Intraspecific interactions between algae with different nutritional histories.

The diatom Phaeodactylum tricornutum was cultured in five different growth regimes to obtain cells with different composition. Pairs of populations subjected to different treatments were then mixed in a communal culture regime that differed from those of origin. After 6 h, the ratio between the two populations was verified by flow cytometry. Alterations in this ratio were found when cells previously grown at 1 mM NH4+ were mixed with GeO2 - and 0.5 mM NH4+ -grown cells. The nutritional background may thus make cells differently suited to new environmental conditions and afford advantages in terms of reproductive potential. Competitive interactions between populations may result from the differences in the expressed proteome and/or in the availability of tools for regulatory responses. This may have relevance to the persistence of phenotypically neutral variants present in the population best suited to the new condition, after the interaction of the conspecifics with different nutritional histories.