Foraging behaviour of caterpillars given a choice of plant genotypes in the presence of insect predators

1. To examine the effects of predators and plant genotype on the behaviour, patterns of herbivory, growth, and survivorship of caterpillars, an experiment was conducted under semi‐natural conditions, with two host plant genotypes (low vs. high iridoid glycosides) of plantain Plantago lanceolata, two kinds of herbivores (noncryptic specialist Junonia coenia vs. cryptic generalist Pyrrharctia isabella), and two levels of caterpillar predation (with and without Podisus maculiventris stinkbugs). 2. Choice tests conducted in the laboratory showed that in three out of four cases, caterpillars preferred leaves from the low iridoid glycoside genotype. 3. In the field experiment, the presence of predators affected the amount of leaf material eaten per plot and the proportion of leaf material eaten by the caterpillars as expected, but it did not affect the use of plant genotypes by Junonia caterpillars within the plots. In contrast, the caterpillar density–predation treatments affected the proportion of leaves eaten by Pyrrharctia caterpillars that were of the low iridoid glycoside genotype, but not entirely as expected. The caterpillars used both genotypes equally when predators were present but the high iridoid glycoside genotype was used more by caterpillars at low density and without predators. 4. The message then is that on the scale that caterpillars could be choosy about intake of iridoid glycosides they were not choosy among plant genotypes; however they were choosy between leaves, which can differ in iridoid glycoside concentration via plant genotype and leaf age.     

Stage-Specific Behavioral Responses of Ageneotettix deorum (Orthoptera: Acrididae) in the Presence of Lycosid Spider Predators

Grasshoppers must gather food while avoiding size-selective predation from other arthropods, especially spiders, potentially leading to a trade-off between foraging and defensive behaviors. This trade-off becomes less intense as prey grow larger and are less susceptible to arthropod predation. Activity budgets were constructed for three nymphal (third- to fifth- instar) and adult life cycle stages of Ageneotettix deorum, a common rangeland grasshopper, for three conditions of predation risk by lycosid spiders (spider absence, spider presence, and presence of a nonlethal, chelicerae-modified spider). In third and fourth instars, exposure to predators resulted in reduced feeding activity, increased time spent in antipredator and defensive behaviors, and reduced general activity compared to individuals not exposed to spiders. No significant shifts in behaviors were observed for fifth-instar nymphs and adult A. deorum in response to spider presence. Activity levels in functional spiders and chelicerae-modified spiders were statistically indistinguishable.     

The importance of within-system spatial variation in drivers of marine ecosystem regime shifts

Comparative analyses of the dynamics of exploited marine ecosystems have led to differing hypotheses regarding the primary causes of observed regime shifts, while many ecosystems have apparently not undergone regime shifts. These varied responses may be partly explained by the decade-old recognition that within-system spatial heterogeneity in key climate and anthropogenic drivers may be important, as recent theoretical examinations have concluded that spatial heterogeneity in environmental characteristics may diminish the tendency for regime shifts. Here, we synthesize recent, empirical within-system spatio-temporal analyses of some temperate and subarctic large marine ecosystems in which regime shifts have (and have not) occurred. Examples from the Baltic Sea, Black Sea, Bengula Current, North Sea, Barents Sea and Eastern Scotian Shelf reveal the largely neglected importance of considering spatial variability in key biotic and abiotic influences and species movements in the context of evaluating and predicting regime shifts. We highlight both the importance of understanding the scale-dependent spatial dynamics of climate influences and key predator–prey interactions to unravel the dynamics of regime shifts, and the utility of spatial downscaling of proposed mechanisms (as evident in the North Sea and Barents Sea) as a means of evaluating hypotheses originally derived from among-system comparisons.     

Prey Specificity and the Importance of Close-Range Chemical Cues in Prey Recognition in the Digger Wasp, Liris niger

Females of the digger wasp species Liris niger paralyzed and layed eggs on six of seven tested cricket species. L. niger females with unmanipulated antennae always rejected the cricket Gryllus bimaculatus, but those without antennal flagella paralyzed and layed eggs on it. Even L. niger females from maggots raised artificially on G. bimaculatus never paralyzed it. L. niger first orients toward a prey visually and then touches the prospective prey briefly with its antennal flagella. This contact determines about the suitability of the prey. The ability to differentiate between prey species required at least one partially unmanipulated antennal flagellum. The responsible sensilla were located on the upper surface of the antennal flagella. Chemical cues which make the cricket Acheta domesticus attractive to L. niger females could be transferred to G. bimaculatus.     

