Self-organized asymmetries in ant foraging: a functional response to food type and colony needs

The dominant paradigm to explain asymmetries in the spatialdistribution of foraging animals is that they track the spatialheterogeneity of their environment. However, in social insects,endogenous spatial asymmetries can emerge within a uniformenvironment as an outcome from the self-organizing processof trail recruitment. We studied how self-organized asymmetries contribute to the exploitation of different food sources (carbohydrateor proteins) in colonies of the aphid-tending ant Lasius nigervarying in their nutritional needs (presence or absence ofbrood). Colonies with brood fed on sucrose sources exhibita higher mobilization of foragers than the other experimentalgroups. Foraging patterns differ greatly according to food type: colonies strongly focus their activity on only one dropletof sucrose, whereas they show a rather homogeneous distributionof foragers between proteinaceous sources. In addition, thepresence of brood in the colony enhances the asymmetry of collectiveforaging for both types of food. These spatial differencesin self-organized foraging patterns allow efficient exploitationof natural resources and play a role in the competitive strategy of this widespread palearctic ant.     

Some size relationships in phytoflagellate motility

Data from the literature are used to assess some hypothesised adaptive advantages of the flagellate life form among phytoplankton. Possible advantages include increased nutrient uptake by movement through a homogeneous medium as opposed to exploitation of spatial hetrogeneity of the environment. Maximal migrational amplitudes and maximal swimming velocities of phytoflagellates were compared to body size. Both were found to increase with size. Relative amplitudes and relative velocities, however, were found to decrease with size. Hydrophysical considerations show that additional gain of nutrients by swimming through a homogeneous medium is only minimal for small flagellates at their attainable swimming velocities. It is suggested that exploitation of environmental heterogeneity in nutrient distribution may be one of the most important advantages for flagellates over coccoid algae.     

Local Perspectives on Environmental Insecurity and Its Influence on Illegal Biodiversity Exploitation

Environmental insecurity is a source and outcome of biodiversity declines and social conflict. One challenge to scaling insecurity reduction policies is that empirical evidence about local attitudes is overwhelmingly missing. We set three objectives: determine how local people rank risk associated with different sources of environmental insecurity; assess perceptions of environmental insecurity, biodiversity exploitation, myths of nature and risk management preferences; and explore relationships between perceptions and biodiversity exploitation. We conducted interviews (N = 88) with residents of Madagascar’s Torotorofotsy Protected Area, 2014. Risk perceptions had a moderate effect on perceptions of environmental insecurity. We found no effects of environmental insecurity on biodiversity exploitation. Results offer one if not the first exploration of local perceptions of illegal biodiversity exploitation and environmental security. Local people’s perception of risk seriousness associated with illegal biodiversity exploitation such as lemur hunting (low overall) may not reflect perceptions of policy-makers (considered to be high). Discord is a key entry point for attention.     

Food stealing in cockroaches

Relationships between food stealing and exploitation of main food sources were investigated in the German cockroach,Blattella germanica (L.) (Dictyoptera: Blattellidae). The occurrence of food stealing during food exploitation was associated with the course of depletion of the main food sources and not with spatial distribution or distance from shelter. Stolen pieces of food always appeared towards the end of exploitation of a food source. Their occurrence appeared to be a consequence of the exploitation of a food source rather than a specific strategy. The proportion of animals of different developmental stages observed with stolen pieces differed significantly from that in the general population. There were proportionally more males, females and large larvae and proportionally less small larvae with stolen pieces than on the main food source. These data suggest that stolen pieces appeared when competition for access to food increased, and that larger cockroaches (adults and larger larvae) were then dominant and benefited from monopolizing stolen pieces of food.     

Exploiting volatile organic compounds in crop protection: A systematic review of 1-octen-3-ol and 3-octanone

