy of the molecular identification. Applied to morphologically indistinguishable early developmental stages, these assays can facilitate studies on species-specific spatio-temporal patterns of larval dispersal and population connectivity to aid fishery management.     

Herbivory in omnivorous fishes: effect of plant secondary metabolites and prey stoichiometry

1. Many animals that consume freshwater macrophytes are omnivorous (i.e., they include both plant and animal matter in their diet). For invertebrate omnivorous consumers, selection of macrophyte species depends partly on the presence of secondary metabolites in plants, plant carbon/nutrient balances and/or physical structure of plants. However, little is known about the mechanisms influencing consumption of macrophytes in aquatic vertebrates. 2. For two fish species, the omnivorous rudd (Scardinius erythrophthalmus) and herbivorous grass carp (Ctenopharyngodon idella), feeding preferences were determined in three choice experiments. We tested (i) whether the presence of secondary metabolites and macrophyte stoichiometry affects macrophyte species selection by fish, (ii) the importance of macrophyte stoichiometry by manipulating the macrophytes experimentally and (iii) the rate of herbivory when the most palatable macrophyte is offered simultaneously with a common animal prey. 3. In a choice experiment with five species of submerged macrophytes (Callitriche sp., Chara globularis, Elodea nuttallii, Myriophyllum spicatum and Potamogeton pectinatus), Myriophyllum was clearly consumed least by both fishes, which strongly correlated with the highest phenolic concentration of this macrophyte. Additionally, a significant negative relationship was found between consumption and C : N ratio of the five macrophytes. The two most consumed macrophytes also had the lowest dry matter concentration (DMC). 4. In a second choice experiment, the C : N ratio of the least (Myriophyllum) and most (Potamogeton) palatable plants was manipulated by growing the macrophytes under fertilised and unfertilised conditions and subsequently feeding them to rudd. The avoidance of consumption of the chemically defended Myriophyllum by rudd was partly alleviated by the lowered C : N ratio. 5. The third choice experiment showed that both fishes preferred animal prey (the amphipod Gammarus pulex) over the most palatable macrophyte (Potamogeton) when offered simultaneously. The C : N ratio of the amphipods was about half that of the lowest C : N ratio measured in the macrophytes. Consumption by the fishes could not clearly be related to C : P or N : P ratios of prey items in any of the experiments. 6. We conclude that omnivorous fish avoid macrophytes that are chemically defended. However, when these defences are only minor, stoichiometry (C : N ratio) in combination with DMC may be a determining factor for consumption by vertebrate facultative herbivores.     

Food selection by freshwater snails in the Gezira irrigation canals,Sudan

Stomach content analysis was carried out on samples of the freshwater snail species Biomphalaria pfeifferi, Bulinus truncatus, Bulinus forskalii (Pulmonata, Planorbidae), Lymnaea natalensis (Pulmonata, Lymnaeidae), Melanoides tuberculata, Cleopatra bulimoides (Prosobranchia, Thiaridae) and Lanistes carinatus (Prosobranchia, Ampullariidae) from different irrigation canals in Sudan. In order to evaluate overlap in diet selection among these species, sites with two or more of the above-mentioned species present were selected. For some species food choice was examined in relation to size groupings. In addition, samples of Marisa cornuarietis (Prosobranchia, Ampullariidae) from small ponds in Sudan, samples of Biomphalaria pfeifferi and Helisoma duryi (Pulmonata, Planorbidae) from drainage canals in an irrigation scheme in northern Tanzania, and samples of H. duryi from fish ponds in the coastal area of Kenya were also analysed. The results indicate a great similarity in the food choice of these species, especially among the pulmonate species. All species feed on fine detritus, epiphytic algae and decaying macrophytes. No fresh fragments of aquatic macrophytes were found and animal remains were found only on a few occasions. However, the stomach contents of the ampullarid species were characterized by large fragments of dead macrophyte tissue, while the composition of the finer particles showed a great resemblance to that of the pulmonate species. The diet of the thiarid species is essentially the same as that of the pulmonate species, although in one site Cleopatra bulimoides showed a greater preference for green algae. Apart from the avoidance of blue-green algae, there was little evidence of selection of certain algal components of the Aufwuchs for the pulmonate species. Detritus constitutes the major component of the stomach content of all these snail species.     

