Movement patterns, social dynamics, and the evolution of cooperation

The structure of social interactions influences many aspects of social life, including the spread of information and behavior, and the evolution of social phenotypes. After dispersal, organisms move around throughout their lives, and the patterns of their movement influence their social encounters over the course of their lifespan. Though both space and mobility are known to influence social evolution, there is little analysis of the influence of specific movement patterns on evolutionary dynamics. We explored the effects of random movement strategies on the evolution of cooperation using an agent-based prisoner’s dilemma model with mobile agents. This is the first systematic analysis of a model in which cooperators and defectors can use different random movement strategies, which we chose to fall on a spectrum between highly exploratory and highly restricted in their search tendencies. Because limited dispersal and restrictions to local neighborhood size are known to influence the ability of cooperators to effectively assort, we also assessed the robustness of our findings with respect to dispersal and local capacity constraints. We show that differences in patterns of movement can dramatically influence the likelihood of cooperator success, and that the effects of different movement patterns are sensitive to environmental assumptions about offspring dispersal and local space constraints. Since local interactions implicitly generate dynamic social interaction networks, we also measured the average number of unique and total interactions over a lifetime and considered how these emergent network dynamics helped explain the results. This work extends what is known about mobility and the evolution of cooperation, and also has general implications for social models with randomly moving agents.     

Nest architecture of a bagworm species: Rhythmic pattern in the arrangement of sticks

Nest architecture of a bagworm species,Clania crameri was examined. Fortytwo bags (nests) were collected from the host plant,Clerodendron indicum and number of sticks used in each bag was counted. Furthermore, length of each stick in each nest was measured (in mm) clockwise one after another serially beginning with the longest stick. The data obtained were subjected to frequency analysis and power spectrum analysis. Results clearly reveal that the larvae of bagworms do not glue together sticks of different size randomly but with a definite pattern.     

Plant architecture and meristem dynamics as the mechanisms determining the diversity of gall-inducing insects

Plant architecture is considered to affect herbivory intensity, but it is one of the least studied factors in plant–insect interactions, especially for gall-inducing insects. This study aimed to investigate the influence of plant architecture on the speciose fauna of gall-inducing insects associated with 17 species of Baccharis. Five architectural variables were evaluated: plant height, number of fourth-level shoots, biomass, average level and number of ramifications. The number of galling species associated with each host plant species was also determined. To test the effects of plant architecture on gall richness at the individual level, we used another data set where the number of fourth-level shoots and gall richness were determined for B. concinna, B. dracunculifolia, and B. ramosissima every 3 weeks during 1 year. The average similarity between host species based on gall fauna was low (9%), but plants with the same architectural pattern tended to support similar gall communities. The most important architectural trait influencing gall richness at the species level was the number of fourth-level shoots, which is indicative of the availability of plant meristems, a fundamental tissue for gall induction and development. This variable also showed a positive correlation with gall richness at the individual level. We propose that variations in gall richness among host species are driven by interspecific differences in plant architecture via availability of young, undifferentiated tissue, which is genetically controlled by the strength of the apical dominance. Plant architecture should have evolutionary consequences for gall communities, promoting insect radiation among architecturally similar plants through host shift and sympatric speciation. We also discuss the role of plant architecture in the global biogeography of gall-inducing insects. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Integrative models of bat rabies immunology, epizootiology and disease demography

Bats are natural reservoirs of rabies. We address the maintenance of the disease in bat colonies by developing individual and population models that generate indicators of risk of rabies to bats, that provide dynamic estimates of effects of rabies on population densities, and that suggest consequences of viral exposures and infections in bats relative to physiological and ecological characteristics of bats in different habitats. We present individual models (within host) for the immune responses to a rabies virus challenge, an immunotypic disease model that describes the evolution of the disease and a disease demographics model, which is structured by immunotypic response governed by immune system efficiency. Model simulations are consistent with available data, characterized by relatively low prevalence of the virus in colonies and much higher prevalence of rabies virus-neutralizing antibodies. Under model conditions, there is a robust non-clinical state that can be attained by the exposed individual that allows persistence of the disease in the population.     

Colony size,social complexity and reproductive conflict in social insects

The broad limits of mature colony size in social insect species are likely to be set by ecological factors. However, any change in colony size has a number of important social consequences. The most fundamental is a change in the expected reproductive potential of workers. If colony size rises, workers experience a fall in their chances of becoming replacement reproductives and, it is shown, increasing selection for mutual inhibition of one another's reproduction (worker policing). As workers’ reproductive potential falls, the degree of dimorphism between reproductive and worker castes (morphological skew) can rise. This helps explain why small societies have low morphological skew and tend to be simple in organization, whereas large societies have high morphological skew and tend to be complex. The social consequences of change in colony size may also alter colony size itself in a process of positive feedback. For these reasons, small societies should be characterized by intense, direct conflict over reproduction and caste determination. By contrast, conflict in large societies should predominantly be over brood composition, and members of these societies should be relatively compliant to manipulation of their caste. Colony size therefore deserves fuller recognition as a key determinant, along with kin structure, of social complexity, the reproductive potential of helpers, the degree of caste differentiation, and the nature of within-group conflict.     

