Leaf litter decomposition differs among genotypes in a local <Emphasis Type="Italic">Betula pendula</Emphasis> population

Ecosystem processes, such as plant litter decomposition, are known to be partly genetically determined, but the magnitude of genetic variation within local populations is still poorly known. We used micropropagated field-grown saplings of 19 Betula pendula genotypes, representing genetic variation in a natural birch population, to examine (1) whether genotype can explain variation in leaf litter decomposition within a local plant population, and (2) whether genotypic variation in litter decomposition is associated with genotypic variation in other plant attributes. We found that a local B. pendula population can have substantial genotypic variation in leaf litter mass loss at the early stages of the decomposition process and that this variation can be associated with genotypic variation in herbivore resistance and leaf concentrations of soluble proteins and total nitrogen (N). Our results are among the first to show that fundamental ecosystem processes can be significantly affected by truly intraspecific genetic variation of a plant species.     

Divergence in morphometric and life history traits in two thermally contrasting Andean populations of Rhinella spinulosa (Anura: Bufonidae)

(1) We studied the variation in characters of two Andean populations of Rhinella spinulosa with different larval thermal regimes as a function of geographic origin and temperature.

(2) In both populations, survival and growth rate were greater at the higher temperature. Size at metamorphosis was only determined by locality, while there was a divergence in growth rate and age at metamorphosis as a function of locality and temperature.

(3) Variation was found in seven of the 12 morphological characters evaluated in post-metamorphic toadlets, which was determined only by their locality of origin.

Interpopulation and interyear variation in germination in Scotch thistle, Onopordum acanthium L., grown in a common garden: Genetics vs environment

Germination patterns were studied among three populations of Scotchthistle, Onopordum acanthium L. (Asteraceae). Cypselas(seeds) were collected twice during the growing season for four consecutiveyears (1996–1999) from plants grown in the same location, theEnvironmental Sciences Western Field Station (ESW) near London, Ontario.Cypselas from 1996 came from plants that had been transplanted as rosettes fromtheir original sites to ESW, while those for 1997–1999 came from plantsgrown from cypselas collected in 1996. Fresh cypselas were put to germinate at25°C, 14 hlight/10°C, 10 h dark for 55 days.Consistent and significant differences in final germination percentages amongpopulations were obtained over the four years. There were also differencesbetween collections within populations in 1996 and 1998. In addition, the finalgermination percentage (collectively) differed widely among years. There was agreater than 30 percent correlation between germination percentage and meandaily maximum temperature during cypsela maturation. Since there were similardifferences among populations every year, it appears that germination patternsof O. acanthium populations have a genetic basis as wellasan environmental one.     

Lorentzian model of roots for understory yellow birch and sugar maple saplings

Total 66 small (<50m(2)), 24 medium (101-200m(2)) and 36 large (201-500m(2)) canopy gaps at the three sites of yellow birch (Betula alleghaniensis Britton) and sugar maple (Acer saccharum Marsh) forests were established in southern Québec, Canada. Half of the gaps were covered by 8x8m(2) shading cloths to mimic a closed canopy. From these gaps, 46 understory yellow birch and 46 sugar maple saplings with different tree ages and sizes were sampled. Single- and multi-variable linear and nonlinear models of root biomass and traits (root surface area, volume, length and endings) were developed and examined. Lorentzian model as a multi-variable nonlinear model was firstly applied to the simulations using both base diameter and height, and performed the best fit to total root biomass in both species with the highest correlation coefficients (R(2)=0.96 and 0.98) and smallest root mean squared deviations (RMSD=7.85 and 7.02) among all the examined models. The model also accurately simulated small fine root (2.0mm in diameter), coarse fine root (>2.0-5.0mm) and coarse root (>5.0mm) biomass (R(2)=0.87-0.99; RMSD=2.24-6.41), and the root traits (R(2)=0.71-0.99; RMSD=0.19-19.38). The study showed yellow birch roots were longer, larger, had more endings (tips) and grew faster than sugar maple roots. The root traits were largely distributed to small fine roots, sharply decreased from small fine roots to coarse fine roots, the fewest in coarse roots except for root volume. When trees were large, coarse root biomass increased more rapidly than fine root biomass, but vise versa when the trees were small.     

