PATTERNS OF COLOR AND NECTAR VARIATION ACROSS AN IPOMOPSIS (POLEMONIACEAE) HYBRID ZONE

Hybridization may uncouple adaptive trait combinations that are presen t in parental species. I studied variation in flower color and reward quality across a hybrid zone of Ipomopsis aggregata and I. tenuituba. Individuals from hybrid populations showed considerable variation in f lower color using corolla reflectance measurements. Flower spectra of such individuals were either intermediate or else resembled those flow ers from the parental species. Ipomopsis aggregata populations had con sistently higher nectar production rates and higher nectar standing cr ops than either I. tenuituba or hybrids. Ipomopsis aggregata flowers a lso produced more dilute nectar than those of hybrids and I. tenuituba , but the actual concentration values were quite variable among popula tions of the same type. Overall, the nectar quality of hybrid flowers most resembled that of I. tenuituba flowers. Based on the observed int erpopulation patterns of color-reward associations in this hybrid zone , pollinators should be able to discriminate against I. tenuituba and hybrid populations and against most individuals within hybrid populati ons. However, they may visit those hybrids that resemble the most rewa rding flower type (I. aggregata). The results emphasize the need for s tudies that address how hybridization affects subsequent plant fitness and the evolutionary dynamics of the species involved.