Km Distant (km + distant)

Distribution by Scientific Domains

Selected Abstracts

The influence of pollinator abundance on the dynamics and efficiency of pollination in agricultural Brassica napus: implications for landscape-scale gene dispersal

Summary 1It is important to understand the pollination processes that generate landscape-scale gene dispersal in plants, particularly in crop plants with genetically modified (GM) varieties. In one such crop, Brassica napus, the situation is complicated by uncertainty over the relative importance of two pollen vectors, wind and insects. 2We investigated pollination in two fields of B. napus that bloomed at different times of year (April vs. July) and attracted different abundances of foraging social bees. Rates of pollen transfer were quantified by counting the pollen grains deposited on stigmas and remaining in the anthers at intervals after flower opening. 3Flowers open in April were adequately pollinated only after 5 days and only 10% received even a single bee visit. Flowers open in July received three bee visits per hour and were fully pollinated within 3 h. 4Based on published measurements of airborne pollen dispersal, we estimate that wind-pollination from a hypothetical field 1 km distant could have fertilized up to 03% of the field's seed when bees were scarce in April but only up to 0007% when bees were abundant in July. 5The efficiency of pollination (the proportion of pollen released from anthers that landed on receptive stigmas) was seven times greater in July (15%) than in April (02%). The relatively high efficiency of insect pollination may help to explain the evolutionary maintenance of entomophily. 6Synthesis and applications. Our results begin to resolve a long-standing inconsistency among previous studies by suggesting that the susceptibility of fields of B. napus to long-distance cross-pollination by wind depends on the level of bee activity. Models for predicting GM gene flow at the landscape-scale in this crop should take this into account. [source]

Orographic influences during winter precipitation events on the Avalon Peninsula, Newfoundland

C E Banfield
Precipitation enhancement over a low coastal hill in winter is demonstrated for particular associations of synoptically determined onshore airflow and local geography encountered over southeastern Newfoundland. Four such cases, involving a mixture of pre-warm-frontal precipitation types at surface temperatures just below freezing, are analysed using comparative surface gauge records from sites at the coast and hill summit and detailed volume scan data from a Doppler radar. Whilst precipitation at the hill summit and upwind coast was of similar overall duration in each case, the surface rates on the hilltop exceeded those at the coast by 1.0,4.0 mm h,1 during different stages of the events. Analysis of the Doppler reflectivity patterns reveals that intensities are especially enhanced near the windward hill crest, supporting the observed association of greatest enhancement with a strong local upslope wind component exceeding 20 m s,1. In the majority of these cases the enhancement is maintained primarily by the ,seeder,feeder' mechanism, which appears to be accelerated during precipitation transitions and with the surface warm front 120,150 km distant; however, a preliminary phase of enhancement due to topographically induced uplift of stable pre-frontal air is also recognised in one case. Copyright 2000 Royal Meteorological Society [source]

Fine-scale spatial genetic structure and dispersal among spotted salamander (Ambystoma maculatum) breeding populations

Abstract We examined fine-scale genetic variation among breeding aggregations of the spotted salamander (Ambystoma maculatum) to quantify dispersal, interpopulation connectivity and population genetic structure. Spotted salamanders rely on temporary ponds or wetlands for aggregate breeding. Adequate breeding sites are relatively isolated from one another and field studies suggest considerable adult site fidelity; therefore, we expected to find population structure and differentiation at small spatial scales. We used microsatellites to estimate population structure and dispersal among 29 breeding aggregations in Tompkins County, New York, USA, an area encompassing 1272 km2. Bayesian and frequency-based analyses revealed fine-scale genetic structure with two genetically defined demes: the North deme included seven breeding ponds, and the South deme included 13 ponds. Nine ponds showed evidence of admixture between these two genetic pools. Bayesian assignment tests for detection of interpopulation dispersal indicate that immigration among ponds is common within demes, and that certain populations serve as sources of immigrants to neighbouring ponds. Likewise, spatial genetic correlation analyses showed that populations , 4.8 km distant from each other show significant genetic correlation that is not evident at higher scales. Within-population levels of relatedness are consistently larger than expected if mating were completely random across ponds, and in the case of a few ponds, within-population processes such as inbreeding or reproductive skew contribute significantly to differentiation from neighbouring ponds. Our data underscore the importance of these within-population processes as a source of genetic diversity across the landscape, despite considerable population connectivity. Our data further suggest that spotted salamander breeding groups behave as metapopulations, with population clusters as functional units, but sufficient migration among demes to allow for potential rescue and recolonization. Amphibian habitats are becoming increasingly fragmented and a clear understanding of dispersal and patterns of population connectivity for taxa with different ecologies and life histories is crucial for their conservation. [source]

Habitat differentiation vs. isolation-by-distance: the genetic population structure of Elymus athericus in European salt marshes

