Life-history traits, pace of life and dispersal among and within five species of Trichogramma wasps: a comparative analysis

Major traits defining the life history of organisms are often not independent from each other, with most of their variation aligning along key axes such as the pace-of-life axis. We can define a pace-of-life axis structuring reproduction and development time as a continuum from less-fecund, longer-developing ″slow″ types to more-fecund, shorter-developing ″fast″ types. Such axes, along with their potential associations or syndromes with other traits such as dispersal, are however not universal; in particular, support for their presence may be taxon and taxonomic scale-dependent. Knowing about such life-history strategies may be especially important for understanding eco-evolutionary dynamics, as these trait syndromes may constrain trait variation or be correlated with other traits. To understand how life-history traits and effective dispersal covary, we measured these traits in controlled conditions for 28 lines from five species of Trichogramma, which are small endoparasitoid wasps frequently used as a biological model in experimental evolution but also in biocontrol against Lepidoptera pests. We found partial evidence of a pace-of-life axis at the interspecific level: species with higher fecundity also had faster development time. However, faster-developing species also were more likely to delay egg-laying, a trait that is usually interpreted as ″slow″. There was no support for similar covariation patterns at the within-species line level. There was limited variation in effective dispersal between species and lines, and accordingly, we did not detect any correlation between effective dispersal probability and life-history traits. We discuss how expanding our experimental design by accounting for the density-dependence of both the pace of life and dispersal might improve our understanding of those traits and how they interact with each other. Overall, our results highlight the importance of exploring covariation at the ″right″ taxonomic scale, or multiple taxonomic scales, to understand the (co)evolution of life-history traits. They also suggest that optimizing both reproductive and development traits to maximize the efficiency of biocontrol may be difficult in programs using only one species

Characterization and modeling of elastomers under tension/torsion small dynamic oscillations superimposed on large static preload

International audienceIntroduction Elastomers are widely used in industry for their anti-vibration properties. One of these applications concerns engine mounts, which are subjected to complex multiaxial loading conditions. In order to take into account this aspect, it has been chosen to focus on tension/torsion experiments. Indeed, performing tension/torsion tests allows to assess several multiaxial states with a unique specimen and a unique testing machine. Besides, typical loading conditions for engine mounts consist in vibrations, caused by either perturbation from the road or excitation of the engine, superimposed on a static preload due to the weight of the engine. Objectives The behavior of elastomers under small dynamic oscillations around a large static preload has received particular attention in the 1960s (for example [1]), and new studies have been recently developed ([2], [3]). The present work is based on Huber & Tsakmakis work ([4]), who studied two finite viscolelastic models (A and B). The main objective is to present multiaxial dynamic experimental results, and to confront them to the linearization of Models A and B. Methodology The used specimen is a dumbbell with a large perfectly cylindrical part. It has been specially designed for large tension/torsion tests. First, a quasi-static step with large strains is performed, applying tension, compression, torsion or combined tension/torsion. Then, small sinusoidal oscillations under tension or torsion are performed. Frequency is fixed and varies between 0.1 Hz and 30 Hz. This second step is applied either after maintaining the preload during one hour, or right after the end of the first step. Results and analysis The efficiency of presented models in predicting the dynamic response of an elastomer around an equilibrium position is discussed. The strain decomposition of Model A is easier to apply in this case, but it is also more restrictive than Model B. Indeed, Model A does not take into account any effects of static preload on viscous response of the oscillations, while Model B does

Characterization of elastomers under simultaneous tension and torsion for application to engine mounts

International audienceABSTRACT: A general procedure is proposed to develop relevant multiaxial tension-torsion experiments that mimic the complex loading conditions undergone by engine mounts in service. First, displacements and forces exerted on the engine mount are measured on an instrumented vehicle. For several loading conditions, the displacements are introduced in a finite element model of the engine mount to determine the corresponding strain fields. To characterize and compare these strain fields, we consider the invariants of the Hencky strain tensor. For a given set of invariants, we determine displacements and angles that must be applied on the samples to reproduce the deformation of the engine mount. The present work focuses on the subsequent experimental campaign. Firstly, a new rubber specimen is designed for simultaneous tension-torsion tests. Its principal re- quirement is that the finite element strain field must be as close as possible to the analytical solution of the simultaneous extension and torsion of a cylinder. The geometry of the new sample is validated with the help of stereo digital images correlation (SDIC) on the lateral surface of the specimen. From SDIC results, rela- tionships between global axial displacement and local extension λ on the one hand, and between global angle and local angle per unit of height τ on the other hand are established. This validated method will be consid- ered in a next future to perform multiaxial quasi-static and dynamic experiments, leading to identification of a visco-hyperelastic model