Taxon-dependent effects of dispersal limitation versus environmental filters on bryophyte assemblages-Multiple perspective studies in land-bridge islands.

To explore the taxon-dependent contribution of dispersal limitation versus environmental filters to bryophyte assemblages. We investigated bryophytes and six environmental variables on 168 islands in the Thousand Island Lake,China. We compared the observed beta diversity with the expected values based on six null models (EE, EF, FE, FF, PE, and PF), detected the partial correlation of beta diversity with geographical distances. We quantified the contributions of spatial versus environmental variables and island isolation per se to species composition (SC) using variance partitioning. We modeled the species-area relationships (SARs) for bryophytes and the other eight biotas. To explore the taxon-dependent effects of spatial versus environmental filters on bryophytes, 16 taxa including five categories (total bryophytes, total mosses, liverworts, acrocarpous, and pleurocarpous mosses) and 11 species-richest families were included in the analyses. The observed beta diversity values were significantly different from the predicted values for all 16 taxa. For all five categories, the observed partial correlations between beta diversity and geographical distance after controlling environmental effects were not only positive, but also significantly different from the predicted values based on the null models. Spatial eigenvectors are more important in shaping SC than environmental variables for all 16 taxa except Brachytheciaceae and Anomodontaceae. Spatial eigenvectors contributed more to SC variation in liverworts than in mosses and in pleurocarpous mosses than in acrocarpous mosses. The effects of island isolation on SC were significant for all five categories, highly varied at the family level. The z values of the SARs for the five bryophyte categories were all larger than those of the other eight biotas. In subtropical fragmented forests, dispersal limitation exerted significant, taxon-dependent effects on bryophyte assemblages. It was dispersal limitation rather than environmental filtering that predominantly regulated the SC patterns of bryophytes.

Substrate of complex fractionated atrial electrograms: evidence by pathologic analysis.

BACKGROUND: Ablation of complex fractionated atrial electrograms (CFAE) is an important adjunctive therapy in atrial fibrillation (AF). The present study was to elucidate the substrate underlying CFAE. METHODS: Nine adult mongrel dogs were involved in the present study. AF was induced through rapid atrial pacing with vagosympathetic nerve stimulation. CFAE was recorded during AF. Ablation was performed at CFAE sites. Based on the location of the ablation scar, the atrial specimens were divided into CFAE and non-CFAE sites. Serial sections of the atrium were stained respectively with hematoxylin-eosin (HE) and the general neural marker protein gene product 9.5 (PGP9.5). We compared the characteristics of the myocardium and the ganglionated plexus (GPs) distribution between the CFAE and non-CFAE sites. RESULTS: The myocardium of non-CFAE sites was well-organized with little intercellular substance. However, the myocardium in the CFAE site was disorganized with more interstitial tissue ((61.7 ± 24.3)% vs. (34.1 ± 9.2)%, P < 0.01). GPs in the CFAE site were more abundant than in non-CFAE sites ((34.45 ± 37.46) bundles/cm(2) vs. (6.73 ± 8.22) bundles/cm(2), P < 0.01). CONCLUSION: The heterogeneity of the myocardium and GPs distribution may account for the substrate of CFAE and serve as a potential target of ablation.

Effect of epicardial fat pad ablation on acute atrial electrical remodeling and inducibility of atrial fibrillation.

BACKGROUND: Atrial electrical remodeling (AER) is the underlying mechanism of atrial fibrillation (AF). The present study investigated the impact of epicardial fat pad (FP) ablation on acute AER (AAER) and inducibility of AF. METHODS AND RESULTS: AAER was performed in 28 mongrel dogs through 4-h rapid atrial pacing (RAP). Before RAP, 14 dogs (ablation group) underwent FP ablation, and the other 14 (control group) underwent a sham procedure. The atrial effective refractory period (ERP) and vulnerability window (VW) of AF were measured with and without bilateral cervical vagosympathetic nerve stimulation (VNS) at the high right atrium, ostium of the coronary sinus (CS) and distal CS before and after every hour of RAP. In the control group, ERP was markedly shortened in the first 2 h of RAP and then stabilized. AF was only slightly induced. After RAP, the time course of ERP with and without VNS was similar. VNS significantly shortened ERP and increased VW before and after RAP. In the ablation group, ERP was significantly prolonged after FP ablation. Moreover, neither VNS nor RAP shortened the ERP or increased the VW. AF could not be induced (VW=0). CONCLUSIONS: RAP resulted in AAER, which may be mediated and aggravated by autonomic activity. Epicardial FP ablation generated denervation, which not only abolishes AF inducibility but also prevents RAP-mediated AAER.