Phytoplankton strategies and time scales in a eutrophic reservoir

Phytoplankton species groups were studied in a eutrophic reservoir at different time scales (daily, weekly, monthly and yearly). Four strategic groups along the r-K continuum were defined and their seasonal time courses were followed. Their temporal distribution of relative biomass reflected resource partitioning because each strategic group dominated the phytoplankton community at different times in the year. However, the relationships between strategic groups changed with the time scale involved. At the daily scale an inverse relationship between r- and K-groups occurred whereas at supradaily scales such relationships did not hold. Species groups reflected strategic groups. No relationship between population growth and losses was found, suggesting that both were not counterbalanced. In the long term (supraannual) the phytoplankton community changed very much in this reservoir, its ecological memory being small as compared with that of lakes.     

Establishment of Transplants on Machine-Graded Ski Runs Above Timberline in the Swiss Alps

The suitability of 24 native species for restoration above the timberline in Switzerland was assessed with demographic monitoring of their populations after transplanting. The plots were laid out in 1985–1986 and 1995–1996 on machine‐graded ski runs using a total of 8,603 transplants of native grasses, legumes and forbs. Establishment conditions were improved with biodegradable wood‐fiber mats and a small addition of garden soil. Transplant survival rates were generally good after 12 years. The regeneration of mixed stands was clearly recognizable because some transplants successfully reproduced by seed, and colonizers immigrated from the adjacent natural vegetation and neighboring restoration plots. Comparative studies of reproductive parameters in transplants and their donor population revealed that differences in seed production may become nonsignificant within a short time span. These fitness features have important diagnostic value for assessing restoration success and provide information on the performance of the same or closely related genotypes in their natural populations and in the restoration site. The plants studied showed species‐specific traits in establishment after transplanting. Most species can be recommended for restoration in the alpine vegetation belt. The risk of restoration failure can be considerably reduced by using species with different life‐history characteristics. From an ecological point of view, this method is a valid alternative to commercial revegetation using seed mixtures of non‐native species and large amounts of fertilizers.     

Interresidue interactions in protein classes

The free energy difference between folded and unfolded state is about the same for most proteins and it is not more than the energy of a few noncovalent interactions. In addition to the numerous noncovalent interactions, some proteins contain one or more disulfide bonds, which, as covalent crosslinks, significantly stabilize their tertiary structure. Correlation between the presence of disulfide bond(s), and the number noncovalent interresidue interactions of various kinds is analyzed here. The number of interactions per residue is almost the same for all protein. Also the number of long-range interactions per residue is the same in all proteins. Proteins with S(SINGLE BOND)S bond(s) (extracellular proteins) have more medium-range and fewer short-range interactions than those without S(SINGLE BOND)S bonds. However, the difference is independent of the number of these covalent crosslinks. We concluded that the different distributions of the various kinds of noncovalent interaction reflect the needs of proteins in the different environments, the extracellular and the intracellular ones, rather than the presence of the disulfide bond(s). We also pointed out that the observed differences in the distributions of short- and medium-range interactions are in good agreement with different secondary structure compositions of extracellular and intracellular proteins. Proteins 27:360–366, 1997. © 1997 Wiley-Liss, Inc.     

Young flying squirrels (Pteromys volans) dispersing in fragmented forests

Dispersal is a key determinant of the population dynamics ofspecies. Thus, a better understanding of how dispersal is affectedby the landscape structure and how animals make decisions aboutmoving across different landscapes is needed. We studied thedispersal of 60 radio-collared juvenile Siberian flying squirrels(Pteromys volans) in southern Finland. The effect of landscapestructure on selected dispersal direction, dispersal distance,and straightness of dispersal path was studied. Flying squirrelswere capable of dispersing over long distances in fragmentedforest landscapes. The patches used as temporary roosting sitesduring dispersal were of a lower quality than were those usedas finally occupied patches. The patches used were larger thanwere patches on average in the study areas. There was a veryclear directional bias in the dispersal path (i.e., it was nearlya straight line), which remained over a large scale, but wide-openareas obstructed the straightness of the path. As the distancesbetween crossed patches increased, short-distance disperserswere found further away from their natal home range. However,there were no differences in the landscape that could explainthe differences between individuals in decisions to remain philopatricor to become short- or long-distance dispersers. In addition,whereas short-distance dispersers dispersed in random directions,long-distance dispersers started to disperse in directions dominatedby preferred habitat. Thus, there were behavioral differencesbetween dispersers. Our results supported the hypotheses statingthat individuals decide to disperse long or short distancesbefore the onset of dispersal.     

