Evolutionary dynamics of hybridization and introgression following the recent colonization of Glossy Ibis (Aves: Plegadis falcinellus) into the New World

Geographic range shifts can cause secondary contact and hybridization between closely related species, revealing mechanisms of species formation and integrity. These dynamics typically play out in restricted geographic regions, but highly vagile species may experience major distributional changes resulting in broad areas of contact. The Glossy Ibis (Plegadis falcinellus) is a dispersive waterbird of the Old World and Australia that colonized eastern North America in the early 19th century and came into contact with the native White‐faced Ibis (P. chihi). Putative hybrids between the two species have been observed across North America. To examine the population genomic consequences of this natural invasion, we sequenced 4,616 ultraconserved elements from 66 individuals sampled across the distributions of falcinellus, chihi, and the Puna Ibis (P. ridgwayi) of South America. We found genomic differentiation among the three species. Loci with high sequence divergence were often shared across all pairwise species comparisons, were associated with regions of high nucleotide diversity, and were concentrated on the Z chromosome. We detected signals of genetic admixture between chihi and falcinellus in individuals both near and far from their core area of sympatry. Genomic cline analyses revealed evidence of greater introgression into falcinellus from chihi, but we found little evidence for selection against hybrids. We also found signals of admixture between ridgwayi and South American populations of chihi. Our results indicate vagile species can experience pervasive introgression upon secondary contact, although we suggest these dynamics may be more ephemeral than the stable hybrid zones often observed in less dispersive organisms.     

Localization of methanol dehydrogenase in two strains of methylotrophic bacteria detected by immunogold labeling.

Antibodies to methanol dehydrogenase purified from Methylobacterium sp. strain AM1 and Methylomonas sp. strain A4 were raised. The antibody preparations were used in indirect immunogold labeling studies. With this approach, methanol dehydrogenase was found to be preferentially localized to the periplasmic region of the methylotroph Methylobacterium sp. strain AM1 and to the intracytoplasmic membrane of the methanotroph Methylomonas sp. strain A4. Antibody cross-reactivity to other methylotrophic bacteria was detected.     

Examination of a freshwater surface microlayer for diel changes in the bacterioneuston

The surface microlayer of a small freshwater pond was sampled every 6–8 hours on four occasions (April, July, September, and November) to examine changes in total and respiring bacterioneuston for diel cycles and comparing them to similar measurements of the bacterioplankton. Dissolved organic carbon (DOC), dissolved reactive phosphorous (DRP) and ammonia nitrogen (NH₃-N) were also measured. Both the mean numbers and enrichments of the two bacterial parameters in the surface microlayer samples showed seasonal differences, but in general, no significant difference (P > 0.05, ANOVA) in the mean numbers of total and respiring bacterioneuston were observed over diel periods except in November. The converse was true for the bacterioplankton. The presence of a visually thick surface film contributed to the results. The mean numbers of bacterioneuston and their enrichments were not correlated to any of the physical/chemical parameters measured.     

Comparison of laboratory and in situ measurements of urea decomposition by a marine diatom

The rate of decomposition of urea in situ by a marine diatom has been compared with laboratory estimated rates, at in situ urea concentrations, using an isolate of the same diatom species. The in situ measurements were made at two stations off the coast of Georgia, U.S.A. At these stations, Stephanopyxis costata Hustedt (Skeletonema costatum), decomposed 7.76 and 4.40 nM urea l⁻¹ h⁻¹. Using a clone of Stephanopyxis costata isolated near Martha's Vineyard, Massachusetts, we obtained a Michaelis-Menten curve for urea decomposition. At the urea concentrations of the two stations near Georgia (0.93 and 0.85 μM) we calculated urea decomposition of 0.27 and 0.13 nM urea l⁻¹ h⁻¹. Thus, the laboratory-determined rates were 3.5 and 3.7% of the actual in situ rates. Measurements of in situ decomposition of an organic solute by one species are rare. The causes of these large differences in urea decomposition rates may possibly be related to temperature or genetic differences between races of S. costata. These data suggest a cautious approach to the application of laborator-determined kinetics to in situ conditions.     