Nest architecture in the western harvester ant,Pogonomyrmex occidentalis (Cresson)

Summary The structure and thermal environment produced by the nest cones of the western harvester ant,Pogonomyrmex occidentalis, are investigated. The nest cone is oriented so that the longest slope faces towards the southeast ad the nest entrance faces the southeast. The temperature of the soil was monitored at thirty-six locations within the nest in order to measure the daily temperature change as a function of depth, aspect and radial distance from the center of peak of the cone. The occupancy of the nest cone by workers and by brood was assessed by core samples taken at different times of day in different portions of the cone. The brood are only present during the midmorning sample and are present in greatest numbers on the eastern side of the cone. The adult workers are present in the cone in highest numbers during the midmorning, virtually absent from the cone during mid-afternoon and returning in smaller numbers at dusk, apparently spending the night near the surface on the eastern side of the mound. The eastern and southern portions of the cone are occupied most frequently while the western side of the cone is nearly vacant. The nest cone is an adaptation which magnifies the amplitude of daily temperature fluctation. By moving to appropriate areas of the nest cone, the ants can take advantage of the increased range of temperature.     

Changes in activity,spatial pattern and social behavior in calves after grouping

The behavior of 2 groups of 6 calves that were managed in 2 different ways were observed, and the development of their behavioral patterns, spatial patterns and social behavior in the groups were discussed, together with the effect on these processes of their social experience before grouping.Twelve 5-month-old Holstein steers, reared alone from one week of age, were divided into 2 groups of 6 calves each; Groups A and B. Calves in Group A were penned together in a 14.4 × 28.8 m pen, and the position and behavior of individuals was observed throughout a continuous 153-h period at 15-min intervals. Aggressive behavior between calves was also recorded. The position of calves was recorded as coordinates on a grid on the pen floor. There were 8 × 16 squares in the grid, and each square measured 1.8 × 1.8 m.Group B was further divided into 3 groups of 2 calves each, which were kept in 9.6 × 14.4 m pens. The pair-mates were changed every 3 days in order to combine all possible pairs in the group. After this treatment, calves were all housed together in a 14.4 × 28.8 m pen, and observed using the same methods and for the same duration as Group A.The lying pattern of Group A was not diurnal until the latter half of the observation, while calves in Group B showed clear-cut diurnal variations from the initial stages. Concerning the spatial patterns; the mean distance to nearest neighbor in Group A tended to decrease and become stable. The ratio between the mean distance to nearest neighbor and the distance expected in random distribution also declined from 0.7 to a significant aggregation of 0.5 (P < 0.05). For Group B, a similar change in the mean distance to the nearest neighbor was observed, although this showed significant aggregation from the first 24-h period (P < 0.05). The mean area occupied by a group in each 24-h period, for both groups, declined for 72 h after grouping and became stable at around 18 m², for both groups, thereafter. The frequency of aggression in Group A declined from 23 times in the first 24-h period to 9 times at the end of the observation period. For Group B, the aggression frequency was 53 times in the first 24-h period, thereafter decreasing rapidly.     

Spatial heterogeneity, social structure and disease dynamics of animal populations

Social groupings, population dynamics and population movements of animals all give rise to spatio-temporal variations in population levels. These variations may be of crucial importance when considering the spread of infectious diseases since infection levels do not increase unless there is a sufficient pool of susceptible individuals. This paper explores the impact of social groupings on the potential for an endemic disease to develop in a spatially explicit model system. Analysis of the model demonstrates that the explicit inclusion of space allows asymmetry between groups to arise when this was not possible in the equivalent spatially homogeneous system. Moreover, differences in movement behaviours for susceptible and infected individuals gives rise to different spatial profiles for the populations. These profiles were not observed in previous work on an epidemic system. The results are discussed in an ecological context with reference to furious and dumb strains of infectious diseases.     

The chikungunya disease: modeling, vector and transmission global dynamics

Models for the transmission of the chikungunya virus to human population are discussed. The chikungunya virus is an alpha arbovirus, first identified in 1953. It is transmitted by Aedes mosquitoes and is responsible for a little documented uncommon acute tropical disease. Models describing the mosquito population dynamics and the virus transmission to the human population are discussed. Global analysis of equilibria are given, which use on the one hand Lyapunov functions and on the other hand results of the theory of competitive systems and stability of periodic orbits.     

