Gap junction reductions precede tissue hyperplasia following temperature-upshift in theDrosophila ts-mutantl(3)c43 hs1

Summary The wing discs of the temperature-sensitiveDrosophila mutantl(3)c43 ^hs1 become hyperplastic when larvae are reared at the restrictive temperature of 25° C or above (Martin et al. 1977). We have previously shown that reductions in gap junctions are correlated with the hyperplasia (Ryerse and Nagel 1984a). We report here that reductions in gap junction surface density, number and percent of the lateral plasma membrane area precede the onset of tissue hyperplasia as defined by the gross appearance of tissue overgrowth in the wing pouch and an increase in cell number. Gap junction reductions begin soon after temperature upshift and become significantly different from non-shifted controls by 16 h. Direct cell counts indicate that there is no difference in the total number of cells in experimental vs control discs until after 16 h when the 28° C discs begin to grow rapidly with a cell doubling time of about 6 h as compared with about 13 h for the 20°C controls. The finding that gap junction reductions precede the onset of tissue hyperplasia is consistent with the idea that gap junctions play a regulatory role in growth control and pattern formation and strengthens our hypothesis (Ryerse and Nagel 1984b) that a minimum number and a specific distribution of gap junctions are required for normal development.     

Pattern formation in fragmented eggs of the short germ insect Schistocerca gregaria

Summary The effect of transverse fragmentation on the segment pattern of the short germ embryo of the locust Schistocerca gregaria has been investigated at two stages subsequent to the formation of the germ anlage. Following fragmentation both anterior and posterior partial embryos were observed, although rarely in a single egg. Anterior partial patterns usually terminated with a segment visible at the time of fragmentation or with the next segment due to appear. Posterior partial patterns began with a wide range of segments depending on the level of fragmentation.Anterior and posterior partial patterns developing in a single egg were usually not complementary and the segments missing sometimes included some segments visible when the embryo was fragmented. Non-complementary patterns resulted following fragmentation in all regions, while complementary patterns only occurred after fragmentation in the visibly-segmented region.The results suggest that following fragmentation isolated posterior portions of the embryo continue to form segments, while isolated anterior regions usually do not. This effect could result from variable damage to an existing pattern of unequally-sized segment primordia, or from the disruption of a process of sequential segmentation in the elongating posterior region of the embryo. The results are broadly compatible with the progress zone model proposed by Summerbell et al. (1973).     

Maternal-effect mutations altering the anterior-posterior pattern of the Drosophila embryo

Summary Mutations in seven different maternal-effect loci on the second chromosome of Drosophila melanogaster all cause alterations in the anterior-posterior pattern of the embryo. Mutations in torso (tor) and trunk (trk) delete the anterior- and posterior-most structures of the embryo. At the same time they shift cellular fates which are normally found in the subterminal regions of the embryo towards the poles. Mutations in vasa (vas), valois (vls), staufen (stau) and tudor (tud) cause two embryonic defects. For one they result in absence of polar plasm, polar granules and pole cells in all eggs produced by mutant females. Secondly, embryos developing inside such eggs show deletions of abdominal segments. In addition, embryos derived from staufen mothers lack anterior head structures, embryos derived from valois mothers frequently fail to cellularize properly. Mutations in exuperantia (exu) cause deletions of anterior head structures, similar to torso, trunk and staufen. However in exu, these head structures are replaced by an inverted posterior end which comprises posterior midgut, proctodeal region, and often malpighian tubules.The effects of all mutations can be traced back to the beginning stages of gastrulation, indicating that the alterations in cellular fates have probably taken place by that time. Analysis of embryos derived from double mutant mothers suggests that these three phenotypic groups of mutants interfere with three different, independent pathways. All three pathways seem to act additively on the system which specifies anterior-posterior cellular fates within the egg.     

The spatial pattern in a natural population of goldenrod (Solidago altissima L.), with particular reference to its change during the shoot growth

In a natural population of Solidago altissima L., the changes in the spatial pattern of shoots in the course of growth were studied. The results obtained were summarized as follows:

1. The spatial pattern changed from clumped to random distribution as plants grew. The change seemed to be resulted from some density-dependent process acting at a small spatial scale, probably the competition for space.
2. Large plants tended to distribute themselves more uniformly over the space than the small ones but at the mature stage of growth such a difference was not obviously recognized. The process of appearance of the small-sized plants during successive periods also seemed to be dependent on local density.
3. Large plants at the early stage of growth tended to survive better, and there was a positive correlation between initial size and the size at maturity.
4. From these results, it is inferred that the change of spatial pattern from clumped to random distribution is largely due to the elimination of small shoots as the result of competition for space among individual shoots.

