On the evolution of omnivory in a community context

Omnivory is extremely common in animals, yet theory predicts that when given a choice of resources specialization should be favored over being generalist. The evolution of a feeding phenotype involves complex interactions with many factors other than resource choice alone, including environmental heterogeneity, resource quality, availability, and interactions with other organisms. We applied an evolutionary simulation model to examine how ecological conditions shape evolution of feeding phenotypes (e.g., omnivory), by varying the quality and availability (absolute and relative) of plant and animal (prey) resources. Resulting feeding phenotypes were defined by the relative contribution of plants and prey to diets of individuals. We characterized organisms using seven traits that were allowed to evolve freely in different simulated environments, and we asked which traits are important for different feeding phenotypes to evolve among interacting organisms. Carnivores, herbivores, and omnivores all coexisted without any requirement in the model for a synergistic effect of eating plant and animal prey. Omnivores were most prevalent when ratio of plants and animal prey was low, and to a lesser degree, when habitat productivity was high. A key result of the model is that omnivores evolved through many different combinations of trait values and environmental contexts. Specific combinations of traits tended to form emergent trait complexes, and under certain environmental conditions, are expressed as omnivorous feeding phenotypes. The results indicate that relative availabilities of plants and prey (over the quality of resources) determine an individual's feeding class and that feeding phenotypes are often the product of convergent evolution of emergent trait complexes under specific environmental conditions. Foraging outcomes appear to be consequences of degree and type of phenotypic specialization for plant and animal prey, navigation and exploitation of the habitat, reproduction, and interactions with other individuals in a heterogeneous environment. Omnivory should not be treated as a fixed strategy, but instead a pattern of phenotypic expression, emerging from diverse genetic sources and coevolving across a range of ecological contexts.     

Quantifying aphid behavioral responses to environmental change

Aphids are the most common vector of plant viruses, and their feeding behavior is an important determinant of virus transmission. Positive effects of global change on aphid performance have been documented, but effects on aphid behavior are not known. We assessed the plant‐mediated behavioral responses of a generalist aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae), to increased CO₂ and nitrogen when feeding on each of three host species: Amaranthus viridis L. (Amaranthaceae), Polygonum persicaria L. (= Persicaria maculosa Gray) (Polygonaceae), and Solanum dulcamara L. (Solanaceae). Via a family of constrained Markov models, we tested the degree to which aphid movements demonstrate preference among host species or plants grown under varying environmental conditions. Entropy rates of the estimated Markov chains were used to further quantify aphid behavior. Our statistical methods provide a general tool for assessing choice and quantitatively comparing animal behavior under different conditions. Aphids displayed strong preferences for the same host species under all growth conditions, indicating that CO₂‐ and N‐induced changes in plant chemistry have minimal effects on host preference. However, entropy rates increased in the presence of non‐preferred hosts, even when preferred hosts were available. We conclude that the presence of a non‐preferred host species affected aphid‐feeding behavior more than changes in plant leaf chemistry when plants were grown under elevated CO₂ and increased N availability.     

Optimal feeding under stoichiometric constraints: a model of compensatory feeding with functional response

When the nutrient content of food is limited, herbivores often increase their feeding rates. Such an increase in the feeding rate is called ‘compensatory feeding’. Although it has a number of implications for herbivore population and plant–forager dynamics, the compensatory feeding is not yet functionally formulated especially in relation with ecological stoichiometry. Therefore, we constructed a simple mathematical model by incorporating the optimal feeding rate into the type II functional response to maximize a forager's growth rate under constraints of carbon or nutritionally important element like phosphorus (P). We used the planktonic herbivore Daphnia as a model herbivore. The model revealed that the optimal feeding rate increased by using excess carbon when relative P content of food was less than a certain level, which is known as the threshold elemental ratio. This level changed with the change of food abundance. It also showed that whether or not foragers should exhibit compensatory feeding depends on their stoichiometric characteristics and digestive traits, and also on the assimilability of a given food. These findings are helpful to test the feeding conditions under which compensatory feeding is advantageous for a given animal. Our model can be easily incorporated into forager population dynamics and prey‐consumer interaction models because the optimal feeding rate can be analytically given.     

