Bottom-up factors influencing riparian willow recovery in Yellowstone National Park

After the elimination of wolves ( Canis lupis L.) in the 1920s, woody riparian plant communities on the northern range of Yellowstone National Park (YNP) declined an estimated 50%. After the reintroduction of wolves in 1995–1996, riparian willows ( Salix spp.) on YNP’s northern range showed significant growth for the first time since the 1920s. However, the pace of willow recovery has not been uniform. Some communities have exceeded 400 cm, while others are still at pre-1995 levels of <80 cm mean height. We took intensive, repeated measurements of abiotic factors, including soil and water-table characteristics, to determine whether these factors might be contributing to the varying pace of willow recovery. Willows at all of our study sites were “short” (<250 cm max. height) prior to 1995 and have recovered to varying degrees since. We contrasted “tall” (>250 cm max. height) willow sites where willows had escaped elk ( Cervus elaphus L.) browsing with “short” willow sites that could still be browsed. Unlike studies that manipulated willow height with fences and artificial dams, we examined sites that had natural growth differences in height since the reintroduction of wolves. Tall willow sites had greater water availability, more-rapid net soil nitrogen mineralization, greater snow depth, lower soil respiration rates, and cooler summer soil temperatures than nearby short willow sites. Most of these differences were measured both in herbaceous areas adjacent to the willow patches and in the willow patches themselves, suggesting that they were not effects of varying willow height recovery but were instead preexisting site differences that may have contributed to increased plant productivity. Our results agree with earlier studies in experimental plots which suggest that the varying pace of willow recovery has been influenced by abiotic limiting factors that interact with top-down reductions in willow browsing by elk.     

Peptido-aminobenzophenones-novel latentiated benzo-1,4-diazepines

Summary It has been shown that cleavage of the N-terminal L-amino acids of a novel series of dipeptide derivatives of 2-aminobenzophenones occurs readily in vivo to give benzo-1,4-diazepines. Such compounds may serve as useful pro-drug forms of minor tranquillizers such as Valium^®.     

Chemical investigation of the seeds ofAlbizzia procera benth

Zusammenfassung Aus dem Samen vonAlbizzia procera Benth wurden ausser Machaerinsäure 4 triterpenoide Sapogenine isoliert (Verbindung A und B, Proceragenin A und B). Es wurde bewiesen, dass die Verbindung A das 28 21-Lacton der Machaerinsäure mit einer Konformationsänderung am Ring D oder E ist, während die Verbindung B als Äthylmachaerinat identifiziert wurde. Bei Proceragenin A und B handelt es sich um Dihydroylactone.

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A part of the work was carried out at the Department of Chemistry, Bose Institute, Calcutta-9, India, and was supported in part by the Ministry of Education, Government of India. — The authors desire to express their sincere thanks to Dr.A. K. Barua, Reader in Chemistry, Bose Institute, Calcutta and to the Rev. Dr.H. Santapau, Director, Botanical Survey of India, Calcutta for their keen interest and encouragement.     

Effect of norepinephrine and vasopressin on carotid sinus baroreceptor activity in the anesthetized rabbit

Summary Norepinephrine (NE) 10^–6 M or vasopressin (VP) 12.5 U/ml were injected into the isolated carotid sinus of anesthetized rabbits. The sinus was exposed either to the arterial pressure or to a pressure controlled reservoir. Multifiber and single fiber recordings were made. Both NE and VP increased baroreceptor activity at all sinus pressures but decreased activity in a few fibers. The results are consistent with the drugs having their effects on smooth muscle fibers in the adventitia.Acknowledgments. This work was supported by grants from the Medical Research Council of Canada and the B.C. Heart Foundation. The authors are grateful to J. Sharp and D. Morton for their excellent assistance.     

The genomic and epidemiological dynamics of human influenza A virus

The evolutionary interaction between influenza A virus and the human immune system, manifest as 'antigenic drift' of the viral haemagglutinin, is one of the best described patterns in molecular evolution. However, little is known about the genome-scale evolutionary dynamics of this pathogen. Similarly, how genomic processes relate to global influenza epidemiology, in which the A/H3N2 and A/H1N1 subtypes co-circulate, is poorly understood. Here through an analysis of 1,302 complete viral genomes sampled from temperate populations in both hemispheres, we show that the genomic evolution of influenza A virus is characterized by a complex interplay between frequent reassortment and periodic selective sweeps. The A/H3N2 and A/H1N1 subtypes exhibit different evolutionary dynamics, with diverse lineages circulating in A/H1N1, indicative of weaker antigenic drift. These results suggest a sink-source model of viral ecology in which new lineages are seeded from a persistent influenza reservoir, which we hypothesize to be located in the tropics, to sink populations in temperate regions.