A field study of prey selection in planktivorous fish larvae

Summary The food selection of larval fish was studied from field samples collected in two areas that differ in productivity. In the area where planktonic primary and secondary production was high the fish larvae showed a tendency to specialise and they selected the largest prey species available as food; in the area of lower production fish were generalists and they fed equally on all size classes.Abundance of prey was found to be one of the decisive factors in the prey selection of planktivorous fish larvae. Large prey species (calanoids) were selected when their absolute abundance was high but when their abundance was low, small-sized cladocerans were preferred. Visibility and stage of life history were also assumed to affect the mode of selection.     

Consumption of leaf detritus by a stream shredder: Influence of tree species and nutrient status

Four species of riparian vegetation (alder, birch, willow and poplar) were fertilized with nitrogen, phosphorus, nitrogen + phosphorus, or no fertilizer (control). The resulting leaf detritus (leached but not microbially colonized) was offered to a stream shredder, Hydatophylax variabilis (Trichoptera: Limnephilidae). In one experiment, shredder consumption of leaf detritus from different nutrient treatments (within tree species) was compared, and in a second experiment, consumption of different tree species (within nutrient treatments) was compared. Larvae preferred leaf detritus from nitrogen + phosphorus treatments (except in poplar where nitrogen treatment was preferred). Alder was preferred over other tree species for all treatments. Chemical and physical analyses of leaf litter showed differences between tree species and nutrient treatments in nutrient content, tannins and leaf toughness. Leaf consumption by larvae was positively associated with nitrogen content and negatively associated with condensed tannin content. Species composition and nutrient status of riparian vegetation may strongly influence detrital food webs in streams.     

The effect of aquatic plant chemistry and morphology on feeding selectivity by the crayfish, Orconectes virilis

SUMMARY. 1. Feeding preference trials conducted with male and female crayfish ( Orconectes virilis ) showed that out of ten submersed aquatic plant species, Chara sp. and Lemna trisulca were the preferred food sources, followed by Myriophyllum exalbescens or Utricularia vulgaris .
2. Analysis of plant fibre, alkaloid, total phosphorus, total and available nitrogen, and organic content showed that crayfish feeding preferences were not related ( P >0.5) to plant fibre or alkaloid content but were negatively correlated ( P <0.05) with plant nutrient content such that species of low nutritional value ( Chara and Lemna ) were consistently preferred.
3. Despite this preference for low nutrient food, daily intake rates by crayfish for phosphorus, nitrogen and organic matter were greatest when feeding on Lemna or Chara due to the large quantity consumed.
4. We suggest that feeding preferences of O. virilis are not determined by plant chemistry but, rather, relate to ease of handling small, short, bottom-dwelling plants such as Chara and Lemna as compared with large erect, roseate or floating-leaved forms. Because crayfish are selective herbivores, their introduction into waters where they do not naturally occur could have a dramatic effect on both the species composition and biomass of submersed plants.     

广西扶绥黑叶猴主要食物种类能量含量的初步研究

能量对灵长类食物选择的影响是营养生态学中重要的组成部分。为了研究黑叶猴食物能量及其对食物选择的影响,采用焦点动物取样法和连续记录法在广西扶绥观察记录野生黑叶猴的觅食行为;每月观察结束后采集被取食的植物部位样本,利用全自动氧弹热量计测定其能量。结果表明,黑叶猴食物中嫩叶最高（58.5%）,其次为果实（12.4%）,其他种类依次为成熟叶（12.1%）、种子（10.6%）、花（4.3%）和树皮（2.4%）。在不同的生活型食物中,乔木占48.5%,灌木占34.6%,藤本和草本分别占19.4%和17.2%。各种食物平均能量为17.09 kJ/g,月平均能量在16.52 -17.61 kJ/g之间变化。种子的能量最高,达19.52 kJ/g,最低为成熟叶,仅为16.84 kJ/g。不同生活型植物中,灌木能量最高,达17.52 kJ/g,草本植物最低,仅为15.73 kJ/g。不同植物种类之间能量有显著的差异（P < 0.001）。取食量最多的15种和最少的15种植物之间平均能量有显著差异（P < 0.001）,但在月份间、雨季和旱季间则无显著差异（P > 0.05）。取食不同种类的时间与其平均能量之间无显著相关关系（P = 0.40）,食物能量含量并非影响黑叶猴食物选择的主要原因,其觅食策略需要进一步的研究。     