Sex-biased dispersal, haplodiploidy and the evolution of helping in social insects

In his famous haplodiploidy hypothesis, W. D. Hamilton proposed that high sister-sister relatedness facilitates the evolution of kin-selected reproductive altruism among Hymenopteran females. Subsequent analyses, however, suggested that haplodiploidy cannot promote altruism unless altruists capitalize on relatedness asymmetries by helping to raise offspring whose sex ratio is more female-biased than the population at large. Here, we show that haplodiploidy is in fact more favourable than is diploidy to the evolution of reproductive altruism on the part of females, provided only that dispersal is male-biased (no sex-ratio bias or active kin discrimination is required). The effect is strong, and applies to the evolution both of sterile female helpers and of helping among breeding females. Moreover, a review of existing data suggests that female philopatry and non-local mating are widespread among nest-building Hymenoptera. We thus conclude that Hamilton was correct in his claim that 'family relationships in the Hymenoptera are potentially very favourable to the evolution of reproductive altruism'.     

Modeling the transmission dynamics and control of hepatitis B virus in China

Hepatitis B is a potentially life-threatening liver infection caused by the hepatitis B virus (HBV) and is a major global health problem. HBV is the most common serious viral infection and a leading cause of death in mainland China. Around 130 million people in China are carriers of HBV, almost a third of the people infected with HBV worldwide and about 10% of the general population in the country; among them 30 million are chronically infected. Every year, 300,000 people die from HBV-related diseases in China, accounting for 40-50% of HBV-related deaths worldwide. Despite an effective vaccination program for newborn babies since the 1990s, which has reduced chronic HBV infection in children, the incidence of hepatitis B is still increasing in China. We propose a mathematical model to understand the transmission dynamics and prevalence of HBV infection in China. Based on the data reported by the Ministry of Health of China, the model provides an approximate estimate of the basic reproduction number R₀=2.406. This indicates that hepatitis B is endemic in China and is approaching its equilibrium with the current immunization program and control measures. Although China made a great progress in increasing coverage among infants with hepatitis B vaccine, it has a long and hard battle to fight in order to significantly reduce the incidence and eventually eradicate the virus.     

Non-linear transmission rates and the dynamics of infectious disease.

This study considers how non-linearities in the transmission of microparasitic infections affect the population dynamics of host-parasite systems in which the disease is potentially lethal to the host. Non-linearities can either lead to a locally stable or unstable host-parasite equilibrium point, depending on the respective contributions of healthy and infected hosts to the functional form of the transmission rate. Analysis of the non-linear transmission model results in a revealing pair of local stability criteria. Specifically, stability requires sufficient total levels of intrinsic growth of the host population and total levels of density-dependent transmission. The most stable systems occur when increases in the density of healthy hosts result in increases in transmission efficiency, and increases in the number of infected hosts result in small decreases in transmission efficiency. These appear to be very reasonable relationships for directly transmitted microparasites.     

Computational insights into the binding pattern of mitochondrial calcium uniporter inhibitor through homology modeling,molecular dynamics simulation,binding free energy prediction and density functional theory calculation

Abstract

The mitochondrial calcium uniporter (MCU) is the critical protein of the inner mitochondrial membrane that is the primary mediator for calcium uptake into the mitochondrial matrix. Herein we built the optimal homology model of human MCU which was refined through all-atom molecular dynamics simulation. Then, the binding mode of known inhibitor was predicted through molecular docking method, along with molecular dynamics simulation and binding free energy calculation to verify the docking result and stability of the protein-inhibitor complex. Finally, density functional theory (DFT) calculation enhanced our understanding of the molecular interaction of MCU inhibitor. Our research would provide a deeper insight into the interactions between human MCU and its inhibitor, which boosts to develop novel therapy against MCU related disease.

Communicated by Ramaswamy H. Sarma     

Influence of landscape and social interactions on transmission of disease in a social cervid

The mechanisms of pathogen transmission are often social behaviours. These occur at local scales and are affected by landscape-scale population structure. Host populations frequently exist in patchy and isolated environments that create a continuum of genetic and social familiarity. Such variability has an important multispatial effect on pathogen spread. We assessed elk dispersal (i.e. likelihood of interdeme pathogen transmission) through spatially explicit genetic analyses. At a landscape scale, the elk population was composed of one cluster within a southeast-to-northwest cline spanning three spatially discrete subpopulations of elk across two protected areas in Manitoba (Canada). Genetic data are consistent with spatial variability in apparent prevalence of bovine tuberculosis (TB) in elk. Given the existing population structure, between-subpopulation spread of disease because of elk dispersal is unlikely. Furthermore, to better understand the risk of spread and distribution of the TB, we used a combination of close-contact logging biotelemetry and genetic data, which highlights how social intercourse may affect pathogen transmission. Our results indicate that close-contact interaction rate and duration did not covary with genetic relatedness. Thus, direct elk-to-elk transmission of disease is unlikely to be constrained to related individuals. That social intercourse in elk is not limited to familial groups provides some evidence pathogen transmission may be density-dependent. We show that the combination of landscape-scale genetics, relatedness and local-scale social behaviours is a promising approach to understand and predict landscape-level pathogen transmission within our system and within all social ungulate systems affected by transmissible diseases.     

