Pollen Ontogeny in Catananche caerulea L. (Compositae: Lactuceae) II. Free Microspore Stage to the Formation of the Male Germ Unit

The development of Catananche caerulea pollen grains from theearly free microspore stage to the formation of the male germunit has been studied using the scanning electron microscope.The differentiation of the elaborate ectexine from primexineand the accompanying cytoplasmic changes in the microsporesare described. Changes in the tapetum, reflecting first theformation of sporopollenin precursors and then of pollenkitt,are also described. The origin of taxonomically important featuresis discussed. Catananche caerulea, Compositae: Lactuceae, microspore mitosis, male germ unit, ontogeny, primexine differentiation, scanning electron microscopy     

The past history and recent decline of Badgers Meles tneles in Essex: an analysis of some of the contributory factors

The past history of the Badger in Essex is reviewed. It is shown that the population has fluctuated in the past, and that heavy gamekeeping pressure probably reduced numbers at the turn of the century, although Badgers were probably never as rare as early recorders believed. In recent years Badgers have been rare or absent in many areas of the county because they did not afford suitable sett sites, and the county as a whole is not particularly good for Badgers. Against this already low-density Badger population, in the 20 years up to the mid-1980s, 36 % of known setts had disappeared, with agricultural activities being the major cause of sett losses, and of the remaining setts there was a 14 % reduction in the number occupied by Badgers. Also, the modal sett size was reduced from six holes to three. Direct disturbance affected nearly a quarter of all viable setts in Essex. The significance of these findings is evaluated, and the effects of changing land use, sett disturbance, Badger digging, road deaths and sub-lethal levels of agricultural chemicals on Badger numbers are discussed and quantified where possible. The possible effects of a continued fragmentation of the Badger population in Essex is reviewed. The need for further research on particular aspects of the problem, and the value of such data in understanding the population pressures facing the Badger elsewhere in Europe, are highlighted.     

Effects of density-dependence and weather on population changes of English passerines using a non-experimental paradigm

The Common Birds Census documents changes in the populations of the more abundant British land birds. Here we analyse the CBC data for various English passerines to discover the separate effects of weather and of density-dependent feedback on their annual population changes. Density dependence is generally apparent in the data from woodland plots, less so in those from farmland. There are clear effects of weather, particularly in farmland. Prolonged snowfall in winter reduces populations of most species; frost and low temperatures appear much less important. Rainfall in March and April increases numbers censused in the spring but this may be an artefact. We discuss ways in which analyses such as these should be taken forward.
We consider whether this work is respectable science, arguing that monitoring through the CBC goes much further than mere surveillance of numbers, that such monitoring is important in wildlife management, and that density dependence is not a bankrupt paradigm. Long-term data gathering is an essential part of ecological science, even in programmes not designed at the outset to test specific hypotheses.     

Origins of diverse feeding ecologies within Conus, a genus of venomous marine gastropods

Specialized predators on polychaetes, fishes, hemichordates or other molluscs, members of the predominantly tropical gastropod genus Conus diversified rapidly during the Miocene to constitute the most species-rich modern marine genus. We used DNA sequence data from mitochondrial and nuclear loci of 76 Conus species to generate species-level phylogenetic hypotheses for this genus and then mapped known diets onto the phylogenies to elucidate the origins and evolutionary histories of different feeding specializations. The results indicate that dramatically new feeding modes arose only a few times, that the most derived feeding modes likely arose in the Miocene, and that much of the known diversity of Conus that was generated during Miocene radiations has survived to the present.     

Phylogeny, classification, and biogeography of the cycloteline Therevinae (Insecta: Diptera: Thereavidae)

Twenty-one members of the Laurasian group of Therevinae (Diptera: Therevidae) are compared using 65 adult morphological characters. Cladistic analysis using parsimony on the 17 ingroup and 4 outgroup taxa provides a well-supported hypothesis of relationships among taxa within the Gyclotelini, tribe nov. The Cyclotelini is a monophyletic assemblage of mostly New World genera, including Anolinga , gen. nov. , Breviperna Irwin, Coleiana , gen. nov. , Crebraseta , gen. nov. , Cyclotelus Walker, Mesonana , gen.nov. , and Ozodiceromyia Bigot. In addition, three Old World genera, Ammothereva Lyneborg, Bugulaverpa , gen. nov. , and Procyclotelus Nagatomi & Lyneborg, are included in the tribe. These ten genera are divided into two monophyletic genus-groups, the Brevipema-group and the Cyclotelus-group. Keys are provided for the genera of Cyclotelini. The tribe, the two informal genus-groups, and all genera are diagnosed; five new genera and six new species are proposed. The biogeographical histories of the genera are discussed in terms of their cladistic relationships using methods of cladistic biogeography. Two major vicariant events account for the current distribution of the tribe. The first relates to the Beringian land bridge connecting western North America and eastern Asia. Second, New World cyclotelines were profoundly affected by the Early Eocene breakup of the archipelagic bridge between North and South America, and the distributions support the hypotheses favouring the continental origin of the Greater Antilles.     