中国微蛛亚科三新纪录属三新种记述(蜘蛛目,皿蛛科)(英文)

记述中国微蛛亚科3新纪录属3新种:巨突蛛属Diplocephaloides Oi,1960,钩状巨突蛛D.uncatus sp.nov.;圆膝蛛属GongylidiumMenge,1868,皱褶圆膝蛛G. rugulosasp.nov.和良次蛛属OiaWunderlich,1973,端突良次蛛O.breviprocessiasp. nov.。模式标本均保存于中国科学院动物研究所,北京。     

Ecotypic differentiation in the grasshopper Chorthippus brunneus: life history varies in relation to climate

Life history variations among 27 populations of the grasshopper Chorthippus brunneus from around the British Isles were examined under laboratory conditions over three generations. Multiple-regression analysis was used to examine the relationship between grasshopper life histories and the climates of their ancestral sites. Grasshoppers from cooler sites were heavier at hatching. Grasshoppers from northern sites grew faster and developed through fewer instars, attaining adulthood earlier, at the expense of adult size. Depending on the measure of adult size used, adults were larger in warmer, sunnier or more southerly locations. Ecotypic differentiation is probably widespread among animals as it is among plants, though it is more rarely demonstrated by zoological studies, especially over the wide geographical scale covered here. Evidence from regression analysis supports the hypothesis that ecotypic differentiation in C. brunneus is an evolutionary response to climatic variation. The existence of intraspecific genetic diversity for climatic adaptations has implications for biodiversity conservation and the understanding of biotic responses to climatic change. It deserves wider recognition. Received: 5 October 1998 / Accepted: 30 June 1999     

Size and structure of bacterial, fungal and nematode communities along an Antarctic environmental gradient

The unusually harsh environmental conditions of terrestrial Antarctic habitats result in ecosystems with simplified trophic structures, where microbial processes are especially dominant as drivers of soil-borne nutrient cycling. We examined soil-borne Antarctic communities (bacteria, fungi and nematodes) at five locations along a southern latitudinal gradient from the Falkland Islands (51 degrees S) to the base of the Antarctic Peninsula (72 degrees S), and compared principally vegetated vs. fell-field locations at three of these sites. Results of molecular (denaturing gradient gel electrophoresis, real-time PCR), biochemical (ergosterol, phospholipid fatty acids) and traditional microbiological (temperature- and medium-related CFU) analyses were related to key soil and environmental properties. Microbial abundance generally showed a significant positive relationship with vegetation and vegetation-associated soil factors (e.g. water content, organic C, total N). Microbial community structure was mainly related to latitude or location and latitude-dependent factors (e.g. mean temperature, NO3, pH). Furthermore, strong interactions between vegetation cover and location were observed, with the effects of vegetation cover being most pronounced in more extreme sites. These results provide insight into the main drivers of microbial community size and structure across a range of terrestrial Antarctic and sub-Antarctic habitats, potentially serving as a useful baseline to study the impact of predicted global warming on these unique and pristine ecosystems.     

The role of sediment type in growth and fecundity of mud snails (Hydrobiidae)

Summary We test the hypothesis that body size and population density of the deposit-feeding gastropod, Hydrobia truncata, are greater in muddy than in sandy habitats as a result of faster growth on fine- compared to coarse-grained sediments. We refute this hypothesis using a combination of field measurements and laboratory experiments. Three out of three populations tested had higher maximal growth rates and two of three populations approached their asymptotic size more quickly on sand than on silt-clay fractions of natural sediment. Growth decreased with increasing snail density and was as high or higher on sand as on silt-clay at all densities. Two populations were more fecund on sand than on silt-clay, and fecundity of the third population was not affected by sediment type. We show that the smaller body sizes observed in snails from the sandiest habitat result from late recruitment of these snails, relative to the other populations.     

