De la métapopulation au voisinage: la génétique des populations en déséquilibre

Tribune LibreInternational audienceThe concept of population is very useful but can sometimes lead to dead ends. Indeed, various questions in population genetics cannot be solved if studied at this level. It is shown that the intensity of dispersion, as far as it is genetically determined, does not respond to selection at the level of the population in its usual sens. A simple theorical model in relation with in-situ observations (on carduus), seems to show that a wider set, the matapopulation (Gill), is necessary to account for the processes concerned. From this viewpoint, instead of considering species as sets of independent populations, it is proposed to consider them as sets of metapopulations where individual populations are regulary founded by the others and then evolve under internal pressures. Are these internal pressures acting at the very population level ? It does not seem so, at least for some, and perhaps for most species, since each individual is likely to mate with a subset which is not representative of the whole. This question has led Wright to formulate the neighbourhood concept. In Thyme, the simultaneous integration of the emerging properties of the 3 levels (Metapopulation, Population and Neighbourhood) allows one to explain a phenomenon (very high proportions of females) which remained incomprehensible as long as one tried to describe it using only the population level

Sex allocation in an hermaphroditic plant: the case of gynodioecy in Thymus vulgaris L.

Rescource allocation to male and female functions was investigated in Thymus vulgaris L. (thyme), a gynodioecious species, in which females produce twice as many seeds as hermaphrodites. Negative correlations were found between male and female fertility of hermaphrodites, providing evidence of a trade-off. There was a high variablility in sexual investment, some of the hermaphrodites functioning almost as males, and others almost as females. Estimation of the relative cost of male and female gametes showed that the female advantage in seed production was mainly due to reallocation of the rescources not allocated to male function into female function. The determination of sex allocation was shown to have a genetic component, and there were some evidence that an interaction between nuclear and cytoplasmic genomes was involved

Long-term grass biomass estimation of pastures from satellite data

The general consensus on future climate projections poses new and increased concerns about climate change and its impacts. Droughts are primarily worrying, since they contribute to altering the composition, distribution, and abundance of species. Grasslands, for example, are the primary source for grazing mammals and modifications in climate determine variation in the available yields for cattle. To support the agriculture sector, international organizations such as the Food and Agriculture Organization (FAO) of the United Nations are promoting the development of dedicated monitoring initiatives, with particular attention for undeveloped and disadvantaged countries. The temporal scale is very important in this context, where long time series of data are required to compute consistent analyses. In this research, we discuss the results regarding long-term grass biomass estimation in an extended African region. The results are obtained by means of a procedure that is mostly automatic and replicable in other contexts. Zambia has been identified as a significant test area due to its vulnerability to the adverse impacts of climate change as a result of its geographic location, socioeconomic stresses, and low adaptive capacity. In fact, analysis and estimations were performed over a long time window (21 years) to identify correlations with climate variables, such as precipitation, to clarify sensitivity to climate change and possible effects already in place. From the analysis, decline in both grass quality and quantity was not currently evident in the study area. However, pastures in the considered area were found to be vulnerable to changing climate and, in particular, to the water shortages accompanying drought periods