Genetically monomorphic invasive populations of the rapa whelk, Rapana venosa.

Rapana venosa is a predatory marine gastropod native to the coastal waters of China, Korea, and Japan. Since the 1940s, R. venosa has been transported around the globe and introduced populations now exist in the Black Sea, the Mediterranean Sea, the Adriatic and Aegean seas, off the coasts of France and The Netherlands, in Chesapeake Bay, Virginia, USA, and in the Rio de la Plata between Uruguay and Argentina. This study surveyed variation in two mitochondrial gene regions to investigate the invasion pathways of R. venosa, identify likely sources for introduced populations, and evaluate current hypotheses of potential transportation vectors. Sequence data were obtained for the mitochondrial cytochrome c oxidase I and NADH dehydrogenase subunit 2 gene regions of 178 individuals from eight native locations and 106 individuals from 12 introduced locations. Collections from within the native range displayed very high levels of genetic variation while collections from all introduced populations showed a complete lack of genetic diversity; a single haplotype was common to all introduced individuals. This finding is consistent with the hypothesis that R. venosa was initially introduced into the Black Sea, and this Black Sea population then served as a source for the other secondary invasions by various introduction vectors including ballast water transport. Although non-native R. venosa populations currently appear to be thriving in their new environments, the lack of genetic variability raises questions regarding the evolutionary persistence of these populations.

Reinvestigating the early resonantly photopumped x-ray laser schemes.

Although H and He-like resonantly photopumped laser schemes were among the earliest methods proposed for producing x-ray lasers, demonstrating these schemes in the laboratory has proved to be elusive. Nevertheless the resonantly photopumped schemes remain interesting both because of their potential to improve the efficiency of lasers that otherwise operate through other process such as recombination and because of their potential for yielding entirely new and relatively efficient lasers. We present an expanded list of candidate lasers that operate by utilizing Ly-alpha or He-alpha radiation from a pump ion to photopump an electron from the ground state of a H or He-like lasant ion to the n = 3 or 4 state, with subsequent lasing between the n = 4 ? n = 3 or n = 3 ? n = 2 states of the H or He-like ion. The example of the potassium-pumped chlorine scheme, which exhibits both 4 ? 3 and 3 ? 2 laser lines, has been modeled extensively, and the results of the calculation are presented.