Genetic control of predator avoidance behaviour in Daphnia

1. The vertical migration behaviour in electrophoretically distinguishable clones of Daphnia magna Straus was investigated. 2. Clones differed significantly in their tendency to stay near the surface of the tank during the light phase of the daily light/dark cycle, indicating that vertical migration has a genetic component. 3. There was a significant difference in behaviour between juvenile and adult Daphnia: overall the juveniles stayed closer to the water surface than the adults, but the characteristic pattern of clonal differences persisted in the juveniles. 4. When an adult population of each clone was exposed to a fish predator in an experimental tank, the position a clone maintained in the tank at the start of the day had a direct effect on its survival. Clones remaining near to the surface of the water suffered greatest predarion.     

On partial local smoothing rules for curve estimation

We compare the performances of local and global rules for smoothingparameter choice, in terms of asymptotic mean squared errorsof the resulting estimators. In some instances there is surprisinglylittle to choose between local and global approaches; our analysisidentifies contexts where the differences are small or large.This work motivates development of smoothing rules that forma ‘half-way house’ between local and global smoothing.There, interpolation provides a basis for partial local smoothing.A key result shows that interpolation on even a coarse gridcan produce a very good approximation to full local smoothing.Our theoretical and numerical results lead us to suggest linearinterpolation of a bandwidth obtained by integral approximationson discrete intervals.     

Population limitation in Palaearctic-African migrant passerines

We report the results of key factor analyses for Sedge Warbler Acrocephalus schoenobaenus, Blackcap Sylvia atricapilla, Whitethroat Sylvia communis and Willow Warbler Pftylloscopus Irochilus based on extensive data from the United Kingdom gathered by the British Trust for Ornithology. These results are compared with those from published key factor analyses based on intensive studies of Swallows Hirundo ruslica, Redstarts Phoenicurus phoenicums and three populations of Pied Flycatchers Fiiedula hypoleuca. Variation in losses between fledging and the following breeding season lk₄ ) accounted for most of the variation in total losses (K_T) for all populations. Breeding performance was poorly correlated with population changes. Density-dependence was found mainly in 6₄, its strength decreasing as average rate of population change increased. There was also evidence of weak density-dependence in the clutch size of Swallows and in Willow Warbler egg losses. Fluctuations in k₄ were correlated with conditions on the wintering grounds in Sedge Warblers, Whitethroats and Swallows, for the first two species these relationships being confirmed by analyses of independent survival estimates based on mark-recapture data. Populations of Sedge Warblers and Whitethroats appear to be limited by competition for resources on the wintering grounds. Removal experiments suggest that Willow Warblers, Pied Flycatchers and perhaps Blackcaps are limited through recruitment to the breeding population, in the case of Pied Flycatchers this limitation being in relation to the availability of nest sites.     

Induction by Butyrate of Differentiated Properties in Cloned Murine Rhabdomyosarcoma Cells

A cell line derived from the murine rhabdomyosarcoma BW10139 (Dexter, Cancer Res. 37: 3136, 1977) was subcloned and examined with respect to growth and myogenic characteristics in the presence and absence of 1 mM butyrate. Without butyrate, these cells behave as typical transformed cells: they grow rapidly and chaotically, do not form multinucleated muscle fibers and have little or no creatine kinase activity. In the presence of 1 mM sodium butyrate or butyric acid, growth slows, cells become arranged in whorl patterns, and creatine kinase activities increase to levels comparable to those found in normal chick myoblasts immediately prior to cell fusion. The increase in creatine kinase activity is detectable within 2 h exposure to butyrate, reaches a maximum by 24 h, and the elevated level can be maintained for at least six weeks. The induction is reversible upon sequential addition, deletion, and readdition of butyrate to the culture medium. Isoenzyme analyses demonstrated that only the BB form of creatine kinease is induced; MM creatine kinase was not detected. Although formation of multinucleated cells increases after exposure to butyrate, no typical myotubes form. The results suggest that this rhabdomyosarcoma cell line can, under appropriate conditions, re-express some properties characteristic of skeletal muscle, but not the complete muscle phenotype.