The trade-off between housing density and sprawl area: Minimising impacts to forest breeding birds

Increasing housing density is generally assumed to confer negative effects on forest breeding birds. This implies we should build at low density over the landscape to conserve these species. However, for a given human population, low-density development must cover a large area, resulting in sprawl. A pertinent question is then: at what housing density are the impacts of a given human population on forest biodiversity minimised? For a given human population, it is unclear whether the impacts on forest biodiversity are less where housing density is high and sprawl area is small or where housing density is low and sprawl area is large. We addressed this question using the abundance, species richness and evenness of forest birds in Ottawa, Ontario and Gatineau, Quebec, Canada. First, we counted breeding birds at 22 sites representing a range of housing densities. We then used these empirical measurements to estimate forest bird abundance, species richness and evenness in four hypothetical development scenarios representing the trade-off between housing density and sprawl area. With the exception of the Undeveloped scenario (i.e., continuous forest), forest birds and forest interior birds were most abundant in the Compact scenario and most speciose in the Semi-compact scenario, whereas forest edge birds were most abundant and speciose in the Dispersed scenario. All three bird groups were most even in the Compact scenario. We conclude that compact housing development (building at high density over a small area) minimises the impacts of a given human population on forest breeding birds.     

Competition by Estrogens for Catecholamine Receptor Binding In Vitro

Abstract: We have examined the ability of various steroids to compete for high-affinity binding of ³H-labeled ligands to catecholamine receptors in membranes prepared from rat cerebral cortex, striatum, and anterior pituitary. Ligands employed were: [³H]WB4101, [³H]prazosin, [³H]yohimbine, and [³H]clonidine (alpha-noradrenergic); [³H]dihydroalprenolol (beta-noradrenergic); [³H]spiperone and [³H]ADTN (dopaminergic). Only the 17β estrogens were effective and only binding of [³H]spiperone and [³H]ADTN in striatum and [³H]WB4101 and [³H]prazosin in cerebral cortex was reduced. Thus putative dopaminergic and alpha₁-noradrenergic sites alone appear to recognize estrogens. A slight competitive effect on [³H]spiperone binding to anterior pituitary membranes was also observed. Among the 17β estrogens tested, the most effective in all cases was the catechol estrogen 2-hydroxyestradiol (2-OHE₂). The ability of 2-OHE₂ (IC₅₀= 20–30 μM) to inhibit ligand binding to alpha₁ receptors was comparable to that of norepinephrine (IC₅₀= 10–20 μM), whereas for dopamine receptors in striatum and pituitary 2-OHE₂ was an order of magnitude less effective than dopamine (IC₃₀= 12 μM) in reducing binding of ³H ligands. Estradiol-17β and 2-hydroxyestrone were also able to inhibit binding, but the order of steroid potency was different for alpha₁ and dopaminergic receptors. Progesterone, testosterone, and corticosterone were without effect in all cases. These results show that there is specificity of steroid interactions with catecholamine receptors in the brain, both in terms of steroid structure and receptor type. The possible relevance of these interactions to neuroendocrine function is discussed.     

Genetic Linkage and Cotransfer of a Novel, vanB-Containing Transposon (Tn5382) and a Low-Affinity Penicillin-Binding Protein 5 Gene in a Clinical Vancomycin-Resistant Enterococcus faecium Isolate

Mechanisms for the intercellular transfer of VanB-type vancomycin resistance determinants and for the almost universal association of these determinants with those for high-level ampicillin resistance remain poorly defined. We report the discovery of Tn5382, a ca. 27-kb putative transposon encoding VanB-type glycopeptide resistance in Enterococcus faecium. Open reading frames internal to the right end of Tn5382 and downstream of the vanX_B dipeptidase gene exhibit significant homology to genes encoding the excisase and integrase of conjugative transposon Tn916. The ends of Tn5382 are also homologous to the ends of Tn916, especially in regions bound by the integrase enzyme. PCR amplification experiments indicate that Tn5382 excises to form a circular intermediate in E. faecium. Integration of Tn5382 in the chromosome of E. faecium C68 has occurred 113 bp downstream of the stop codon for the pbp5 gene, which encodes high-level ampicillin resistance in this clinical isolate. Transfer of vancomycin, ampicillin, and tetracycline resistance from C68 to an E. faecium recipient strain occurs at low frequency in vitro and is associated with acquisition of a 130- to 160-kb segment of DNA that contains Tn5382, the pbp5 gene, and its putative repressor gene, psr. The interenterococcal transfer of this large chromosomal element appears to be the primary mechanism for vanB operon spread in northeast Ohio. These results expand the known family of Tn916-related transposons, suggest a mechanism for vanB operon entry into and dissemination among enterococci, and provide an explanation for the nearly universal association of vancomycin and high-level ampicillin resistance in clinical E. faecium strains.     