The 21st century has brought new challenges to the agri-food industry due to population growth, global warming, and greater public awareness of environmental issues. Ensuring global food security for future generations is crucial. However, pests, weeds, and diseases still significantly contribute to crop losses, and the availability of effective conventional synthetic pesticides is decreasing. To address this, new and diverse pest management tools are needed. One pest management tool showing potential for invertebrate pest management is the exploitation of volatile organic compounds (VOCs)—in particular, the compounds 1-octen-3-ol and 3-octanone. This review aims to explore the extent to which 1-octen-3-ol and 3-octanone show potential in the future management of invertebrate crop and animal pests. A significant increase in the rate of publication of literature on the use of 1-octen-3-ol and 3-octanone in crop protection since 2018 is identified by this review, therefore, showing the potential importance of these compounds for use in future pest management. This review also identifies key interactions between naturally occurring biosynthesised 1-octen-3-ol and 3-octanone, and a range of invertebrate targets. Many of these interactions with key crop pests are sourced from the taxonomic families Lamiaceae, Fabaceae, and Trichomaceae. However, analysis of the practical application of these sources in an integrated pest management programme identifies clear limitations with the use of naturally occurring biosynthesised 1-octen-3-ol and 3-octanone. Rather, future focus should be placed on the development and exploitation of synthesised nature identical 1-octen-3-ol and 3-octanone for use as a biopesticide product. Overall, 1-octen-3-ol and 3-octanone show potential for exploitation in future crop protection, being abundant in source and diversity of invertebrate interactions. However, their use as a naturally occurring biosynthesised chemical is likely not practical for direct implementation in crop protection. Rather, focus should be placed on the development and exploitation of synthesised nature identical variants of these compounds for use as a biopesticide.     

Near-field absorption in a circular cylinder from electric and magnetic line sources

A homogeneous, lossy circular cylinder is used as a simple model of a biological object in which interior heating is produced by the absorption of electromagnetic waves. For this model, we determined the optimum frequency, polarization, orientation and shape of applicators. Analytical and numerical results are given for both electric and magnetic line sources, with three different polarizations relative to the cylinder. Coupling efficiencies and contour plots are presented for a range of parameters. One particularly interesting result is the production of maximum energy deposition at the center of a cylinder of muscle tissue when exposed in the 100-MHz frequency range by the use of four applicators surrounding the cylinder.     

Nectar exploitation by herbivores and their parasitoids is a function of flower species and relative humidity

In conservation biological control, diversification of the agro ecosystem with flowering vegetation is seen as an important tool to support the broad range of predators and parasitoids that require nectar and pollen sources to survive and reproduce. In order to identify flowering plants that provide suitable food sources for natural enemies without supporting the pest species, we analyzed the exploitation of 19 flowering plants by two important lepidopteran cabbage pests, Pieris rapae and Plutella xylostella, and their hymenopteran parasitoids, Cotesia glomerata and Diadegma semiclausum. The experiments were conducted at 90% r.h., while Pieris rapae was tested both at 45% r.h. and at 90% r.h. At 45 ± 5% r.h., corresponding with field conditions at which P. rapae is predominantly active, the butterfly was unable to feed on a number of exposed floral nectar sources whose nectar was successfully exploited at 90% r.h. The broader nectar exploitation by P. rapae at the high humidity is presumably explained by the resulting decrease in nectar viscosity. When comparing D. semiclausum and its herbivorous host P. xylostella, the herbivore exploited a broader range of plants. However, those plants that benefited both the parasitoid and the herbivore had a much stronger effect on the longevity of the parasitoid. The results from the accessibility bioassay suggest that flowers where nectar is not accessible can have a negative impact on insect survival presumably by stimulating foraging without providing accessible nectar. Our results underline the importance of considering species-specific environmental conditions when fine-tuning the choice of nectar sources to be used in conservation biological control programs.     

How does resource supply affect evolutionary diversification?

The availability of different resources in the environment can affect the outcomes of evolutionary diversification. A unimodal distribution of diversity with resource supply has been widely observed and explained previously in the context of selection acting in a spatially heterogeneous environment. Here, we propose an alternative mechanism to explain the relationship between resource supply and diversification that is based on selection for exploitation of different resources. To test this mechanism, we conducted a selection experiment using the bacterium Pseudomonas fluorescens in spatially homogeneous environments over a wide range of resource supply rates. Our results show that niche diversification peaks at intermediate levels of resource availability. We suggest that this unimodal relationship is due to evolutionary diversification that is driven by competition for resources but constrained by the ecological opportunity represented by different resource types. These processes may underlie some general patterns of diversity, including latitudinal gradients in species richness and the effects of anthropogenic enrichment of the environment.     

Out of sight but not out of mind: modulation of recruitment according to home range marking in ants

Animals can acquire a global knowledge about their environment that exceeds their individual capacities by estimating the local density and activity of nestmates in an area. In ants, home range marking can indicate the density and activity of nestmates, allowing scouts to assess the potential interest of the area as a foraging site. We investigated how home range marking through footprints influences the foraging behaviour of Lasius niger scouts at a sugary food source (1 M, 1.5 ml). Over a marked apparatus the discovery time of food sources decreased while the probability of scouts recruiting nestmates and of continuing to lay a trail increased. For ants making U turns on their return to the nest, home range marking helped them to resume laying a trail after the U turn and delayed the occurrence of the U turn. As a result, the trail intensity and the rate at which information about food was conveyed by scouts to nestmates depended on home range marking. Such modulation of information reduces the number of foragers mobilized to less frequented areas that are potentially dangerous and promotes recruitment and exploitation of food sources to better known sites.     

