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31.
Adam H. Porter Remo Wenger Hansjürg Geiger Adolf Scholl Arthur M. Shapiro 《Evolution; international journal of organic evolution》1997,51(5):1561-1573
The pierid butterflies Pontia daplidice and P. edusa, parapatrically distributed in southern Europe, have very similar morphologies and life histories, but show fixed differences at four allozyme markers. We sampled these allozymes in a 28-population transect north of Genoa in Italy, through the hybrid zone where these taxa meet. We used the numerical techniques developed for hybrid zone analysis to study the patterns of genetic differentiation and their underlying evolutionary causes. The hybrid zone is characterized by a very short and steep central region, flanked by broad tails of introgression extended up to 100 km in either direction. From mean two-locus disequilibium of D = 0.148 (maximum-likelihood two-unit support limits 0.139-0.153), and after accounting for minor differences in the center locations of the single-locus clines, which act to bias the dispersal estimate, we estimated a dispersal rate of σ = 4.4 (3.7-5.5) km/gen1/2. The effective selection needed to maintain the steep central portion is strong, 0.47 < s? < 0.64, when combined over potential intrinsic (genetic background) and extrinsic (ecological) sources of selection. The clines in allozyme loci showed variation that was significantly different between the most divergent shapes, and the differences are attributable to different degrees of introgression on the edusa side of the zone. The average selection acting on individual allozyme loci was high at s???e 1.5%, but because of the narrowness of the central region of the cline, we suspect that this estimate is somewhat biased by selection on loci closely linked to the allozyme markers. A common question for taxa that show fixed allozyme differences in parapatry is whether or not they are genetically isolated. A fairly general measure of genetic isolation across hybrid zones is the time, T, that it takes a neutral allele to cross the hybrid zone and recombine into the opposite genetic background, given by T = (β/σ)2, where β is the barrier strength of the hybrid zone. Genetic isolation in the Pontia zone is weak, with T 25 generations for most allozyme markers. By this measure, populations of daplidice and edusa on opposite sides of the hybrid zone share more identical-by-descent alleles than do populations of phenotypically pure daplidice in, say, France and Morocco. Accordingly, we think it best for systematists to consider edusa as a well-marked subspecies of P. daplidice. 相似文献
32.
Gustav Adolf Zwanziger 《Plant Systematics and Evolution》1880,30(3):91-93
Ohne Zusammenfassung 相似文献
33.
Adolf Bernhard Meyer 《Journal of Ornithology》1874,22(1):74-76
Ohne Zusammenfassung 相似文献
34.
Dr. Adolf Remane 《Zoomorphology》1926,5(4):625-754
Ohne Zusammenfassung 相似文献
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37.
Giorgia?BeffaEmail author Tiziana?Pedrotta Daniele?Colombaroli Paul?D.?Henne Jacqueline?F.?N.?van Leeuwen Pascal?Süsstrunk Petra?Kaltenrieder Carole?Adolf Hendrik?Vogel Salvatore?Pasta Flavio?S.?Anselmetti Erika?Gobet Willy?Tinner 《Vegetation History and Archaeobotany》2016,25(3):271-289
Little is known about the vegetation and fire history of Sardinia, and especially the long-term history of the thermo-Mediterranean belt that encompasses its entire coastal lowlands. A new sedimentary record from a coastal lake based on pollen, spores, macrofossils and microscopic charcoal analysis is used to reconstruct the vegetation and fire history in north-eastern Sardinia. During the mid-Holocene (c. 8,100–5,300 cal bp), the vegetation around Stagno di Sa Curcurica was characterised by dense Erica scoparia and E. arborea stands, which were favoured by high fire activity. Fire incidence declined and evergreen broadleaved forests of Quercus ilex expanded at the beginning of the late Holocene. We relate the observed vegetation and fire dynamics to climatic change, specifically moister and cooler summers and drier and milder winters after 5,300 cal bp. Agricultural activities occurred since the Neolithic and intensified after c. 7,000 cal bp. Around 2,750 cal bp, a further decline of fire incidence and Erica communities occurred, while Quercus ilex expanded and open-land communities became more abundant. This vegetation shift coincided with the historically documented beginning of Phoenician period, which was followed by Punic and Roman civilizations in Sardinia. The vegetational change at around 2,750 cal bp was possibly advantaged by a further shift to moister and cooler summers and drier and milder winters. Triggers for climate changes at 5,300 and 2,750 cal bp may have been gradual, orbitally-induced changes in summer and winter insolation, as well as centennial-scale atmospheric reorganizations. Open evergreen broadleaved forests persisted until the twentieth century, when they were partly substituted by widespread artificial pine plantations. Our results imply that highly flammable Erica vegetation, as reconstructed for the mid-Holocene, could re-emerge as a dominant vegetation type due to increasing drought and fire, as anticipated under global change conditions. 相似文献
38.
