Monstrozní, obří, tajemné, vražedné, vymykající se známým fyzikálním zákonům, přímo nepozorovatelné brány do jiných vesmírů... Jen málokteré objekty v kosmu se honosí tak barvitými a rozpruplnými označeními jako černé díry. A současně málokteré tolik dráždí zvědavost nejen veřejnosti, ale také astronomů, kosmologů a (astro)fyziků, kteří se snaží kousek po kousku odrhrnout roušku jejich tajemství. Černé díry se však nehodlají vzdát a vzdorovitě připravují jedno překvapení za druhým. and Jana Olivová, Michal Švanda.
Název Centrum pro výzkum věřejného mínění nebo jeho zkratku CVVM zná asi každý. Přinejmenším z televizního zpravodajství týkajícího se stranických preferencí, volebních modelů či předvolebních průzkumů. Málokdo však ví, že jed o pracoviště Sociologického ústavu AV ČR. Ještě překvapivější bude asi zjištění, že v CVVM pracuje pouhých 15 lidí. and Luděk Svoboda.
Proč se nekříží kočka se psem? Proč se sice může zkřížit kůň s oslem, ale jejich potomci - mulové či mezci - jsou neplodní? Z jakého důvodu jsou někdy strilní i kříženci dvou blízce příbuzných poddruhů, třeba myší, a souvisí to nějak se vznikem nových živočišných druhů? Jeden z nejdůležitějších článků tété záhady odhalil Jiří Forejt z Ústavu molekulární genetiky Akademie věd ČR, kterýá identifikoval první gen u savců zodpovědný za samčí neplodnost mezidruhových kříženců, přečetl ho a ukázal, jak je regulován. and Jana Olivová, Stanislava Kyselová.
Survival and Lt50 after exposures at constant low temperature were compared to the values obtained at alternating temperatures in two active (summer acclimated) temperate terrestrial arthropods. The experimental regimes used interruptions - daily transfers from the lower temperature to various higher temperatures for two hours or to one high temperature for Various durations. In both species the alternating conditions improved survival, implying reparation of the chill injury. In the collembolan Orchesella cincta, there was a maximum Lt50 when the higher exposure temperature was equal to the temperature of rearing (19°C). In the bug Pyrrhocoris apterus, Lt50 increased strongly with increasing higher temperature from 0 to 15°C, and was subsequently constant over the entire physiological range suitable for development (to 35°C). Exposure at 0°C was harmful if continuously applied, but survival increased, relative to a constant exposure at -5°C, if the temperature alternated between -5 and 0°C., Zdeněk Hanč, Oldřich Nedvěd, and Lit
Winter climate determines the success of the two main reproductive strategies employed by aphids. Permanent parthenogens survive as parthenogenetic females in mild winters, but are regularly eliminated by low temperatures; while cyclical parthenogens, which switch to sexual reproduction by the end of summer, produce every year fertilised diapausing eggs resistant to frost.
We have studied the variation in sexual morph production of several clones of the cereal aphid Rhopalosiphum padi (L.) showing both strategies. Twenty clones of this species differing by their geographic origin and their mode of reproduction were placed in two laboratory environments mimicking the changes of photoperiod and thermoperiod occurring naturally from the end of summer and during the autumn in oceanic and continental conditions. The analysis of clonal responses in both climatic conditions showed (i) a wide variation in investment of clones in sexual reproduction with, in particular, evidence for a mixed strategy employed by clones producing both sexuals without ceasing parthenogenetic reproduction, (ii) no geographic adaptation among clones belonging to cyclical parthenogenetic populations, (iii) an earlier production of sexuals in continental conditions and a higher production of males in oceanic conditions.
Furthermore, we have compared the dates of first appearance of sexuals in our experiments with those occurring in the field based on a suction trap database and found that sexuals were caught in nature at least four weeks earlier than in the lab. These results underline the need for a better understanding of the influence of the whole array of environmental factors inducing the transition from parthenogenetic to sexual reproduction in aphids., Maurice Hullé, Damien Maurice, Claude Rispe, Jean-Christophe Simon, and Lit
Cold hardiness of larvae of the summer fruit tortrix moth, Adoxophyes orana (Fischer von Rosslerstamm) (Lepidoptera: Tortricidae) was examined in the laboratory. Supercooling point of field collected larvae increased significantly from a mean value of -23.9°C in February 1998 to -16.9°C in June 1998. Mean supercooling points for laboratory diapause and non-diapause larvae were -20.7°C and -17.2°C respectively. Short period of acclimation (10 days at 0°C) significantly decreased supercooling point to -24.7°C for laboratory diapause larvae. Acclimation for 12 days at 5°C decreased supercooling point to -19.4°C for non-diapause larvae. Pre-freeze mortality for diapause and non-diapause larvae was also studied. Constant exposure of diapause larvae at -5°C resulted in high mortality (63.1%) after a period of 30 days. in contrast, only 6 days at -5°C were sufficient to cause 100% mortality of non-diapause larvae. Mortality of non-diapause larvae reached 100% after 12 and 18 days at 0 and 5°C respectively. The importance of these findings for the overwintering strategy of A. orana is discussed., Panagiotis G. Milonas, Mathilde Savopoulou-Soultani, and Lit