Asexual queen succession mediates an accelerated colony life cycle in the termite Silvestritermes minutus.

Mixed modes of reproduction, combining sexual processes with thelytokous parthenogenesis, occur in all major clades of social insects. In several species of termites, queens maximize their genetic input into nondispersing replacement queens through parthenogenesis, while maintaining genetically diverse sterile offspring and dispersing reproductives via sexual reproduction. This so-called asexual queen succession (AQS) has multiple independent origins and its presumed advantages are diverse as well, ranging from multiplication of colony reproductive potential to extension of its lifespan beyond that of the foundress. However, how AQS shapes colony life cycles under natural conditions remains poorly known. The neotropical termite Silvestritermes minutus inhabits small but conspicuous nests, offering a unique opportunity to investigate the impact of AQS on life history. We report on its breeding system, life cycle and sex allocation using social structure census in 137 nests and genotyping of 12 colonies at 12 microsatellite loci. We show that colonies are established by an outbred pair of primary reproductives. In less than 2 years, the foundress is replaced by multiple neotenic queens, arising mostly through automixis with central fusion. Sterile castes, male and most (93%) female dispersers are produced sexually. Colony reproduction is usually restricted to a single dispersal of alates with unbiased sex ratio, taking place after 3 years. We conclude that S. minutus benefits from AQS to maximize colony growth rate and alate production within a very short life cycle rather than to extend colony lifespan. This highlights the versatile role of AQS in different cases of its polyphyletic origin.

Adaptive dynamics of cuticular hydrocarbons in Drosophila.

Cuticular hydrocarbons (CHCs) are hydrophobic compounds deposited on the arthropod cuticle that are of functional significance with respect to stress tolerance, social interactions and mating dynamics. We characterized CHC profiles in natural populations of Drosophila melanogaster at five levels: across a latitudinal transect in the eastern United States, as a function of developmental temperature during culture, across seasonal time in replicate years, and as a function of rapid evolution in experimental mesocosms in the field. Furthermore, we also characterized spatial and temporal changes in allele frequencies for SNPs in genes that are associated with the production and chemical profile of CHCs. Our data demonstrate a striking degree of parallelism for clinal and seasonal variation in CHCs in this taxon; CHC profiles also demonstrate significant plasticity in response to rearing temperature, and the observed patterns of plasticity parallel the spatiotemporal patterns observed in nature. We find that these congruent shifts in CHC profiles across time and space are also mirrored by predictable shifts in allele frequencies at SNPs associated with CHC chain length. Finally, we observed rapid and predictable evolution of CHC profiles in experimental mesocosms in the field. Together, these data strongly suggest that CHC profiles respond rapidly and adaptively to environmental parameters that covary with latitude and season, and that this response reflects the process of local adaptation in natural populations of D. melanogaster.

Explosive backpacks in old termite workers.

By nature, defensive behavior is risky. In social insects, such behavior is more likely to occur in individuals whose potential for other tasks is diminished. We show that workers of the termite Neocapritermes taracua develop an exceptional two-component suicidal apparatus consisting of copper-containing protein crystals, stored in external pouches, and internal salivary glands. During aggressive encounters, their bodies rupture, and the crystals react with the salivary gland secretion to produce a toxic droplet. Both the amount of defensive substances and the readiness to explode increase with workers' age, as their food-collecting ability declines.

Parametric uncertainties and influence of the dead volume representation in modelling simulated moving bed separation processes.

In this study, a systematic numerical procedure for identifying the model parameters of simulated moving bed (SMB) separation processes is developed. The parameters are first estimated by minimizing a weighted least-squares criterion using experimental data from batch experiments, e.g. the time evolution of the concentration of elution peaks. Then, a cross-validation is achieved using data from experiments in SMB operation. At this stage, the importance of a careful modelling of the dead volumes within the SMB process is highlighted. In addition, confidence intervals on the estimated parameters and on the predicted concentration profiles are evaluated.

Respiratory concerts revealed by scanning microrespirography in a termite Prorhinotermes simplex (Isoptera: Rhinotermitidae).

Respiratory metabolism of different developmental stages (larvae, pseudergates, nymphs, soldiers, neotenic reproductives; 0.6-4.5 mg body mass) of Prorhinotermes simplex was individually monitored by scanning respirographic method sensitive to subnanoliter amounts of O(2) consumption or CO(2) output per minute. Specimens exposed to dry air after removal from the colony performed enormously large, discontinuous bursts of CO(2) lasting usually 2 min. The volume of CO(2) produced during the burst often surpassed the volume of the whole body and it was 10- to 20-fold in excess of the air-filled endogenous tracheal volume. The initial velocity of CO(2) production during the burst was more than 90-fold faster in comparison to O(2) consumption. In the presence of enough moisture within the respiratory vessel, the termites breathed continuously without any larger outburst of CO(2). This fact fully corroborates validity of the so-called water retention theory in discontinuous CO(2) release. The highest rates of O(2) consumption were found in the second instar larvae (0.9 mg, 1000-2000 microl O(2)/g/h), the soldier caste was intermediate (700 microl O(2)/g/h) while pseudergates and neotenic reproductives consumed between 300 and 600 microl O(2)/g/h, at 25 degrees C. All developmental stages feeding on a cellulose diet had CO(2)/O(2) values (RQ) over 1 (1.2-1.4, i.e. carbohydrate metabolism), pigmented soldiers fed by the workers had RQ around 0.75 (predominating lipid or protein metabolism). The unusually large, sudden eruptions of CO(2) in specimens exposed to dry air allow us to make the following conclusions: (1) the bursts were due to special chemical processes, such as by enzymatic hydration of carbonic acid by carbonic anhydrase and; (2) the bulk of chemically evolved gaseous CO(2) escaped from the body by a mass flow supported by active ventilation, not by a passive diffusion. These results demonstrated that the periodic emissions of CO(2) and the associated homeostatic regulation of the respiratory acidaemia were under perfect physiological control. The termites could thus actively select the type of CO(2) release best suited to the extant environmental or internal physiological conditions, i.e. from a completely continuous respiration to occasionally cyclic or completely discontinuous CO(2) release.

