A hybrid behavioural rule of adaptation and drift explains the emergent architecture of antagonistic networks

Ecological processes that can realistically account for network architectures are central to our understanding of how species assemble and function in ecosystems. Consumer species are constantly selecting and adjusting which resource species are to be exploited in an antagonistic network. Here we incorporate a hybrid behavioural rule of adaptive interaction switching and random drift into a bipartite network model. Predictions are insensitive to the model parameters and the initial network structures, and agree extremely well with the observed levels of modularity, nestedness and node-degree distributions for 61 real networks. Evolutionary and community assemblage histories only indirectly affect network structure by defining the size and complexity of ecological networks, whereas adaptive interaction switching and random drift carve out the details of network architecture at the faster ecological time scale. The hybrid behavioural rule of both adaptation and drift could well be the key processes for structure emergence in real ecological networks.     

Root responses to legume plants integrate information on nitrogen availability and neighbour identity

Rhizobial symbiosis is known to increase the nitrogen availability in the rhizosphere of legumes. Therefore, it has been hypothesized that other plants’ roots should forage towards legume neighbours, but avoid non-legume neighbours. Yet, root distribution responding to legume plants as opposed to non-legumes has not yet been rigorously tested and might well be subject to integration of multiple environmental cues.In this study, wedevised an outdoor mesocosm experiment to examine root distributions of the two plant species Pilosella officinarum and Arenaria serpyllifolia in a two-factorial design. While one factor was ‘neighbour identity’, where plants were exposed to different legume or non-legume neighbours, the other factor was ‘nitrogen supply’. In the latter the nutrient-poor soil was supplemented with either nitrogen-free or with nitrogen-containing fertilizer.Unexpectedly, of all treatments that included a legume neighbour (eight different species or factor combinations), we found merely one case of root aggregation towards a legume neighbour (P. officinarum towards Medicago minima under nitrogen-fertilized conditions). In this very treatment, also P. officinarum root–shoot allocation was strongly increased, indicating that neighbour recognition is coupled with a contesting strategy.Considering the various response modes of the tested species towards the different legume and non-legume neighbours, we can conclude that roots integrate information on neighbour identity and resource availability in a complex manner. Especially the integration of neighbour identity in root decisions must be a vital aptitude for plants to cope with their complex biotic and abiotic environment in the field.     

Effects of the Addition of Humic Substances on Soil Protease Activities in Andosols in the Presence of Cadmium

Cadmium extraction, sorption, and immobilization seem to be the effective mechanisms in detoxification of Cd-contaminated soil. Humic substances present in soils may play an important role both in controlling the negative effects of pollution with Cd and in stabilizing soil enzymes. In this context, we have compared the effects of humic substances on soil protease activities in the presence and absence of Cd in forest and cultivated field soil samples. The samples were taken from surface soils of Andosols in a single upland area of the Kanto district in Japan. Humic substances extracted from the two soils showed differences in elemental composition, the degree of condensation of aromatic groups, and the proportions of major functional groups. Compared with the control soil samples, those with added humic substances showed a significant increase in protease activities, even in the presence of Cd (10 and 50 mg Cd kg^?1 soil). However, the addition of Cd decreased the protease activities, protein contents, and soil pH in both soil samples at each of the two levels of humic substance fortification (+5% and +10%). Moreover, protease activities showed significant negative correlation with exchangeable Cd, but adding humic substances did not lead to a reduction in either sample. Thus, although the addition of humic substances increased and stabilized protease activities, it did not lead to a clear reversal of enzyme inhibition by Cd. The obtained results indicate that in both soil samples the humic substances used in this study did not have sufficient affinity to adsorb Cd, and the impact on enzyme activities depends on the difference in chemical characteristics of the added organic matter, as suggested by the difference in enhancement of protease activities between forest and cultivated field soil samples.     

Size‐correlated morpho‐physiology of the aroid vine Rhodospatha oblongata along a vertical gradient in a Brazilian rain forest

In this work, we analyse morpho‐physiological modifications presented during the allomorphic growth of the aroid vine Rhodospatha oblongata Poepp throughout its ascent into the forest canopy. We test the hypothesis that morphological modifications in the root, shoot and leaf are followed by a gradual improvement of the xylem vascular system in order to increase water acquisition and transport as body size increases. The characterisation of these structural modifications was based on 30–35 specimens divided into six size classes. The dimensions of shoots, leaves and roots were quantified and qualified. The transition from the terrestrial to the epiphytic phase was followed by a simultaneous increase of leaf number and lamina area, together with increased length and diameter of the petiole. Furthermore, as the plant grows, the shoot internodes become shorter and thicker. However, occurrence of aerial roots is the most important characteristic in the ascending phase. In taller individuals, the increase in number of roots with wider xylem vessels guarantees an increased theoretical xylem hydraulic conductance for this growth phase. Along an acropetal direction of the same shoot, the diameter of xylem vessels increased, while the number of vessels per stele area decreased, in contrast with such allometric models as that of West, Brown and Enquist, showing that xylem vessel number and diameter taper in a reverse manner along the same direction. Such structural changes of R. oblongata allow improved foraging for light and water, facilitating the survival of bigger‐sized plants of this vine in the canopy.     

