9707649 Stratton The fundamental niche of an organism can be quantified by a performance curve, relating fitness to underlying resource gradients. This project will measure genetic variation in parameters of fitness reaction norms of Arabidopsis thaliana over gradients of light, water, and nutrients. Components of genetic variance for the shape of those reaction norms will be estimated to test the hypotheses that 1) there is more genetic variation for niche position than niche width. 2) that there are negative genetic correlations between the breadth of performance curves and maximum fitness (the jack of all trades is master of none hypothesis) and 3) that such tradeoffs are most apparent in comparisons among populations rather than within. Although the standing genetic variance governs the short-term response to selection, long term constraints depend on pleiotropic effects of individual loci. Thus, quantitative trait loci affecting the shape of fitness reaction norms will be mapped using a recombinant inbred population of Arabidopsis to test the hypothesis 4) that loci which affect fitness at one end of the resource gradient have negative pleiotropic effects maximal fitness or on performance at the other extreme. Populations can respond to changes in the environment by shifting their niche position or by increasing niche breadth. Despite a long history of theoretical work, predicting the response of real populations is an empirical problem which depends on the amount and pattern of genetic variation in parameters of the fitness reaction norm. Tradeoffs between maximal fitness and breadth of adaptation are often assumed but rarely documented. Moreover, the possibility that independent loci affect performance at different ends of the resource gradient means that populations may be able to expand their niche without detrimental effects on performance in other environments.