A.-C. Bockelmann
Abstract We investigated genetic differentiation among populations of the clonal grass Elymus athericus, a common salt-marsh species occurring along the Wadden Sea coast of Europe. While E. athericus traditionally occurs in the high salt marsh, it recently also invaded lower parts of the marsh. In one of the first analyses of the genetic population structure in salt-marsh species, we were interested in population differentiation through isolation-by-distance, and among strongly divergent habitats (low and high marsh) in this wind- and water-dispersed species. High and low marsh habitats were sampled at six sites throughout the Wadden Sea. Based on reciprocal transplantation experiments conducted earlier revealing lower survival of foreign genotypes we predicted reduced gene flow among habitats. Accordingly, an analysis with polymorphic cross-species microsatellite primers revealed significant genetic differentiation between high and low marsh habitats already on a very small scale (< 100 m), while isolation-by-distance was present only on larger scales (60,443 km). In an analysis of molecular variance we found that 14% of the genetic variance could be explained by the differentiation between habitats, as compared to only 8.9% to geographical (isolation-by-distance) effects among six sites 2.5,443 km distant from each other. This suggests that markedly different selection regimes between these habitats, in particular intraspecific competition and herbivory, result in habitat adaptation and restricted gene flow over distances as small as 80 m. Hence, the genetic population structure of plant species can only be understood when considering geographical and selection-mediated restrictions to gene flow simultaneously. [source]

A microsatellite-based estimation of clonal diversity and population subdivision in Zostera marina, a marine flowering plant

T. B. H. Reusch
Abstract We examined the genetic population structure in eelgrass (Zostera marina L.), the dominant seagrass species of the northern hemisphere, over spatial scales from 12 km to 10 000 km using the polymorphism of DNA microsatellites. Twelve populations were genotyped for six loci representing a total of 67 alleles. Populations sampled included the North Sea (four), the Baltic Sea (three), the western Atlantic (two), the eastern Atlantic (one), the Mediterranean Sea (one) and the eastern Pacific (one). Microsatellites revealed substantial genetic variation in a plant group with low allozyme diversity. Average expected heterozygosities per population (monoclonal populations excluded) ranged from 0.32 to 0.61 (mean = 0.48) and allele numbers varied between 3.3 and 6.7 (mean = 4.7). Using the expected frequency of multilocus genotypes within populations, we distinguished ramets from genetic individuals (i.e. equivalent to clones). Differences in clonal diversity among populations varied widely and ranged from maximal diversity (i.e. all ramets with different genotype) to near or total monoclonality (two populations). All multiple sampled ramets were excluded from further analysis of genetic differentiation within and between populations. All but one population were in Hardy,Weinberg equilibrium, indicating that Zostera marina is predominantly outcrossing. From a regression of the pairwise population differentiation with distance, we obtained an effective population size Ne of 2440,5000. The overall genetic differentiation among eelgrass populations, assessed as , (a standardized estimate of Slatkin's RST) was 0.384 (95% CI 0.34,0.44, P < 0.001). Genetic differentiation was weak among three North Sea populations situated 12,42 km distant from one another, suggesting that tidal currents result in an efficient exchange of propagules. In the Baltic and in Nova Scotia, a small but statistically significant fraction of the genetic variance was distributed between populations (, = 0.029,0.053) at scales of 15,35 km. Pairwise genetic differentiation between European populations were correlated with distance between populations up to a distance of 4500 km (linear differentiation-by-distance model, R2 = 0.67). In contrast, both Nova Scotian populations were genetically much closer to North Sea and Baltic populations than expected from their geographical distance (pairwise , = 0.03,0.08, P < 0.01). A biogeographical cluster of Canadian with Baltic/North Sea populations was also supported using a neighbour-joining tree based on Cavalli,Sforza's chord distance. Relatedness between populations may be very different from predictions based on geographical vicinity. [source]

Home range dynamics of the yellow-footed rock-wallaby (Petrogale xanthopus celeris) in central-western Queensland

Abstract Analyses of the interspecific differences in macropod home range size suggest that habitat productivity exerts a greater influence on range size than does body mass. This relationship is also apparent within the rock-wallaby genus. Lim reported that yellow-footed rock-wallabies (Petrogale xanthopus xanthopus) inhabiting the semi-arid Flinders Ranges (South Australia) had a mean home range of 170 ha. While consistent with the hypothesis that species inhabiting less productive habitats will require larger ranges to fulfil their energetic requirements, the ranges reported by Lim were considerably larger than those observed for heavier sympatric macropods. The aim of the current study was to document the home range dynamics of P. x. celeris in central-western Queensland and undertake a comparison with those reported for their southern counterparts. Wallaby movements were monitored at Idalia National Park, between winter 1992 and winter 1994. Male foraging ranges (95% fixed kernel; 15.4 ha, SD = 7.8 ha) were found to be significantly larger than those of female wallabies (11.3 ha, SD = 4.9 ha). Because of varying distances to the wallabies' favoured foraging ground (i.e. an adjacent herb field), the direction in which the wallabies moved to forage also significantly affected range size. Mean home range size was estimated to be 23.5 ha (SD = 15.2 ha; 95% fixed kernel) and 67.5 ha (SD = 22.4 ha; 100% minimum convex polygon). The discrepancy between these two estimates resulted from the exclusion of locations, from the 95% kernel estimates, when the wallabies moved to a water source 1.5 km distant from the colony site. The observed foraging and home ranges approximated those that could be expected for a macropod inhabiting the semi-arid zone (i.e. 2.4 times larger-than-predicted from body mass alone). Possible reasons for the disparity between the current study and that of Lim are examined. [source]