Feeding selectivity,food assimilability and demand of the Baikal invader <Emphasis Type="Italic">Gmelinoides fasciatus</Emphasis> (Stebbing, 1899) in Lake Ladoga

Feeding selectivity and assimilability of the Baikal invader Gmelinoides fasciatus (Stebbing, 1899) in Lake Ladoga at feeding by various types of plant and animal food have been studied experimentally. The food demand has been assessed at different assimilation levels. Freshwater shrimp G. fasciatus has been shown to have distinct selective capacity with respect to different kinds of plant and animal food.     

Laser Microdissection (LM): Applications to plant materials

Abstract

In recent years, Laser Microdissection (LM), which has been widely used in animal biology, has been adapted to plant tissues. This short paper focuses on some technical aspects concerning plant sample preparation for LM technology, with particular attention to the application of gene expression and proteomics studies. Examples derived from the use of different LM methods are reported and their applications to plant–microbe interactions are explored.     

Hierarchical resource selection by impala in a savanna environment

The factors that affect resource selection by a foraging herbivore can vary according to the resources or conditions associated with particular levels of organization in the environment, and to the scales over which the herbivore perceives and responds to those resources and conditions. To investigate the role of forage in this hierarchical process, we studied resource selection by a mixed‐feeding large herbivore, the impala (Aepyceros melampus). We focussed on three spatial scales: plant species, feeding station and feeding patch. In paired sites where impala were and were not observed, we identified the plant species from which animals fed, the attributes of the plants, and the characteristics of the broader site. Across all three scales, plant species available as forage was central in determining resource selection by impala. At the species level, that effect was modified by the nutritional quality (greenness) and whether it was during a period of forage abundance or scarcity (season). At the feeding‐station level, overall greenness and biomass of the station were important, but their effects were modified by the season. At the feeding‐patch level, broader‐scale factors such as the type of vegetation cover had an important influence on resource selection. The grass Panicum maximum was a preferred forage species and a key resource determining the locations of feeding impala. Our findings support the idea that selection by a foraging herbivore at fine scales (i.e. diet selection) can have consequences for broader‐scale selection that result in observed patterns of habitat use and animal distribution.     

Seasonal and geographical influences on the feeding ecology of giraffes in the Luangwa Valley,Zambia: 1973–2014

Obtaining longitudinal data about the feeding ecology of long‐lived iteroparous mammals is rare, but enhances our understanding of how the environment influences niche breadth and dietary diversity within a species. We analysed forty years of feeding records obtained from a population of Thornicroft's giraffes (Giraffa camelopardalis thornicrofti) living in the Luangwa Valley, Zambia. Giraffes are browsers that have been reported to feed primarily upon Acacia leaves, but their feeding ecology in some locations conflict with this interpretation. Giraffes in the Luangwa Valley fed on 93 identified plant species, but only a few contributed to the bulk of the diet. Niche breadth was quite large (Shannon‐Weiner Diversity Index H′ = 3.699) and about 13% more diverse during the dry, than wet, season. Key species eaten during the dry season were very consistent across decades, with Kigelia africana and Capparis tomentosa prominent at this time. The evolutionary ecology of giraffes has probably benefitted from a foraging strategy that includes a variable and high‐quality diet during the hot, dry season, when feeding pressures are greatest. Giraffe feeding ecology has evolved in conjunction with their physiology, anatomy and morphology, resulting in an animal that is well adapted for survival in an arid environment.     

Benefits and potential trade‐offs associated with yeast‐like symbionts during virulence adaptation in a phloem‐feeding planthopper

Insect herbivores form symbioses with a diversity of prokaryotic and eukaryotic microorganisms. A role for endosymbionts during host feeding on nutrient‐poor diets – including phloem – is now supported by a large body of evidence. Furthermore, symbiont‐herbivore associations have been implicated in feeding preferences by host races (mainly aphids) on multiple plant species. However, the role of symbionts in mediating herbivore preferences between varieties of the same plant species has received little research attention despite the implications for virulence adaptation to resistant crops. This study investigates the role of yeast‐like symbionts (YLS) in virulence adaptation and host plant switching among populations of the brown planthopper, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), that were selected on various rice [Oryza sativa L. (Poaceae)] lines differing in their resistance against herbivores. Planthopper fitness (nymph weight) declined where YLS densities were depleted through heat treatment. However, compared to normal symbiotic planthoppers, the depletion of symbionts did not generally change the relative fitness of planthoppers (each ‘adapted’ to a single natal host) when switched to feed on a range of rice lines (exposed hosts). In some cases, this occurred despite differences in YLS density responses to the various hosts. Furthermore, we detected no fitness costs associated with YLS in adapted populations. Therefore, the results of this study suggest that, whereas YLS are essential for planthopper nutrition, changes in YLS density play little role during virulence adaptation and host plant switching by the brown planthopper.     

