近交对单倍体-二倍体种群平衡遗传多态性的影响

本文通过对一个双等位基因位点在产雄孤雌生殖遗传体系下不完全同胞交配的模拟 ,研究了在显性、共显性和超显性遗传模式下近交对平衡多态性的影响。结果显示 :相对于二倍体 -二倍体种群 ,不完全同胞交配会减少产雄孤雌生殖种群的遗传变异。然而 ,在各种情况下 ,近交对单倍体 -二倍体种群的总体影响不如对二倍体 -二倍体种群极端     

A molecular phylogeny of the checkered beetles and a description of Epiclininae a new subfamily (Coleoptera: Cleroidea: Cleridae)

We provide the first molecular phylogeny of the clerid lineage (Coleoptera: Cleridae, Thanerocleridae) within the superfamily Cleroidea to examine the two most recently proposed hypotheses of higher level classification. Phylogenetic relationships of checkered beetles were inferred from approximately ～5000 nt of both nuclear and mitochondrial rDNA (28S, 16S and 12S) and the mitochondrial protein‐coding gene COI. A worldwide sample of ～70 genera representing almost a quarter of generic diversity of the clerid lineage was included and phylogenies were reconstructed using Bayesian and Maximum Likelihood approaches. Results support the monophyly of many proposed subfamilies but were not entirely congruent with either current classification system. The subfamilial relationships within the Cleridae are resolved with support for three main lineages. Tillinae are supported as the sister group to all other subfamilies within the Cleridae, whereas Thaneroclerinae, Korynetinae and a new subfamily formally described here, Epiclininae subf.n ., form a sister group to Clerinae + Hydnocerinae.     

Gravity sensing in oat coleoptiles: scatter in growth orientation under different g-conditions

Dark-grown oat seedlings depart from the expected vertical orientation, suggesting that the coleoptile is less responsive to the lateral component of a gravitational stimulus than would be expected. This phenomenon was studied by investigating the gravitropic curvatures of oat (Avena sativa L. cv. Seger) coleoptiles at 10g and over a range of longitudinally applied centripetal accelerations up to 19·4g. In most experiments, the plants were grown and observed at a particular g-level throughout the experiment. Time-lapse video recordings permitted studies of the scatter, measured as the variability of the plants' angle from the vertical (or root mean square value, RMS). The coleoptiles' heights at the end of the experiments were not significantly altered under the centrifugation. Scatter increased with plant age and decreased with increasing g. It decreased in an almost linear fashion as a function of the logarithm of the g-acceleration. In a series of experiments, the g-level was changed from 10g to a higher test g-acceleration. The scatter was then reduced within half an hour after the g-transition. It is pointed out that the experiments confirm that the scatter is g-related but that it was not predicted quantitatively by present theories of the oat coleoptile's gravitropic response kinematics.     

The Carbon Economy of Clonal Plants of Trifolium repens L.

Fluxes of carbon between sources and sinks were quantified forclonal plants of Trifolium repens L. (cv. Blanca) in two glasshouseexperiments. Carbon sources were (a) leaves on the parent (=main)stolon apex, or (b) leaves on either young or old branches,and the major sinks of interest were the parent stolon apex,branches, and the adventitious root arising at the same parentstolon node as a young source branch. Defoliation treatmentswere applied to the parent stolon and/or branches (excludingsource branches). Carbon moved freely from the parent stolon to branches and vice-versa;these bidirectional exchanges of C provided important supplementarysources of carbohydrate for the sinks and buffered them againstthe effects of defoliation. Young branches exported more C tothe parent plant (mean=6.3µmol d^–1) than they importedfrom leaves on the parent stolon (5·2µmol d^–1)which, in turn, exceeded the amount fixed by leaves on the branchand utilized within the branch itself (2·7µmold^–1). In contrast, the C economy of old branches was largelyself-contained with, on average, 25·4µmol d^–1exported to the parent plant, 1·8µmol d^–1imported from the parent, and 63·0µmol d^–1fixed and utilized by the branch itself. Thus the growth ofyoung branches was immediately reduced by removal of parentstolon leaves, but old branches were unaffected. An estimated 42% of the C utilized by the main stolon apex originatedfrom branches, while by far the largest proportion (84%) ofthe C used for growth of young nodal roots originated from theassociated branch and not from leaves on the parent stolon towhich the root was directly attached. Key words: Trifolium repens, clonal growth, carbon economy, physiological integration, defoliation     

Spatial and temporal variability in the structure of a tropical forest

This study examines spatial and temporal variation in the forest structure of the Kibale National Park, Uganda by contrasting tree density, tree size, and forest composition among four areas each separated by less than 15 km, and by quantifying changes in the composition of one of these forests over a 20‐year period. Densities of some tree species differed markedly between sites, and some species common at one location were absent at others. Monthly phenological monitoring demonstrated that it was not uncommon for phenological patterns to differ between the forests. To examine temporal variation in the tree composition over a 20‐year period, a sampling regime that was carried out in the early 1970s was replicated on the floristic composition of one of these sites, using identical methods in the same sampling areas. While no form of human intervention occurred in this area between the early 1970s and 1992, there were marked changes in the densities of some tree species. Twenty‐seven percent of the identified species increased in abundance, 33% decreased, and 40% remained relatively unchanged. The observed spatial and temporal variation in forest composition could be the result of abiotic factors, such as altitude or rainfall, or biotic factors such as elephant and/or human influences on ecosystem dynamics; the implications of this variation for frugivores are discussed.     

Growth and variation in the Silurian proetide trilobite Aulacopleura konincki and its implications for trilobite palaeobiology

Morphometric analysis of growth in Aulacopleura konincki reveals several important features: (1) morphological variability is approximately constant throughout growth, increasing slightly in later ontogeny; (2) shape is more tightly constrained than the numbers of postcephalic segments, which can be quite variable; and (3) a major ontogenetic transition occurs at glabellar lengths of about 1.7 mm. This transition divides the ontogeny into two distinct growth phases, is smooth rather than abrupt, and is expressed as changes in growth trajectories, especially in the pygidium. The transition is not strictly correlated with the number of thoracic or pygidial segments. These results suggest a re-evaluation of the concepts of meraspid and holaspid growth stages in A. konincki , using growth trajectories rather than thoracic segment number to define the stages. Developmental flexibility in holaspid segment numbers in this phylogenetically advanced trilobite suggests that environmental factors, rather than phylogenetic constraint, may explain variations in segment production patterns within some advanced Trilobita. Morphometrics, trilobites, ontogeny, variability, segmentation, Silurian, Czech Republic.