Ultrastructure of epidermal glands in neotenic reproductives of the termite Prorhinotermes simplex (Isoptera: Rhinotermitidae).

The ultrastructure of epidermal glands in neotenic reproductives of Prorhinotermes simplex is described and their development is compared among young and old neotenics of both sexes. Secretory cells forming the epidermal gland are attached to the cuticle all over the body. The glands are formed by class 1 and class 3 secretory cells and corresponding canal cells with secretory function. Class 1 cells are sandglass-like and class 3 secretory units are located among them. Class 1 cells contain predominantly tubular endoplasmic reticulum, the major part represents the smooth and the minor the rough form. Numerous electron dense granules occur in the cytoplasm, they are always disintegrated prior to be released. Class 3 secretory cells contain a large amount of vacuoles, which are always lucent in males while newly produced vacuoles are dense in females. Dense vacuoles are frequently transformed into lucent ones before being released. Canal cells are locally equipped with microvilli. The conducting canal is surrounded by an electron dense secretion of regular inner structure. The cytoplasm of the canal cell contains numerous mitochondria, rough endoplasmic reticulum and a large proportion of microtubules. The young neotenic reproductives differ from the old ones by a lower amount of secretory products. Epidermal glands probably produce substances inhibiting the occurrence of superfluous reproductives.

Stability parameter estimation at ambient temperature from studies at elevated temperatures.

The determination of specific kinetic constants k(i) in pH-profile studies is often undertaken at ambient temperature. However, when dealing with a drug substance that is stable at ambient temperature, the pH-profile study is conducted at a chosen elevated temperature and the kinetic parameters are given at this particular elevated temperature. But in stability studies we generally need kinetic constants at ambient or storage temperature for practical reasons (information and storage conditions of formulation). To assess this ambient kinetic information from studies at elevated temperatures, cumulative sequential steps are usually employed with very few statistical concerns on the final estimates. The statistical problems on these final estimates in cumulative procedures are highlighted in many papers. Because these stability parameters are useful for drug formulation and storage conditions, good practical decisions have to be made on the basis of statistically unbiased identified parameters. We propose in this paper a nonlinear model that allows the direct determination of specific activation energies E(ai) that are linked to the specific kinetic constants k(i). Hence, a mathematical relationship between drug concentration C, pH, temperature T, and time t is obtained. Kinetic data from acetylsalicylic acid (ASA) hydrolysis (first-order kinetics) are used to validate the model. The results show that it is possible to obtain directly, by an extrapolation procedure, the kinetic parameters (specific kinetic constants k(i), specific activation energies E(ai), and dissociation constant pK(a)) at low temperature from data gathered at elevated temperatures using more meaningful statistics.

Improved kinetic parameter estimation in pH-profile data treatment.

Statistical problems in temperature stability parameter estimation have been the subject of many papers whereas statistics in, pH-profile parameter estimation have focused little attention. However, the conventional two step method used in data treatment in both cases leads to identical statistical problems. The aim of this study is then to introduce a method that improves statistics in pH-profile parameter estimation. A one step non-linear method that takes into account the errors in drug content determination is proposed. A mathematical relationship between drug content C, pH and time t is tested. The proposed method allows the estimation of the specific kinetic constants and the dissociation constant (pK(a)) in a single run. The most likely experimental initial drug contents C(0j),. where j is the index of a given experiment, are also determined. This approach that takes into account all relevant experimental information for the estimation of kinetic parameters is more rigorous from a statistical viewpoint than the classical two step methods. Kinetic data from acetylsalicylic acid (ASA) hydrolysis was used for the tests.

Incorporating batch effects in the estimation of drug stability parameters using an Arrhenius model.

The nonlinear estimation of drug stability parameters (energy of activation Ea and shelf-life tY) by conventional approaches employs equations relating drug content determination C at time t and temperature T. The identification procedures lead to the determination of only one initial drug content C0 for several different experiments. However, it is well known that because of experimental concentration variation or of intentional modification of the experimental schedule, there are as many initial drug contents as experiments. For these reasons, a method which takes into account batch effects is proposed to determine stability parameters and also all initial drug contents C0j where j is the index of experiment in one step. This method is more accurate from a statistical viewpoint and is suitable for data treatment in pharmaceutical industries where the initial drug content of each batch entering the stability program can be checked a posteriori. The application of this method is shown on real kinetic data from the hydrolysis of acetylsalicylic acid (ASA).

Multidrug resistance modifies polyamines uptake in P388 murine lymphoma cells: experimental and modeling approach.

Polyamines (putrescine, spermidine and spermine) are ubiquitous compounds, essential for cell growth. This paper compares the polyamine transport between sensitive P388 murine lymphoma cells and two multidrug resistant P388 sublines with the assistance of an experimental model. This new model allows the characterisation of the whole polyamines uptake and efflux. Three parameters are identified by the model: two rate constants (K+ for the uptake and K- for the efflux) which are considered as physical constants specific to the transport of one polyamine in one cell type, and Ci(o) which represents the initial intracellular concentration. This model well describes our experimental results of polyamine transport across the P388 cell plasma membrane. Multidrug resistant P388 cells exhibit spermine uptake significantly higher than that of sensitive cells when on the opposite, putrescine enters more rapidly into the sensitive P388 cells. In conclusion, comparison of polyamine transport between sensitive and multidrug resistant P388 phenotypes shows large and significant differences.