because experimental manipulation of upright Aquilegia pubescens flowers to the pendent orientation reduced hawkmoth visitation by an order of magnitude (Fulton and Hodges, 1999). One bee-pollinated species, Aquilegia jonesii, has upright flowers; however, the entire plant is only 2–10 cm tall and the flowers are held just above the foliage (Munz, 1946). Given these constraints, upright flowers offer the best access to the spurs and pollen by bee pollinators.

Perhaps one of the most visually striking features of the North American adaptive radiation of Aquilegia is the diversity of floral color, resulting from multiple, independent shifts (Figs. 2.1 and 2.2). Using the same Aquilegia phylogeny as for pollinator transitions, Whittall et al. (2006b) reconstructed the ancestral states for the presence (blue or red) or absence (yellow or white) of floral anthocyanins and inferred a significant trend of 7 independent losses and no gains (Fig. 2.2). These shifts in color appear to be largely adaptive because all 5 inferred shifts to hawkmoth pollination are coincident with loss of anthocyanin production (Whittall et al.,

FIGURE 2.1 Photographs of Aquilegia flowers. (A) A. coerulea (blue/white). (B) A. scopulorum, which can be polymorphic for blue (Left) and white (Right) flowers. (C) A. longissima (yellow). (D). A. saximontana (purple). (E) A. flavescens (yellow). (F) A. pubescens (white). (G) A. formosa (red/yellow). (H) Natural hybrids between A. formosa and A. pubescens. Photos by N. Derieg (A, B, D, E, and G) and S. Hodges (C, F, and H).