Biotic and abiotic stress effects on nitrogen chemistry in the salt marsh cordgrassSpartina alterniflora (Poaceae)

Summary Planthopper (Insecta: Homoptera) feeding stress induces a senesence-like response in the leaves ofSpartina alterniflora characterized by decreased soluble protein, an increased total amino acid pool, and elevated levels of 10 individual amino acids. Increased proline and tryptophan in response to planthopper feeding could not be fully explained by protein degradation. Low degrees of soil salinity stress resulted in an increased total free amino acid pool and elevated levels of 7 amino acids. Anaerobic soil stress resulted in decreased glutamic acid and increased asparagine. Low salinity and anaerobic stress had no effect on soluble protein levels. Glycinebetaine was not affected by the stresses examined in this study.     

Sediment manganese and biogenic silica as geochemical indicators in estuarine salt marshes of coastal Georgia, USA

Salt-marsh estuarine sediments are not homogeneous. It is obvious that a steady state cannot be assumed if the depositional environments under which salt marshes accumulate change from subtidal through non-vegetated intertidal to vegetated intertidal state during their formation. In addition to these, the supply of sedimentary material depends on the tidal prism which changes as salt marshes are formed. Based on the study of cores collected in the estuarine region of Georgia, USA, it was found that the Mn/Al ratios in sediments of marsh cores change from subtidal through non-vegetated intertidal to vegetated intertidal. The relative variation of biogenic silica preserved in sediments of marsh core reflects the relative supply rate of organic carbon (phytoplankton) produced in the water column to the sediment surface at the time of deposition. In this paper it is proposed that sediment manganese and biogenic silica may be applied as geochemical indicators of changing depositional environments and organic carbon originating from phytoplankton in the estuarine salt marsh sediments.     

Short-term and long-term facilitation of goose grazing by livestock in the Dutch Wadden Sea area

We studied the impact of livestock grazing on the distribution ofBranta bernicla bernicla (Dark-bellied Brent goose) in the Dutch Wadden Sea during spring. It was hypothesized that livestock facilitate short-term (within-season) grazing for geese as well as long-term (over years). Therefore we measured grazing pressure by geese in salt marsh and polder areas that were either grazed (spring-grazed) or ungrazed during spring (summer-grazed). Additionally, we carried out a preference experiment with captive geese to test the preference between spring-grazed and summer-grazed polder swards. We furthermore compared patterns of use by geese between long-term ungrazed and grazed salt marshes. In May, there is a difference in grazing pressure by geese between polder pastures that are grazed or ungrazed during spring. In this month, the ungrazed polder pastures are abandoned and the geese shift to either the grazed polder pastures or to the salt marsh. Vegetation in the polder that had been spring-grazed had a lower canopy height and a higher tiller density than summer-grazed vegetation. The captive geese in the preference experiment showed a clear preference for vegetation that had been spring-grazed by sheep over ungrazed vegetation. Goose grazing pressure was negatively correlated to canopy height, both on the polder and on the salt marsh. Within the plant communities dominated byFestuca rubra andPuccinellia maritima, marshes that were intensively grazed by livestock generally had higher grazing pressure by geese than long-term ungrazed or lightly grazed salt marshes.     

Growth and development of nauplii and copepodites of the estuarine copepod Acartia tonsa from southern Europe (Ria de Aveiro, Portugal) under saturating food conditions

A temperature-dependent growth model is presented for nauplii and copepodites of the estuarine calanoid copepod Acartia tonsa from southern Europe (Portugal). Development was followed from egg to adult in the laboratory at four temperatures (10, 15, 18 and 22°C) and under saturating food conditions (>1,000 μg C l⁻¹). Development times versus incubation temperature were fitted to a Belehradek’s function, showing that development times decreased with increasing incubation temperature: at 10°C, A. tonsa need 40.3 days to reach adult stage, decreasing to 8.9 days when reared at 22°C. ANCOVA (homogeneity of slopes) showed that temperature (P<0.001) and growth phase (P<0.01) had a significant effect on the growth rate. Over the range of temperatures tested in this study, highest weight-specific growth rates were found during naupliar development (NI–NVI) and varied from 0.185 day⁻¹ (10°C) to 0.880 day⁻¹ (22°C) with a Q ₁₀ equal to 3.66. During copepodite growth (CI–CV), the weight-specific growth rates ranged from 0.125 day⁻¹ (10°C) to 0.488 day⁻¹ (22°C) with a Q ₁₀ equal to 3.12. The weight-specific growth rates (g) followed temperature (T) by a linear relationship and described as ln g=−2.962+0.130 T (r ²=0.99, P<0.001) for naupliar stages and ln g=−3.134+0.114T (r ²=0.97, P<0.001) for copepodite stages. By comparing in situ growth rates (juvenile growth and fecundity) for A. tonsa taken from the literature with the temperature-dependent growth model defined here we suggest that the adult females of A. tonsa are more frequently food limited than juveniles.     

