Evolutionary shifts to self-fertilisation restricted to geographic range margins in North American Arabidopsis lyrata.

Cross-fertilisation predominates in eukaryotes, but shifts to self-fertilisation are common and ecologically and evolutionarily important. Reproductive assurance under outcross gamete limitation is one eco-evolutionary process held responsible for the shift to selfing. Although small effective population size is a situation where selfing plants could theoretically benefit from reproductive assurance, empirical tests of the role of population size are rare. Here, we show that selfing evolved repeatedly at range margins, where historical demographic processes produced low effective population sizes. Outcrossing populations of North American Arabidopsis lyrata have low genetic diversity at geographic margins, with a signature of post-glacial range expansion in the north and rear-edge isolation in the south. Selfing populations occur at the margins of two genetic groups and never in their interior. These results corroborate small effective population size as the promoter of self-fertilisation and have important implications for our understanding of species turnover, range limits and range dynamics.

Pelvic mass: CT-guided interstitial catheter implantation with high-dose-rate remote afterloader.

A technique is presented for computed tomography (CT)-guided interstitial catheter placement and treatment planning for high-dose-rate brachytherapy. In a 66-year-old woman with adenocarcinoma of unknown origin that had metastasized to the right ilium, interstitial brachytherapy catheters were placed by means of CT guidance. With use of a treatment planning system with dose optimization, an excellent dose distribution was obtained with minimal dose being delivered to the surrounding critical tissues. For selected patients, this procedure can provide effective and safe local treatment for solid tumors.