Prey selectivity affects reproductive success of a corallivorous reef fish

Most animals consume a narrower range of food resources than is potentially available in the environment, but the underlying basis for these preferences is often poorly understood. Foraging theory predicts that prey selection should represent a trade-off between prey preferences based on nutritional value and prey availability. That is, species should consume preferred prey when available, but select less preferred prey when preferred prey is rare. We employed both field observation and laboratory experiments to examine the relationship between prey selection and preferences in the obligate coral-feeding filefish, Oxymonacanthus longirostris. To determine the drivers of prey selection, we experimentally established prey preferences in choice arenas and tested the consequences of prey preferences for key fitness-related parameters. Field studies showed that individuals fed almost exclusively on live corals from the genus Acropora. While diet was dominated by the most abundant species, Acropora nobilis, fish appeared to preferentially select rarer acroporids, such as A. millepora and A. hyacinthus. Prey choice experiments confirmed strong preferences for these corals, suggesting that field consumption is constrained by availability. In a longer-term feeding experiment, reproductive pairs fed on non-preferred corals exhibited dramatic reductions to body weight, and in hepatic and gonad condition, compared with those fed preferred corals. The majority of pairs fed preferred corals spawned frequently, while no spawning was observed for any pairs fed a non-preferred species of coral. These experiments suggest that fish distinguish between available corals based on their intrinsic value as prey, that reproductive success is dependent on the presence of particular coral species, and that differential loss of preferred corals could have serious consequences for the population success of these dietary specialists.     

Snail–periphyton interactions in a prairie lacustrine wetland

This study examined the effects of nutrients and macrophytes on snail grazers and periphyton in a prairie wetland food web. Snails (Gyraulus circumstriatus) and periphyton in large enclosures in a lacustrine wetland, Delta Marsh, MB, Canada were subjected to two experimental treatments, nutrient addition (nitrogen, phosphorus) and macrophyte exclusion (using a porous geotextile carpet) during July and August. Snail biomass and periphyton biomass (on both artificial substrata and submerged macrophytes) increased over time in all treatments, representing seasonal growth. Snail biomass was three times higher on macrophytes than on artificial substrata. In response to nutrient addition, snail biomass was significantly elevated over time on macrophytes but not on artificial substrata. Conversely, periphyton biomass was higher on artificial substrata but not on macrophytes in response to nutrient addition. Snail biomass and periphyton biomass on artificial substrata showed no response to macrophyte exclusion. Snail biomass on all substrata was inversely correlated with turbidity, whereas periphyton biomass showed no relationship with turbidity. Timing of nutrient additions to wetlands may influence whether the response occurs primarily in phytoplankton or in periphyton and macrophytes.     

Detritus and nutrient dynamics in the shore zone of lakes: a review

The importance of detritus varies greatly among shore zones of lakes, but in a large majority of these regions detrital pathways prevail. Aside from a great spatial and seasonal variability, macrophytes and bottom sediments appear to be dominant stores of nutrients in these habitats. Macrophytes hold a central position in nutrient cycling in the shore-littoral lake zones. They are the main source of autochthonous detritus as they prevail in the total biomass of littoral organisms, and they are only rarely available as direct food of consumers. Various processes and interactions determine the role of macrophytes in nutrients dynamics. These are: the intensity of nutrient uptake and translocation, release of nutrients by healthy plants and from decomposing plants, exchange of elements between macrophytes and their periphyton, as well as interception of seston by macrophyte stands. Particular plant species differ in their time of dying and susceptibility to decomposition. The changes in decomposing material (size structure of particles and nutrient content) mean that detritus in various stages of decomposition differs in its role in trophic dynamics of shore-littoral lake zones. Several types of shore regions as regards detritus sources and retention level are discussed.     