     

Establishment of microscale vegetation pattern in maritime chaparral after fire

We quantified microscale pattern in vegetation and seed assemblages along a 24 m transect before and for two years following a controlled burn in chamise (Adenostoma fasciculatum) chaparral in central coastal California. Our objective was to document scale-dependent correlation between pre-burn seed assemblages, pre-burn canopy cover, microtopography, soil temperatures during burning, post-burn seed assemblages and post-burn vegetation. Scale-dependent correlations among pre- and post-burn seed densities, maximum soil temperatures during burning, microtopography and post-burn vegetation were measured based on two-term local covariance analysis.Seed distribution varied among species prior to fire, with seeds of some annual species concentrated in gap areas. Maximum soil temperatures during burning ranged from less than 50 °C to 225 °C, and were generally lowest in gaps in the pre-burn canopy. These gaps were associated with local topographic depressions. After burning, readily germinable seeds were concentrated in or near gaps in the pre-burn canopy. Germination of different species was variously enhanced, diminished or unchanged by the passage of fire. Post-burn vegetation was very patchy, with some areas nearly devoid of seedlings and other areas, especially pre-burn canopy gaps, supporting numerous seedlings. Seedling recruitment patterns in the second year were generally highly correlated with patterns in pre-burn seed banks and first year vegetation. Although many species exhibited similar recruitment patterns, several different mechanisms may have been responsible for the origin of those patterns.     

Explanation and prediction in vegetation science

A definition of vegetation science is given, spanning 6 levels of integration and stressing the interrelations among them. The problems of realism are discussed. The selection of levels is related to the adequate correspondence between conceptualization and research aims. Pattern and process are introduced as the central concepts of vegetation science. The perception of reality is dependent on the spatial and temporal scale chosen. The concept of noise is discussed in relation to stochasticity and randomness of events. Traces of essentialism are found both in classification of communities and habitat ecology. Classification is important, particularly the coexistence of alternative classification approaches. Organicism as a basis of vegetation research is rejected because the organismic view is inadequate on higher integration levels. The concept of function is redefined in a non-teleologic way.Present vegetation ecological research is inductivistic. One possible alternative to inductivism is falsificationism. The major domain of this approach is hypothesis testing, which will become more important. Progress can only be reached by a maximum degree of communication among scientific individuals.Predictive ecology is partly based on historic explanation, partly on complementary approaches. Characters of vegetation worthwhile to be predicted are listed and the necessary requirements for vegetation science to become predictive are discussed. A major requirement is the development of succession and life-history theory. A further elaboration of the individualistic concept will be a main task of vegetation science in the near future.     

红池坝地区草地红三叶草的空间分布型

植物种群的空间分布型是生物在特定的条件下形成的,它反映了植物种群个体的散布状态以及对环境的适应性和生境对植物影响的生态反映的生态学关系,是一条可以了解凭种类组成研究演替的研究途径 森下正明(Morisita,1959)提出了扩散指数Io(Morisita's index);美国的Lloyd,(1967)提出了平均拥挤度(Mean crowding,m)这个颇有兴趣     

The spatial distribution pattern of the brown planthopperNilaparvata lugens Stål (Homoptera: Delphacidae) in west Java,Indonesia

Spatial distribution pattern of the brown planthopper (BPH) was analyzed at 9 experimental fields in the northern part of West Java during two consecutive rice cropping seasons, i.e., wet and dry seasons. The population of each developmental stage and wing form of BPH at each location showed consistent departure from the random (Poisson) distribution, the variances of the densities in most cases exceeding their means. Namely, the distribution pattern of BPH per hill of rice plant was found to have a general tendency to be aggregated or contagious and to fit fairly well to the negative binomial model. The tendency for aggregation was further confirmed by both the β-values of -m regression being larger than unity and the C_A-values being larger than zero for each developmental stage. Although significant variations in the distribution pattern as measured by β- or C_A-value were observed between different developmental stages, between wing forms and among locations, the degree of aggregation for a given developmental stage at each experimental field remained fairly stable throughout the crop period, despite wide temporal changes in population density. Possible factors to explain these characteristics of the spatial distribution pattern of the BPH in West Java were discussed with reference to the process generating it.     

Optokinetic speed control and estimation of travel distance in walking honeybees

Honeybees returning from foraging trips were video-filmed while they walked through a narrow transparent gangway to reach the hive entrance. On their way they were presented with black-and-white gratings viewed underneath as well as to both sides of the gangway. Bees could exit the gangway through one of two or three side exits installed at different distances from the gangway entrance. In one set of experiments, the substrate on which the bees walked was moved either in the bee's direction or against it. In another set of experiments, the substrate was stationary, but the pattern was moved in one or the other direction. The bee's walking speed (WS) was evaluated from the video tapes. When the substrate moved against, or the pattern in the bee's direction, in either case decreasing the speed of pattern flow (PFS), the bees increased WS, and, at the same time, they preferred the more distant exit. When the substrate moved in, or the pattern against the bee's direction, thus increasing PFS, WS decreased and the bees preferred the nearer exit. These results suggest that the speed of optic flow controls the speed of locomotion and might therefore also serve for assessing the distance travelled.Abbreviations PFS pattern-flow speed - WS walking speed Dedicated to Hans-Jochen Autrum, editor emeritus, for help in giving birth to this and many other papers over very many years, often with criticism but nevertheless with encouragement and sympathy.