Terpenes and phenolics in response to nitrogen fertilization: A test of the carbon/nutrient balance hypothesis

Nitrogen fertilization resulted in a linear increase in the growth ofAbies grandis seedlings, but linear decrease in foliage concentrations of phenolic compounds. These data are consistent with the inverse relationship between growth and production of carbonbased secondary chemicals predicted by the carbon/nutrient balance (CNB) hypothesis. However, in contrast to predictions of the CNB hypothesis, nitrogen fertilization had no effect on foliage terpene concentrations. The results suggest that not all carbon-based chemicals respond in the same manner to environmental variation, and that the carbon/nutrient balance hypothesis does not adequately explain all patterns of environmentally-induced variation in secondary metabolism.     

Integrating soil carbon cycling with that of nitrogen and phosphorus in the watershed model SWAT: Theory and model testing

In this paper we describe and test a sub-model that integrates the cycling of carbon (C), nitrogen (N) and phosphorus (P) in the Soil Water Assessment Tool (SWAT) watershed model. The core of the sub-model is a multi-layer, one-pool soil organic carbon (S_C) algorithm, in which the decomposition rate of S_C and input rate to S_C (through decomposition and humification of residues) depend on the current size of S_C. The organic N and P fluxes are coupled to that of C and depend on the available mineral N and P, and the C:N and N:P ratios of the decomposing pools. Tillage explicitly affects the soil organic matter turnover rate through tool-specific coefficients. Unlike most models, the turnover of soil organic matter does not follow first order kinetics. Each soil layer has a specific maximum capacity to accumulate C or C saturation (S_x) that depends on texture and controls the turnover rate. It is shown in an analytical solution that S_x is a parameter with major influence in the model C dynamics. Testing with a 65-yr data set from the dryland wheat growing region in Oregon shows that the model adequately simulates the S_C dynamics in the topsoil (top 0.3 m) for three different treatments. Three key model parameters, the optimal decomposition and humification rates and a factor controlling the effect of soil moisture and temperature on the decomposition rate, showed low uncertainty as determined by generalized likelihood uncertainty estimation. Nonetheless, the parameter set that provided accurate simulations in the topsoil tended to overestimate S_C in the subsoil, suggesting that a mechanism that expresses at depth might not be represented in the current sub-model structure. The explicit integration of C, N, and P fluxes allows for a more cohesive simulation of nutrient cycling in the SWAT model. The sub-model has to be tested in forestland and rangeland in addition to agricultural land, and in diverse soils with extreme properties such high or low pH, an organic horizon, or volcanic soils.     

Aluminium in tea plantations: mobility in soils and plants, and the influence of nitrogen fertilization

The levels of extractable aluminum (Al) in soils of tea plantations, Al concentrations in tea leaves and the impact of nitrogen fertilization on these two parameters were investigated. In addition, the properties of soils from tea plantations were compared to those from soils of adjacent non-tea fields to evaluate the effect of land use conversion (from non-tea soils to tea soils). Exchangeable Al (extracted in 1 mol l⁻¹ KCl) ranged from 0.03 to 7.32 cmol_c kg⁻¹ in 94 tea fields and decreased rapidly with increasing soil pH. In comparison with non-tea soils, tea soils had a significantly lower pH and exchangeable Mg²⁺ concentration but higher organic matter contents and exchangeable K⁺ concentration. Contents of extractable Al were not different (P > 0.05) between these two soils. The concentrations of Al in mature tea leaves correlated significantly with exchangeable Al in soil samples taken at a depth of 20–40 cm and with exchangeable Al saturations in soil sampled at␣depths of 0–20 and 20–40 cm. In the pot experiment, nitrogen fertilization significantly increased extractable Al levels but decreased soil pH and the levels of exchangeable base cations. Nevertheless, the levels of Al in mature leaves and young shoots were significantly reduced by the application of large amounts of N fertilizer.     

