Plant strategies along mountain vegetation gradients: a test of two theories

Abstract. We test the predictions of two theories on plant strategies along vegetation gradients of a North Scandinavian mountain area, from herb-rich birch forests at 250 m. a.s.l. to the summit at 1530 m. a.s.l. According to Grime's theory, stressful physical conditions select for an adaptational syndrome called S-strategy. The theory predicts that the prevalence of S-strategic features increases monotonically from forests to high-alpine boulder fields. Alternatively, the traits that Grime regards as S-strategic can be interpreted as adaptations to high natural-grazing pressure which culminates in moderately stressful habitats: productive enough to sustain grazers but yet so barren that moderate grazer densities suffice to deplete the vegetation. The observed vegetation patterns support this alternative view. We thus suggest that Grime's triangle should be revised as to make the role of grazing as the central causal factor behind the third strategy explicit.     

Dynamics of voles and small mustelids in the taiga landscape of northern Fennoscandia in relation to habitat quality

In the forests of northern Fennoscandia during the I980's, the dynamics of microtine rodents changed from multiannual high amplitude fluctuations (cycles) to, depending on species, fluctuations with a strong seasonal component or fluctuations with smaller amplitude and lower frequency. Microtine and predator data from the Pallasjarvi area, Finnish Lapland, suggest that this transition took place at different rates in different parts of the taiga landscape. Generally, densities in forest habitats have been primarily seasonal since 198S-86. In mesic spruce taiga and in drier forest habitats microtines had a prolonged peak in 1981-83 and a crash in 1984-83. At the timberline, however, microtine populations dropped from peak to low densities already in 1982-83 but the final crash did not occur until spring 1985. The synchronous decrease in microtines densities in all habitat types in 1984-85 coincided with increase in weasel activity. Activity of other carnivores was consistently high in mesic lowland habitats. The data support following three conjectures. 1) Periodic abundance of least weasels is crucial for sustained vole cycles. 2) Predominance of stoats and other generalist predators lead to less regular fluctuations with a strong seasonal component where density declines occur in autumn and early winter. 3) In barren tundra areas, the vegetation cannot sustain high densities of microtines and. consequently, predation is not a necessary condition for population crashes.     

Control of Nuclear and Nucleolar Localization of Nuclear Inclusion Protein a of Picorna-Like Potato virus A in Nicotiana Species

The multifunctional nuclear inclusion protein a (NIa) of potyviruses (genus Potyvirus; Potyviridae) accumulates in the nucleus of virus-infected cells for unknown reasons. In this study, two regions in the viral genome-linked protein (VPg) domain of NIa in Potato virus A (PVA) were found to constitute nuclear and nucleolar localization signals (NLS) in plant cells (Nicotiana spp). Amino acid substitutions in both NLS I (residues 4 to 9) and NLS II (residues 41 to 50) prevented nuclear localization, whereas mutations in either single NLS did not. Mutations in either NLS, however, prevented nucleolar localization and prevented or diminished virus replication in protoplasts, accumulation in infected plant tissues, and/or systemic movement in plants. One NLS mutant was partially complemented by the wild-type VPg expressed in transgenic plants. Furthermore, NLS I controlled NIa accumulation in Cajal bodies. The VPg domain interacted with fibrillarin, a nucleolar protein, and depletion of fibrillarin reduced PVA accumulation. Overexpression of VPg in leaf tissues interfered with cosuppression of gene expression (i.e., RNA silencing), whereas NLS I and NLS II mutants, which exhibited reduced nuclear and nucleolar localization, showed no such activity. These results demonstrate that some of the most essential viral functions required for completion of the infection cycle are tightly linked to regulation of the NIa nuclear and nucleolar localization.     

Functional analysis of the C(–188)A polymorphism of the human leptin promoter

Mutational analysis of the promoter region of the leptin gene in morbidly obese Finnish subjects had revealed a previously unidentified C(–188)A polymorphism in the proximal promoter that showed a weak association with elevated serum leptin levels in obese male carriers of the variant (–188A) allele. In this study we demonstrated that neither expression of reporter gene constructs driven by wild-type (–188C) or variant (–188A) proximal promoter regions, nor assay of binding of cellular proteins reveal a genotype-related difference in promoter activity. Received: 16 April 1998 / Accepted: 8 July 1998     

Flow cytometric quantitative determination of ingestion by phagocytes needs the distinguishing of overlapping populations of binding and ingesting cells.

BACKGROUND: The use of flow cytometry with fluorescently labeled particles provides the means to examine quantitatively the phagocytotic capacity of an individual phagocyte. This report describes an improved flow cytometric method of analysis for kinetic measurement of phagocytosis of fluorescein isothiocyanate (FITC)-labeled zymosan particles by human leukocytes. METHODS: FITC-labeled zymosan was incubated with leukocyte suspension, and at selected time intervals fluorescence positive neutrophils were divided by phagocytotic gates into three subpopulations: neutrophils that were neither binding nor ingesting particles, neutrophils that were only binding particles (binding cells), and neutrophils that were binding and ingesting particles (ingesting cells). For the distinction between internalized and surface-bound FITC-labeled zymosan, trypan blue (1.2 mg/ml) was used to quench surface-bound fluorescence. RESULTS: The technical challenges related to settings of phagocytotic gates and derivation of phagocytotic equations were presented. From 28 control samples, numerical values of mean fluorescence intensities and percentages of phagocytotic subpopulations inside phagocytotic gates before and after quenching were inserted into phagocytotic equations and corrected phagocytotic parameters were calculated. Calculated parameters were surprisingly constant across individuals. CONCLUSIONS: Essential elements of the present method appeared to be partial quenching of extracellular fluorescence with trypan blue and distinguishing between overlapping populations of binding and ingesting cells. Corrections using derived phagocytotic equations proved necessary for accurate kinetic phagocytotic measurements. Corrections were less necessary when the ingestion process was finished.     

Dynamics of local expansion by an introduced species: Pterostichus melanarius Ill. (Coleoptera, Carabidae) in Alberta, Canada

A recently established population of Pterostichus melanarius Ill., a wing-dimorphic, introduced carabid beetle species, was studied over a 7-year period in Alberta, Canada. We monitored local colonization, and tested classical hypotheses about spatial and temporal changes in proportion of flight-wing morphs in the Carabidae. Between 1991 and 1997, a sizable population in a road verge (0.17 individuals/trap/day in 1991) expanded only slowly into an adjacent aspen-poplar forest: the catch of 0.005 ind./trap/day in the forest in 1997 was not significantly higher than that of 0.001 ind./trap/day in 1991. However, a significantly higher proportion of P. melanarius were macropterous, long-winged (LW) in the forest (80%) than in the road verge and at the forest edge (54%). This supports the hypothesis that newly established populations are characterized by a high proportion of LW individuals, and further indicates that dispersal from the road verge into the forest has taken place primarily through flight. The overall proportion of flightless, brachypterous individuals (SW) captured at the study site increased from 39% in 1991 and 1992 to 57% in 1997, supporting the hypothesis that the proportion of SW individuals will increase with time since establishment of a population. Captures of P. melanarius in the forest were patchy and concentrated in particular areas throughout the study. However, these bridgehead’ populations did not grow or expand obviously, suggesting that populations adapt to forest conditions or reach some threshold size before effective expansion.