Temporal dynamics of seed excretion by wild ungulates: implications for plant dispersal

Dispersal is a key process in metapopulation dynamics as it conditions species' spatial responses to gradients of abiotic and biotic conditions and triggers individual and gene flows. In the numerous plants that are dispersed through seed consumption by herbivores (endozoochory), the distance and effectiveness of dispersal is determined by the combined effects of seed retention time in the vector's digestive system, the spatial extent of its movements, and the ability of the seeds to germinate once released. Estimating these three parameters from experimental data is therefore crucial to calibrate mechanistic metacommunity models of plant–herbivore interactions. In this study, we jointly estimated the retention time and germination probability of six herbaceous plants transported by roe deer (Capreolus capreolus), red deer (Cervus elaphus), and wild boar (Sus scrofa) through feeding experiments and a Bayesian dynamic model. Retention time was longer in the nonruminant wild boar (>36 h) than in the two ruminant species (roe deer: 18–36 h, red deer: 3–36 h). In the two ruminants, but not in wild boar, small and round seeds were excreted faster than large ones. Low germination probabilities of the excreted seeds reflected the high cost imposed by endozoochory on plant survival. Trait‐mediated variations in retention time and germination probability among animal and plant species may impact plant dispersal distances and interact with biotic and abiotic conditions at the release site to shape the spatial patterns of dispersed plant species.     

Prey feeding increases water stress in the omnivorous predator Dicyphus hesperus

The effects of water stress (produced by water deprivation and prey feeding) on plant feeding were investigated in the omnivorous predator Dicyphus hesperus Knight (Hemiptera: Miridae). The objective was to determine if prey feeding aggravated water deficits and thus increased plant feeding. We measured plant feeding in a factorial experiment where female D. hesperus were prepared for experiments by providing or withholding water and/or prey for 24 h. We then evaluated the amount of plant feeding on Nicotiana tabacum seedlings by the direct observation of insects at three different densities of the prey, Ephestia kuehniella eggs. The amount of plant feeding, as measured by frequency of plant feeding bouts and time spent plant feeding during observation, was significantly greater for water‐deprived individuals than for those that had been provided with water. Individuals that had been provided with prey fed on plants at a significantly higher frequency than prey‐deprived individuals at two of the prey densities used in the experiment. These results support the hypothesis that plant feeding in zoophytophagous Hemiptera facilitates prey feeding by providing water that is essential for predation.     

Additive main effect and multiplicative interaction model for a diallel-cross analysis

Diallel mating designs have proved informative in determining the inheritance of quantitative traits of interest to plant breeders. Apart from the well-established analyses of a complete diallel, the two-way factorial data structure of this design lends itself to analysis by the additive-main-effects-and-multiplicative-interaction (AMMI) model. This research article describes the joint application of the AMMI model and Griffing’s method 1, model I, to gain insight into the breeding value of inbred lines in a self-pollinated crop such as disomic, hexaploid bread wheat. Data from a multi-environment trial of a complete diallel cross between eight lines adapted to the East African highlands were analyzed to provide an example of this joint analysis. This combined approach identified not only the direction of a cross, i.e. which parent should be male or female, but also which crosses produce offspring showing F₁ heterosis. Received: 10 June 2000 / Accepted: 31 July 2000     

Malacorhinus irregularis for biological control of Mimosa pigra: host-specificity,life cycle,and establishment in Australia