Phylogenetic systematics and biogeography of hummingbirds: Bayesian and maximum likelihood analyses of partitioned data and selection of an appropriate partitioning strategy

Hummingbirds are an important model system in avian biology, but to date the group has been the subject of remarkably few phylogenetic investigations. Here we present partitioned Bayesian and maximum likelihood phylogenetic analyses for 151 of approximately 330 species of hummingbirds and 12 outgroup taxa based on two protein-coding mitochondrial genes (ND2 and ND4), flanking tRNAs, and two nuclear introns (AK1 and BFib). We analyzed these data under several partitioning strategies ranging between unpartitioned and a maximum of nine partitions. In order to select a statistically justified partitioning strategy following partitioned Bayesian analysis, we considered four alternative criteria including Bayes factors, modified versions of the Akaike information criterion for small sample sizes (AIC(c)), Bayesian information criterion (BIC), and a decision-theoretic methodology (DT). Following partitioned maximum likelihood analyses, we selected a best-fitting strategy using hierarchical likelihood ratio tests (hLRTS), the conventional AICc, BIC, and DT, concluding that the most stringent criterion, the performance-based DT, was the most appropriate methodology for selecting amongst partitioning strategies. In the context of our well-resolved and well-supported phylogenetic estimate, we consider the historical biogeography of hummingbirds using ancestral state reconstructions of (1) primary geographic region of occurrence (i.e., South America, Central America, North America, Greater Antilles, Lesser Antilles), (2) Andean or non-Andean geographic distribution, and (3) minimum elevational occurrence. These analyses indicate that the basal hummingbird assemblages originated in the lowlands of South America, that most of the principle clades of hummingbirds (all but Mountain Gems and possibly Bees) originated on this continent, and that there have been many (at least 30) independent invasions of other primary landmasses, especially Central America.     

Proteomic analysis of human placental syncytiotrophoblast microvesicles in preeclampsia

Background

Placental syncytiotrophoblast microvesicles (STBM) are shed into the maternal circulation during normal pregnancy. STBM circulate in significantly increased amounts in preeclampsia (PE) and are considered to be among contributors to the exaggerated proinflammatory, procoagulant state of PE. However, protein composition of STBM in normal pregnancy and PE remains unknown. We therefore sought to determine the protein components of STBM and whether STBM protein expressions differ in preeclamptic and normal pregnancies.Patients with PE (n = 3) and normal pregnant controls (n = 6) were recruited. STBM were prepared from placental explant culture supernatant. STBM proteins were analyzed by a combination of 1D Gel-LC-MS/MS. Protein expressions levels were quantified using spectral counts and validated by immunohistochemistry.

Results

Over 400 proteins were identified in the STBM samples. Among these, 25 proteins were found to be differentially expressed in preeclampsia compared to healthy pregnant controls, including integrins, annexins and histones.

Conclusion

STBM proteins include those that are implicated in immune response, coagulation, oxidative stress, apoptosis as well as lipid metabolism pathways. Differential protein expressions of STBM suggest their pathophysiological relevance in PE.

Electronic supplementary material

The online version of this article (doi:10.1186/1559-0275-11-40) contains supplementary material, which is available to authorized users.     

Comparison of Two Direct-Count Methods for Determining Metabolizing Bacteria in Freshwater

Planktonic bacteria collected from several freshwater environments and cultured bacteria were used to compare two methods for determining the numbers of metabolizing bacteria. The methods used were (i) reduction of 2-(ρ-iodophenyl)-3-(ρ-nitrophenyl)-5-phenyl tetrazolium chloride 2-(ρ-iodophenyl)-3-(ρ-nitrophenyl)-5-phenyl to tetrazolium chloride-formazan and (ii) elongation of cells by using yeast extract and nalidixic acid. No statistically significant difference was found between methods in determining metabolizing bacteria, although significant differences (P < 0.05) were found when comparing numbers of total bacteria. A combination of the two methods yielded significant changes, both positive and negative, in the numbers of metabolizing bacteria.