Genotype variation in bark texture drives lichen community assembly across multiple environments.

A major goal of community genetics is to understand the influence of genetic variation within a species on ecological communities. Although well-documented for some organisms, additional research is necessary to understand the relative and interactive effects of genotype and environment on biodiversity, identify mechanisms through which tree genotype influences communities, and connect this emerging field with existing themes in ecology. We employ an underutilized but ecologically significant group of organisms, epiphytic bark lichens, to understand the relative importance of Populus angustifolia (narrowleaf cottonwood) genotype and environment on associated organisms within the context of community assembly and host ontogeny. Several key findings emerged. (1) In a single common garden, tree genotype explained 18-33% and 51% of the variation in lichen community variables and rough bark cover, respectively. (2) Across replicated common gardens, tree genotype affected lichen species richness, total lichen cover, lichen species composition, and rough bark cover, whereas environment only influenced composition and there were no genotype by environment interactions. (3) Rough bark cover was positively correlated with total lichen cover and richness, and was associated with a shift in species composition; these patterns occurred with variation in rough bark cover among tree genotypes of the same age in common gardens and with increasing rough bark cover along a -40 year tree age gradient in a natural riparian stand. (4) In a common garden, 20-year-old parent trees with smooth bark had poorly developed lichen communities, similar to their 10-year-old ramets (root suckers) growing in close proximity, while parent trees with high rough bark cover had more developed communities than their ramets. These findings indicate that epiphytic lichens are influenced by host genotype, an effect that is robust across divergent environments. Furthermore, the response to tree genotype is likely the result of genetic variation in the timing of the ontogenetic shift from smooth to rough bark allowing communities on some genotypes to assemble faster than those on other genotypes. Organisms outside the typical sphere of community genetics, such as lichens, can help address critical issues and connect plant genotype effects to long-established streams of biological research, such as ontogeny and community assembly.

Computed tomography and magnetic resonance imaging of diffuse pigmented villonodular synovitis: report of a case.

We describe the computed tomographic (CT) and magnetic resonance imaging (MRI) features of a surgically proven case of diffuse pigmented villonodular synovitis (PVNS) of the knee in a 34-year-old woman. A complex mass consisting of solid and multicystic components was clearly demonstrated by CT and MRI. The solid part showed homogeneous hypodense attenuation relative to adjacent muscles on CT scans, but it showed inhomogeneous signal intensity on spin echo T1- and T2-weighted images (WI). The solid component enhanced homogeneously on CT scans but heterogeneously on MR images. Multiseptated enhancement of the cystic component on both CT and MR images were displayed. All of the above features were better demonstrated on MRI. Multiple marked hypointense round and patchy areas, and also a few areas isointense to subcutaneous fat within the lesion were also found on T1WI, proton density WI and T2WI. These characteristic MRI features of PVNS correlated well with its histologic structures: depositions of hemosiderin and fat in the proliferative synovial villi and bloody cystic content. These features may help to distinguish PVNS from other disease entities arising from the synovium.

Magnetic resonance imaging of acoustic schwannomas.

The magnetic resonance imaging (MRI) findings of 27 histologically proven acoustic schwannomas in 24 patients (13 men, 11 women, age 20-79 yr) are described in detail. Three patients had bilateral tumors. Twenty-two tumors (82%) had intra- and extracanalicular components, three tumors (11%) were limited to the internal auditory canal (IAC) and two tumors (7%) were limited to the cerebellopontine angle (CPA). The diameters of extracanalicular lesions in the CPA ranged from 12 to 50 mm, and most of them were round in shape. All IAC portions of CPA tumors had a funnel-shaped appearance on the axial images and short-club-shaped configuration on the coronal images. There was strong homogeneous contrast enhancement of the solid components in 12 tumors (44%) and heterogeneous enhancement in 15 tumors (56%). The cystic components of the tumors correlated well with the histologic features. All tumors could be demonstrated in their enterity by MRI. The "short-club sign", first described in this study, helped to confirm the intracanalicular component of acoustic schwannomas, which were usually found in the cerebellar cistern. The results of this study show that MRI is a sensitive imaging modality for the assessment of acoustic schwannomas located at the CPA or IAC, or in both regions. MRI is non-invasive and does not involve ionizing radiation. It should be considered the imaging examination of choice to evaluate patients with suspected acoustic schwannomas.

Magnetic resonance imaging of Ebstein's anomaly: report of two cases.

Among 388 cases of congenital heart disease with magnetic resonance imaging (MRI) from September 1990 to February 1992, we came across two cases of Ebstein's anomaly. They had been previously diagnosed as Ebstein's anomaly by echocardiography and cinecardioangiography. The first case was a three-year-old boy with complex congenital heart disease that included Ebstein's anomaly, a double-outlet right ventricle, pulmonary hypertension, tricuspid regurgitation, mitral regurgitation, a ventricular septal defect and an atrial septal defect. The second was a 13-year-old boy who also had Ebstein's anomaly, but had received a tricuspid valve replacement at the age of five. In Ebstein's anomaly, we found that MRI offers exquisite endocardial and epicardial details. We anticipate that in the future MRI will help to eliminate invasive studies.