New insights into virulence evolution in multigroup hosts

Many of the standard predictions in evolutionary epidemiology result from models in which all hosts are equally susceptible to acquiring an infection and equally capable of resisting pathogens once an infection has been established. This contrasts with the empirical reality that natural host populations are typically composed of individuals with various susceptibilities and vulnerabilities to pathogen exploitation that can influence all aspects of a given pathogen's transmission-virulence phenotype. In these structured host settings, host-dependent variation in the virulence-transmission trade-off plays an important role in determining pathogen evolution. By deriving some game-theoretic equilibrium expressions that describe pathogen evolution in heterogeneous host populations, the contribution of host heterogeneity to the direction of evolution in host exploitation is made explicit. Within this framework, qualitative departures from predictions derived from theory utilizing a homogeneous host assumption can be seen as a manifestation of Simpson's paradox in an evolutionary setting. By reconsidering some predictions from homogeneous host theory through the lens of this new perspective, it can be seen that many standard predictions are actually special cases that result when homogeneity in immunity parameters is imposed on host populations.     

大庆油田开发中石油类污染物对地下水环境影响模拟分析

分析了大庆市龙南油田开发建设工程对地下水环境的污染来源及污染途径,针对本油田工程工艺分析的特点,建立了石油类污染物在地下水环境中迁移、转化的数学模型,模型中考虑了石油类污染物的降解性和较强的吸附性,推导了连续源情况下地下水中石类污染物运移解析式并进行了预测分析,从而为油田开发建设工程环境影响评价提供了重要依据。     

Ambiguity of the solution of the inverse problem of electroencephalography

It has been shown for homogeneous conducting medium that if different stationary distributions of current sources form identical potential fields on the plane boundary, the difference between these two distributions is the distribution of current sources with all multiple moments equaling zero. Examples of current source distributions are presented which satisfy this condition.     

Ants as biological indicators of human impact in mangroves of the southeastern coast of Bahia, Brazil

Mangroves are common in estuaries along the Atlantic coast of Brazil. Although plant diversity is low, this ecosystem supports a range of animals, offering some resources for non-aquatic organisms. Many insects live in mangroves and, between them, many ant species that are exclusively arboreous. Mangroves throughout the world suffer from high levels of human impact, and this is particularly true for southeastern Bahia, where land-uses include traditional crab and fish exploitation, urban development, refuse pollution, recreation, and timber extraction. The ants of 13 mangrove sites, representing a range of levels of human use, have been studied along 250 km of the southern Bahia littoral, between Itacaré and Porto Seguro. Ants were sampled both inside and on the periphery of the tidal zone, using entomological rainbow, baiting, collect of hollow branches and pit-fall. A total of 108 species have been collected, with the richest genera being Camponotus and Pseudomyrmex, and the most frequent belonging to the genera Azteca and Crematogaster. The ant community living on the periphery of mangrove areas is rather homogeneous regardless of the degree of environmental perturbation, but varies markedly with the disturbance inside the mangroves themselves. The evolution of richness of the both communities, mangrove and periphery, is negatively related to the human effects, even limited to the periphery. Ant communities therefore have the potential to be useful as biological indicators of ecological impacts of land-use in these mangrove systems.     

Spatial Genetic Structure Patterns of Phenotype-Limited and Boundary-Limited Expanding Populations: A Simulation Study

Range expansions may create a unique spatial genetic pattern characterized by alternate genetically homogeneous domains and allele frequency clines. Previous attempts to model range expansions have mainly focused on the loss of genetic diversity during expansions. Using individual-based models, we examined spatial genetic patterns under two expansion scenarios, boundary-limited range expansions (BLRE) and phenotype-limited range expansions (PhLRE). Our simulation revealed that the genetic diversity within populations lost quickly during the range expansion, while the genetic difference accumulated between populations. Consequently, accompanying the expansions, the overall diversity featured a slow decrease. Specifically, during BLREs, high speed of boundary motion facilitated the maintenance of total genetic diversity and sharpened genetic clines. Very slight constraints on boundary motion of BLREs drastically narrowed the homogeneous domains and increased the allele frequency fluctuations from those levels exhibited by PhLREs. Even stronger constraints, however, surprisingly brought the width of homogeneous domains and the allele frequency fluctuations back to the normal levels of PhLREs. Furthermore, high migration rates maintained a higher total genetic diversity than low ones did during PhLREs. Whereas, the total genetic diversities during BLREs showed a contrary pattern: higher when migration was low than those when migration was high. Besides, the increase of migration rates helped maintain a greater number of homogeneous domains during PhLREs, but their effects on the number of homogeneous domains during BLREs were not monotonous. Previous studies have showed that the homogenous domains can merge to form a few broad domains as the expansion went on, leading to fewer homogeneous domains. Our simulations, meanwhile, revealed that the range expansions could also rebuild homogeneous domains from the clines during the range expansion. It is possible that that the number of homogeneous domains was determined by the interaction of merging and newly emerging homogeneous domains.     