Malacorhinus irregularis Jacoby (Coleoptera: Chrysomelidae: Galerucinae: Galerucini), from Mexico is identified as a potential biological control agent for Mimosa pigra L. (Mimosaceae), a serious weed of northern Australia and Asia. The adults feed on leaves of the host, and the larvae develop on seedlings, roots, and perhaps other plant parts. The damage to the target plant is substantial, indicating that this insect could be an effective control agent. Host-specificity tests examined the suitability of seedlings and leaves for larval development, and suitability of leaves for adult feeding. In no-choice tests, no larval development occurred on any of the 81 test plant species other than M. pigra. The extent of adult feeding on the test plants was negligible in the tests using a choice-minus-control design, being less than 1% of that which occurred on M. pigra. We conclude that M. irregularis is a specialist on its host and the risk associated with its release in Australia is low. It was released in infestations of M. pigra in the Northern Territory of Australia in 2000. Establishment and abundance was monitored at one site where the number and distribution of adult beetles fluctuated widely as soil moisture conditions varied through the seasons. Adults were found for two years after release and local defoliation of plants was attributed to this species. Although only limited observations were made, adult feeding was not recorded from Neptunia major (Benth). Windler plants growing in close proximity to M. pigra, indicating specificity under field conditions.     

The evolving functions of DNA methylation

DNA methylation is an ancient process found in all domains of life. Although the enzymes that mediate methylation have remained highly conserved, DNA methylation has been adapted for a variety of uses throughout evolution, including defense against transposable elements and control of gene expression. Defects in DNA methylation are linked to human diseases, including cancer. Methylation has been lost several times in the course of animal and fungal evolution, thus limiting the opportunity for study in common model organisms. In the past decade, plants have emerged as a premier model system for genetic dissection of DNA methylation. A recent combination of plant genetics with powerful genomic approaches has led to a number of exciting discoveries and promises many more.     

Analysis of plant-derived miRNAs in animal small RNA datasets

ABSTRACT: BACKGROUND: Plants contain significant quantities of small RNAs (sRNAs) derived from various sRNA biogenesis pathways. Many of these sRNAs play regulatory roles in plants. Previous analysis revealed that numerous sRNAs in corn, rice and soybean seeds have high sequence similarity to animal genes. However, exogenous RNA is considered to be unstable within the gastrointestinal tract of many animals, thus limiting potential for any adverse effects from consumption of dietary RNA. A recent paper reported that putative plant miRNAs were detected in animal plasma and serum, presumably acquired through ingestion, and may have a functional impact in the consuming organisms. RESULTS: To address the question of how common this phenomenon could be, we searched for plant miRNAs sequences in public sRNA datasets from various tissues of mammals, chicken and insects. Our analyses revealed that plant miRNAs were present in the animal sRNA datasets, and significantly miR168 was extremely over-represented. Furthermore, all or nearly all (>96%) miR168 sequences were monocot derived for most datasets, including datasets for two insects reared on dicot plants in their respective experiments. To investigate if plant-derived miRNAs, including miR168, could accumulate and move systemically in insects, we conducted insect feeding studies for three insects including corn rootworm, which has been shown to be responsive to plant-produced long double-stranded RNAs. CONCLUSIONS: Our analyses suggest that the observed plant miRNAs in animal sRNA datasets can originate in the process of sequencing, and that accumulation of plant miRNAs via dietary exposure is not universal in animals.     

Indirect genetic effects on the relationships between production and feeding behaviour traits in growing Duroc pigs

