Postdoctoral Research Fellowship in Molecular Evolution

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The composition of seed oils varies widely between taxa and could either be the result of relaxation from selection or selection for or against certain compositions given the particular circumstances of the seeds of a species. Preliminary analyses show clearly that there is a latitudinal shift in the proportion of saturated vs. unsaturated fat in seeds; on average, tropical species have 2 to more than 4 times the saturated vs. unsaturated fat content of temperate species. The work proposed here seeks to determine whether the adaptive significance of this difference lies in selection for lower oil solidification temperatures in cool germinating temperate species. Both phylogenetic and experimental methods are employed to strengthen the investigation. Two groups of plants are employed: the Viguiera complex (Asteraceae) and the tribe Cyclantherae (Cucurbitaceae). For selected species in each, oil solidification temperature and composition are determined and then mapped on phylogenies to determine the pattern of evolution of these traits. The phylogeny of the Viguiera complex is known, and that of the Cyclantherae will be determined from DNA sequence data. Experiments will be conducted to determine the degree of plasticity of oil solidification temperature in response to growing temperature. Finally, the performance of seeds germinating at different temperatures will be assessed and checked to see if it is in accordance with the hypothesis.