Two colonisation stages generate two different patterns of genetic diversity within native and invasive ranges of Ulex europaeus.

Genetic diversity and the way a species is introduced influence the capacity of populations of invasive species to persist in, and adapt to, their new environment. The diversity of introduced populations affects their evolutionary potential, which is particularly important for species that have invaded a wide range of habitats and climates, such as European gorse, Ulex europaeus. This species originated in the Iberian peninsula and colonised Europe in the Neolithic; over the course of the past two centuries it was introduced to, and has become invasive in, other continents. We characterised neutral genetic diversity and its structure in the native range and in invaded regions. By coupling these results with historical data, we have identified the way in which gorse populations were introduced and the consequences of introduction history on genetic diversity. Our study is based on the genotyping of individuals from 18 populations at six microsatellite loci. As U. europaeus is an allohexaploid species, we used recently developed tools that take into account genotypic ambiguity. Our results show that genetic diversity in gorse is very high and mainly contained within populations. We confirm that colonisation occurred in two stages. During the first stage, gorse spread out naturally from Spain towards northern Europe, losing some genetic diversity. During the second stage, gorse was introduced by humans into different regions of the world, from northern Europe. These introductions resulted in the loss of rare alleles but did not significantly reduce genetic diversity and thus the evolutionary potential of this invasive species.

Gynodioecy in structured populations: understanding fine-scale sex ratio variation in Beta vulgaris ssp. maritima.

Natural selection, random processes and gene flow are known to generate sex ratio variations among sexually polymorphic plant populations. In gynodioecious species, in which hermaphrodites and females coexist, the relative effect of these processes on the maintenance of sex polymorphism is still up for debate. The aim of this study was to document sex ratio and cytonuclear genetic variation at a very local scale in wind-pollinated gynodioecious Beta vulgaris ssp. maritima and attempt to elucidate which processes explained the observed variation. The study sites were characterized by geographically distinct patches of individuals and appeared to be dynamic entities, with recurrent establishment of distinct haplotypes through independent founder events. Along with substantial variation in sex ratio and unexpectedly low gene flow within study sites, our results showed a high genetic differentiation among a mosaic of genetically distinct demes, with isolation by distance or abrupt genetic discontinuities taking place within a few tens of metres. Overall, random founder events with restricted gene flow could be primary determinants of sex structure, by promoting the clumping of sex-determining genes. Such high levels of sex structure provide a landscape for differential selection acting on sex-determining genes, which could modify the conditions of maintenance of gynodioecy in structured populations.

Perirenal textiloma: MR and serial CT appearance.

We describe changes in imaging features of a textiloma (retained surgical sponge or retained foreign body) left in the renal fossa after exploratory renal surgery. One year after the initial surgery, the MR aspect of the textiloma was not specific, with a homogeneous low signal intensity on T1-weighted images. Serial CT examinations over 4 years demonstrated progressive growth and calcification of the mass which appeared pseudocystic with a peripheral inflammatory wall. Granulomas caused by a retained surgical sponge should be considered as a cause of retroperitoneal mass in patients with a history of prior surgery.

[Subarachnoid rupture of supratentorial dermoid cyst: CT and MRI aspects]. / Rupture sous-arachnoïdienne d'un kyste dermoïde supratentoriel: aspect TDM et IRM.

We report a case of ruptured subarachnoid dermoid cyst which was explored with both CT and MRI. This rare condition results from the accumulation of a large amount of fat with a characteristic aspect at-imaging. Rupture causes fat dissemination in the subarachnoid space. In most cases, CT or MRI can provide sure diagnosis of the tumor and of rupture.