X chromosome drive in a widespread Palearctic woodland fly, Drosophila testacea.

Selfish genes that bias their own transmission during meiosis can spread rapidly in populations, even if they contribute negatively to the fitness of their host. Driving X chromosomes provide a clear example of this type of selfish propagation. These chromosomes have important evolutionary and ecological consequences, and can be found in a broad range of taxa including plants, mammals and insects. Here, we report a new case of X chromosome drive (X drive) in a widespread woodland fly, Drosophila testacea. We show that males carrying the driving X (SR males) sire 80-100% female offspring and possess a diagnostic X chromosome haplotype that is perfectly associated with the sex ratio distortion phenotype. We find that the majority of sons produced by SR males are sterile and appear to lack a Y chromosome, suggesting that meiotic defects involving the Y chromosome may underlie X drive in this species. Abnormalities in sperm cysts of SR males reflect that some spermatids are failing to develop properly, confirming that drive is acting during gametogenesis. By screening wild-caught flies using progeny sex ratios and a diagnostic marker, we demonstrate that the driving X is present in wild populations at a frequency of ~ 10% and that suppressors of drive are segregating in the same population. The testacea species group appears to be a hot spot for X drive, and D. testacea is a promising model to compare driving X chromosomes in closely related species, some of which may even be younger than the chromosomes themselves.

Transcriptome analysis provides insight into venom evolution in a seed-parasitic wasp, Megastigmus spermotrophus.

One of the most striking host range transitions is the evolution of plant parasitism from animal parasitism. Parasitoid wasps that have secondarily evolved to attack plants (ie gall wasps and seed-feeders) demonstrate intimate associations with their hosts, yet the mechanism of plant-host manipulation is currently not known. There is, however, emerging evidence suggesting that ovipositional secretions play a role in plant manipulation. To investigate whether parasites have modified pre-existing adaptations to facilitate dramatic host shifts we aimed to characterize the expression of venom proteins in a plant parasite using a collection of parasitoid venom sequences as a guide. The transcriptome of a seed-feeding wasp, Megastigmus spermotrophus, was assembled de novo and three putative venoms were found to be highly expressed in adult females. One of these putative venoms, aspartylglucosaminidase, has been previously identified as a major venom component in two distantly related parasitoid wasps (Asobara tabida and Leptopilina heterotoma) and may have originated via gene duplication within the Hymenoptera. Our study shows that M. spermotrophus, a specialized plant parasite, expresses putative venom transcripts that share homology to venoms identified in Nasonia vitripennis (both superfamily Chalcidoidea), which suggests that M. spermotrophus may have co-opted pre-existing machinery to develop as a plant parasite.

Endosymbiont costs and benefits in a parasitoid infected with both Wolbachia and Cardinium.

Theory suggests that maternally inherited endosymbionts can promote their spread and persistence in host populations by enhancing the production of daughters by infected hosts, either by improving overall host fitness, or through reproductive manipulation. In the doubly infected parasitoid wasp Encarsia inaron, Wolbachia manipulates host reproduction through cytoplasmic incompatibility (CI), but Cardinium does not. We investigated the fitness costs and/or benefits of infection by each bacterium in differentially cured E. inaron as a potential explanation for persistence of Cardinium in this population. We introgressed lines infected with Wolbachia, Cardinium or both with the cured line to create a similar genetic background, and evaluated several parasitoid fitness parameters. We found that symbiont infection resulted in both fitness costs and benefits for E. inaron. The cost was lower initial egg load for all infected wasps. The benefit was increased survivorship, which in turn increased male production for wasps infected with only Cardinium. Female production was unaffected by symbiont infection; we therefore have not yet identified a causal fitness effect that can explain the persistence of Cardinium in the population. Interestingly, the Cardinium survivorship benefit was not evident when Wolbachia was also present in the host, and the reproduction of doubly infected individuals did not differ significantly from uninfected wasps. Therefore, the results of our study show that even when multiple infections seem to have no effect on a host, there may be a complex interaction of costs and benefits among symbionts.

Population dynamics and rapid spread of Cardinium, a bacterial endosymbiont causing cytoplasmic incompatibility in Encarsia pergandiella (Hymenoptera: Aphelinidae).

