排序方式: 共有18条查询结果,搜索用时 11 毫秒
1.
TORBEN MOTH IVERSEN JENS THORUP KARINA KJELDSEN NIELS THYSSEN 《Freshwater Biology》1991,26(2):189-198
SUMMARY. 1. Population growth rates and relative competitive abilities of the rotifer Keratella cochlearis f. tecta and the small-bodied cladoceran Daphnia ambigua were studied under different schedules of food addition but equal total food quantity (per 4-day interval). The initial population growth rate of Keratella was significantly affected by the feeding schedule and by the presence of competitors, while that of Daphnia was affected by neither factor. Population densities of both species tended to increase as the frequency of food addition increased.
2. Daphnia suppressed and excluded Keratella from mixed-species cultures when food was provided intermittently at a high concentration, but it failed to exclude the rotifer when food was provided in a near-continuous supply at low concentration. Keratella had only a minor suppressive effect on Daphnia in all mixed-species treatments.
3. Starvation experiments indicate that Daphnia is able to withstand food shortages for significantly longer periods of time than Keratella . These and other results indicate that the outcome of interspecific competition between these species may be influenced by me frequency and concentration at which food is supplied. Daphnia ambigua is competitively superior to K. cochlearis when food is concentrated or 'pulsed', but much less so when ambient food levels are chronically low. Patterns of food availability may have important effects in determining the relative abundance of rotifers and small cladocerans in natural zooplankton communities. 相似文献
2. Daphnia suppressed and excluded Keratella from mixed-species cultures when food was provided intermittently at a high concentration, but it failed to exclude the rotifer when food was provided in a near-continuous supply at low concentration. Keratella had only a minor suppressive effect on Daphnia in all mixed-species treatments.
3. Starvation experiments indicate that Daphnia is able to withstand food shortages for significantly longer periods of time than Keratella . These and other results indicate that the outcome of interspecific competition between these species may be influenced by me frequency and concentration at which food is supplied. Daphnia ambigua is competitively superior to K. cochlearis when food is concentrated or 'pulsed', but much less so when ambient food levels are chronically low. Patterns of food availability may have important effects in determining the relative abundance of rotifers and small cladocerans in natural zooplankton communities. 相似文献
2.
3.
KARINA LUCAS SILVA-BRANDÃO VERA NISAKA SOLFERINI 《Biological journal of the Linnean Society. Linnean Society of London》2007,90(2):247-261
Molecular phylogenetic analyses were conducted to determine relationships and to investigate character evolution for the Troidini/Aristolochia interaction, in an attempt to answer the following questions: (1) what is the present pattern of use of Aristolochia by these butterflies; (2) is the pattern we see today related to the phylogeny of plants or to their chemical composition; (3) can the geographical distribution of Aristolochia explain the host plant use observed today; and (4) how did the interaction between Troidini and Aristolochia evolve? Analyses of character optimization suggest that the current pattern of host plant use of these butterflies does not seem to be constrained by the phylogeny of their food plants, neither by the secondary chemicals in these plants nor by their geographical similarity. The current host plant use in these butterflies seems to be simply opportunistic, with species with a wider geographical range using more species of host plants than those with a more restricted distribution. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 90 , 247–261. 相似文献
4.
Efficiency of selection, as measured by single nucleotide polymorphism variation, is dependent on inbreeding rate in Drosophila melanogaster 总被引:1,自引:1,他引:0
DITTE DEMONTIS † CINO PERTOLDI ‡ VOLKER LOESCHCKE KARINA MIKKELSEN TOMAS AXELSSON§ TORSTEN NYGAARD KRISTENSEN ¶ 《Molecular ecology》2009,18(22):4551-4563
It is often hypothesized that slow inbreeding causes less inbreeding depression than fast inbreeding at the same absolute level of inbreeding. Possible explanations for this phenomenon include the more efficient purging of deleterious alleles and more efficient selection for heterozygote individuals during slow, when compared with fast, inbreeding. We studied the impact of inbreeding rate on the loss of heterozygosity and on morphological traits in Drosophila melanogaster. We analysed five noninbred control lines, 10 fast inbred lines and 10 slow inbred lines; the inbred lines all had an expected inbreeding coefficient of approximately 0.25. Forty single nucleotide polymorphisms in DNA coding regions were genotyped, and we measured the size and shape of wings and counted the number of sternopleural bristles on the genotyped individuals. We found a significantly higher level of genetic variation in the slow inbred lines than in the fast inbred lines. This higher genetic variation was resulting from a large contribution from a few loci and a smaller effect from several loci. We attributed the increased heterozygosity in the slow inbred lines to the favouring of heterozygous individuals over homozygous individuals by natural selection, either by associative over‐dominance or balancing selection, or a combination of both. Furthermore, we found a significant polynomial correlation between genetic variance and wing size and shape in the fast inbred lines. This was caused by a greater number of homozygous individuals among the fast inbred lines with small, narrow wings, which indicated inbreeding depression. Our results demonstrated that the same amount of inbreeding can have different effects on genetic variance depending on the inbreeding rate, with slow inbreeding leading to higher genetic variance than fast inbreeding. These results increase our understanding of the genetic basis of the common observation that slow inbred lines express less inbreeding depression than fast inbred lines. In addition, this has more general implications for the importance of selection in maintaining genetic variation. 相似文献
5.
