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71.
Malaria-infective biting at different hours of the night 总被引:3,自引:0,他引:3
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75.
JUKKA JOKELA CURTIS M. LIVELY MARK F. DYBDAHL JENNIFER A. FOX 《Biological journal of the Linnean Society. Linnean Society of London》2003,79(1):165-181
Sexual reproduction within natural populations of most plants and animals continues to remain an enigma in evolutionary biology. That the enigma persists is not for lack of testable hypotheses but rather because of the lack of suitable study systems in which sexual and asexual females coexist. Here we review our studies on one such organism, the freshwater snail Potamopyrgus antipodarum (Gray). We also present new data that bear on hypotheses for the maintenance of sex and its relationship to clonal diversity. We have found that sexual populations of the snail are composed of diploid females and males, while clonal populations are composed of a high diversity of triploid apomictic females. Sexual and asexual individuals coexist in stable frequencies in many ‘mixed’ populations; genetic data indicate that clones from these mixed populations originated from the local population of sexual individuals without interspecific hybridization. Field data show that clonal and sexual snails have completely overlapping life histories, but individual clonal genotypes are less variable than individuals from the sympatric sexual population. Field data also show segregation of clones among depth‐specific habitat zones within a lake, but clonal diversity remains high even within habitats. A new laboratory experiment revealed extensive clonal variation in reproductive rate, a result which suggests that clonal diversity would be low in nature without some form of frequency‐dependent selection. New results from a long‐term field study of a natural, asexual population reveal that clonal diversity remained nearly constant over a 10‐year period. Nonetheless, clonal turnover occurs, and it occurs in a manner that is consistent with parasite‐mediated, frequency‐dependent selection. Reciprocal cross‐infection experiments have further shown that parasites are more infective to sympatric host snails than to allopatric snails, and that they are also more infective to common clones than rare clones within asexual host populations. Hence we suggest that sexual reproduction in these snails may be maintained, at least in part, by locally adapted parasites. Parasite‐mediated selection possibly also contributes to the maintenance of local clonal diversity within habitats, while clonal selection may be responsible for the distribution of clones among habitats. © 2003 The Linnean Society of London. Biological Journal of the Linnean Society 2003, 79 , 165–181. 相似文献
76.
SYNOPSIS. Sensitivity to pentamidine of bloodstream forms and culture forms of Trypanosoma brucei brucei, strains of this subspecies, and strains of T. brucei rhodesiense characteristically differs in vitro. Analyses of transport parameters for pentamidine uptake in these organisms show differences that correspond with drug sensitivity. Long slender bloodstream forms of T. b. brucei have a high affinity for the drug and high rates of uptake as indicated by Km and Vmax values for [3H]pentamidine transport. Although pentamidine and stilbamidine resistance is associated with dyskinetoplasty. this condition does not itself confer resistance to pentamidine nor does it affect pentamidine transport. However, drug-resistant strains show lower rates for pentamidine transport as does T. b. rhodesiense, which is characteristically less sensitive to the drug. Of all the forms and strains studied, procyclic trypomastigotes were least sensitive to pentamidine and had a remarkable ability to exclude the drug. 相似文献
77.
Forbes SH; Hogg JT; Buchanan FC; Crawford AM; Allendorf FW 《Molecular biology and evolution》1995,12(6):1106-1113
We compared genotypes at eight (AC)n microsatellite loci in domestic sheep
(Ovis aries) and wild Rocky Mountain bighorn sheep (O. canadensis). The
domestic sheep had greater genetic variation, higher allele-size variances,
and larger allele sizes than the wild sheep. Accumulating evidence from
higher taxonomic comparisons shows that these parameters are biased if
microsatellite loci are selected in one taxon and used in another. Our
results demonstrate similar biases between congeneric species. We compared
standard measures of genetic variation, differentiation, and distance
within and between species (H, D, FST) to newer measures based on
allele-size variance (SW, SB, RST). The size-based distances better
detected species-level divergence, but standard measures better
distinguished allopatric populations. Empirical calibration of these
measures at the subspecies level is needed to establish their useful
ranges.
相似文献
78.
Malformin inhibits wet and dry weight, nitrogen accumulation,and cell wall, RNA, DNA and protein synthesis in Phaseolus vulgaris.The relative proportion of dry matter and nitrogen in malformedtissues is increased in the ethanol soluble fraction and decreasedin the residue remaining after hydrolysis with 0.5 N HCl. Inhibitionof cell wall and protein synthesis was generally greater thaninhibition of nitrogen accumulation and RNA and DNA synthesis.The effects of malformin on the composition of P. vulgaris aresimilar to alterations in composition reported for ethylene,and opposite to those reported for gibberellic acid.
1This research was supported by grant GB-7158 from the NationalScience Foundation and grant E-146-F from the American CancerSociety.
2Journal Paper No. 3509 of the Purdue Agricultural ExperimentStation. (Received October 23, 1968; ) 相似文献
79.
CURTIS I. S.; HE C.; JORDI W. J. R. M.; DAVELAAR E.; POWER J. B.; DE LAAT A. M. M.; DAVEY M. R. 《Annals of botany》1999,83(5):559-567
TheAgrobacteriumT-cytgene was transferred into lettuce,LatucasativaSaladin using a genotype-independent transformationprocedure employing a supervirulentAgrobacterium tumefaciensstraincarrying the binary vector pMOG23. Kanamycin-resistant shootswere initiated from inoculated explants only when sites weredeleted within the T-cytpromoter. In culture, kanamycin-resistantshoots exhibited several phenotypes, including gall production,reduced internode length (dwarfism) and vitrification togetherwith differences in rooting. Rooted, neomycin phosphotransferase(NPTII)-positive plants recovered from their abnormal phenotypeand self pollinated to produce viable seed, following transferto the glasshouse. Kanamycin-resistant lettuce plants exhibitedincreased cytokinin and chlorophyll contents compared to non-transformedplants, physiological features which could benefit long-termstorage of this leafy vegetable.Copyright 1999 Annals of BotanyCompany Agrobacterium-mediated transformation, cytokinins,Lactuca sativaL., pigmentation, T-cytexpression, lettuce. 相似文献
80.
Andrew Yates Cliburn Chan Jessica Strid Simon Moon Robin Callard Andrew JT George Jaroslav Stark 《BMC bioinformatics》2007,8(1):196