Abstract
PremiseA key question in plant dispersal via animal vectors is where and why fruit colors vary between species and how color relates to other fruit traits. To better understand the factors shaping the evolution of fruit color diversity, we tested for the existence of syndromes of traits (color, morphology, and nutrition) in the fruits of Viburnum. We placed these results in a larger phylogenetic context and reconstructed ancestral states to assess how Viburnum fruit traits have evolved across the clade.ResultsWe find that blue Viburnum fruits are not very juicy, and have high lipid content and large, round endocarps surrounded by a small quantity of pulp. Red fruits display the opposite suite of traits: they are very juicy with low lipid content and smaller, flatter endocarps. The ancestral Viburnum fruit may have gone through a sequence of color changes before maturation (green to yellow to red to black), though our reconstructions are equivocal. In one major clade of Viburnum (Nectarotinus), fruits mature synchronously with reduced intermediate color stages. Most transitions between fruit colors occurred in this synchronously fruiting clade.ConclusionsIt is widely accepted that fruit trait diversity has primarily been driven by the differing perceptual abilities of bird versus mammal frugivores. Yet within a clade of largely bird-dispersed fruits, we find clear correlations between color, morphology, and nutrition. These correlations are likely driven by a shift from sequential to synchronous development, followed by diversification in color, nutrition, and morphology. A deeper understanding of fruit evolution within clades will elucidate the degree to which such syndromes structure extant fruit diversity.
Highlights
Fleshy fruits play an essential role in the lives of many plant species, attracting animal dispersers who consume the fruit and carry the seeds away from the parent [1]
We have focused on correlated evolution between color, nutritional content, and morphology — the entire “package” that dispersers interact with
The syndromes we identify, as well as the potential significance of developmental trajectory, highlight that there are many under-explored aspects of fleshy fruit diversity
Summary
Fleshy fruits play an essential role in the lives of many plant species, attracting animal dispersers who consume the fruit and carry the seeds away from the parent [1]. Animal dispersers receive nutrients and calories by consuming the fleshy pulp of the fruit [2, 3], while plants receive dispersal services, enabling gene flow, escape from predation and pathogens, and range expansion [4, 5]. The primary hypothesis to explain variation in these visual traits has been selection by animals via their perceptual abilities, behavior, and physiology According to this hypothesis, most fruits can be classified as either “bird fruits” (small, brightly colored) or “mammal fruits” (large, dull in color, possibly with a husk or rind) [6, 8, 9]. Birds and mammals are obviously heterogeneous groups with varying visual systems, body sizes, and abilities to manipulate their food, and the simplistic classification into “bird” or “mammal” syndromes does not adequately reflect fruit trait diversity
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