Traffic dynamics of the leaf-cutting ant, Atta cephalotes

Colonies of Atta cephalotes (Myrmicinae: Formicidae) construct cleared paths between their nest and the vegetation sources at which they harvest leaf tissue. Here, we employ ideas from traffic engineering to study streams of laden and unladen ants on these paths. The relationship between average traffic speed and the concentration of workers on the road surface follows a relationship similar to what is expected by analogy to fluid dynamics. Although the traffic is composed of eusocial organisms with a common interest in group success, the coarse-grained behavior of Atta traffic displays little more coordination than a moving fluid. The relationship between speed and concentration implies that maximum flow rates (which are likely to be closely tied to colony-level rates of resource acquisition) occur at a relatively high concentration that keeps individual speeds well below their "free flow" maximum. We predict that this optimal concentration will characterize peak traffic throughout a trail network, and we propose a simple behavioral mechanism that would allow trails to be cleared to the correct width to provide the optimal concentration. Collisions (including encounters for antennation) are common in leaf-cutting ant traffic because traffic is not segregated into unidirectional streams. Nonetheless, we find a counterintuitive suggestion that flow rates (with concentration differences statistically removed) are higher when traffic is near a 50:50 mix of outbound and returning ants than when it contains majority flows in a single direction. Mixed-direction traffic may help disperse laden ants with reduced agility, thereby preventing inhomogeneities in the traffic stream that could clog the trail.     

Summary of measured radiofrequency electric and magnetic fields (10 kHz to 30 GHz) in the general and work environment

We have plotted data from a number of studies on the range of radiofrequency (RF) field levels associated with a variety of environmental and occupational sources. Field intensity is shown in units of volts/meter (V/m) for electric field strength and amps/meter (A/m) for magnetic field strength. Duty factors, modulation frequencies, and modulation indices are also reported for some sources. This paper is organized into seven sections, each cataloging sources into appropriate RF frequency bands from very-low frequency (VLF) to super-high frequency (SHF), and covers frequencies from 10 kHz to 30 GHz. Sources included in this summary are the following: Coast Guard navigational transmitters, a Navy VLF transmitter, computer visual display terminals (VDTs), induction stoves or range tops, industrial induction and dielectric heaters, radio and television broadcast transmitters, amateur and citizens band (CB) transmitters, medical diathermy and electrosurgical units, mobile and handheld transmitters, cordless and cellular telephones, microwave ovens, microwave terrestrial relay and satellite uplinks, and police, air traffic, and aircraft onboard radars. For the sources included in this summary, the strongest fields are found near industrial induction and dielectric heaters, and close to the radiating elements or transmitter leads of high power antenna systems. Handheld transmitters can produce near fields of about 500 V/m at the antenna. Fields in the general urban environment are principally associated with radio and TV broadcast services and measure about 0.1 V/m root-mean-square (rms). Peak fields from air traffic radars sampled in one urban environment were about 10 V/m, 300 times greater than the rms value of 0.03 V/m when the duty factor associated with antenna rotation and pulsing are factored in. Bioelectromagnetics 18: 563–577, 1997. Published 1997 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

To be or not to be faithful: flexible fidelity to foraging trails in the leaf‐cutting ant Acromyrmex lobicornis

1. Ants using trails to forage have to select between two alternative routes at bifurcations, using two, potentially conflicting, sources of information to make their decision: individual experience to return to a previous successful foraging site (i.e. fidelity) and ant traffic. In the field, we investigated which of these two types of information individuals of the leaf‐cutting ant Acromyrmex lobicornis Emery use to decide which foraging route to take. 2. We measured the proportion of foraging ants returning to each trail of bifurcations the following day, and for 4–7 consecutive days. We then experimentally increased ant traffic on one trail of the bifurcation by adding additional food sources to examine the effect of increased ant traffic on the decision that ants make. 3. Binomial tests showed that for 62% of the trails, ant fidelity was relatively more important than ant traffic in deciding which bifurcation to follow, suggesting the importance of previous experience. 4. When information conflict was generated by experimentally increasing ant traffic along the trail with less foraging activity, most ants relied on ant traffic to decide. However, in 33% of these bifurcations, ants were still faithful to their trail. Thus, there is some degree of flexibility in the decisions that A. lobicornis make to access food resources. 5. This flexible fidelity results in individual variation in the response of workers to different levels of ant traffic, and allows the colony to simultaneously exploit both established and recently discovered food patches, aiding efficient food gathering.     