Impact of insect defoliation on forest carbon balance as assessed with a canopy assimilation model 总被引:1,自引:0,他引:1
KARINA V. R. SCHÄFER KENNETH L. CLARK NICHOLAS SKOWRONSKI ERIK P. HAMERLYNCK 《Global Change Biology》2010,16(2):546-560
Disturbances such as fire, hurricanes, and herbivory often result in the net release of CO2 from forests to the atmosphere, but the magnitude of carbon (C) loss is poorly quantified and difficult to predict. Here, we investigate the carbon balance of an oak/pine forest in the New Jersey Pine Barrens using the Canopy Conductance Constrained Carbon Assimilation (4C‐A) model. The 4C‐A model utilizes whole‐tree sap‐flux and leaf‐level photosynthetic gas exchange measurements at distinct canopy levels to estimate canopy assimilation. After model parameterization, sensitivity analyses, and evaluation against eddy flux measurements made in 2006, the model was used to predict C assimilation for an undisturbed year in 2005, and in 2007 when the stand was completely defoliated for 2–3 weeks during an infestation of gypsy moths (Lymantria dispar L.). Following defoliation, only 50% of the foliage reemerged in a second flush. In 2007, canopy net assimilation (AnC), as modeled with the 4C‐A, was reduced to approximately 75% of AnC in 2006 (940 vs. 1240 g C m?2 a?1). Overall, net primary production (NPP) in 2007 was approximately 240 g C m?2 a?1 (vs. 250 g C m?2 a?1 in 2006), with 60% of NPP allocated to foliage production, a short‐term carbon pool. Woody biomass accumulation, a long‐term carbon pool, was reduced by 20% compared with the previous year (72 vs. 57 g C m?2 a?1 in 2006 and 2007, respectively). The overall impact of the defoliation spanned 21% of upland forests (320 km2) in the New Jersey Pine Barrens, representing a significant amount of overall C not being taken up from the atmosphere by the forest, thus not accumulated in the biosphere. 相似文献
6.
7.
8.
CÉLINE CARRET FABIEN WALAS BERNARD CARCY NATHALIE GRANDE ÉRIC PRÉCIGOUT KARINA MOUBRI THEO P. SCHETTERS RÉ GORENFLOT 《The Journal of eukaryotic microbiology》1999,46(3):298-301
The parasites Babesia canis and Babesia gibsoni (phylum Apicomplexa) are responsible for canine babesiosis throughout the world. Babesia canis was previously described as a group of three biologically different subspecies, namely B. canis canis, B. canis vogeli, and B. canis rossi. We report partial sequences of small subunit ribosomal RNA gene (ssu-rDNA) of each subspecies amplified in vitro with primers derived from a semi-conserved region of the ssu-rDNA genes in other Babesia species. The polymerase chain reaction combined with a restriction fragment length polymorphism analysis, using HinfI and TaqI restriction enzymes, confirmed the separation of B. canis into three subspecies. These sequences were compared with previously published sequences of other Babesia species. A phylogenetic approach showed that the three subspecies of B. canis belong to the clade of Babesia species sensu stricto where B. canis canis clusters with B. canis rossi whereas B. canis vogeli might form a monophyletic group with the cluster B. divergens and B. odocoilei. Our results show that the three subspecies of B. canis can readily be differentiated at the molecular level and suggest that they might be considered as true species. 相似文献
9.
KARINA A. MORELLI ELOISA REVALDAVES CLAUDIO OLIVEIRA FAUSTO FORESTI 《Molecular ecology resources》2007,7(1):32-34
Leporinus macrocephalus is a species endemic to the Paraguay River basin and an important fishery resource, as well as a valuable species in aquaculture programs. A total of eight polymorphic microsatellite loci were isolated and characterized. A population survey was conducted involving 45 specimens whereby a large number of alleles (range 5–17 among loci), a highly observed (0.1667–0.6129) and an expected (0.6967–0.9448) heterozygosity was detected, indicating its usefulness in population genetics studies. Cross‐species amplification was successful in eight Characiformes species. 相似文献
10.
Summary The present study was undertaken to describe the morphological and organizational modifications that occur in apyrene and eupyrene spermatozoa along the male adult reproductive tract of the butterfly, Euptoieta hegesia. Testis, vas deferens, vesicula seminalis and ductus ejaculatorius were studied by transmission electron microscopy. In the testis, both sperm types are organized into cysts; apyrene sperm are devoid of extracellular structures while eupyrene ones have lacinate and reticular appendages. In the testis basal region, both sperm pass through an epithelial barrier and lose their cystic envelope. The eupyrene morphological and organizational modifications are more drastic than the apyrene ones. From the vas deferens to the ductus ejaculatorius, apyrene sperm are dispersed in the lumen and acquire several concentric layers that are formed by the folding of their abundant cell membrane. The apyrene distribution observed here suggests that their functions include eupyrene transportation. Eupyrene sperm, however, remain aggregated along the tract. In the vas deferens, they are covered by a filamentous material that develops into a homogeneous matrix surrounding the spermatozoa coat in the vesicula seminalis and the ductus ejaculatorius. Eupyrene sperm undergo complex morphological changes that include the loss of lacinate appendages and the formation of a dense and heterogeneous extracellular coat. The formation of the matrix and the coat in eupyrene extratesticular sperm is related to the loss of lacinate appendages. These changes are in general extracellular and are probably important for sperm maturation. 相似文献