Modeling fish dynamics and effects of stress in a hydrologically pulsed ecosystem

Many wetlands undergo seasonal cycles in precipitation and water depth.This environmental seasonality is echoed in patterns of production of fishbiomass, which, in turn, influence the phenology of other components of thefood web, including wading birds. Human activities, such as drainage orother alterations of the hydrology, can exacerbate these natural cycles andresult in detrimental stresses on fish production and the higher trophic levels dependent on this production. In this paper we model theseasonal pattern of fish production in a freshwater marsh, with specialreference to the Everglades/Big Cypress region of southern Florida.The model illustrates the temporal pattern of production through theyear, which can result in very high densities of fish at the end of ahydroperiod (period of flooding), aswell as the importance of ponds and other deep depressions, both as refugia and sinks during dry periods. The model predicts that: (1) there is an effective threshold in the length of the hydroperiod that must beexceeded for high fish-population densities to be produced, (2) large,piscivorous fishes do not appear tohave a major impact on smaller fishes in the marsh habitat, and (3) therecovery of small-fish populations in the marsh following a major droughtmay require up to a year. The last of these results is relevant toassessing anthropogenic impacts on marsh production, as these effectsmay increase the severity and frequency of droughts.     

Cost of autotomy drives ontogenetic switching of anti-predator mechanisms under developmental constraints in a land snail

Autotomy of body parts offers various prey animals immediate benefits of survival in compensation for considerable costs. I found that a land snail Satsuma caliginosa of populations coexisting with a snail-eating snake Pareas iwasakii survived the snake predation by autotomizing its foot, whereas those out of the snake range rarely survived. Regeneration of a lost foot completed in a few weeks but imposed a delay of shell growth. Imprints of autotomy were found in greater than 10 per cent of S. caliginosa in the snake range but in only less than 1 per cent out of it, simultaneously demonstrating intense predation by the snakes and high efficiency of autotomy for surviving snake predation in the wild. However, in experiments, mature S. caliginosa performed autotomy less frequently. Instead of the costly autotomy, they can use defensive denticles on the inside of their shell apertures. Owing to the constraints from the additive growth of shells, most pulmonate snails can produce these denticles only when they have fully grown up. Thus, this developmental constraint limits the availability of the modified aperture, resulting in ontogenetic switching of the alternative defences. This study illustrates how costs of adaptation operate in the evolution of life-history strategies under developmental constraints     

Structure of fish assemblages along spatial gradients in a deep subtropical reservoir (Itaipu Reservoir,Brazil-Paraguay border)

Synopsis We assessed the structure of the fish assemblages in the Itaipu Reservoir (Paraná River, Brazil-Paraguay) along a longitudinal or river-dam gradient (composed of riverine, transitional and lacustrine zones) and transversal or upstream–downstream gradients of the tributaries (composed of lotic and lentic stretches of tributaries and reservoir shores). We sampled stations distributed along the environmental gradients quarterly during two years. We caught mostly piscivorous, detritivorous and insectivorous fishes. The structure of the whole fish assemblage both at the regional spatial scale and at the zones of each gradient was significantly non-random according to null models and ordination analysis. When the assemblage was broken into groups, the piscivores and detritivores as well as the predators and prey showed significant non-random structure whereas the insectivores, omnivores, herbivores, benthophages and mud-eaters showed random structure. The first groups are those that had more species and the last mentioned are those with fewer species. The tributaries varied more in composition among themselves than the reservoir shores, showing a high heterogeneity in the transversal gradient. The most widespread species was the introduced piscivore Plagioscion squamosissimus. The loricariids were most abundant in the lotic and lentic stretches of the tributaries. We also observed temporal variability in species composition, mainly in the reservoir shores possibly due to the influence of the upstream floodplain on the migratory fish that periodically use the reservoir as feeding habitat. In the tributaries, the temporal changes were less predictable. A combination of habitat preferences and interactions among species, especially predator–prey relations, might be responsible for the observed structure patterns.     

Probing the Ubiquinone Reduction Site in Bovine Mitochondrial Complex I Using a Series of Synthetic Ubiquinones and Inhibitors

Studies of the structure–activity relationships of ubiquinones and specific inhibitors are helpful to probe the structural and functional features of the ubiquinone reduction site of bovine heart mitochondrial complex I. Bulky exogenous short-chain ubiquinones serve as sufficient electron acceptors from the physiological ubiquinone reduction site of bovine complex I. This feature is in marked contrast to other respiratory enzymes such as mitochondrial complexes II and III. For various complex I inhibitors, including the most potent inhibitors, acetogenins, the essential structural factors that markedly affect the inhibitory potency are not necessarily obvious. Thus, the loose recognition by the enzyme of substrate and inhibitor structures may reflect the large cavitylike structure of the ubiquinone (or inhibitor) binding domain in the enzyme. On the other hand, several phenomena are difficult to explain by a simple one-catalytic site model for ubiquinone.     

