Abstract
Selection at the group level is proposed to be an evolutionary process occurring in the context of multilevel selection in natura. In artificial selection experiments, selecting at the community level can allow to find multispecies assemblages that are more efficient than a single species at solving a given problem. In such procedures, the main difficulty is to find a balance between variation and heritability, which are both essential for selection to act. The aim of our study was to determine if the way of creating offspring units of selection from parental units, called “reproduction method”, could influence artificial selection efficiency through a differential in the variation/heritability balance. Selecting microbial communities depending on their biomass production and propagating them either one by one or in a mix of three communities, we showed that there were only transient phases of divergence between the two reproduction methods with a loss of the effect of artificial selection on community phenotype at certain cycles and a low heritability. However, mixing parental communities was more efficient at increasing biomass production than using a single parental community (+5% of biomass). We discussed the role of differences in community richness and structure in explaining these results.
Highlights
From a theoretical standpoint, the three conditions stated by Lewontin (1970) for selection to occur, i.e., (i) the existence of phenotypic variation, (ii) the existence of a link between this variation and a differential in fitness, (iii) the heritability of the variation, can be completed at the group level
The linear mixed model showed that the cycle factor had a strong effect on biomass production (77% of the explained variance; mean square of the cycle factor divided by the total mean square excluding that of the residuals) as well as its interaction with the selection treatment (11%) and the three-way interaction: cycleby-selection treatment-by-reproduction method (9%; Table S1)
An experiment demonstrated that the variance of the community property (CO2 emission) and the heritability of this property declined along selection cycles, confirming the importance of the sampling effect in explaining differences in and collapse of the selected property (Blouin et al, 2015). This points out a paradox in community selection: a minimal variance resulting from community dynamics is necessary for selection to act, but if this variance occurs through the butterfly effect, it could prevent any heritability between parents and their offspring (Penn, 2003)
Summary
The three conditions stated by Lewontin (1970) for selection to occur, i.e., (i) the existence of phenotypic variation, (ii) the existence of a link between this variation and a differential in fitness, (iii) the heritability of the variation, can be completed at the group level. Artificial selection at the group level in experimental conditions has been proven effective in changing a phenotypic trait of the group and in changing the fitness of the individuals composing this group (Goodnight and Stevens, 1997). If the considered selection unit is a population, genetically-based among-individuals interactions can be selected. If we consider higher levels such as communities, selection at higher levels than the population can occur through genetically-based between-species interactions, such as syntrophy (obligately mutualistic metabolism; Morris et al, 2013)
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