Pyrrolizidine alkaloids between plants and insects: A new chapter of an old story

Summary Among alkaloids the pyrrolizidine alkaloids (PAs) play a unique role in the interactions between plants and adapted insects. InSenecio spp. (Asteraceae) PAs are synthesized in the roots as alkaloidN-oxides which are specifically translocated into shootsvia the phloem-path and channeled to the preferred sites of storage (e.g. inflorescences) where they are stored in the cell vacuoles. In differentSenecio spp. senecionineN-oxide is produced as the common product of biosynthesis, which subsequentlyvia a number of simple but specific reactions is transformed into typical speciesspecific PA-patterns. Insects from diverse taxa sequester PAs for their own defense. Lepidopterans (e.g. arctiids such asTyria jacobaeae andCreatonotos transiens) may hydrolyze plant acquired ester-PAs and convert the resulting necine base into insect-specific PAs by esterification with an acid of their own metabolism. Adapted arctiids and the grasshopperZonocerus take up PAs in the state of the tertiary amine.N-Oxides are reduced in the guts prior to uptake. In the bodies the tertiary PAs are rapidlyN-oxidized by a specific mixed-function oxigenase and are maintained in theN-oxide state. The importance of the reversible interconversion of the nontoxicN-oxide (pro-toxine) into the toxic tertiary alkaloid is discussed as the specific feature of PAs in plant-insect interactions.     

Chromium in intertidal sediments of the Clyde,UK: potential for remobilisation and bioaccumulation

Detailed surveys of intertidal sediments have been performed along the north and south shores of the Inner Clyde estuary, UK. Surface sediment data reveal significant spatial variation in Cr content and an association with major sediment characteristics and location within the estuary. Depth variation for Cr and other heavy metals cannot be explained by variation in major geochemical controls such as grain size and organic matter and highlights the impact of historical contamination on sediment quality. These elevated levels at depth may still have environmental impact through redox-reactivity, in association with iron and manganese. Sequential extraction of sediments and pore water analysis of Cr(VI) and Cr(III) provide detailed information on release potential from the sediments. The implication of Cr mobility for biota in the estuary has been assessed by the analysis of a common marine bivalve, Mytilus edulis (Blue Mussel) and a burrowing polychaete, Nereis diversicolor (rag worm) from a number of survey sites. Bioconcentration factors for Mytilus indicate that the weakly held portion of sediment Cr is available for uptake and in the case of Nereis, bioaccumulation appears to be inhibited by sediment organic matter.     

Loss of organic matter and nutrients from a coastal dune heath in Northwest Denmark caused by fire

The loss of organic matter and nutrients due to a natural fire in a Danish coastal dune heath system (175 ha) was studied for three heath types: dryEmpetrum nigrum heath, moistE. nigrum-Vaccinium uliginosum heath, and wetErica tetralix-Molinia coerulea heath. The highest loss of organic matter, as well as N, P and K, was found in the moist heath (67%, 68%, 20% and 25% respectively). The lowest loss was found in the wet heath (35%, 28%, 14%, and 11% respectively). The loss in the dry heath was intermediate. For the burnt heath in total, loss of organic matter, N, P and K of about 13000, 192, 10 and 6 tons respectively, was estimated. Processes of nutrient loss by fire and regeneration of nutrients are discussed.     

Patterns of brood division and an absence of behavioral plasticity in a neotropical passerine

Studies of parental behavior in various habitats provide an opportunity to gain insight into how different environments may mold strategies of parental care. Brood division by parents has been hypothesized to occur facultatively within and among species. Brood division occurs when each parent cares for specific offspring within a brood. We studied brood division in a neotropical passerine, the western slaty antshrike (Thamnophilus atrinucha). Our results present a unique picture of a highly specialized example of avian brood division. Division was a fixed behavioral pattern in the population studied: all broods divided by fledging and remained divided during the entire post-fledging period. Brood division before fledging, a previously unreported phenomenon, occurred in 40% of nests observed. Parents that preferentially fed a certain offspring (defined as their focal offspring) in the nest fed the same individual after fledging. Each parent fed only its focal offspring in broods of one and two. The male parent cared for the heavier offspring and the first offspring to leave the nest. Siblings were segregated spatially during the time of highest predation risk. These observations suggest that a consistently high risk of predation on offspring has favored initial spatial segregation and inflexibility of brood division behavior in this species. Factors other than predation risk alone may explain the observed patterns of long-term, perfect brood division. Because high predation is common and relatively predictable in the tropics, selection for fixed brood division may be stronger in tropical birds than in the temperate zone.     

Determinants of male spacing behavior in microtines: an experimental manipulation of female spatial distribution and density

Theory on microtine mating systems predicts that male spacing behavior will be related to female spatial and temporal distribution. However, data from a natural population of field voles, Microtus agrestis, indicated a potential influence of female density on the spacing behavior of males. Therefore, I experimentally investigated the relative importance of female density and female spatial distribution for the spacing behavior of males in M. agrestis. Males were radio-tracked in enclosed natural habitats in which females at different densities were placed in two different spatial arrangements: clumped versus even distribution. Female density was the main factor determining male spacing behavior. At the high female density males had smaller home ranges and moved shorter distances between radio-tracking recordings. Also, home ranges were more exclusive at high female density. However, since there was a significant positive correlation between home range size and range overlap, range exclusiveness seemed to be influenced by female density indirectly through the effect of range size. Female spatial distribution, on the other hand, had no influence on male home range exclusiveness.     