The genetics of foraging behaviour: artificial selection for food choice in larvae of the fruitfly,Drosophila melanogaster

Artificial selection for choice between high protein content and high energy content of food was performed for 44 generations of fruitfly larvae. There were significant responses to selection both in a line selected to choose high energy food and in a line selected to choose high protein food. Both lines showed a significantly higher preference for the selected food type than did the control line. The line selected for high energy food also showed a significant increase in response over the generations. Since the selection resulted in lines that differed significantly from controls and from each other, there must be some genetic basis for food choice behaviour. Realized heritability was very low in both selected lines. Viability, as measured by larval weight, pupation time, emergence time and adult size, was significantly higher for flies raised on high protein food than for those raised on high energy food.     

Towards a cognitive niche: divergent foraging strategies resulting from limited cognitive ability of foraging herbivores in a spatially complex environment.

A model was developed to explain one mechanism whereby differential optimal foraging strategies can occur between species as a result of selection for competition avoidance. This is the primary requirement for niche differentiation to evolve without a difference in the underlying foraging ability or morphology. The model used an individual-based patch choice mechanism, whereby herbivores move from patch to patch seeking food with the highest nutrient intake characteristics. The choice of patch was governed by a parameter, mu, which determined to what extent information in the landscape at different distances from the herbivore was used by it to make foraging decisions. A genetic algorithm was used to optimise the value, mu, in a complex landscape. The value of mu quickly converged to a single value with stabilising selection occurring when there was only a single species foraging. When there was a competing species with a fixed value of mu, the value of mu evolved to be above or below the mean for the single species mean depending on whether the value of mu for the competitor was below, or above the single-species mean, respectively. This was indicative of niche segregation. However mu tended to vary unstably over time when allowed to vary simultaneously in both species, although there was evidence for interaction between the two values. These results indicate that there can be a competitive advantage in choosing a cognitive strategy that is complementary to that used by other species.     

Antibacterial factors in skin mucus of rabbitfishes

Aqueous extracts from the skin mucus of two species of rabbitfishes Siganus fuscescens and S. guttatus showed antibacterial activity against gram-negative bacteria. Stability tests and chromatographic analyses suggested that the S. fuscescens antibacterial factor is an acidic glycoprotein with a molecular mass of 400 kDa.     

Criteria for Native Food Plant Collection in Northeastern Brazil

Different criteria are used by human populations around the world in the selection of preferred natural resources. In this study, the following hypotheses were tested: 1) the preference for food native species is related to the number of uses for which the species are cited; 2) the categories of food and medicinal use equally influence the selection of a species as preferred; 3) the preference among native food species is related to its frequency and abundance in the areas of collection. Data collection on species preference was conducted in communities located near the Araripe National Forest (FLONA) in Ceará, Northeastern, Brazil. Both the hypothesis that the preference would relate to the number of uses attributed to species and the hypothesis that food and medicinal categories equally influence the selection of species as preferred ones were corroborated. It was concluded in this study that people optimize both use and collection of native resources using criteria such as the versatility of uses for species and the abundance of the resource in the preferred collection areas. It is believed that this trend may be an adaptive strategy adopted by local communities for the exploitation of native resources.     