Genetic mosaics of ecosystem functioning across aspen-dominated landscapes

Genetic diversity is the foundation of all biodiversity, and the genetic variation within species is increasingly recognized as being important to ecosystem level processes. Recent research demonstrates that plant genotype influences above- and belowground communities as well as basic ecosystem functions. However, the extent to which plant genotypes create spatial mosaics of genetically mediated ecosystem processes in natural forests is uncertain. We use Populus tremuloides as a model system to demonstrate the importance of plant genotype on carbon and nitrogen cycling in natural systems. We identified 24 distinct P. tremuloides clones with multiple ramets across 25 km² in southern Wisconsin, United States, using microsatellite makers. We then sampled clone leaf chemistry and belowground nutrient content and microbial extracellular enzyme activity. Aspen-induced variation in belowground carbon and nitrogen content, and microbial activity, varied widely among clones. Variation in green leaf chemistry and belowground microbial activity were correlated with genetic distance among clones, such that more genetically distant clones created more divergent patches of ecosystem processes. These data suggest that aspen genotypes create spatial mosaics of genetically mediated ecosystem functioning across natural landscapes and can therefore have evolutionary consequences for co-occurring species.     

Competitiveness of endophytic Phialocephala fortinii s.l. – Acephala applanata strains in Norway spruce roots

Dark septate endophytes of the Phialocephala fortinii s.l. – Acephala applanata species complex (PAC) are presumed to be the most abundant root colonizing endophytes of conifers across the Northern hemisphere. To test the competitiveness of different PAC strains, PAC-free Picea abies saplings were inoculated with five different PAC strains by planting them in pre-colonized substrates. Saplings were left to grow for six weeks and then transplanted crosswise into a substrate colonized by one of the other four strains for a further two weeks. PAC were isolated and genotyped using microsatellite markers. The power of colonization, i.e. the ability of colonizing roots already colonized by another PAC strain, and the power of retention, i.e. the ability of a resident strain of not being suppressed by an invading PAC strain, were calculated for each strain in every combination. The experiment was run twice under two different climatic conditions. Our results show that PAC strains differ (1) in their ability to colonize PAC-free, non-sterile roots, (2) in resistance against being suppressed by another PAC strain and (3) in their ability to invade roots already colonized by another PAC strain. In addition, both the PAC–PAC and the PAC-host interactions depend on the climatic conditions.     

Does intraspecific hybridization contribute to the evolution of invasiveness?: an experimental test

One of the major objectives of research on invasive species is to determine the relative importance of different evolutionary and ecological forces in the invasion process. It was recently suggested that post-introduction intraspecific hybridization between previously isolated genotypes could produce novel and/or heterotic progeny that might express enhanced invasiveness. We tested this hypothesis with Silene latifolia, a European native that has successfully invaded North America and has previously been shown to have undergone genetic change since its introduction. In a common garden experiment we compared the performance of plants derived from within and between population crosses from eight European and 18 North American populations. Results showed that there was no significant effect of crossing distance on progeny phenotype. Furthermore, progeny from within or between population crosses did not differ in size, reproductive output or survival. Collectively, these results suggest that the invasive phenotype of S. latifolia is likely the result of natural selection and/or genetic drift rather than intraspecific hybridization.     

