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Our intuitive understanding of adaptation by natural selection is dominated by the power of selection at early ages in large populations. Yet, as the forces of natural selection fall with adult age, we expect adaptation to be attenuated with age. Explicit simulations of age-dependent adaptation suggest that populations adapt to a novel environment quickly at early ages, but only slowly and incompletely at later adult ages. Experimental tests for age-dependent adaptation to a novel diet were performed on populations of Drosophila melanogaster. The results support the prediction that populations should perform better on an ancestral, long-abandoned diet, compared to an evolutionarily recent diet, only at later ages. D. melanogaster populations also perform poorly on a novel diet compared to an evolutionarily recent diet that has been sustained for hundreds of generations, particularly at earlier ages. Additional experiments demonstrate that the timing of the shift to better performance in our populations on the long-abandoned diet is dependent on when the forces of natural selection weaken in the evolutionary history of experimental populations. Taken together, these experimental findings suggest that the forces of natural selection scale the rate of adaptation to novel environments.

While diuron residues are being detected more frequently in agricultural soils, there is limited information available regarding their potential phytotoxicity to non-target grain crops. This study aims to determine robust phytotoxicity thresholds for three common, but contrasting, crop species (canola, chickpea, and wheat) exposed to a range of diuron concentrations and to determine how loamy sand soil can change the toxicity thresholds relative to an inert sand. The log-logistic non-linear regression model proved most effective in determining toxicity thresholds by analysing crop responses to diuron. Canola was the most sensitive to diuron in sand followed by wheat and chickpea. Diuron exhibits higher phytotoxicity in sand compared to loamy sand, with ED50 values (which is the dose at which diuron causes a 50% decrease in plant growth) of 0.03 mg kg-1 and 0.07 mg kg-1 for canola shoot biomass inhibition and 0.01 mg kg-1 and 0.06 mg kg-1 for root dry weight reduction, respectively. The ED50 values for wheat shoot biomass (0.11 and 0.24 mg kg-1) in sand and loamy sand, respectively, and the ED50 values for root growth inhibition are 0.14 mg kg-1 in sand and 0.19 mg kg-1 in loamy sand. These values were lower than label concentrations and previously estimated average and maximum diuron residue loads (0.17 and 0.29 mg kg-1) in Western Australia paddocks. The larger ED50 values of diuron in the loamy sand can be attributed to higher soil organic matter and cation exchange capacity that decreased bio-available diuron levels. Average diuron residue loads in Western Australia crop fields exceed the ED50 value emphasizes the need for careful planning of crop rotations to avoid crop phytotoxicity from soil-borne diuron residues. Further study is needed to determine the effect of a wider range of soil properties such as pH, clay content, and soil organic matter on the phytotoxicity risk of diuron to rotational crops. [ABSTRACT FROM AUTHOR]

The roles of history, chance and selection have long been debated in evolutionary biology. Though uniform selection is expected to lead to convergent evolution between populations, contrasting histories and chance events might prevent them from attaining the same adaptive state, rendering evolution somewhat unpredictable. The predictability of evolution has been supported by several studies documenting repeatable adaptive radiations and convergence in both nature and laboratory. However, other studies suggest divergence among populations adapting to the same environment. Despite the relevance of this issue, empirical data is lacking for real-time adaptation of sexual populations with deeply divergent histories and ample standing genetic variation across fitness-related traits. Here we analyse the real-time evolutionary dynamics of Drosophila subobscura populations, previously differentiated along the European cline, when colonizing a new common environment. By analysing several life-history, physiological and morphological traits, we show that populations quickly converge to the same adaptive state through different evolutionary paths. In contrast with other studies, all analysed traits fully converged regardless of their association with fitness. Selection was able to erase the signature of history in highly differentiated populations after just a short number of generations, leading to consistent patterns of convergent evolution.