Heterogeneity in White Blood Cells Has Potential to Confound DNA Methylation Measurements

Epigenetic studies are commonly conducted on DNA from tissue samples. However, tissues are ensembles of cells that may each have their own epigenetic profile, and therefore inter-individual cellular heterogeneity may compromise these studies. Here, we explore the potential for such confounding on DNA methylation measurement outcomes when using DNA from whole blood. DNA methylation was measured using pyrosequencing-based methodology in whole blood (n = 50–179) and in two white blood cell fractions (n = 20), isolated using density gradient centrifugation, in four CGIs (CpG Islands) located in genes HHEX (10 CpG sites assayed), KCNJ11 (8 CpGs), KCNQ1 (4 CpGs) and PM20D1 (7 CpGs). Cellular heterogeneity (variation in proportional white blood cell counts of neutrophils, lymphocytes, monocytes, eosinophils and basophils, counted by an automated cell counter) explained up to 40% (p<0.0001) of the inter-individual variation in whole blood DNA methylation levels in the HHEX CGI, but not a significant proportion of the variation in the other three CGIs tested. DNA methylation levels in the two cell fractions, polymorphonuclear and mononuclear cells, differed significantly in the HHEX CGI; specifically the average absolute difference ranged between 3.4–15.7 percentage points per CpG site. In the other three CGIs tested, methylation levels in the two fractions did not differ significantly, and/or the difference was more moderate. In the examined CGIs, methylation levels were highly correlated between cell fractions. In summary, our analysis detects region-specific differential DNA methylation between white blood cell subtypes, which can confound the outcome of whole blood DNA methylation measurements. Finally, by demonstrating the high correlation between methylation levels in cell fractions, our results suggest a possibility to use a proportional number of a single white blood cell type to correct for this confounding effect in analyses.     

Evaluating the effectiveness of road mitigation measures

The last 20 years have seen a dramatic increase in efforts to mitigate the negative effects of roads and traffic on wildlife, including fencing to prevent wildlife-vehicle collisions and wildlife crossing structures to facilitate landscape connectivity. While not necessarily explicitly articulated, the fundamental drivers behind road mitigation are human safety, animal welfare, and/or wildlife conservation. Concomitant with the increased effort to mitigate has been a focus on evaluating road mitigation. So far, research has mainly focussed on assessing the use of wildlife crossing structures, demonstrating that a broad range of species use them. However, this research has done little to address the question of the effectiveness of crossing structures, because use of a wildlife crossing structure does not necessarily equate to its effectiveness. The paucity of studies directly examining the effectiveness of crossing structures is exacerbated by the fact that such studies are often poorly designed, which limits the level of inference that can be made. Without well performed evaluations of the effectiveness of road mitigation measures, we may endanger the viability of wildlife populations and inefficiently use financial resources by installing structures that are not as effective as we think they are. In this paper we outline the essential elements of a good experimental design for such assessments and prioritize the parameters to be measured. The framework we propose will facilitate collaboration between road agencies and scientists to undertake research programs that fully evaluate effectiveness of road mitigation measures. We discuss the added value of road mitigation evaluations for policy makers and transportation agencies and provide recommendations on how to incorporate such evaluations in road planning practices.     

Fecundity determines the extinction threshold in a Canadian assemblage of longhorned beetles (Coleoptera: Cerambycidae)

Reproductive rate has been suggested to have a positive effect on the amount of habitat loss a species can tolerate while emigration from habitat patches has been suggested to have both positive and negative effects. Forest fragmentation has been suggested to have negative effects on forest species. We determined the extinction threshold for 12 species of saproxylic (dead wood dependent) longhorned beetles (Coleoptera: Cerambycidae) using trap catch data from Ontario, Canada. We also determined the maximum egg production of each species and whether they were likely to move outside of forest patches. We found a strong negative relationship between reproductive rate and the minimum habitat amount required for species presence. This relationship is obscured if the scale of investigation is not appropriate for the study organism. As well, species caught moving outside forest habitat had lower extinction thresholds than species not caught moving outside forest but this was not significant after accounting for reproductive rate. Fragmentation did not have an effect on the minimum habitat requirements. These relationships can inform predictions of which species will be most affected by habitat loss.     

THE FLORAL AND EXTRA-FLORAL NECTARIES OF PASSIFLORA. I. THE FLORAL NECTARY

Floral nectary development and nectar secretion in three species of Passiflora were investigated with light and electron microscopy. The nectary ring results from the activity of an intercalary meristem. Increased starch deposition in the amyloplasts of the secretory cells parallels maturation of the nectary phloem. Large membrane-bound protein bodies are observed consistently in phloem parenchyma cells, but their function is presently unknown. The stored starch serves as the main source of nectar sugars at anthesis. Plastid envelope integrity is maintained during starch degradation, and there is no evidence of participation of endoplasmic reticulum or Golgi in the secretion of pre-nectar. It is concluded that in these starchy nectaries granulocrine secretion, commonly reported for floral nectaries, does not occur.