The genetics of transient populations: Research at the metapopulation level

The metapopulation concept allows us to generate new models, in which each single local population is in disequilibrium (from both demographic and genetic points of view) but the whole is stable. We review recent empirical and theoretical results showing the relevance of the metapopulation level, in particular for understanding the evolution of those traits that do not experience the same selective forces during the different demographic stages of each local population.     

Mesure journaliére sur cycle végétatif complet des échanges gazeux: photosynthése, transpiration et respiration nocturne ďune culture de Maïs conduite sur colonnes de sol

Daily measurement of gas exchanges during a complete growth cycle: photosynthesis, transpiration and night respiration in a soil culture of maize. During a complete growth cycle, photosynthesis (P), night-respiration (R) and transpiration (T) have been measured daily for maize (Zea mays L. cv. INRA F7 × F2) in a self-regulating growth chamber. P and T varied according to three different kinetics. During the growing period there was a fast and concomitant variation of both P and T, which could be filled to a power function of time. During the fructification period we observed a linear decrease of P and T. Finally, during the senescence period P decreased to zero, whereas T kept a value higher than the evaporation of the naked soil. In the first two periods, the P/T ratio decreased as leaves aged. From this we could deduce that a slow increase of stomatal resistance (RS) and mesophyll resistance (RM) took place. R increased until the panicle appeared; it remained constant during fructification and then it decreased with senescence. Each nitrogen supply induced a transient increase of R. Finally, a water stress led to a greater decrease of P than of R, but the after effect of water stress disappeared a day later. These results were compared with those obtained in hydroponic conditions.