The Adaptive Significance of Inflorescence Pigmentation and its Potential Influence on the Diversification Dynamics of North American Sedges (Carex, Cyperaceae)

Abstract

Although pollinator-driven selection is known to generate pigmentation variation in plants, the contribution of abiotic factors in the evolution of pigmentation is still poorly understood. This is largely due to a lack of research on pigmentation variation in wind-pollinated (anemophilous) plants, where the confounding effect of pollinators can be excluded. Here, I study pigmentation variation in Carex, the world’s largest anemophilous genus. Using 456 North American species, I use phylogenetic comparative methods to test (1) whether darker inflorescence parts are correlated with short growing seasons and (2) whether inflorescence pigmentation has affected the diversification dynamics of Carex throughout time. I also examine UV irradiance and precipitation at both the interspecific and intraspecific (four wide-ranging species, >100 accessions each) levels, factors previously associated with floral darkness at high altitude and latitude. At the inter- and intraspecific level, darker inflorescence parts are associated with short growing seasons, as seen in arctic and alpine regions. Additionally, dark pigmentation is associated with stronger UV irradiance and higher precipitation in the intraspecific dataset. Finally, despite the adaptive importance of pigmentation in arctic and alpine regions, it has not contributed to the diversification dynamics of Carex. The results suggest that climatic conditions can promote pigmentation variation in anemophilous plants, and are most consistent with the hypothesis that dark inflorescence parts accelerate reproductive development by absorbing solar energy. Finally, despite the adaptive importance of pigmentation in arctic and alpine regions, it has not contributed to the diversification dynamics of Carex.