Production of sexuals in a fission-performing ant: Dual effects of queen pheromones and colony size

Models based on the kin selection theory predict that in social hymenopterans, queens may favor a lower investment in the production of sexuals than workers. However, in perennial colonies, this conflict may be tuned down by colony-level selection because of the trade off between colony survival and reproductive allocation. In this study, we present a survey of sexual production in colonies of Aphaenogaster senilis, a common species of ant in the Iberian Peninsula. Similar to most species that reproduce by fission, males were found in large excess compared to gynes (172:1). Sexuals were more likely to be found in queenless than in queenright (QR) field colonies. However, we also found a few gynes and numerous males in very large QR colonies. We compared these data with those available in the literature for A. rudis, a congeneric species from North America that has independent colony founding. The sex ratio in this species was only five males for each female, and sexuals were mostly found in QR nests, irrespective of colony size. We confirmed queen inhibition of sexual production in A. senilis in laboratory experiments and provide evidence that this inhibition is mediated by a nonvolatile pheromone. To seek the potential source of such a queen pheromone, we analyzed the secretions of two conspicuous exocrine glands, the Dufour's and postpharyngeal glands (DG and PPG, respectively) in both queens and workers. Both secretions were composed of hydrocarbons, but that of DG also contained small quantities of tetradecanal and hexadecanal. The hydrocarbon profile of the DG and PPG showed notable caste specificity suggesting a role in caste-related behavior. The PPG secretions also differed between colonies suggesting its role in colony-level recognition. We suggest that in A. senilis, there are two modes of colony fission: First, in very large colonies, gynes are produced, probably because of the dilution of the queen pheromone, and consequently one or more gynes leave the mother colony with workers and brood to found a new nest. This is beneficial at the colony level because it avoids the production of costly sexuals in small colonies. However, because the queen and workers have different optima for sexual production, we hypothesize that queens tend to overproduce the pheromone to delay their production. This in turn may drive workers to leave the mother colony during nest relocation and to produce sexuals once they are away from the queen's influence, creating a second mode of colony fission. © 2007 Springer-Verlag.Peer Reviewe

Experiment selection for the discrimination of semi-quantitative models of dynamical systems

Modeling an experimental system often results in a number of alternative models that are all justified by the available experimental data. To discriminate among these models, additional experiments are needed. Existing methods for the selection of discriminatory experiments in statistics and in artificial intelligence are often based on an entropy criterion, the so-called information increment. A limitation of these methods is that they are not well-adapted to discriminating models of dynamical systems under conditions of limited measurability. Moreover, there are no generic procedures for computing the information increment of an experiment when the models are qualitative or semi-quantitative. This has motivated the development of a method for the selection of experiments to discriminate among semi-quantitative models of dynamical systems. The method has been implemented on top of existing implementations of the qualitative and semi-quantitative simulation techniques QSIM, Q2, and Q3. The applicability of the method to real-world problems is illustrated by means of an example in population biology: the discrimination of four competing models of the growth of phytoplankton in a bioreactor. The models have traditionally been considered equivalent for all practical purposes. Using our model discrimination approach and experimental data we show, however, that two of them are superior for describing phytoplankton growth under a wide range of experimental conditions. (c) 2005 Elsevier B.V. All rights reserved

Behavioural consequences of hypergravity in developing rats

Gravity represents a stable reference for the nervous system. When the individual is increasing in size and weight, gravity may influence several aspects of the sensory and motor developments. To clarify this role, we studied age-dependent modifications of several exteroceptive and proprioceptive reflexes in five groups of rats conceived, born and reared in hypergravity (2 g). Rats were transferred to normal gravity (I g) at P5 (post-natal day 5), P 10, P 15, P21, and P27. Aspects of neural development and adaptation to I g were assessed until P40. Hypergravity induced a delay in growth and a retardation in the development of contact-righting, air-righting, and negative geotaxis. However, we found an advance in eye opening by about 2-3 days in HG-P5 and HG-P10 rats and an increase in grip-time. No differences were found in tail and grasp reflexes. Our results show that hypergravity leads to a retarded development of motor aspects which are mainly dependent upon the vestibular systern. (C) 2004 Elsevier B.V. All rights reserved

Efficient transfer of chromosome-based DNA constructs into mammalian cells

Artificial chromosomes, engineered minichromosomes and other chromosome-based DNA constructs are promising new vectors for use in gene therapy, protein production and transgenics. However, a major drawback in the application of chromosome-based DNA is the lack of a suitable and convenient procedure for large-scale cellular introduction, which is particularly frustrated by their size (1 by 2 mum). Here we present a method to transfer Artificial Chromosome Expression systems (ACEs) into mammalian cells, which relies on a combined approach of using cationic amphiphiles and high frequency ultrasound. Thus, when cells were preincubated with liposomes consisting of the cationic lipid SAINT-2 and the phospholipid dioleoylphosphatidylethanolamine (molar ratio 1: 1), followed by ultrasound, ACEs could be introduced into mammalian cells, which resulted in the expression of ACEs-harbored reporter genes, such as Green Fluorescent Protein. Depending on cell type, transfection efficiencies ranged from 12% to 53%. Interestingly, no detectable delivery occurred when cells were treated alone with either ultrasound or liposomes. Evidence is provided, based on cellular entry of differently sized beads and trypan-blue permeation, which supports a mechanism in which integration of the lipids creates unstable membrane domains, which are particularly prone to ultrasound-induced pore formation. Time- and temperature-dependent experiments indicate that these pores display a transient stability. Hence, following ultrasound, the pores disappear as a function of time as suggested by a time-window for ACEs entry, and trypan blue exclusion, 80% of the cells becoming stained immediately following ultrasound, dropping to approximately 20% after 30 min. Co-expression of different genes in conjunction with fluorescence in situ hybridization (FISH) analysis indicates that the current procedure provides a means to introduce functionally active artificial chromosomes into eukaryotic cells. (C) 2004 Elsevier B.V. All rights reserved

ISO-SWS spectra of OH/IR stars

We present the spectra of 5 OH/IR stars observed with the Short Wavelength Spectrometer (SWS) on board the Infrared Space Observatory (ISO). The spectra are dominated by dust features, both in the amorphous and crystalline state and illustrate the influence of the mass loss rate on the observed spectral features