Propagule pressure and colony social organization are associated with the successful invasion and rapid range expansion of fire ants in China

We characterized patterns of genetic variation in populations of the fire ant Solenopsis invicta in China using mitochondrial DNA sequences and nuclear microsatellite loci to test predictions as to how propagule pressure and subsequent dispersal following establishment jointly shape the invasion success of this ant in this recently invaded area. Fire ants in Wuchuan (Guangdong Province) are genetically differentiated from those found in other large infested areas of China. The immediate source of ants in Wuchuan appears to be somewhere near Texas, which ranks first among the southern USA infested states in the exportation of goods to China. Most colonies from spatially distant, outlying areas in China are genetically similar to one another and appear to share a common source (Wuchuan, Guangdong Province), suggesting that long‐distance jump dispersal has been a prevalent means of recent spread of fire ants in China. Furthermore, most colonies at outlier sites are of the polygyne social form (featuring multiple egg‐laying queens per nest), reinforcing the important role of this social form in the successful invasion of new areas and subsequent range expansion following invasion. Several analyses consistently revealed characteristic signatures of genetic bottlenecks for S. invicta populations in China. The results of this study highlight the invasive potential of this pest ant, suggest that the magnitude of international trade may serve as a predictor of propagule pressure and indicate that rates and patterns of subsequent range expansion are partly determined by the interplay between species traits and the trade and transportation networks.     

Changes in composition of cuticular biochemicals of the facultatively polygynous ant Petalomyrmex phylax during range expansion in Cameroon with respect to social, spatial and genetic variation

In social insects, biochemicals found at the surface of the cuticle are involved in the recognition process and in protection against desiccation and pathogens. However, the relative contribution of evolutionary forces in shaping diversity of these biochemicals remains largely unresolved in ants. We determined the composition of epicuticular biochemicals for workers sampled in 12 populations of the ant Petalomyrmex phylax from Cameroon. Genetic variation at 12 microsatellite markers was used to infer population history and to provide null expectations under the neutrality hypothesis. Genetic data suggest a recent southward range expansion of this ant species. Furthermore, there is a decline southward in the numbers of queens present in mature colonies. Here, we contrast the pattern of biochemical variation against genetic, social and spatial parameters. We thus provide the first estimates of the relative contribution of neutral and selective processes on variation of ant cuticular profile. Populations in migration-drift disequilibrium showed reduction of within-population variation for genetic markers as well as for cuticular profiles. In these populations, the cuticular profile became biased towards a limited number of high molecular weight molecules. Within- and among-population biochemical variation was explained by both genetic and social variation and by the spatial distribution of populations. We therefore propose that during range expansion of P. phylax, the composition of epicuticular compounds has been affected by a combination of neutral processes - genetic drift and spatially limited dispersal - and spatially varying selection, social organization and environmental effects.     

A four-dimensional simulation model of tumour response to radiotherapy in vivo: parametric validation considering radiosensitivity, genetic profile and fractionation

The aim of this paper is to present the current state of a four-dimensional simulation model of solid tumour growth and response to radiotherapy developed by our group. The most prominent points of the algorithms describing the fundamental biological phenomena involved are outlined. A specific application of the model to a selected clinical case of glioblastoma multiforme is described and comparative studies are performed, using various exploratory values of the model parameters. Qualitative agreement with clinical observations has been achieved. Special emphasis is laid on the variability of radiosensitivity parameters throughout the cell cycle and on the influence of the genetic profile of the tumour on its radiosensitivity. The results of the simulation are three-dimensionally reconstructed. A valuable tool for getting insight into the biology of tumour growth and response to radiotherapy and at the same time an advanced patient specific decision support system is expected to emerge after the completion of the necessary extensive clinical evaluation.