Soft song in song sparrows: response of males and females to an enigmatic signal

Low-amplitude “soft song” is used by a variety of songbirds; in some species during aggressive encounters, in others during courtship, and yet others in both these contexts. In song sparrows (Melospiza melodia), soft song has thus far been observed only in aggressive encounters, where its production is a more reliable predictor of attack than any other signaling behavior. We used song playback to test the response of both male and female song sparrows to soft song. The design of the playback experiments took into account the existence of two classes of soft song: crystallized soft song, which consists of song types also found in the broadcast repertoire, and warbled soft song, which consists of less-structured song types not found in the broadcast repertoire. Female song sparrows responded with significantly less courtship display to the playback of crystallized soft song than to that of normal broadcast song, and response to warbled soft song was if anything lower than to that of crystallized soft song. Male song sparrows responded equally aggressively to normal broadcast song as to crystallized soft song, and equally aggressively to warbled soft song as to crystallized soft song. The female results support the conclusion that neither form of soft song functions in courtship. The male results suggest that the reliability of soft song as a signal of aggressive intent is not maintained by a receiver retaliation rule.     

Structure and resilience of the social network in an insect colony as a function of colony size

Social interactions are critical to the organization of worker activities in insect colonies and their consequent ecological success. The structure of this interaction network is therefore crucial to our understanding of colony organization and functioning. In this paper, I study the properties of the interaction network in the colonies of the social wasp Ropalidia marginata. I find that the network is characterized by a uniform connectivity among individuals with increasing heterogeneity as colonies become larger. Important network parameters are found to be correlated with colony size and I investigate how this is reflected in the organization of work in colonies of different sizes. Finally, I test the resilience of these interaction networks by experimental removal of individuals from the colony and discuss the structural properties of the network that are related to resilience in a social network. This contribution is part of the special issue “Social Networks: new perspectives” (Guest Editors: J. Krause, D. Lusseau, and R. James).     

Odour-guided social behaviour in newborn and young cats: an analytical survey

Summary. This article surveys early chemosensory mechanisms regulating behaviour in neonatal and juvenile domestic cats (Felis sylvestris catus). It aims to retrieve material from the available literature which may promote a better understanding of the semiochemical system that supports female-to-kitten exchanges. Studies dealing with the development of olfaction from birth through weaning are presented in three sections. The first aims at locating developmental periods suitable for applying analytical procedures combining behaviour and chemistry. The second section offers a survey of observational and experimental work related to the role of olfaction in the social and feeding behaviour of kittens before weaning. The final section traces the current knowledge on the odour sources and substrates that may be involved in early mother-kitten transactions.     

New insights in analysing parasitoid attracting synomones: early volatile emission and use of stir bar sorptive extraction

Summary. It is well known that feeding by Pieris brassicae caterpillars on cabbage leaves triggers the release of volatiles that attract natural antagonists such as the parasitoid Cotesia glomerata. The temporal dynamics in the emissions of parasitoid attracting volatiles has never been elucidated in this system. In a time course experiment, caterpillar infested leaves attracted the parasitoid within one hour after infestation. At such an early stage of infestation, as much as fifty percent of the parasitoids flew towards the infested plant in a wind tunnel bioassay, while only five percent flew towards the non-infested control plant. Three hours after infestation and later, the response to the volatiles from the infested plant reached its maximum and then continued at a constantly high level for the remaining 14 hours of the experiment. Chemical analyses of volatiles collected from infested leaves at short time intervals during the first 24 hours identified a total of ten compounds, comprising green leaf volatiles, terpenoids, and a nitrile. Significant increase of emission within the first 5 hours following initial herbivory was detected for (Z)-3-hexen-1-ol, (Z)-3-hexen-1-yl acetate, cineole and benzylcyanide. Subsequently, a coupled bioassay-chemical analysis procedure was developed allowing for testing and analyzing the same sample for future identification of the bioactive compounds. This was achieved by using stir bar sorptive extraction for the analysis of solvent extracts of caterpillar-damaged leaves.     

