DIVERSIFICATION IN TEMPORALLY FLUCTUATING ENVIRONMENTS: EFFECT OF THE ENVIRONMENTAL GRAIN IN EXPERIMENTAL BACTERIAL POPULATIONS.
Venail P.A., Kaltz O., Olivieri I., Pommier T. and Mouquet N. (2011).
Journal of Evolutionary Biology, 24, 2485-2495, doi:10.1111/j.1420-9101.2011.02376.x
Key message :Although theory established the necessary conditions for diversification in temporally heterogeneous environments, empirical evidence remains controversial. One possible explanation is the difficulty of designing experiments including the relevant range of temporal grains and the appropriate environmental trade-offs. Here, we experimentally explore the impact of the grain on the diversification of the bacterium Pseudomonas fluorescens SBW25 in a temporally fluctuating environment by including 20 different pairs of environments and four temporal grains. In general, higher levels of diversity were observed at intermediate temporal grains. This resulted in part from the enhanced capacity of disruptive selection to generate negative genotypic correlations in performance at intermediate grains. However, the evolution of reciprocal specialization was an uncommon outcome. Although the temporal heterogeneity is in theory less powerful than the spatial heterogeneity to generate and maintain the diversity, our results show that diversification under temporal heterogeneity is possible provided appropriate environmental grains.
A. Flow chart of the experimental design used for calculations of genotypic diversity: inconsistency and GV. After 32 transfers, for all the temporally fluctuating treatments (a) (1, 2, 4 and 8) we randomly sampled eight genotypes from each selection line and assayed them on the two sources of the environmental pair (a and b) to calculate the inconsistency and genotypic variance. (b) For the spatial treatment, we measured the inconsistency and genotypic variance by randomly picking four genotypes from each evolved line after 16 days in constant environments and pooling the eight genotypes. This treatment represented a spatially divided population and was used as a theoretical upper boundary for diversification. B. Effect of temporal environmental grain on genotypic diversity. (a) Higher levels of inconsistency were observed when mixing genotypes from two selection lines (spatial treatment, open circle) than in any other treatment. Among the temporal treatments, the intermediate grain treatment (4-day) presented higher levels of inconsistency than fine grain treatments (1- and 2-day). (b) Higher levels of genotypic variance were observed when mixing genotypes from two selection lines (spatial treatment, open circle) than in any other treatment. Among the temporal treatments the unimodality test confirmed a peak of genotypic variance within the range of temporal grains included in the experiment (5.04 days).
OTHER TOPICS: Aesthetics of Biodiversity, Biodiversity & Ecosystem Functioning, Biogeography, Macroecology & Ecophylogenetics, Experimental Evolution,
Functional Biogeography, Functional Rarity, Metacommunities, Metaecosystems, Reviews and Synthesis, Trophic Biogeography & Metaweb