Poor male function favours the coexistence of sexual and asexual relatives

Classical models of the evolution of sex typically assume that an asexual lineage, once derived, is reproductively separate from the sexual lineage from which it was derived. However, many asexuals, including hermaphrodite plants, produce male gametes capable of fertilising the eggs of co-existing sexuals, giving rise to sexual and asexual progeny. This male function of asexuals may be poor, and it has been proposed that this could favour sexuality and adversely affect the successful establishment of asexual lineages. We show that things are more complicated than this; the effect is frequency-dependent and poor male function may sometimes favour asexuality. In a spatially distributed population of flowering plants, it can prevent the successful invasion of either reproductive mode by the other via long-range dispersal. Consequently invasions must be driven by short-range dispersal, and are therefore extremely slow. Thus poor male function favours long-term co-existence of sexuals and asexuals. When coupled with the superior ability of asexuals to colonise virgin territory after an Ice Age, it may explain current ecological distribution patterns.     

Cell membrane lipid molecular dynamics in a solenoid versus a magnetically shielded room

The generalized polarization function of the fluorescent probe 2-dimethylamino-6-lauroylnaphthalene has been used to evaluate the lipid dynamics in Friend erythroleukemia cell membrane. The values of this function varied during the culture growth cycle, showing decreased lipid dynamics 24–48 h from the cell seeding. When the cycle occurred in a solenoid producing a magnetic field of 70 μT at 50 Hz in addition to the 45 μT DC of the earth (short-term 4-day exposure), the membrane lipid dynamics during this same time-period decreased by about 10% (P < .04). After long-term (184 days) or extremely long-term (395 days) exposure of the cells to the magnetic field, little additional variation in the membrane lipid dynamics was observed, suggesting an adaptation phenomenon. A variation of membrane lipid dynamics was also observed due to in vitro cell differentiation (P < .02). Nevertheless, the exposure of both undifferentiating and differentiating cells to a highly attenuated magnetic field in a magnetically shielded room (20 nT DC plus 2.5 pT AC) did not induce any modification of membrane lipid dynamics. Bioelectromagnetics 19:107–111, 1998. © 1998 Wiley-Liss, Inc.     

Impact of short- and medium-chain organic acids, acylcarnitines, and acyl-CoAs onmitochondrial energy metabolism

Accumulation of organic acids as well as their CoA and carnitine esters in tissues and body fluids is a common finding in organic acidurias, beta-oxidation defects, Reye syndrome, and Jamaican vomiting sickness. Pathomechanistic approaches for these disorders have been often focused on the effect of accumulating organic acids on mitochondrial energy metabolism, whereas little is known about the pathophysiologic role of short- and medium-chain acyl-CoAs and acylcarnitines. Therefore, we investigated the impact of short- and medium-chain organic acids, acylcarnitines, and acyl-CoAs on central components of mitochondrial energy metabolism, namely alpha-ketoglutarate dehydrogenase complex, pyruvate dehydrogenase complex, and single enzyme complexes I-V of respiratory chain. Although at varying degree, all acyl-CoAs had an inhibitory effect on pyruvate dehydrogenase complex and alpha-ketoglutarate dehydrogenase complex activity. Effect sizes were critically dependent on chain length and number of functional groups. Unexpectedly, octanoyl-CoA was shown to inhibit complex III. The inhibition was noncompetitive regarding reduced ubiquinone and uncompetitive regarding cytochrome c. In addition, octanoyl-CoA caused a blue shift in the gamma band of the absorption spectrum of reduced complex III. This effect may play a role in the pathogenesis of medium-chain and multiple acyl-CoA dehydrogenase deficiency, Reye syndrome, and Jamaican vomiting sickness which are inherited and acquired conditions of intracellular accumulation of octanoyl-CoA.