Know thine enemy: why some weaver ants do but others do not

Recognition systems involve 3 components: an expression component, a perception component, and an action or response component. Disentangling the perception component from the action component can be difficult, as the absence of a discriminatory response may result from either a difference in perception or action. Social insects generally defend their colony against intruding conspecifics and provide a useful model for exploring recognition systems. However, whether differences in behavior at the colony or individual level result from the perception or action component of the recognition system is largely unknown. Furthermore, variation at the individual level has remained largely unexplored because research on social insects often focuses on the colony rather than on the individual. Using some novel behavioral bioassays, we here show that variation in the aggressive behavior of individual weaver ants (Oecophylla smaragdina L.) arises more from the identity of the recipient than of the intruder and, contrary to previous findings, that this often results from perceptual differences. We suggest that recognition in weaver ants may involve a template based on the individual’s odor prior to intermingling with other odors rather than on a common odor. We also argue that a common odor might be more important for the survival of the colony than a shared template. Conversely, possessing a range of templates may provide a colony with additional fitness benefits. By focusing on the differences among individual workers within colonies, this study reveals complexities in nest mate recognition that might otherwise have gone unnoticed

Tests for exponentiality against NBUE alternatives: a Monte Carlo comparison

Testing of various classes of life distributions has been addressed in the literature for more than 45 years. In this paper, we consider the problem of testing exponentiality (which essentially implies no ageing) against positive ageing which is captured by the fairly large class of new better than used in expectation (NBUE) distributions. These tests of exponentiality against NBUE alternatives are discussed and compared. The empirical size of the tests is obtained by simulations. Power comparisons for different popular alternatives are done using Monte Carlo simulations. These comparisons are made for both small and large sample sizes. The paper concludes with a discussion in which suggestions are made regarding the choices of the test when a particular alternative is suspected

Reminiscences on Influential Papers

Reminiscences on Parallel evaluation of multi-join queries. (Proc. SIGMOD Conf. 1995), Annita Wilschut, Jan Flokstra, Peter M.G. Apers

Evolution of nesting habitats and metapleural glands in ants

The metapleural gland is a unique and complex structure located on the propodeum of ants. Given its function in immune defence against microbes, it has undoubtedly played an important role in the ecological success of ants by enforcing colony hygiene and preventing diseases. Although this gland has an important antimicrobial function, it has been lost several times. It has been proposed that these losses are due to a shift in nesting habit, i.e. ants living in trees can afford to loose the metapleural gland because this environment harbours fewer microbes. Here we test this idea, the 'Arboreality Hypothesis', by constructing a phylogeny for 48 formicine ant species using eight markers (nuclear and mitochondrial) and Bayesian tree building methods. Character mapping for the presence/absence of the gland and nesting habitat was carried out with SIMMAP including 1000 trees from the posterior distribution of the MCMC run. Our results show several independent losses and regains of the metapleural gland across the subfamily. We also find a significant correlation between the two traits, suggesting that the 'Arboreality Hypothesis' can indeed explain the pattern of presence/absence of the metapleural gland in this group of ants

Incomplete penetrance: the role of stochasticity in developmental cell colonization

Available online: 3 June 2015Cell colonization during embryonic development involves cells migrating and proliferating over growing tissues. Unsuccessful colonization, resulting from genetic causes, can result in various birth defects. However not all individuals with the same mutation show the disease. This is termed incomplete penetrance, and it even extends to discordancy in monozygotic (identical) twins. A one-dimensional agent-based model of cell migration and proliferation within a growing tissue is presented, where the position of every cell is recorded at any time. We develop a new model that approximates this agent-based process – rather than requiring the precise configuration of cells within the tissue, the new model records the total number of cells, the position of the most advanced cell, and then invokes an approximation for how the cells are distributed. The probability mass function (PMF) for the most advanced cell is obtained for both the agent-based model and its approximation. The two PMFs compare extremely well, but using the approximation is computationally faster. Success or failure of colonization is probabilistic. For example for sufficiently high proliferation rate the colonization is assured. However, if the proliferation rate is sufficiently low, there will be a lower, say 50%, chance of success. These results provide insights into the puzzle of incomplete penetrance of a disease phenotype, especially in monozygotic twins. Indeed, stochastic cell behavior (amplified by disease-causing mutations) within the colonization process may play a key role in incomplete penetrance, rather than differences in genes, their expression or environmental conditions.Benjamin J. Binder, Kerry A. Landman, Donald F. Newgreen, Joshua V. Ros

Twin Paradox and the logical foundation of relativity theory

We study the foundation of space-time theory in the framework of first-order logic (FOL). Since the foundation of mathematics has been successfully carried through (via set theory) in FOL, it is not entirely impossible to do the same for space-time theory (or relativity). First we recall a simple and streamlined FOL-axiomatization SpecRel of special relativity from the literature. SpecRel is complete with respect to questions about inertial motion. Then we ask ourselves whether we can prove usual relativistic properties of accelerated motion (e.g., clocks in acceleration) in SpecRel. As it turns out, this is practically equivalent to asking whether SpecRel is strong enough to "handle" (or treat) accelerated observers. We show that there is a mathematical principle called induction (IND) coming from real analysis which needs to be added to SpecRel in order to handle situations involving relativistic acceleration. We present an extended version AccRel of SpecRel which is strong enough to handle accelerated motion, in particular, accelerated observers. Among others, we show that the Twin Paradox becomes provable in AccRel, but it is not provable without IND.Comment: 24 pages, 6 figure

Quasi two dimensional spin correlations in the triangular lattice bilayer spin glass LuCoGaO4

We present a single crystal time of flight neutron scattering study of the static and dynamic spin correlations in LuCoGaO4, a quasi two dimensional dilute triangular lattice antiferromagnetic spin glass material. This system is based on Co2 ions that are randomly distributed on triangular bilayers within the YbFe2O4 type, hexagonal crystal structure. Antiferromagnetic short range two dimensional correlations at wave vectors Q 1 3,1 3,L develop within the bilayers at temperatures as high as TCW amp; 8764; 100 K and extend over roughly five unit cells at temperatures below Tg 19 K. These two dimensional static correlations are observed as diffuse rods of neutron scattering intensity along c and display a continuous spin freezing process in their energy dependence. Aside from exhibiting these typical spin glass characteristics, this insulating material reveals a novel gapped magnetic resonant spin excitation at E amp; 8764; 12 meV localized around Q 1 3,1 3,L . The temperature dependence of the spin gap associated with this two dimensional excitation correlates with the evolution of the static correlations into the spin glass state ground state.We associate it with the effect of the staggered exchange field acting on the Seff 1 2 Ising like doublet of the Co2 moment

Spatio-Temporal Dynamics of Caddisflies in Streams of Southern Western Ghats

The dynamics of physico-chemical factors and their effects on caddisfly communities were examined in 29 streams of southern Western Ghats. Monthly samples were collected from the Thadaganachiamman stream of Sirumalai Hills, Tamil Nadu from May 2006 to April 2007. Southwest and northeast monsoons favored the existence of caddisfly population in streams. A total of 20 caddisfly taxa were collected from 29 streams of southern Western Ghats. Hydropsyche (Trichoptera: Hydropsychidae) were more widely distributed throughout sampling sites than were the other taxa. Canonical correspondence analysis showed that elevation was a major variable and pH, stream order, and stream substrates were minor variables affecting taxa richness. These results suggested that habitat heterogeneity and seasonal changes were stronger predictors of caddisfly assemblages than large-scale patterns in landscape diversity