Under-reporting of road traffic mortality in developing countries: application of a capture-recapture statistical model to refine mortality estimates

Road traffic injuries are a major cause of preventable death in sub-Saharan Africa. Accurate epidemiologic data are scarce and under-reporting from primary data sources is common. Our objectives were to estimate the incidence of road traffic deaths in Malawi using capture-recapture statistical analysis and determine what future efforts will best improve upon this estimate. Our capture-recapture model combined primary data from both police and hospital-based registries over a one year period (July 2008 to June 2009). The mortality incidences from the primary data sources were 0.075 and 0.051 deaths/1000 person-years, respectively. Using capture-recapture analysis, the combined incidence of road traffic deaths ranged 0.192-0.209 deaths/1000 person-years. Additionally, police data were more likely to include victims who were male, drivers or pedestrians, and victims from incidents with greater than one vehicle involved. We concluded that capture-recapture analysis is a good tool to estimate the incidence of road traffic deaths, and that capture-recapture analysis overcomes limitations of incomplete data sources. The World Health Organization estimated incidence of road traffic deaths for Malawi utilizing a binomial regression model and survey data and found a similar estimate despite strikingly different methods, suggesting both approaches are valid. Further research should seek to improve capture-recapture data through utilization of more than two data sources and improving accuracy of matches by minimizing missing data, application of geographic information systems, and use of names and civil registration numbers if available.     

Patch Exploitation,Patch-leaving and Pre-emptive Patch Defence in the Parasitoid Wasp Trissolcus basalis (Insecta: Scelionidae)

Female parasitoids forage for host resources essential to the development of their offspring, so patch exploitation decisions have a direct influence on their fitness. This paper analyses the patch exploitation behaviour and patch-leaving decisions of the parasitoid wasp Trissolcus basalis (Hymenoptera: Scelionidae), when searching alone on patches of host eggs in the laboratory. Oviposition behaviour was examined in detail and the temporal and sequential structure of patch exploitation was analysed. Time inhomogeneities representing major behavioural change points during patch visits were identified, and the behavioural sequence within homogeneous periods was summarised. As the patch neared full depletion, wasps switched from a repetitive cycle of host examination and oviposition to a ‘leaving routine’, in which they alternated between searching on and off the patch, before abruptly leaving it. Despite the absence of competitors, females remained on the patch for up to 5 h after initiating the leaving routine, and periodically interrupted it to engage in bouts of active patch defence. Such pre-emptive patch defence was more pronounced when the patch was larger and the resource value therefore greater. This unique patch-leaving strategy is interpreted as an adaptation to high levels of resource competition and the consequent risk of losing offspring through superparasitism by competitors.     

Feature Selection via Chaotic Antlion Optimization

Background

Selecting a subset of relevant properties from a large set of features that describe a dataset is a challenging machine learning task. In biology, for instance, the advances in the available technologies enable the generation of a very large number of biomarkers that describe the data. Choosing the more informative markers along with performing a high-accuracy classification over the data can be a daunting task, particularly if the data are high dimensional. An often adopted approach is to formulate the feature selection problem as a biobjective optimization problem, with the aim of maximizing the performance of the data analysis model (the quality of the data training fitting) while minimizing the number of features used.

Results

We propose an optimization approach for the feature selection problem that considers a “chaotic” version of the antlion optimizer method, a nature-inspired algorithm that mimics the hunting mechanism of antlions in nature. The balance between exploration of the search space and exploitation of the best solutions is a challenge in multi-objective optimization. The exploration/exploitation rate is controlled by the parameter I that limits the random walk range of the ants/prey. This variable is increased iteratively in a quasi-linear manner to decrease the exploration rate as the optimization progresses. The quasi-linear decrease in the variable I may lead to immature convergence in some cases and trapping in local minima in other cases. The chaotic system proposed here attempts to improve the tradeoff between exploration and exploitation. The methodology is evaluated using different chaotic maps on a number of feature selection datasets. To ensure generality, we used ten biological datasets, but we also used other types of data from various sources. The results are compared with the particle swarm optimizer and with genetic algorithm variants for feature selection using a set of quality metrics.