Performance and feeding behaviour traits in growing pigs could be affected by social interaction effects when animals are raised in group. So, properly knowing the genetic correlations between direct and social interaction effects among performance and feeding behaviour traits could improve the accuracy of the genetic evaluations. Our aim was to explore the role of feeding behaviour traits (FBT) and indirect genetic effects (IGEs) in the genetic evaluations of growing pigs. Thus, genetic parameters were estimated for production traits (PT): average daily gain, average daily feed consumption, feed conversion ratio and backfat thickness; as well as for FBT: average daily feeding rate, average daily feeding frequency, average daily occupation time and average daily time between consecutive visits. Traits were recorded in 1144 Duroc pigs during the fattening period. Two bivariate models were fitted: classic animal model and an animal model fitting IGE. Estimations were done following Bayesian procedures. Heritability estimates obtained with classic animal model for all studied traits were medium-high. The additional heritable variation captured by IGE supposed that the ratios of total genetic variance to phenotypic variance (T²) were higher than the heritability estimates obtained with the classic model, except for occupation time trait, when a lower value (0.20 ± 0.19) was estimated. This is due to a high and negative correlation between IGE and direct genetic effects (DGEs) of this particular trait (−0.78 ± 0.27). Results from classic animal model do not evidence a clear role of FBT to improve the accuracy of breeding value predictions for PT; only average daily feeding rate seems to show a positive correlation (around 0.50 to 0.60) with average daily gain, average daily feed consumption and backfat thickness. However, when IGE model was fitted, the number of estimates of genetic correlations between FBT and PT showing a relevant magnitude increased, generally for the correlations between IGE of FBT and DGE of PT; or particularly for the correlations between IGE of average daily feeding frequency, and the IGE of all the PT, except average daily gain. Thus, in evaluations using the animal model with IGE fitted, the inclusion of FBT could aid the improvement of the accuracy of breeding value predictions for PT. This is a consequence of the improved genetic relationships between traits that can be fitted when considering such models.     

Zoophytophagy in the plantbug Nesidiocoris tenuis

1 The zoophytophagy of Nesidiocoris tenuis (Reuter) (Heteroptera: Miridae) was characterized in relation to prey availability and environmental factors by: (i) monitoring its population dynamics in tomato greenhouses; (ii) analysis of the influence of N. tenuis and whitefly density, temperature and humidity on the intensity of N. tenuis plant feeding; and (iii) laboratory assays under controlled conditions to determine the intensity of plant feeding in relation to prey availability, temperature and humidity. 2 A negative relationship was found between plant feeding and predated whiteflies in tomato greenhouses. Plant feeding was directly related to N. tenuis density and temperature and inversely related to whitefly density. The significance of prey availability and temperature was corroborated in laboratory assays. The intensification of plant feeding at low prey density indicates switching from zoophagy to phytophagy as prey become scarce. 3 Nesidiocoris tenuis showed a typical predator dynamic in relation to variance in prey density. Populations increased after whitefly outbreaks and decreased after whitefly had been depleted. The rapid decrease of N. tenuis populations after whitefly decreased, however, suggests that plants are a poorer nutrient source than whitefly for this species.     

Quantitative trait loci for yield and yield components in an Oryza sativa×Oryza rufipogon BC2F2 population evaluated in an upland environment

An advanced backcross breeding strategy was used to identify quantitative trait loci (QTLs) associated with eight agronomic traits in a BC₂F₂ population derived from an interspecific cross between Caiapo, an upland Oryza sativa subsp. japonica rice variety from Brazil, and an accession of Oryza rufipogon from Malaysia. Caiapo is one of the most-widely grown dryland cultivars in Latin America and may be planted as a monoculture or in a multicropping system with pastures. The objectives of this study were: (1) to determine whether trait-enhancing QTLs from O. rufipogon would be detected in 274 BC₂F₂ families grown under the drought-prone, acid soil conditions to which Caiapo was adapted, (2) to compare the performance with and without pasture competition, and (3) to compare putative QTL-containing regions identified in this study with those previously reported for populations adapted to irrigated, low-land conditions. Based on analyses of 125 SSLP and RFLP markers distributed throughout the genome and using single-point, interval, and composite interval mapping, two putative O. rufipogon derived QTLs were detected for yield, 13 for yield components, four for maturity and six for plant height.We conclude that advanced backcross QTL analysis offers a useful germplasm enhancement strategy for the genetic improvement of cultivars adapted to stress-prone environments. Although the phenotypic performance of the wild germplasm would not suggest its value as a breeding parent, it is noteworthy that 56% of the trait-enhancing QTLs identified in this study were derived from O. rufipogon. This figure is similar to the 51% of favorable QTLs derived from the same parent in crosses with a high-yielding hybrid rice cultivar evaluated under irrigated conditions in a previous study. In conclusion, parallel studies in rice using AB-QTL analysis provide increasing evidence that certain regions of the rice genome are likely to harbor genes of interest for plant improvement in multiple environments. Received: 3 September 1999 / Accepted: 16 May 2000     

