The maintenance of flower colour polymorphism in self-pollinating <i>Boechera stricta</i>

Abstract

Pollinator-mediated selection cannot explain why flower colour polymorphisms exist in self-pollinating plants. There is a tight link between plant stress response and anthocyanin pigment production, which means that abiotic stress, such as UV radiation or drought, and biotic stress, such as herbivory or competition, can also affect flower colour selection indirectly. I used Boechera stricta to test whether environmental factors are responsible for flower colour polymorphism in self-pollinating plants, and evaluate 1) the biotic and abiotic correlates of flower colour variation, 2) the fitness consequences of this polymorphism, and 3) whether flower colour variation and ultimately pigment production are plastic traits. I sampled at Gothic, Colorado along an elevational range of approximately 2700m to 3400m, where I visited 11 locations and sampled from six 15m transects randomly per location. I measured plant growth and reproduction, along with abiotic and biotic factors that may correlate with flower colour. I also analyzed data from the long-term common garden experiment run by the Anderson lab to determine plasticity of flower colour. The observational data are still under analyses, but we have analyzed some of the common garden data and can conclude that 1) lower elevation plants are more likely to produce pink or purple flowers, and 2) pink or purple flowered plants have lower herbivore damage than white flowered plants. Water availability and natural enemies may play important roles in the first pattern because lower elevations generally show lower precipitation and a greater influence of biotic interactions. Plants with pigmented flowers may also induce greater herbivore-resistance compounds due to the shared biosynthetic pathway of anthocyanin and other flavonoids. This may present indirect selection on flower colour if herbivores influence chemical resistance traits in these plants. However, we will need to analyze the observational data to determine how these abiotic and biotic factors correlate with flower colour, and analyze heritability from the common garden.

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