An enhanced expression of ABC 1 transporter in circulating leukocytes as a potential molecular marker for the diagnostics of glaucoma

Summary. Objective: Glaucoma is a neurodegenerative disease. Since vascular dysregulation is supposed to be a risk factor for the development of glaucomatous damage, the preventive treatment might slow down the disease development. The efficiency of the therapeutic treatment depends particularly on a drug efflux pump regulated by ABC transporters. ABC 1 is also known to participate on the vascular regulation. This study was focused on the comparative analysis of ABC 1 expression levels in circulating leukocytes of non-glaucomatous individuals and glaucoma patients.Results and conclusions: The expression rates of ABC 1 were significantly increased in leukocytes of glaucoma patients compared to non-glaucomatous individuals. The expression level of ABC 1 was, furthermore, highly homogeneous in glaucoma patients. In contrast, these expression levels in non-glaucomatous individuals were extremely heterogeneous. This transporter acts as the energy-dependent unidirectional transmembrane cholesterol efflux pump and can export a wide range of hydrophobic drugs. Additionally an observed enhanced ABC 1 expression in circulating leukocytes may be implicated in the vascular regulation mechanisms of glaucoma. We proposed the enhanced expression of ABC 1 in leukocytes as a potential marker for the diagnostics and ex vivo molecular monitoring of glaucoma.     

The dynamics of a Lotka–Volterra predator–prey model with state dependent impulsive harvest for predator

According to the economic and biological aspects of renewable resources management, we propose a Lotka–Volterra predator–prey model with state dependent impulsive harvest. By using the Poincaré map, some conditions for the existence and stability of positive periodic solution are obtained. Moreover, we show that there is no periodic solution with order larger than or equal to three under some conditions. Numerical results are carried out to illustrate the feasibility of our main results. The bifurcation diagrams of periodic solutions are obtained by using the numerical simulations, and it is shown that a chaotic solution is generated via a cascade of period-doubling bifurcations, which implies that the presence of pulses makes the dynamic behavior more complex.     

The genetic architecture of a niche: variation and covariation in host use traits in the Colorado potato beetle

The genetic basis of host plant use by phytophagous insects can provide insight into the evolution of ecological niches, especially phenomena such as specialization and phylogenetic conservatism. We carried out a quantitative genetic analysis of multiple host use traits, estimated on five species of host plants, in the Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae). Mean values of all characters varied among host plants, providing evidence that adaptation to plants may require evolution of both behavioral (preference) and post-ingestive physiological (performance) characteristics. Significant additive genetic variation was detected for several characters on several hosts, but not in the capacity to use the two major hosts, a pattern that might be caused by directional selection. No negative genetic correlations across hosts were detected for any 'performance' traits, i.e. we found no evidence of trade-offs in fitness on different plants. Larval consumption was positively genetically correlated across host plants, suggesting that diet generalization might evolve as a distinct trait, rather than by independent evolution of feeding responses to each plant species, but several other traits did not show this pattern. We explored genetic correlations among traits expressed on a given plant species, in a first effort to shed light on the number of independent traits that may evolve in response to selection for host-plant utilization. Most traits were not correlated with each other, implying that adaptation to a novel potential host could be a complex, multidimensional 'character' that might constrain adaptation and contribute to the pronounced ecological specialization and the phylogenetic niche conservatism that characterize many clades of phytophagous insects.     

Role of phosphorus and nitrogen for bacteria and phytopankton development in a large shallow lake