Sex pheromones and their potential role in the evolution of reproductive isolation in small ermine moths (Yponomeutidae)

Summary Sex pheromone communication in the nine European species of small ermine moths (Yponomeuta) is reviewed in regard to the potential role of pheromones in the speciation process. Six of the nine species studied (viz.,Y. evonymellus, Y. cagnagellus, Y. padellus, Y. irrorellus, Y. plumbellus, andY. vigintipunctatus) use a mixture of (E)-11-and (Z)-11-tetradecenyl acetate in different ratios as primary pheromone components, with combinations of tetradecyl acetate, (Z)-9-tetradecenyl acetate, (Z)-11-hexadecenyl acetate and the corresponding alcohols of the acetates as additional pheromone components. Analysis of (Z)- to (E)-11-tetradecenyl acetate ratios produced by individual females of these species demonstrated significant variation among females of all species. However, the ranges of ratios produced byY. cagnagellus, Y. irrorellus, andY. plumbellus, sharing the same host-plant species, spindle tree, did not overlap. Niche separation of all six species mentioned required consideration of at least one additional pheromone component or of temporal aspects. The remaining three species,i.e. Y. malinellus, Y. mahalebellus andY. rorellus, have pheromones that differ qualitatively.Biosynthetic routes to the pheromone components identified are proposed on the basis of fatty acid pheromone precursors found in the pheromone glands. A phylogenetic tree for the genus is constructed based on allozyme frequency data and changes in pheromone composition are superimposed on this tree. We suggest that the ancestral ermine moth pheromone is a mixture of (Z)-11- and (E)-11-tetradecenyl acetate and the corresponding alcohols, and a scenario of how present-day patterns evolved is outlined. The pheromone differences among the three species using spindle tree as their host-plant might have evolved throughreproductive character displacement upon secondary contact between populations that had already diverged genetically in allopatry. Pheromone differences within the so-calledpadellus-complex (includingY. cagnagellus, Y. mahalebellus, Y. malinellus, Y. padellus, andY. rorellus) in which species might have originated sympatrically, may have evolved byreinforcing selection as these species still hybridise and produce viable offspring when confined in cages. The role of pheromones in reproductive isolation amongYponomeuta species is emphasised by (1) the function of pheromone components of some of the species as behavioural antagonists to other species, (2) the cross-attraction under experimental conditions between allochronic species with similar pheromones, and (3) the formation of hybrids in the laboratory between species that are isolated in nature by pheromone differences.     

Levels of polyandry and intracolonial genetic relationships in Apis florea

DNA was extracted from worker and drone pupae of each of five colonies of the dwarf honey bee Apis florea. Polymerase chain reactions (PCR) were conducted on DNA extracts using five sets of primers known to amplify microsatellite loci in A. mellifera. Based on microsatellite allele distributions, queens of the five colonies mated with at least 5–14 drones. This is up to 3 times previous maximum estimates obtained from sperm counts. The discrepancy between sperm count and microsatellite estimates of the number of matings in A. florea suggests that despite direct injection of semen into the spermatheacal duct, either A. florea drones inject only a small proportion of their semen, or queens are able to rapidly expel excess semen after mating. A model of sexual selection (first proposed by Koeniger and Koeniger) is discussed in which males attempt to gain reproductive dominance by increasing ejaculate volume and direct injection of spermatozoa into the spermatheca, while queens attempt to maintain polyandry by retaining only a small fraction of each male's ejaculate. It is shown, at least in this limited sample, that the effective number of matings is lower in A. florea than in A. mellifera.     

Larval behavior of predacious sister-species: orientation,molting site,and survival in Chrysopa

Field and laboratory studies compared two features of larval behavior in a pair of predacious sisterspecies of green lacewings: one (Chrysopa slossonae) a specialist on a single species of colonial aphids (the woolly alder aphid) that occur on branches and trunks of alder trees, the other (C. quadripunctata) a general aphid feeder whose primary prey is dispersed on foliage of diverse types of trees. First, a few hours after hatching, larvae of the two species develop significantly different phototactic responses; the differences correspond well with the spatial distributions of their prey. Most C. slossonae exhibited negative phototaxis, a response that helps move hatchlings inward on alder trees toward the woolly alder aphid colonies, whereas most C. quadripunctata hatchlings showed positive orientation to light, a response that tends to keep them in tree canopies with their prey. Second, in greenhouse experiments, a significantly greater proportion of C. slossonae larvae (second instars) molted within woolly alder aphid colonies and remained with the aphids than did C. quadripunctata larvae. These differences indicate that the specialist larvae have evolved a high degree of behavioral fidelity to their prey. However, larvae (second instars) of the two species that were released near ant-tended woolly alder aphid colonies in the field had similar recovery (= survival) rates. Consequently, natural selection may not act on behavioral traits that influence larval fidelity to prey during the late second and early third instars.