Mating, parasites and other trials of life in social insects

Females of many animal species mate with several different males, despite the extra costs. Recent studies in social insects now suggest that the resulting increase in genotypic variance in offspring is beneficial under selection by parasites. This finding also helps to understand the evolution and maintenance of sexual reproduction.     

The presence of bifidobacteria in social insects,fish and reptiles

The occurrence and species distribution of bifidobacteria in the digestive tract of important representatives of social insects such as ants, bees, wasps and bumblebees as well as the incidence of bifidobacteria in fecal samples of several species of vertebrates representied mainly by reptiles was assigned by culture-independent method based on DGGE and real time PCR. Bifidobacteria were present in the gut of most social insects — honey bees, wasps, cockroaches and bumblebees, except for ants. In honey bees, where the counts of bifidobacteria ranged from 2 to 8 % of the total bacteria, the most common species seemed to be Bifidobacterium indicum. Proportion of bifidobacteria was found in broad range from 0.1 to 35–37 % in wasps and cockroaches; the variance of bifidobacteria in bumblebees was lower, ranging from 1 to 7 % of total bacterial count. Among studied vertebrates, the detectable presence of bifidobacteria was found only in trout (1.1 %) and geckos (0.2 %), but large amount of these bacteria was observed in Vietnamese box turtle, where bifidobacteria represented nearly one-fourth (22 %) of total bacterial counts.     

Nest niche dynamics of Meyer's Parrot Poicephalus meyeri in the Okavango Delta,Botswana

Meyer's Parrot Poicephalus meyeri is the only cavity-nesting bird species that breeds during winter in the Okavango Delta. This is facilitated by exclusive access to arthropod larvae incubating inside and feeding on fruits and pods in their diet. To minimise predation risk and overcome low overnight temperatures they have specialised, non-random nest cavity preferences that restrict them to 4.5% of the available nest cavities in the study area. Here we evaluated the nest niche of Meyer's Parrot by studying the nest tree preferences and ecological context of all nest cavities to determine factors that may restrict breeding success in disturbed or altered habitat. Although specific nest tree preferences were significantly different between host tree species, Meyer's Parrot preferred trees greater than 14 m in height that were in relatively poor condition (e.g. portion of the canopy dead). A comparison of nest tree characteristics (n = 75) and the availability of these tree specifications in a representative sample of the different habitat types (n = 1 129) within the sample area indicated that Meyer's Parrot are dependent on riverine forest, Acacia-Combretum marginal woodland and dry mopane woodland for nesting opportunities. Disturbance to hardwood trees by African elephants Loxodonta africana and fungal attack (e.g. Coriolus versicolor) are likely important dynamics in supporting healthy Meyer's Parrot populations and cavity-nesting bird communities.     

Division of labour and colony efficiency in social insects: effects of interactions between genetic architecture, colony kin structure and rate of perturbations

The efficiency of social insect colonies critically depends on their ability to efficiently allocate workers to the various tasks which need to be performed. While numerous models have investigated the mechanisms allowing an efficient colony response to external changes in the environment and internal perturbations, little attention has been devoted to the genetic architecture underlying task specialization. We used artificial evolution to compare the performances of three simple genetic architectures underlying within-colony variation in response thresholds of workers to five tasks. In the 'deterministic mapping' system, the thresholds of individuals for each of the five tasks is strictly genetically determined. In the second genetic architecture ('probabilistic mapping'), the genes only influence the probability of engaging in one of the tasks. Finally, in the 'dynamic mapping' system, the propensity of workers to engage in one of the five tasks depends not only on their own genotype, but also on the behavioural phenotypes of other colony members. We found that the deterministic mapping system performed well only when colonies consisted of unrelated individuals and were not subjected to perturbations in task allocation. The probabilistic mapping system performed well for colonies of related and unrelated individuals when there were no perturbations. Finally, the dynamic mapping system performed well under all conditions and was much more efficient than the two other mapping systems when there were perturbations. Overall, our simulations reveal that the type of mapping between genotype and individual behaviour greatly influences the dynamics of task specialization and colony productivity. Our simulations also reveal complex interactions between the mode of mapping, level of within-colony relatedness and risk of colony perturbations.