Adaptive radiation in Hawaiian Tetramolopium has resulted in three separate sections distinguished by a host of morphological and ecological traits. Tetramolopium humile (section Alpinum) and T. rockii (section Tetramolopium) are representative of their sections. The main vegetative differences between these sections are plant height, leaf size, and leaf thickness. A suite of reproductive features characterizes section Tetramolopium, and are associated with a switch in breeding system (gynomonoecy to monoecy). We measured four vegetative and 12 reproductive trait differences in an F2 population from a cross between these species, and used a genetic linkage map of 66 molecular markers (RFLP and RAPD) to conduct a QTL analysis. The aim was to gain an understanding of the genetic changes associated with the early stages of divergence in the adaptive radiation. Forty-six putative QTL were obtained over all traits with 76% explaining less than 20% of the phenotypic variance for a trait. QTL of very large effect were found for leaf width (R2 53%), ray floret number (R2 65%), and ray to disk floret ratio (R2 83%). Although reproductive features exhibit dominance in the F1, only ray floret number and the ray to disk floret ratio had D/A ratios over 1. All QTL occur in 21 genomic regions of 10 cM in size, and the QTL of largest effect for each trait occur on 7 of the 9 linkage groups. The location of the QTL explaining the greatest amount of phenotypic variation for each trait results in a minimum of 11 genomic regions necessary to account for the majority of the variation exhibited by the 16 traits measured. The results from this study suggest that morphological evolution associated with adaptive radiation in Hawaiian Tetramolopium does not have a simple genetic basis.

Key words: adaptive radiation, Asteraceae, morphological evolution, QTL, Tetramolopium