Pollinator attractors: petaloidy and petal epidermal cell shape in close relatives of snapdragon

Abstract

The diversity of angiosperms in floral form and development has been an area of interest for biologists. A multitude of studies investigating the evolution of flowering plants have attempted to determine why angiosperms are so diverse. One possible major contributor to flower form diversity is pollinator pressure. The interactions between flowers and their pollinators have important ecological and evolutionary consequences, with co-evolution often occuring. Many studies have looked at suites of floral traits that affect pollinator visitation, which have been coined pollination syndromes (Fenster et al., 2004). These traits include but are not limited to, flower color, flower orientation, landing platforms, and nectar guides. With the increase in genetic tools, and the utilization of model species such as Antirrhinum majus(Plantaginaceae) and Arabidopsis thaliana (Brassicaeae), many studies are looking at the geneitc architecture of floral traits. Studies have determined the genetic blueprint for floral oragn identity, as well as in traits asociated with pollination syndromes including flower color and symmetry. Using members of the Antirrhineae tribe (Plantaginaceae) makes it easier to effectively use the resources from A. majus, or snapdragon. Chapter 1 investigates the applicability of the sliding boundary model for petaloid sepal formation in Rhodochiton atrosanguineum, a close relative of snapdragon. We were interested in determing if the petaloid sepals of R. atrosanguineum had true petal identity, or were merely just colorful sepals. Chapter 2 focuses on possible petal function, and not merely petal identity. Conical cells are found on roughly 80% of angiosperms (Kay et al., 1981) and are thought to be a marker for petal identity. However, conical cells are thought to be absent mostly in hummingbird pollinated flowers, though no studies have looked at this in depth (Christensen and Hansen, 1998). For this chapter, we investigated possible correlated evolution between petal epidermal cell shape and pollination system.