Aims The superior performance of many non-indigenous species in a new range can be attributed to different factors such as pre-adaptation to environmental conditions in new areas or to factors inherent to displacement...Aims The superior performance of many non-indigenous species in a new range can be attributed to different factors such as pre-adaptation to environmental conditions in new areas or to factors inherent to displacement mechanisms such as loss of co-evolved pathogens and herbivores that increase the speed of evolutionary change towards a shift in allocation from defence to growth and reproduction.To assess the importance of the different mechanisms governing the success of Conyza canadensis,a globally successful invader,we simultaneously tested several recent hypotheses potentially explaining the factors leading to biological invasion.Methods We tested(i)whether plants from the non-native range showed a higher fitness than plants from the native North American range,(ii)whether they differed in resistance against an invasive generalist herbivore,the slug Arion lusitanicus and against a recently established specialist aphid herbivore,Uroleucon erigeronense and(iii)experimentally assessed whether C.canadensis releases allelopathic chemicals that have harmful effects on competing species in the nonnative range.We compared populations along a similar latitudinal gradient both in the native North American and invasive European range and analysed patterns of adaptive clinal variation in biomass production.Important Findings The invasion success of C.canadensis in Europe cannot be attributed to a single trait,but to a combination of factors.Invasive plants benefited from increased growth and above all,increased reproduction(a key trait in an annual plant)and were less attacked by a co-migrated specialist enemy.The observed loss of defence against generalist slugs did not translate into a decreased fitness as invasive C.canadensis plants showed a high re-growth potential.In contrast to earlier in vitro studies,we detected no allelopathic effects on the competing flora in the non-native range.The latitudinal cline in vegetative biomass production in the non-native range observed in our common garden study indicates a high adaptive potential.However,only further genetic studies will provide conclusive evidence whether the differentiation in the non-native range is caused by pre-adaptation and sorting-out processes of putatively repeatedly introduced populations of this composite,long-distance disperser with highly volatile seeds or evolved de novo as a rapid response to new selection pressures in the nonnative range.展开更多
A new measurement of the reactor antineutrino flux and energy spectrum by the Daya Bay reactor neutrino experiment is reported. The antineutrinos were generated by six 2.9 GWth nuclear reactors and detected by eight a...A new measurement of the reactor antineutrino flux and energy spectrum by the Daya Bay reactor neutrino experiment is reported. The antineutrinos were generated by six 2.9 GWth nuclear reactors and detected by eight antineutrino detectors deployed in two near（560 m and 600 m flux-weighted baselines） and one far（1640 m flux-weighted baseline） underground experimental halls. With 621 days of data, more than 1.2 million inverse beta decay（IBD） candidates were detected. The IBD yield in the eight detectors was measured, and the ratio of measured to predicted flux was found to be 0.946±0.020（0.992±0.021） for the Huber＋Mueller（ILL＋Vogel） model. A 2.9σ deviation was found in the measured IBD positron energy spectrum compared to the predictions. In particular, an excess of events in the region of 4–6 MeV was found in the measured spectrum, with a local significance of 4.4σ. A reactor antineutrino spectrum weighted by the IBD cross section is extracted for model-independent predictions.展开更多
基金This work was supported by a grant from the Swiss National Science Foundation to J.J.(nr.3100AO-104006).
文摘Aims The superior performance of many non-indigenous species in a new range can be attributed to different factors such as pre-adaptation to environmental conditions in new areas or to factors inherent to displacement mechanisms such as loss of co-evolved pathogens and herbivores that increase the speed of evolutionary change towards a shift in allocation from defence to growth and reproduction.To assess the importance of the different mechanisms governing the success of Conyza canadensis,a globally successful invader,we simultaneously tested several recent hypotheses potentially explaining the factors leading to biological invasion.Methods We tested(i)whether plants from the non-native range showed a higher fitness than plants from the native North American range,(ii)whether they differed in resistance against an invasive generalist herbivore,the slug Arion lusitanicus and against a recently established specialist aphid herbivore,Uroleucon erigeronense and(iii)experimentally assessed whether C.canadensis releases allelopathic chemicals that have harmful effects on competing species in the nonnative range.We compared populations along a similar latitudinal gradient both in the native North American and invasive European range and analysed patterns of adaptive clinal variation in biomass production.Important Findings The invasion success of C.canadensis in Europe cannot be attributed to a single trait,but to a combination of factors.Invasive plants benefited from increased growth and above all,increased reproduction(a key trait in an annual plant)and were less attacked by a co-migrated specialist enemy.The observed loss of defence against generalist slugs did not translate into a decreased fitness as invasive C.canadensis plants showed a high re-growth potential.In contrast to earlier in vitro studies,we detected no allelopathic effects on the competing flora in the non-native range.The latitudinal cline in vegetative biomass production in the non-native range observed in our common garden study indicates a high adaptive potential.However,only further genetic studies will provide conclusive evidence whether the differentiation in the non-native range is caused by pre-adaptation and sorting-out processes of putatively repeatedly introduced populations of this composite,long-distance disperser with highly volatile seeds or evolved de novo as a rapid response to new selection pressures in the nonnative range.
基金Supported in part by the Ministry of Science and Technology of Chinathe United States Department of Energy,the Chinese Academy of Sciences+11 种基金the CAS Center for Excellence in Particle Physicsthe National Natural Science Foundation of Chinathe Guangdong provincial governmentthe Shenzhen municipal governmentthe China General Nuclear Power Groupthe Research Grants Council of the Hong Kong Special Administrative Region of Chinathe MOST and MOE in Taiwanthe U.S.National Science Foundationthe Ministry of Education,Youth and Sports of the Czech Republicthe Joint Institute of Nuclear Research in Dubna,Russiathe NSFC-RFBR joint research programthe National Commission for Scientific and Technological Research of Chile
文摘A new measurement of the reactor antineutrino flux and energy spectrum by the Daya Bay reactor neutrino experiment is reported. The antineutrinos were generated by six 2.9 GWth nuclear reactors and detected by eight antineutrino detectors deployed in two near（560 m and 600 m flux-weighted baselines） and one far（1640 m flux-weighted baseline） underground experimental halls. With 621 days of data, more than 1.2 million inverse beta decay（IBD） candidates were detected. The IBD yield in the eight detectors was measured, and the ratio of measured to predicted flux was found to be 0.946±0.020（0.992±0.021） for the Huber＋Mueller（ILL＋Vogel） model. A 2.9σ deviation was found in the measured IBD positron energy spectrum compared to the predictions. In particular, an excess of events in the region of 4–6 MeV was found in the measured spectrum, with a local significance of 4.4σ. A reactor antineutrino spectrum weighted by the IBD cross section is extracted for model-independent predictions.
