Gene interactions constrain the course of evolution of phosphine resistance in the lesser grain borer, Rhyzopertha dominica

Phosphine, a widely used fumigant for the protection of stored grain from insect pests, kills organisms indirectly by inducing oxidative stress. High levels of heritable resistance to phosphine in the insect pest of stored grain, Rhyzopertha dominica have been detected in Asia, Australia and South America. In order to understand the evolution of phosphine resistance and to isolate the responsible genes, we have undertaken genetic linkage analysis of fully sensitive (QRD14), moderately resistant (QRD369) and highly resistant (QRD569) strains of R. dominica collected in Australia. We previously determined that two loci, rph1 and rph2, confer high-level resistance on strain QRD569, which was collected in 1997. We have now confirmed that rph1 is responsible for the moderate resistance of strain QRD369, which was collected in 1990, and is shared with a highly resistant strain from the same geographical region, QRD569. In contrast, rph2 by itself confers only very weak resistance, either as a heterozygote or as a homozygote and was not discovered in the field until weak resistance (probably due to rph1) had become ubiquitous. Thus, high-level resistance against phosphine has evolved via stepwise acquisition of resistance alleles, first at rph1 and thereafter at rph2. The semi-dominance of rph2 together with the synergistic interaction between rph1 and rph2 would have led to rapid selection for homozygosity. A lack of visible fitness cost associated with alleles at either locus suggests that the resistance phenotype will persist in the field

Multivariate selection shapes environment-dependent variation in the clonal morphology of a red seaweed

Within-individual strategies of variation (e.g., phenotypic plasticity) are particularly relevant to modular organisms, in which ramets of the same genetic individual may encounter diverse environments imposing diverse patterns of selection. Hence, measuring selection in heterogeneous environments is essential to understanding whether environment-dependent phenotypic change enhances the fitness of modular individuals. In sublittoral marine habitats, competition for light and space among modular taxa generates extreme patchiness in resource availability. Little is known, however, of the potential for plasticity within individuals to arise from spatially-variable selection in such systems. We tested whether plasticity enhances genet-level fitness in Asparagopsis armata, a clonal seaweed in which correlated traits mediate morphological responses to variation in light. Using the capacity for rapid, clonal growth to measure fitness, we identified aspects of ramet morphology targeted by selection in two contrasting light environments and compared patterns of selection across environments. We found that directional selection on single traits, coupled with linear and nonlinear selection on multi-trait interactions, shape ramet morphology within environments and favor different phenotypes in each. Evidence of environment-dependent, multivariate selection on correlated traits is novel for any marine modular organism and demonstrates that seaweeds, such as A. armata, may potentially adapt to environmental heterogeneity via plasticity in clonal morphology

Self-similarity in ultrafast nonlinear optics

International audienceRecent developments in nonlinear optics have led to the discovery of a new class of ultrashort pulse, the `optical similariton'. Optical similaritons arise when the interaction of nonlinearity, dispersion and gain in a high-power fibre amplifier causes the shape of an arbitrary input pulse to converge asymptotically to a pulse whose shape is self-similar. In comparison with optical solitons, which rely on a delicate balance of nonlinearity and anomalous dispersion and which can become unstable with increasing intensity, similaritons are more robust at high pulse powers. The simplicity and widespread availability of the components needed to build a self-similar amplifier capable of producing optical similaritons provides a convenient experimental platform to explore the fundamental nature of dynamical self-similarity. Here, we provide an overview of self-similar pulse propagation and scaling in optical fibre amplifiers, and their use in the development of high-power ultrafast optical sources, pulse synthesis and all-optical pulse regeneration