Quantitative variation within and among populations of Arabis serrata Fr. & Sav. (Brassicaceae)

Phenotypic and genetic variation within and among eight populations of Arabis serrata are documented in this study. This species shows great morphological variation throughout its geographical distribution in Japan. Plants are located in habitats with different types of soils and degree of disturbance. Half-sibs progenies from eight populations were collected and cultivated in a garden experiment. Nine morphological traits representing size and shape of rosette leaves were recorded. Univariate analyses of measured traits showed that phenotypic means differed among populations for all characters. Leaves of plants from disturbed habitats had the longest petioles (lanceolate) and plants from limestone habitats showed the most roundness in leaf shape (ovate). The northernmost populations always revealed the smallest leaves. Multivariate principal component analyses also showed that leaf shape and size varied among populations. The first three principal components explained 98.5% of the variation. Coefficients of variation had a very wide range and differed from one population to another. Some traits (e.g. leaf width/leaf length ratio) were consistently less variable while others (e.g. leaf area and petiole length) were more plastic. All traits had significant genetic variance in all populations. Intra-class correlation coefficients differed for most of the traits and each population presented a different range of values. Most of the leaf traits were intercorrelated in all the populations studied, although some populations were integrated more tightly for some traits. Populations of A. serrata are differentiated in phenotypic means but they display a mosaic of traits with slight morphological differences in each locality (i.e. a quantitative genetic variation). Some traits can be correlated to the habitats that they occupy but for some of them it is difficult to assign an actual adaptive value.     

Modelling flow patterns in conical dendroid graptolites

Life-sized wire models of several different morphologies of conical dendroid graptolites were tested in a flume to observe the flow patterns within the rhabdosome. Testing over a range of unidirectional current speeds from 3 to 15 cm/s showed that upward-directed currents are produced within the cone, and a significant amount of the water that enters the cone through the upstream wall exits the top opening. These upward currents were most evident at speeds of 3–10 cm/s. Shorter cones, wide cones, less porous mesh, and downstream tilting each increased the amount of water exiting the top of the cone, especially at higher speeds. These findings are consistent with a mode of feeding in which conical forms received afferent currents into the sides of the cones, where food particles were captured, and waste efferent currents went out the top opening. This does not support the hypothesis that downward-directed, ciliary feeding currents produced the force necessary to propel the earliest planktic graptolites into the water column in the evolutionary transition from a benthic to a planktic mode of life. The suggestion that differing rhabdosomal morphologies may represent adaptations to differing paleocurrent regimes is supported. Dendroid rhabdosomal morphology may prove to be a useful paleoenvironmental tool, particularly as an indicator of current strengths, especially in fine-grained sediments where other current-indicative structures may be lacking. Graptolite, dendroid, flow, feeding, paleoecology.     

Key‐factor/key‐stage analysis of long‐term life table data for a fruit gall midge,Asphondylia sphaera (Diptera: Cecidomyiidae)

1. Population dynamics of Asphondylia sphaera Monzen (Diptera: Cecidomyiidae), a species that induces fruit galls on Ligustrum japonicum (Oleaceae), was studied from 1970 to 1996 in broad‐leaved evergreen forests in Kagoshima, southern Japan. The numbers of fruit galls and emerging adults fluctuated greatly from year to year along with alternate year flowering of the host plant. 2. To detect density‐dependent and independent forces operating on the A. sphaera population and to assess the relative strength of top‐down and bottom‐up effects, we used the method of Key‐factor/key‐stage analysis, which allowed us to avoid various problems of the conventional key‐factor analysis. 3. Five factors and seven stages were distinguished in the life tables. Key‐factor/key‐stage analysis indicated that the number of flower buds made the largest contribution to the annual changes in total survival rate by operating through the proportion of eggs and first instars that survived abortion of host flower buds and flowers, which contributed most to density‐dependency. 4. The population dynamics of A. sphaera has been strongly influenced by the bottom‐up effects of both the abundance of flower buds and the abortion of flowers of L. japonicum. 5. A top‐down effect of Bracon asphondyliae Maeto (Hymenoptera: Braconidae) was weakly density‐dependent and contributed less to the total survival rate. Abiotic factors, such as summer and winter temperatures and the effect of typhoons were negligible.     

Nitrogen deposition causes widespread loss of species richness in British habitats

We use national scale data to test the hypothesis that nitrogen (N) deposition is strongly negatively correlated with plant species richness in a wide range of ecosystem types. Vegetation plots from a national ecological surveillance programme were drawn from heathland, acid, calcareous and mesotrophic grassland habitats. Mean species number and mean plant traits were calculated for each plot and related to atmospheric N deposition. There was a significant reduction in species richness with N deposition in acid grassland and heathland even after fitting covarying factors. In acid grassland and heathland, evidence from trait changes suggested that acidification rather than increased fertility was responsible for species loss. In contrast, calcareous grassland showed evidence of eutrophication in response to increasing N deposition. Loss of species richness from chronic N deposition is apparent in infertile grasslands and heathland. Mechanisms associated with loss of species richness differ between habitats so mitigation of N deposition should be targeted to habitat type.     

Myxosoma cerebralis: In Vitro Sporulation of the Myxosporidan of Salmonid Whirling Disease

SYNOPSIS. Trophozoites and other pre-spore stages of the myxosporidan Myxosoma cerebralis were taken from infected rainbow trout ( Salmo gairdneri ) and cultured in vitro. Cultures eventually yielded mature spores capable of discharging their polar capsules. This is the first report of culture of a myxosporidan.