Flower clades and fruit clades: trade-offs in color diversification across angiosperms

Abstract

PREMISEFlowers and fruits are two major phases of plant reproduction which often use colorful signals to attract animal mutualists. Fleshy fruits develop from the ovaries of flowers, and both organs use the same suites of pigments to create color. Due to these developmental links and functional similarities, we sought to test for correlations in flower and fruit color lability across clades. METHODSWe selected 51 clades (2989 species) of animal-pollinated and animal-dispersed plants and scored flower and fruit color into eight discrete (human-perceived) categories for the same set of species in each clade. We used stochastic character mapping to estimate the number and rates of transitions among colors in flowers and fruits. KEY RESULTSWe demonstrate a negative correlation in the number of transitions in flower and fruit color across clades (R2 = 0.48, p < 0.001). Among animal-pollinated and animal-dispersed clades, the majority (67%) are "fruit clades" biased towards fruit color lability, while a minority (29%) are "flower clades" biased towards flower color lability. We further show that clades with many yellow- or orange-flowered species also tend to have those colors in their fruits, and that red flowers are more common in "flower clades" while green and brown fruits are more common in "fruit clades". CONCLUSIONSThese patterns suggest that clades specialize on one phase of reproduction or the other. Possible explanations include constraints on energetic investment into either pollination or dispersal, and environmental factors that select for color diversification in one organ but not the other. This variation is also likely shaped by the underlying structure of pigment pathways that contribute to color in both organs.