WHITKUS, RICHARD1*, HAHN DOAN2, VINCENT WENG3, and TIMOTHY LOWREY4. 1Sonoma State University, Rohnert Park, CA 94928; 2University of California, Los Angeles, CA 90024; 3University of California, Riverside, CA 92521; 4University of New Mexico, Albuquerque, NM 87131. - A QTL analysis of intersectional differences in Hawaiian Tetramolopium (Asteraceae).
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