Relationship between the seed rain and the establishment of vegetation in two areas abandoned after peat harvesting

In this study the number and species composition of diaspores dispersing into two newly abandoned peat harvesting areas in Finland were investigated. In an area abandoned six years earlier a total of 2978 living seeds m⁻², representing 18 species, was captured by using water-filled traps during two summers. In a one-year-old succession area the total number of living seeds m⁻² was 2241, representing 16 plant species. The soil seed banks were found to be empty of viable seeds. In neither area there appeared to be any relation between number of dispersing seeds and of plant individuals of the same species in the pioneer vegetation. It is suggested that unfavourable conditions on the soil surface for seed germination and seedling growth of most dispersed species are majors factor in determining the structure of the established vegetation.     

Variation in the carbon content of two Asplanchna species

The rotifers of the genus Asplanchna were sampled four times during the summer from eight lakes of different types. The mean individual carbon content in the population varied between 0.15–0.66 µg C ind.^-1 (n = 21) for A. priodonta and 1.0–1.6 µg C ind.^-1 (n = 3) for A. herricki. The carbon content and the size of A. priodonta varied considerably between the populations of both different lakes and dates.The carbon level of both Asplanchna species (sample mean 0.2–1% of wet weight) was considerably lower than is generally found for rotifers. Much of the variation of carbon level could be explained by an inverse relationship with wet weight. The high variation in the carbon content of individuals suggests that Asplanch population may adapt their mean body size to fit prevailing environmental conditions.     

Trimethyloxonium modification of single batrachotoxin-activated sodium channels in planar bilayers. Changes in unit conductance and in block by saxitoxin and calcium

Single batrachotoxin-activated sodium channels from rat brain were modified by trimethyloxonium (TMO) after incorporation in planar lipid bilayers. TMO modification eliminated saxitoxin (STX) sensitivity, reduced the single channel conductance by 37%, and reduced calcium block of inward sodium currents. These effects always occurred concomitantly, in an all-or-none fashion. Calcium and STX protected sodium channels from TMO modification with potencies similar to their affinities for block. Calcium inhibited STX binding to rat brain membrane vesicles and relieved toxin block of channels in bilayers, apparently by competing with STX for the toxin binding site. These results suggest that toxins, permeant cations, and blocking cations can interact with a common site on the sodium channel near the extracellular surface. It is likely that permeant cations transiently bind to this superficial site, as the first of several steps in passing inward through the channel.     

The importance of bacterial utilization of released phytoplankton photosynthate in two humic forest lakes in southern Finland

Bacterial utilization of photosynthetically fixed dissolved organic carbon (PDOC) released from natural phytoplankton assemblages was studied in two small, extremely humic, forest lakes in southern Finland. Bacterial activity (measured as uptake of ¹⁴C-glucose) and phytoplankton photosynthesis (measured as light uptake of ¹⁴CO₂) could be most effectively separated using Nuclepore filters of pore size 1–2 μm. Released PDOC was 10–67% of total phytoplankton carbon fixation during in situ experiments, and represented about 0.1% of total DOC. Net uptake of PDOC by bacteria was found to be about 20% during 24 hour laboratory incubations, although about 40% of PDOC present at the start of an experiment could be utilized by bacteria during a 24 hour period. PDOC does not provide a quantitatively important substrate supply for bacterial respiration in humic forest lakes.     

Cold and hyperosmolar fluids in canine trachea: vascular and smooth muscle tone and albumin flux

We have studied the effects of liquids of various osmolalities and temperatures on the tracheal vasculature, smooth muscle tone, and transepithelial albumin flux. In 10 anesthetized dogs a 10- to 13-cm length of cervical trachea was cannulated to allow instillation of fluids into its lumen. The cranial tracheal arteries were perfused at constant flow, with monitoring of the perfusion pressures (Ptr) and the external tracheal diameter (Dtr). Control fluid was Krebs-Henseleit solution (KH) with NaCl added to result in a 325-mosM solution (isotonic). Hypertonic solutions were KH with NaCl (warm hypertonic) or glucose (hypertonic glucose) added to result in a 800-mosM solution. All solutions were at 38 degrees C, with isotonic and the hypertonic NaCl solutions also given at 18 degrees C (cold isotonic and cold hypertonic). Fluorescent labeled albumin was given intravenously, and the change in fluorescence in the fluid was measured during each 15-min period. Changing from warm isotonic to cold isotonic decreased Dtr and Ptr. Changing from warm isotonic to warm hypertonic or hypertonic glucose decreased Ptr with no change in Dtr. The cold hypertonic responses were not different from cold isotonic responses. Warm hypertonic solution increased albumin flux into the tracheal lumen over a 15-min period to three times that of the control period, persisting for 15 min after replacement with warm isotonic solution. Cooling induces a vasodilation and smooth muscle contraction of the trachea, whereas hypertonic solutions result in vasodilation and, if osmolality is increased with NaCl, an increase in albumin flux into the tracheal lumen.     