Nutrient (P and N) enrichment experiments in small enclosures (20 l) were carried out to determine P and/or N limitation of bacterioplankton in Lake Võrtsjärv. The specific interest of the study was to test if it is possible to detect nutrient `physiological' or growth (rate) limitation of bacterioplankton and competition for nutrients (N and P) with phytoplankton in generally nutrient rich lake. Thymidine and leucine incorporation; leucine aminopeptidase, -D-glucosidase and alkaline phosphatase activity, total count of bacteria, chlorophyll a concentration and primary production as well as the concentrations of different chemical forms of N and P were followed during 4–5 days of the experiment. To address the question of the interactions between nutrients, bacterio- and phytoplankton, experimental and seasonal data sets were included in the analyses. Phosphorus (P) had a positive effect on bacterioplankton in enclosure experiments in June 1997; no effects of nutrients were found in September 1996, while in May 1996, P affected mainly the phytoplankton. On the seasonal scale, the development of bacterioplankton was connected to primary production, total phosphorus and temperature. In enrichment experiments, bacterioplankton was mainly related with primary productivity but the possible importance of bacterial grazers could be presumed. Thus, no evidence was found for nutrient growth limitation and/or competition for N and/or P, rather bacterioplankton depended on organic food supply originating from phytoplankton.     

Localization of a site for interaction with hepatic male-specific proteins in two rat estrogen sulfotransferase genes

Using electromobility shift assay the interaction of fragments of two paralogous rat estrogen sulfotransferase (Ste) genes with proteins of nuclear extracts from male and female rat liver was studied. Male-specific DNA–protein complexes were revealed with labeled oligonucleotides corresponding to fragments +1150/+1449, +1358/+1449, +1397/+1449, and +1417/+1449 of intron 1 of the Ste1 gene. The removal of a 20 bp region corresponding to the sequence +1430/+1449, or even either 5"- or 3"-terminal 5 bp of this region abolished the selective interaction of the oligonucleotides with the malespecific protein(s). According to the results of the experiments on mutual competition of the oligonucleotides, the fragment of the Ste2 gene corresponding to the sequence +1397/+1449 of the Ste1 gene formed complexes with the same male-specific protein(s) as the fragment of the Ste1 gene did. The data suggest the mapped element to participate in gender differentiation of the expression of the Ste1 and Ste2 genes.     

The use of chlorophyll fluorescence as a screening method for cold tolerance in maize

Chlorosis in maize (Zea mays L.) is a common phenomenon in the 12 to 17°C temperature range. A newly developed chlorophyll-fluorescence technique was used to elucidate the underlying subcellular processes of resistance to chlorosis. Four populations were used that were developed by divergent mass selection for contrasting resistance to chlorosis in a cold-tolerant dent and a cold-tolerant flint population. Young plants from the four populations were kept for six days at 17/10, 15/10 and 13/10°C (day/night). After 1, 3 and 6 days various chlorophyll-fluorescence parameters were determined. The measurements were done on leaf 4. Differences were not uniform for all fluorescence properties. The resistant and susceptible populations of the two sets differed for the Q-quenching which is related to the electron transport rate in the chloroplast. For the E-quenching which is related to the Calvin cycle activity, the resistant dent differed significantly from the other three populations. The ratio Fm/Fo (related to the transfer of absorbed light-energy from antennae pigments to reaction centers in the chloroplast) was higher for the resistant dent population than for the susceptible one. The flint types did not differ for this property.Apparently, divergent mass selection for chlorosis resistance resulted in various changes at the subcellular level that are not necessarily comparable for flint and dent types.When after 6 days the temperature was raised from 13°C to 17°C, the fluorescence signals led to the conclusion that there was a full recovery of various processes after two days, except for the metabolic activity of the susceptible flint.     

The effect of using the Breeding Soundness Evaluation as a selection criterion for Santa Gertrudis bulls on bulls in subsequent generations

Results of Breeding Soundness Evaluations (BSE) used to select Santa Gertrudis bulls over a 10-yr period were analyzed in retrospect to determine the effect on bulls in subsequent generations. Bulls were tested at three ages: 16 mo (n = 1,936), 20 mo (n = 3,111) and at maturity (≥ 24 mo, n = 3,814). Scrotal circumference (SC) and sperm motility and morphology were evaluated. Sixteen-mo-old bulls were required to have an SC ≥ 30 cm to be tested. During 1977 to 1980, 20-mo-old bulls with an SC < 30 cm were culled, and the minimum SC was increased to 32 cm during 1981 to 1986. Mature bulls during this period were required to have an SC ≥ 35 cm to be tested. A BSE < 60 was considered a failing score, and bulls were culled at this level. There was a positive correlation between SC and sperm motility and SC and sperm morphology in 16-mo-old and 20-mo-old but not in mature bulls (P < 0.0001). The percentage of bulls passing the BSE was positively correlated with SC at all ages (P < 0.0001), and the passing rate increased over the years (P < 0.0001). Scrotal circumference increased over the years in bulls that passed the BSE (P < 0.0001). This increase with years was not as apparent in the semen quality traits measured. By using the BSE and a minimum SC to select prospective herd sires, the proportion of bulls passing the BSE is expected to increase in subsequent generations. Santa Gertrudis bulls can be reliably selected for use as herd sires at 16 mo of age.     