Cytoplasmic incompatibility (CI) is a common phenotype of maternally inherited bacterial symbionts of arthropods; in its simplest expression, uninfected females produce few or no viable progeny when mated to infected males. Infected females thus experience a reproductive advantage relative to that of uninfected females, with the potential for the symbiont to spread rapidly. CI population dynamics are predicted to depend primarily on the strength of incompatibility, the fitness cost of the infection and how faithfully symbionts are inherited. Although the bacterial symbiont lineage Wolbachia has been most identified with the CI phenotype, an unrelated bacterium, Cardinium may also cause CI. In the first examination of population dynamics of CI-inducing Cardinium, we used population cages of the parasitic wasp Encarsia pergandiella (Hymenoptera: Aphelinidae) with varying initial infection frequencies to test a model of invasion. Cardinium was found to spread rapidly in all populations, even in cases where the initial infection frequency was well below the predicted invasion threshold frequency. The discrepancy between the modeled and actual results is best explained by weaker CI than measured in the lab and a cryptic fitness benefit to the infection.

Cytoplasmic incompatibility in the parasitic wasp Encarsia inaron: disentangling the roles of Cardinium and Wolbachia symbionts.

Many bacterial endosymbionts of insects are capable of manipulating their host's reproduction for their own benefit. The most common strategy of manipulation is cytoplasmic incompatibility (CI), in which embryonic mortality results from matings between uninfected females and infected males. In contrast, embryos develop normally in infected females, whether or not their mate is infected, and infected progeny are produced. In this way, the proportion of infected females increases in the insect population, thereby promoting the spread of the maternally inherited bacteria. However, what happens when multiple endosymbionts inhabit the same host? The parasitoid wasp Encarsia inaron is naturally infected with two unrelated endosymbionts, Cardinium and Wolbachia, both of which have been documented to cause CI in other insects. Doubly infected wasps show the CI phenotype. We differentially cured E. inaron of each endosymbiont, and crossed hosts of different infection status to determine whether either or both bacteria caused the observed CI phenotype in this parasitoid, and whether the two symbionts interacted within their common host. We found that Wolbachia caused CI in E. inaron, but Cardinium did not. We did not find evidence that Cardinium was able to modify or rescue Wolbachia-induced CI, nor did we find that Cardinium caused progeny sex ratio distortion, leaving the role of Cardinium in E. inaron a mystery.

Focal hepatic masses and fatty infiltration detected by enhanced dynamic CT.

A prospective evaluation of 185 consecutive patients with abdominal pain or suspected hepatic malignancy was performed to compare the diagnostic accuracy of contrast material-enhanced incremental dynamic computed tomography (IDCT) scans with plain CT scans for detection of hepatic masses and fatty infiltration of the liver. After a series of nondynamic plain CT scans, patients were examined at 7.5 scans/min during intravenous injection of 50 g of iodinated contrast material. Enhanced IDCT study was found to be an accurate, reproducible technique for liver evaluation. Of 155 neoplasms measured in 59 patients, liver-to-lesion differences of less than 10 HU were seen in only two tumors in IDCT scans as compared with 31 in plain CT scans. These differences were not significantly affected by lesion size for neoplasms greater than 6 mm in diameter. A confident diagnosis of fatty infiltration (23 patients) could be made when the spleen-minus-liver difference was 25 HU on enhanced IDCT scans and 10 HU on plain CT scans. In eight patients with liver metastases, there was little variation in the attenuation values of normal-appearing liver between serial examination studies (8 HU average).

Air gap technique for digital subtraction angiography of the extracranial carotid arteries.

The technique of applying an air gap between the patient and the x-ray detector reduces scattered radiation from the patient's neck sufficiently to allow performance of DSA of the extracranial carotid arteries with the antiscatter grid removed. When compared with the conventional grid technique, air gap allows 25 to 88% reduction of mA without increasing the kVp or exposure time and without loss of spatial resolution or diagnostic image quality. These considerable patient radiation-exposure savings can be implemented on DSA systems that use ordinary under-table x-ray tube fluoroscopic equipment without the purchase of additional hardware.

Abnormal course of nasogastric tube in traumatic rupture of left hemidiaphragm.

In a review of 17 surgically proven cases of acute traumatic diaphragmatic hernia, a nasogastric tube had been inserted preoperatively in eight. In six of these patients the tube followed a characteristic course, indicating the diagnosis of gastric herniation into the left hemithorax. In four cases the passage of the tubing established the diagnosis; in the other two cases the diagnosis was suggested by plain films alone, but subsequent passage of the nasogastric tube provided confirmation.