X-Ray Characterization of Melanins—II

Structural modeling of amorphous eumelanin has been carried out by comparing calculated data, S(q) and RDF(r), in reciprocal and real space, respectively, for limited random network models with the experimental X-ray scattering data of tyrosine melanin (Cheng et al., 1994). A basic picture of the atomic arrangements in amorphous eumelanin, which accounts for the short and intermediate range order, has been formulated. This reveals domains of a fundamental “particle” dimension of R～ 15 Å, consisting of a paracrystalline array of disordered planar networks polymerized by 4-8 DHI monomers with a graphite-like stacking spacing of ～ 3.45 Å, 4-5 layers thick.     

Imprint of past environmental regimes on structure and succession of a deep-sea hydrothermal vent community

Dramatic perturbations of ecological communities through rapid shifts in environmental regime do not always result in complete mortality of residents. Instead, legacy individuals may remain and influence the succession and composition of subsequent communities. We used a reciprocal transplant experiment to investigate whether a legacy effect is detectable in communities experiencing an abrupt increase or decrease in hydrothermal fluid flux at deep-sea vents. Vent habitats are characterized by strong gradients in productivity and physico-chemical stressors, both of which tend to increase with increasing vent fluid flux. In our experiments, many species survived transplantation from cool (water temperatures <2°C above ambient) to warm (4–30°C above ambient) habitats, resulting in significantly higher species richness on transplanted than remaining experimental substrata. A legacy effect was much less apparent in transplantation from warm to cool habitat, although a few vestimentiferan tubeworms, normally restricted to warm habitat, survived transplantation. The asymmetry in influence of legacy individuals suggests that productivity enhancement may outweigh potential physiological stress in setting limits to distributions of vent invertebrates. This influence of biological processes contrasts with theory developed in the rocky intertidal that predicts the predominance of physical control at the high-stress end of an environmental gradient. Prediction of successional transitions in vents and other habitats experiencing regime shifts in which remnant species may survive must take into account the possible influence of historical effects.     

Heterogeneous dispersal of tree litterfall corresponding with patchy canopy structure in a temperate mixed forest

Spatial dispersal patterns of fine litter were analyzed in relation to forest structure within a temperate mixed stand, in northeastern Japan. The canopy layer was a mosaic of two types of patches, those of shade-tolerant Abies firma (estimated age being 81–146 yrs.) and early successional deciduous broad-leaved trees (about 45 yrs. of age). Litter input to the forest floor was observed for a period of three years using 38 traps set at a height of 1.2 m. The average annual total of fine litter was 6.233 (dw.) metric tons hectare^-1, 85.7% of the total litterfall. Fine litter was mostly leaves from the overstory (about 64%). Litter distribution maps were drawn, using the Davis's grid method, of the total fine litter and its two main elements, namely A. firma (a 36.1% share) and deciduous broad-leaved species (36.7%). The mosaic distribution of heterogeneous patches of litter was seem to corresponded with distribution of the canopy structure.     

The use of IAA to overcome interspecific hybrid inviability in reciprocal crosses between Nicotiana tabacum L. and N. repanda Willd.

Summary Flowering hybrid plants were obtained from reciprocal crosses between N. tabacum L. (2n=48) and N. repanda Willd. (2n = 48), in which cross incompatibility and hybrid inviability were manifested. Stylar pollination and ovule culture were used to overcome the cross incompatibility of stylar barriers and ovular death. It was shown that application of 2 mg/l indole-3-acetic acid (IAA) during the growth period, from the fiveto six-leaf stage to the flowering stage, is a useful and easy method to overcome hybrid inviability.     

Problems of joint display of species and site scores in correspondence analysis

Joint plots of species and site scores in correspondence analysis can be interpreted so that points which are in the same direction from the origin are closely associated. Species and site scores can thus be compared. Within each set of scores the location of points is also meaningful. Owing to the unimodal species response model which can be recovered by the correspondence analysis, the location of the species points in respect to the site points indicates the location of the optimum when direct weighted averages are used. However, when the eigenvalue of the solution is low, very different joint plots are derived when the set which is used for computing the weighted averages for the other set is changed. This makes the interpretation of the between-set proximities in the joint plot vague. Generally, it is not possible to deduce the species composition of a site or sites where a species occurs from the joint plot, although for some pairs of species and sites this is justified. Although the proximity interpretation is not possible in every case, a joint plot display can greatly enhance the interpretation of results.     

Effect of reciprocal crossing of selected lines of mice

Summary Mass selection of mice was conducted in populations of various size for 16 generations. Each selected population (E) corresponded to an analogous unselected population (C). The experiment was conducted in three replicates. After the 16th generation the replicates of the selected and control lines were crossed.Reciprocal crossing within the control lines gave better results than reciprocal crossing of the selected lines, despite the fact that the selected mice were characterised by a higher inbreeding coefficient. Larger effects were also obtained when crossing smaller rather than larger populations. This result is understandable since the animals from the smaller populations were characterised by higher inbreeding coefficients.The effect of heterosis was higher upon crossing the control lines rather than the selected ones and this caused a decreased the response to selection in almost all the traits investigated.This work was partly supported by U.S. Department of Agriculture, Grant No. FG-Po-348/JB-13/, Project No. PL-ARS-68