Nutrient contents predict the bamboo‐leaf‐based diet of Assamese macaques living in limestone forests of southwest Guangxi,China

Determining the nutrient factors influencing food choice provides important insight into the feeding strategy of animals, which is crucial for understanding their behavioral response to environmental changes. A bamboo‐leaf‐based diet is rare among mammals. Animals’ food choice and nutritional goals have been explained by several frameworks; however, the influence of nutrients on food choice in bamboo‐leaf‐based macaques is not yet available. Assamese macaques (Macaca assamensis) inhabiting limestone forests are characterized by such a bamboo‐leaf‐based diet, predominantly consuming young leaves of Bonia saxatilis, a shrubby, karst‐endemic bamboo. We studied the feeding behavior of one group of Assamese macaques using instantaneous scan sampling in limestone forests of the Guangxi Nonggang National Nature Reserve in southwest Guangxi, China. We compared the nutrient content of staple food and nonfood items and examine the role of key nutrients in the food selection of macaques. Our results showed that young leaves of bamboo B. saxatilis contained more water, crude protein, phosphorus, and less tannin than nonfood items. Furthermore, staple foods contained a higher content of water and less content of calcium than nonfood items. More specifically, quantities of water, crude protein, calcium, and phosphorus in food items were critical factors affecting feeding time on a specific plant item. Our results suggest that young bamboo leaves could meet macaques’ required protein and water intake, while enabling them to maintain their mineral balance, consequently facilitating to maintain the primates’ bamboo‐leaf‐diet in the limestone forest. Our findings confirm the effects of nutrient contents in food choice of Assamese macaques, highlighting the importance of the nutrient contents in maintaining their bamboo‐based diet and the need to increase the knowledge on their nutritional strategy adapted to the bamboo‐dominated diet inhabiting the unique limestone habitat.     

Seasonal changes in the use of feeding resources by fish in stands of aquatic macrophytes in an Amazonian floodplain,Brazil

This study aimed to characterize the food intake by the fish assemblage inhabiting aquatic macrophytes stands, evaluating the changes in food availability among the periods of the hydrologic cycle and the trophic responses of the fish assemblage along with food availability. Fish sampling was conducted in stands of aquatic macrophytes (predominantly Paspalum repens, Poaceae) along banks of the Trombetas River during the four hydrologic periods (rising, high, receding, and low water level) that represent different phenological conditions of the habitat. The food consumption by the fish assemblage was analyzed for 41 species with stomach contents. The assemblage fed mainly on aquatic insects, periphytic algae and detritus. Food availability analysis showed that food resources changed among periods. Fifteen species were present in more than one period and most of those species showed dietary changes along with the hydrologic cycle, feeding mainly on invertebrates in the rising water period and periphytic algae and detritus in receding and low water periods. Only four species showed sufficient numbers to be analyzed in relation to diet and food availability along the at least three hydrologic periods, two of which showed a positive correlation between diet and food availability for three of the four periods; the other two species did not show this correlation, and presented omnivorous habits. In all cases, the selectivity values for the most important food items were near zero, indicating that intake was not motivated by feeding preference. Our results suggest that both trophic plasticity and omnivorous diets are important adaptations for species that inhabit temporally variable habitats such as aquatic macrophytes stands.     

Avoiding Toxic Levels of Essential Minerals: A Forgotten Factor in Deer Diet Preferences

Ungulates select diets with high energy, protein, and sodium contents. However, it is scarcely known the influence of essential minerals other than Na in diet preferences. Moreover, almost no information is available about the possible influence of toxic levels of essential minerals on avoidance of certain plant species. The aim of this research was to test the relative importance of mineral content of plants in diet selection by red deer (Cervus elaphus) in an annual basis. We determined mineral, protein and ash content in 35 common Mediterranean plant species (the most common ones in the study area). These plant species were previously classified as preferred and non-preferred. We found that deer preferred plants with low contents of Ca, Mg, K, P, S, Cu, Sr and Zn. The model obtained was greatly accurate identifying the preferred plant species (91.3% of correct assignments). After a detailed analysis of these minerals (considering deficiencies and toxicity levels both in preferred and non-preferred plants) we suggest that the avoidance of excessive sulphur in diet (i.e., selection for plants with low sulphur content) seems to override the maximization for other nutrients. Low sulphur content seems to be a forgotten factor with certain relevance for explaining diet selection in deer. Recent studies in livestock support this conclusion, which is highlighted here for the first time in diet selection by a wild large herbivore. Our results suggest that future studies should also take into account the toxicity levels of minerals as potential drivers of preferences.