Digestion, growth and reproductive performance of the zoophytophagous rove beetle Philonthus quisquiliarius (Coleoptera: Staphylinidae) fed on animal and plant based diets

The zoophytophagous feeding habits of larvae and adults of the rove beetle, Philonthus quisquiliarius (Gyllenhal) (Coleoptera: Staphylinidae), are reported for the first time. This study evaluates the effects of different feeding regimes on its growth and reproductive performance (i.e., larval growth, adult weight gain, consumption, fecundity and fertility) and digestive physiology. Larvae presented similar growth rates when fed on living animal or on green plant material for 48h. However, higher consumption rates and lower efficiencies of conversion of digested matter to body mass were obtained when leaves were consumed. Adults presented also positive weight gains regardless of the food consumed (plant or animal material). Interestingly, the highest weight gain rate and efficiency of digestion resulted when adults fed on a rearing diet containing nutrients from both animals and plants. Moreover, we have found negative effects upon P. quisquiliarius fecundity and fertility when supplemental plant nutrients were removed from the optimum rearing diet. Physiological adaptations to allow trophic switching between predation and phytophagy have been found, such as the higher ratio of α-amylase activity to protease activity to deal with the inverted protein-carbohydrate ratio of plant versus animal tissues. Furthermore, this species has an arsenal of digestive proteases whose activity is affected by the type of diet ingested. All together, our results suggest that P. quisquiliarius needs certain nutrients, which are obtained only from plant material. This knowledge will help to understand the complex trophic interactions that occur in agroecosystems.     

Adaptive and Cross-Protective Responses of Pseudomonas sp. DJ-12 to Several Aromatics and Other Stress Shocks

Pseudomonas sp. DJ-12 cells were subjected to mild treatments of stress such as exposure to biphenyl, 4-chlorobiphenyl (4CB), 4-hydroxybenzoate (4HBA), ethanol, and heat, and then were examined for production of stress-shock proteins and morphological changes. The adapted cells were then subjected to lethal stress conditions such as 200 mm 4CB, 100 mm biphenyl, 10 mm 4HBA, 20% ethanol, and 46°C to examine crossly protective responses to the stresses. Several stress-shock proteins including DnaK and GroEL were newly synthesized in the adapted cells. Some of them were commonly produced by those stresses separately treated. The cells treated with these aromatic hydrocarbons showed destructive openings on the cell envelopes. On the other hand, those cells treated with ethanol or heat displayed irregular rod shapes with wrinkled surfaces. The adapted cells to each stress under sublethal conditions exhibited increased resistance to the same stress of lethal conditions. The cells adapted with 5 mm 4HBA showed greater protection for survival than those adapted by other stresses. In addition, those adapted cells showed increased resistance to other stresses as a cross-protection phenomenon. The cells adapted to 42°C exhibited markedly increased resistance to the lethal stresses of 46°C as well as to 20% ethanol. Received: 20 December 2000/Accepted: 26 January 2001     

Feeding rates of a mammalian browser confirm the predictions of a ‘foodscape’ model of its habitat

Adequate nutrition is a fundamental requirement for the maintenance and growth of populations, but complex interactions between nutrients and plant toxins make it difficult to link variation in plant quality to the ecology of wild herbivores. We asked whether a ‘foodscape’ model of habitat that uses near-infrared spectroscopy to describe the palatability of individual trees in the landscape, predicted the foraging decisions of a mammalian browser, the koala (Phascolarctos cinereus). Specifically, we considered four behavioural decision points at which nutritional quality may influence an animal’s decision. These were: which tree to enter, whether to feed from that tree, when to stop eating, and how long to remain in that tree. There were trends for koalas to feed in eucalypt trees that were more palatable than unvisited neighbouring conspecific trees, and than trees that they visited but did not eat. Koalas ate longer meals in more palatable trees, and stayed longer and spent more time feeding per visit to these trees. Using more traditional chemical analyses, we identified that an interaction between the concentrations of formylated phloroglucinol compounds (a group of plant secondary metabolites) and available N (an integrated measure of tannins, digestibility and N) influenced feeding. The study shows that foodscape models that combine spatial information with integrated measures of food quality are a powerful tool to predict the feeding behaviour of herbivores in a landscape.