The impact of intralacustrine introductions with regard to space utilization and competition for territories to a cichlid fish community in Lake Malawi,Africa

At Thumbi Island West in Lake Malawi, a number of cichlid species was introduced from elsewhere in the lake some 20 years ago. These are now, in part, well established and could have an effect on the indigenous fish fauna. Repeated removals of the males of the introduced species from their territories were undertaken and artificial miniature reefs were established to find out whether the emptied existing territories or the newly established potential territories would be occupied by indigenous species. The results show that the emptied territories were almost invariably re-occupied by either a male of the introduced species conspecific to the previous territory holder or they remained empty. The newly established miniature reefs were not occupied by territorial males of either introduced or indigenous species but by young fish of a variety of species.     

The distribution and abundance of wheat roots in a dense,structured subsoil – implications for water uptake

We analysed the abundance, spatial distribution and soil contact of wheat roots in dense, structured subsoil to determine whether incomplete extraction of subsoil water was due to root system limitations. Intact soil cores were collected to 1.6 m below wheat crops at maturity on a red Kandosol in southern Australia. Wheat roots, remnant roots, soil pores and root–soil contact were quantified at fresh breaks in the soil cores. In surface soil layers (<0.6 m) 30–40% of roots were clumped within pores and cracks in the soil, increasing to 85–100% in the subsoil (>0.6 m), where 44% of roots were in pores with at least three other roots. Most pores contained no roots, with occupancy declining from 20% in surface layers to 5% in subsoil. Wheat roots clumped into pores contacted the surrounding soil via numerous root hairs, whereas roots in cracks were appressed to the soil surface and had very few root hairs. Calculations assuming good root–soil contact indicated that root density was sufficient to extract available subsoil water, suggesting that uptake is constrained at the root–soil interface. To increase extraction of subsoil water, genetic targets could include increasing root–soil contact with denser root hairs, and increasing root proliferation to utilize existing soil pores.     

The <Emphasis Type="Italic">CLCA</Emphasis> gene locus as a modulator of the gastrointestinal basic defect in cystic fibrosis

To determine whether the CLCA gene family of calcium-activated chloride channels is a modulator of the basic defect of cystic fibrosis (CF), an association study was performed with polymorphic microsatellite markers covering a 40-Mbp region spanning the CLCA gene locus on human chromosome 1p in CF patients displaying CF transmembrane conductance regulator (CFTR)-independent residual chloride conductance in gastrointestinal epithelia. Statistically significant association of the electrophysiological phenotype with the allele distribution of markers 5 of and within the CLCA locus was observed. Transmission disequilibrium and the significance of the association decreased within the locus from hCLCA2 towards hCLCA4. Expression of hCLCA1 and hCLCA4 in human rectal mucosa was proven by microarray analysis. The CLCA gene region was identified to encode mediators of DIDS-sensitive anion conductance in the human gastrointestinal tract that modulate the CF basic defect.     

Amino acids as a nitrogen source for tomato seedlings: The use of dual-labeled (C, N) glycine to test for direct uptake by tomato seedlings

Direct uptake of organic nitrogen (ON) compounds, rather than inorganic N, by plant roots has been hypothesized to constitute a significant pathway for plant nutrition. The aim of this study was to test whether tomatoes (Solanum lycopersicum cv. Huying932) can take up ON directly from the soil by using ¹⁵NH₄Cl, K¹⁵NO₃, 1, 2-¹³C₂¹⁵N-glycine labeling techniques. The ¹³C and ¹⁵N in the plants increased significantly indicating that a portion of the glycine-N was taken up in the form of intact amino acids by the tomatoes within 48 h after injection into the soil. Regression analysis of excess ¹³C against excess ¹⁵N showed that approximately 21% of the supplied glycine-N was taken up intact by the tomatoes. Atom% excesses of ¹⁵N and ¹³C in the roots were higher than in any shoots. Results also indicated rapid turnover of amino acids (e.g., glycine) by soil microorganisms, and the poor competitive ability of tomatoes in absorbing amino acids from the soil solution. This implies that tomatoes can take up ON in an intact form from the soil despite the rapid turnover of organic N usually found under such conditions. Given the influence of climatic change and N pollution, further studies investigating the functional ecological implications of ON in horticultural ecosystems are warranted.