Identification of gonadotropic and antigonadotropic factors from the nervous part of the corpora cardiaca in the African locust

Summary

The nervous part of the locust corpora cardiaca (NCC) was extracted using 70% methanol and subjected to fast protein liquid chromatography (FPLC). Twenty fractions were collected and injected into females from the end of the IIIrd larval instar to day-12 of the adult life to screen the effects on metamorphosis, body pigmentation, and oocyte growth. The rate of juvenile hormone (JH) biosynthesis by the corpora allata of injected animals was evaluated in vitro. One fraction was found to stimulate ovarian maturation, and 3 to delay oocyte growth. None of them disturbed (i) either metamorphosis and body color (which are JH dependent), or (ii) rate of JH biosynthesis. Of the 3 fractions which inhibited ovarian maturation, 2 of them were identified as the neuroparsins A and B. The results clearly illustrate that antagonist factors from the brain are involved in the regulation of ovarian maturation in the locust.     

The importance of location and visual cues during foraging in the German wasp (Vespula germanica F.) (Hymenoptera: Vespidae)

Abstract

The way in which foraging wasps use cues for prey location and choice appears to depend on both the context and on the type of prey. Vespula germanica is an opportunistic, generalist prey forager, and individual wasp foragers often return to hunt at sites of previous hunting success. In this paper, we studied which cues are used by this wasp when relocating a food source. Particularly we analysed the response to a displaced visual cue versus a foraging location at which either honey or cat food had been previously presented. We conclude that location is used over a displaced visual cue for directing wasp hovering, although the landing response is directed differently according to bait type. When wasps are exploiting cat food, location also elicits landing, but if they are exploiting honey, a displaced visual cue elicits landing more frequently than location.     

Tool use by aquatic animals

Tool-use research has focused primarily on land-based animals, with less consideration given to aquatic animals and the environmental challenges and conditions they face. Here, we review aquatic tool use and examine the contributing ecological, physiological, cognitive and social factors. Tool use among aquatic animals is rare but taxonomically diverse, occurring in fish, cephalopods, mammals, crabs, urchins and possibly gastropods. While additional research is required, the scarcity of tool use can likely be attributable to the characteristics of aquatic habitats, which are generally not conducive to tool use. Nonetheless, studying tool use by aquatic animals provides insights into the conditions that promote and inhibit tool-use behaviour across biomes. Like land-based tool users, aquatic animals tend to find tools on the substrate and use tools during foraging. However, unlike on land, tool users in water often use other animals (and their products) and water itself as a tool. Among sea otters and dolphins, the two aquatic tool users studied in greatest detail, some individuals specialize in tool use, which is vertically socially transmitted possibly because of their long dependency periods. In all, the contrasts between aquatic- and land-based tool users enlighten our understanding of the adaptive value of tool-use behaviour.     

α-Tocospiro C,a novel cytotoxic α-tocopheroid from Cirsium setosum

α-Tocospiro C (1), the first example of nor-α-tocopheroid possessing unusual 7,8-dimethyl-1-oxaspiro[4.4]non-7-ene-6,9-dione carbon skeleton, was isolated and characterized from Cirsium setosum. Its structure and absolute configuration were determined by extensive spectroscopic methods, especially 2D NMR and ECD data analysis. The biosynthetic pathway was postulated. α-Tocospiro C (1) exhibited significant selective cytotoxic activities against human colon cancer (HCT8) cells, with IC₅₀ values of 0.03 μM.     

Intersexual variation in the foraging ecology of sexually monochromatic Western Wood‐Pewees

ABSTRACT Investigators generally pool observations of males and females in studies of the foraging behavior of sexually monochromatic songbirds. However, such pooling can obscure possible intersexual differences. We compared the foraging behavior of male and female Western Wood‐Pewees (Contopus sordidulus), a sexually monochromatic species, in the Sierra Nevada Mountains of California during the breeding seasons of 2007 and 2008. We recorded 143 foraging observations (male N= 74, female N= 69). Overall, mean foraging rates of females (2.8 attacks/min) were higher (P < 0.001) than those of males (1.1 attacks/min). In addition, female foraging rates were significantly higher during incubation than during the nest building, nestling, and fledgling periods. When foraging, males perched higher above ground than females (means = 17.1 and 6.7 m, respectively). Differences between male and female Western Wood‐Pewees in foraging rates and perch heights suggest that males may spend more time on vigilance while females focus on foraging quickly during incubation and when feeding nestlings. Because metrics such as foraging attack rates are sometimes used as indicators of habitat quality and we found that rates can differ between the sexes and among nesting stages, investigators should consider the possibility of such differences when assessing habitat quality, especially for sexually monochromatic species of birds.     

Metabolic control at the cytosol–mitochondria interface in different growth phases of CHO cells

Metabolism at the cytosol–mitochondria interface and its regulation is of major importance particularly for efficient production of biopharmaceuticals in Chinese hamster ovary (CHO) cells but also in many diseases. We used a novel systems-oriented approach combining dynamic metabolic flux analysis and determination of compartmental enzyme activities to obtain systems level information with functional, spatial and temporal resolution. Integrating these multiple levels of information, we were able to investigate the interaction of glycolysis and TCA cycle and its metabolic control. We characterized metabolic phases in CHO batch cultivation and assessed metabolic efficiency extending the concept of metabolic ratios. Comparing in situ enzyme activities including their compartmental localization with in vivo metabolic fluxes, we were able to identify limiting steps in glycolysis and TCA cycle. Our data point to a significant contribution of substrate channeling to glycolytic regulation. We show how glycolytic channeling heavily affects the availability of pyruvate for the mitochondria. Finally, we show that the activities of transaminases and anaplerotic enzymes are tailored to permit a balanced supply of pyruvate and oxaloacetate to the TCA cycle in the respective metabolic states. We demonstrate that knowledge about metabolic control can be gained by correlating in vivo metabolic flux dynamics with time and space resolved in situ enzyme activities.