Colour, design and reward: phenotypic integration of fleshy fruit displays

Abstract

The functional or structural linkage among traits [phenotypic integration (PI)] within complex structures can constrain the evolutionary response of individual traits. To analyse whether frugivores with distinct sensory ecology have shaped the patterns of fruit diversification differently, we compared PI values of fleshy fruits that are consumed by birds and mammals. We used phylogenetic comparative analyses of PI among 13 morphological, nutritional and visual fruit traits from 111 Mediterranean plant species. Results showed that morphological traits had higher PI values than nutritional and colour traits. Visual and nutritional traits show positive phylogenetic covariance, while negative covariation occurs between fruits size and nutrients. Importantly, fruits consumed by birds were relatively more integrated than fruits consumed partly or solely by mammals. Hence, we show that major groups of mutualistic frugivores can shape the covariance among some fruit traits differently and thereby influence fruit diversification.

Birds see the true colours of fruits to live off the fat of the land

“…Previously, we have shown that-independent of plant phylogeny-fruit colour is associated with their lipid contents, and fruit brightness is associated with their contents of non-structural carbohydrates across 111 species of fleshy-fruited plants in southern Spain [13]. More specifically, phylogenetically independent contrasts of lipid and sugar contents correlated most closely with hue and brightness, whereas morphological and other nutritional traits (e.g.…”

“…These fruits encompass a broad variation in colour and brightness, ranging from white to black, and nutritional contents (e.g. mean lipid content 7% of dry fruit-pulp mass, ranging between 0.8% and 58%) [13]. Using paired t-tests on log-transformed variables, we then analysed whether the colour variables differed between the groups of relatively high and relatively low nutritional contents, respectively.…”

“…We thus selected 46 congeneric species belonging to 23 genera that are broadly distributed throughout the phylogeny of Mediterranean species [13] (see electronic supplementary material, table S1). For each genus, we selected the species with the highest and lowest content of each main nutrient (lipid, sugar, protein).…”

“…The information about pulp nutrients and fruit colours used in this study was obtained from the western Mediterranean fleshy-fruit dataset [13]. Briefly, the contents of crude lipids in fruit pulp (percentage of pulp dry mass) were analysed by Soxhlet extraction.…”

“…Yet, recent studies on visual communication among fleshy-fruited plants and seed dispersers concluded that fruit colours reliably indicate fruit nutritional rewards in distinct communities [12,13]. Because only one study on pollination of Turnera ulmifolia demonstrated selection on the covariance between sensory traits and plant rewards [14], the covariance between fruit colours and nutrients is probably best explicable as by-product information originating from pleiotropy or similar biochemical pathways of nutrients and pigments [12,13]. As such, it is unclear whether animals commonly select the reliability of plant-animal communication.…”