Relative apparent synapomorphy analysis (RASA). I: The statistical measurement of phylogenetic signal

We have developed a new approach to the measurement of phylogenetic signal in character state matrices called relative apparent synapomorphy analysis (RASA). RASA provides a deterministic, statistical measure of natural cladistic hierarchy (phylogenetic signal) in character state matrices. The method works by determining whether a measure of the rate of increase of cladistic similarity among pairs of taxa as a function of phenetic similarity is greater than a null equiprobable rate of increase. Our investigation of the utility and limitations of RASA using simulated and bacteriophage T7 data sets indicates that the method has numerous advantages over existing measures of signal. A first advantage is computational efficiency. A second advantage is that RASA employs known methods of statistical inference, providing measurable sensitivity and power. The performance of RASA is examined under various conditions of branching evolution as the number of characters, character states per character, and mutations per branch length are varied. RASA appears to provide an unbiased and reliable measure of phylogenetic signal, and the general approach promises to be useful in the development of new techniques that should increase the rigor and reliability of phylogenetic estimates.      

Variation in heat-shock proteins among species of desert fishes (Poeciliidae, Poeciliopsis)

Analysis of the heat-shock proteins (hsps) of six closely related species of Poeciliopsis demonstrated the existence of biochemical diversity in the hsp100, hsp70, hsp60, and hsp30 protein families among species. Each species expressed five to seven hsp70-related isoforms. Constitutive 70-kD isoforms were identical among species, but four different patterns of heat-inducible isoforms were seen in these six species. Members of the hsp70 family of molecular chaperones are included among the most highly conserved proteins known, and the possibility of variation in hsp70 among closely related species has rarely been addressed. The hsp30 family is known to be less conserved than the hsp70 family, and, as expected, the Poeciliopsis hsp30 patterns showed more variation. Most of the hsp30 isoforms characteristic of a particular species were unique to that species. Hsp100 and hsp60 were identical in five of the species, but alternate isoforms were found in P. monacha. The small size and limited geographical distribution of the P. monacha population have probably contributed to the uniqueness of the monacha pattern. Two of the species were shown to acquire thermotolerance, the ability to withstand normally lethal temperatures when subjected to a gradual temperature increase. Rapid-heating protocols commonly used to establish critical thermal maxima of organisms do not include this inducible component of thermoresistance and therefore do not adequately assess an organism's capacity to withstand thermal stress.      

Interaction of workplace demands and cardiovascular reactivity in progression of carotid atherosclerosis: population based study.

OBJECTIVE: To examine the combined influence of workplace demands and changes in blood pressure induced by stress on the progression of carotid atherosclerosis. DESIGN: Population based follow up study of unestablished as well as traditional risk factors for carotid atherosclerosis, ischaemic heart disease, and other outcomes. SETTING: Eastern Finland. SUBJECTS: 591 men aged 42-60 who were fully employed at baseline and had complete data on the measures of carotid atherosclerosis, job demands, blood pressure reactivity, and covariates. MAIN OUTCOME MEASURES: Change in ultrasonographically assessed intima-media thickness of the right and left common carotid arteries from baseline to 4 year follow up. RESULTS: Significant interactions between workplace demands and stress induced reactivity were observed for all measures of progression (P < 0.04). Men with large changes in systolic blood pressure (20 mm Hg or greater) in anticipation of a maximal exercise test and with high job demands had 10-40% greater progression of mean (0.138 v 0.123 mm) and maximum (0.320 v 0.261 mm) intima-media thickness and plaque height (0.347 v 0.264) than men who were less reactive and had fewer job demands. Similar results were obtained after excluding men with prevalent ischaemic heart disease at baseline. Findings were strongest among men with at least 20% stenosis or non-stenotic plaque at baseline. In this subgroup reactive men with high job demands had more than 46% greater atherosclerotic progression than the others. Adjustment for atherosclerotic risk factors did not alter the results. CONCLUSIONS: Men who showed stress induced blood pressure reactivity and who reported high job demands experienced the greatest atherosclerotic progression, showing the association between dispositional risk characteristics and contextual determinants of disease and suggesting that behaviourally evoked cardiovascular reactivity may have a role in atherogenesis.     

Variation in heat shock proteins within tropical and desert species of poeciliid fishes

The 70-kilodalton heat shock protein (hsp70) family of molecular chaperones, which contains both stress-inducible and normally abundant constitutive members, is highly conserved across distantly related taxa. Analysis of this protein family in individuals from an outbred population of tropical topminnows, Poeciliopsis gracilis, showed that while constitutive hsp70 family members showed no variation in protein isoforms, inducibly synthesized hsp70 was polymorphic. Several species of Poeciliopsis adapted to desert environments exhibited lower levels of inducible hsp70 polymorphism than the tropical species, but constitutive forms were identical to those in P. gracilis, as they were in the confamilial species Gambusia affinis. These differences suggest that inducible and constitutive members of this family are under different evolutionary constraints and may indicate differences in their function within the cell. Also, northern desert species of Poeciliopsis synthesize a subset of the inducible hsp70 isoforms seen in tropical species. This distribution supports the theory that ancestral tropical fish migrated northward and colonized desert streams; the subsequent decrease in variation of inducible hsp70 may have been due to genetic drift or a consequence of adaptation to the desert environment. Higher levels of variability were found when the 30- kilodalton heat shock protein (hsp30) family was analyzed within different strains of two desert species of Poeciliopsis and also in wild-caught individuals of Gambusia affinis. In both cases the distribution of hsp30 isoform diversity was similar to that seen previously with allozyme polymorphisms.