Independent Evolution of White Phenotype in Endangered Native Oregon Delphiniums
Abstract
The pale larkspur (Delphinium leucophaeum) is an Oregon state-listed endangered species with a native range that broadly overlaps with the Portland metropolitan area. The majority of its remaining populations are managed by city, Metro, state and land-conservancy entities. The pale larkspur differs from other larkspurs, having white floral parts instead of the more typical purple floral coloration caused by pigments produced from the flavonoid metabolic pathway. A second state-listed endangered larkspur species, the peacock larkspur (D. pavonaceum), is found in central/southern Willamette Valley and shows a remarkably similar floral phenotype to D. leucophaeum. To better understand the biology of the floral pigmentation, we used LC-MS to determine the flavonoid pigment quantities in flowers of D. leucophaeum, D. pavonaceum, as well as their purple-flowered relatives. The purple flowers contained the flavonoid pigment, delphinidin which produces blue-purple coloration in many plants. By contrast, the floral tissue of the two white species lacked delphinidin, instead showing higher levels of flavonoids called flavonols (particularly quercetin) which absorb UV-light but are reflective in the visible wavelengths. Flavonols are important anti-oxidants and help plants deal with light, heat, UV-radiation, and drought stress. The mechanism for producing white flowers is similar for the two endangered species and results from a tradeoff among flavonoid pigments and may reflect independent evolution of white flowers or a past role for introgressive hybridization between the taxa. Increased production of flavonols may indicate an adaptive evolutionary response to abiotic stressors in the environments in which the two species grow.
Independent Evolution of White Phenotype in Endangered Native Oregon Delphiniums
The pale larkspur (Delphinium leucophaeum) is an Oregon state-listed endangered species with a native range that broadly overlaps with the Portland metropolitan area. The majority of its remaining populations are managed by city, Metro, state and land-conservancy entities. The pale larkspur differs from other larkspurs, having white floral parts instead of the more typical purple floral coloration caused by pigments produced from the flavonoid metabolic pathway. A second state-listed endangered larkspur species, the peacock larkspur (D. pavonaceum), is found in central/southern Willamette Valley and shows a remarkably similar floral phenotype to D. leucophaeum. To better understand the biology of the floral pigmentation, we used LC-MS to determine the flavonoid pigment quantities in flowers of D. leucophaeum, D. pavonaceum, as well as their purple-flowered relatives. The purple flowers contained the flavonoid pigment, delphinidin which produces blue-purple coloration in many plants. By contrast, the floral tissue of the two white species lacked delphinidin, instead showing higher levels of flavonoids called flavonols (particularly quercetin) which absorb UV-light but are reflective in the visible wavelengths. Flavonols are important anti-oxidants and help plants deal with light, heat, UV-radiation, and drought stress. The mechanism for producing white flowers is similar for the two endangered species and results from a tradeoff among flavonoid pigments and may reflect independent evolution of white flowers or a past role for introgressive hybridization between the taxa. Increased production of flavonols may indicate an adaptive evolutionary response to abiotic stressors in the environments in which the two species grow.