Flowering and fruiting phenology of a xerochamaephytic shrub community from the mountain of Mallorca (Balearic islands,Spain)

A study of the flowering and fruiting phenology was undertaken for twenty species of the xerochamaephytic communities that characterize the mountain-crest areas of the island of Majorca (Balearic Islands, Spain). The flowering period of the species considered extends from March to November, with the majority flowering during the spring and early summer, and a peak in June. The flowering duration at the species level is longest for Rosmarinus officinalis var. palaui (which flowered in spring and autumn) and was shortest for Genista majorica and Rubia balearica. In this community, three strategies were observed that may serve to reduce interspecific competition between pollinators: 1) pollination specialization of white-pink flowers; 2) high diversification of yellow flower pollinators; and 3) the divergence in flowering time of less common flower colours. The flowering duration of individual plants and whole populations are positively correlated, which may indicate that individuals of each population optimize the time which is phenologically useful. The flowering of the spiny cushion species of the community is characterized by a smaller intraspecific overlap in comparison to the other species examined. This revised version was published online in June 2006 with corrections to the Cover Date.     

Modulation of lipogenic enzymes, fatty acid synthase and Δ9-desaturase, in relation to migration in the western sandpiper (Calidris mauri)

Long-distance migration in birds is characterized physiologically by periods of rapid fattening and lipogenesis, and increased desaturation of fatty acids stored in adipose tissue. We investigated seasonal, age- and sex-related differences in activities of two lipogenic enzymes, fatty acid synthase and Δ⁹-desaturase, in relation to migration in the small, Arctic-nesting western sandpiper (Calidris mauri). Migration, and associated lipogenesis and fattening, involved marked upregulation of these enzymes in this species. However, this increase in enzyme activity was only seen in actively migrating birds during spring migration, when fatty acid synthase and Δ⁹-desaturase levels increased by 53% and 113%, respectively, compared to non-migrating birds. There was no change in fatty acid synthase enzyme activity during the premigration period, even though body mass of adult birds increased significantly during this period. Similarly, there was no increase in Δ⁹-desaturase activity during premigration, despite the fact that birds increase the proportion of monounsaturated fatty acids in their fat stores at this time. We suggest that upregulation of lipogenic enzymes is required to support high rates of mass gain (0.4 g day⁻¹) during short (1–4 day) periods at stop-over sites. However, slower rates of mass gain (0.09 g day⁻¹) over several weeks prior to migration can be achieved without any increase in tissue-specific enzyme activity. Accepted: 29 November 1999     

新疆早二叠世阿克苏柯坪珊瑚的种内变异

通过对产自新疆柯坪地区的阿克苏柯坪珊瑚(Kepingophyllum aksuense)的大量薄片观察,发现该类珊瑚在珊瑚体单骸形态、横板带宽度与泡沫板带宽度之比、隔壁长度、横板的形态、隔壁数目、隔壁数目与珊瑚骸直径之比等六个方面存在很大变异。此外,该类珊瑚中存在明显的周期性生长变异现象,表现在泡沫板的排列疏密相间。与模式标本的对比研究发现,此类珊瑚的群体间变异相对较小。     

A revision of the systematics of panther worms (Hofstenia spp., Acoela), with notes on color variation and genetic variation within the genus

Species of the genus Hofstenia are voracious predators and among the largest and most colorful of the Acoela. They are known from Japan, the Red Sea, the North Atlantic islands of Bermuda and the Bahamas, and the Caribbean and in a variety of habitats including the rocky intertidal, among Thalassia sea grass, on filamentous algae and decaying mangrove leaves. Certain color morphs associated with each of these habitats seem to have confused the taxonomy of the group. While brown-and-white banding and spotting patterns of Hofstenia miamia and Hofstenia giselae are distinctive for species associated with mangrove leaves and Thallasia sp. and are likely to be cryptic for these specific environments, we find some evidence to suggest that the coloration is mimicry of a nudibranch with aposematic coloration. The common plan in these patterns is one with three variously solid or spotted lighter cross bands on a dark background. Our examination of museum type material and live specimens of Hofstenia collected from Bahamas, Belize, Bermuda, and Panama revealed no internal morphological differences between the Hofstenia species occurring in the Caribbean. Similarly, our analyses of 18S and 28S molecular sequence data revealed no significant differences among specimens. Accordingly, we declare that Hofstenia giselae is a junior synonym of Hofstenia miamia, the three-banded panther worm. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users. Handling editor: K. Martons