We examined the influence of N or P depletion, alternate N‐ or P‐sources, salinity, and temperature on karlotoxin (KmTx) production in strains of Karlodinium veneficum (D. Ballant.) J. Larsen, an ichthyotoxic dinoflagellate that shows a high degree of variability of toxicity in situ. The six strains examined represented KmTx 1 (CCMP 1974, MD 2) and KmTx 2 (CCMP 2064, CCMP 2283, MBM1) producers, and one strain that did not produce detectable karlotoxin under nutrient‐replete growth conditions (MD 5). We hypothesized that growth‐limiting conditions would result in higher cell quotas of karlotoxin. KmTx was present in toxic strains during all growth phases and increased in stationary and senescent phase cultures under low N or P, generally 2‐ to 5‐fold but with some observations in the 10‐ to 15‐fold range. No karlotoxin was observed under low‐N or low‐P conditions in the nontoxic strain MD 5. Nutrient‐quality (NO3, NH4, urea, and glycerophosphate) did not affect growth rate, but growth on NH4 produced 2‐ to 3‐fold higher cellular toxicity and a 50% higher ratio of KmTx 1‐1:KmTx 1‐3 in CCMP 1974. CCMP 1974 showed higher cellular toxicity at low salinity (≤5 ppt) and high temperature (25°C). Our results suggested that given the presence of a toxic strain of K. veneficum in situ, the existence of environmental conditions that favor cellular accumulation of karlotoxin is likely a significant factor underlying K. veneficum–related fish kills that require both high cell densities (104 · mL?1) and high cellular toxin quotas relative to those generally observed in nutrient‐replete cultures. 相似文献
39.
Ute Möllmann Lothar Heinisch Adolf Bauernfeind Thilo Köhler Dorothe Ankel-Fuchs 《Biometals》2009,22(4):615-624
The outer membrane permeability barrier is an important resistance factor of bacterial pathogens. In combination with drug
inactivating enzymes, target alteration and efflux, it can increase resistance dramatically. A strategy to overcome this membrane-mediated
resistance is the misuse of bacterial transport systems. Most promising are those for iron transport. They are vital for virulence
and survival of bacteria in the infected host, where iron depletion is a defense mechanism against invading pathogens. We
synthesized biomimetic siderophores as shuttle vectors for active transport of antibiotics through the bacterial membrane.
Structure activity relationship studies resulted in siderophore aminopenicillin conjugates that were highly active against
Gram-negative pathogens which play a crucial role in destructive lung infections in cystic fibrosis patients and in severe
nosocomial infections. The mechanism of action and the uptake of the compounds via specific iron siderophore transport routes
were demonstrated. The novel conjugates were active against systemic Pseudomonas aeruginosa infections in mice with ED50 values comparable to the quinolone ofloxacin and show low toxicity. 相似文献
40.
Rainer Beck Frank Adolf Carolin Weimer Britta Bruegger Felix T. Wieland 《Traffic (Copenhagen, Denmark)》2009,10(3):307-315
Golgi-derived coat protein I (COPI) vesicles mediate transport in the early secretory pathway. The minimal machinery required for COPI vesicle formation from Golgi membranes in vitro consists of (i) the hetero-heptameric protein complex coatomer, (ii) the small guanosine triphosphatase ADP-ribosylation factor 1 (Arf1) and (iii) transmembrane proteins that function as coat receptors, such as p24 proteins. Various and opposing reports exist on a role of ArfGAP1 in COPI vesicle biogenesis. In this study, we show that, in contrast to data in the literature, ArfGAP1 is not required for COPI vesicle formation. To investigate roles of ArfGAP1 in vesicle formation, we titrated the enzyme into a defined reconstitution assay to form and purify COPI vesicles. We find that catalytic amounts of Arf1GAP1 significantly reduce the yield of purified COPI vesicles and that Arf1 rather than ArfGAP1 constitutes a stoichiometric component of the COPI coat. Combining the controversial reports with the results presented in this study, we suggest a novel role for ArfGAP1 in membrane trafficking. 相似文献