Kim Valenta and Omer Nevo
Wild fruits come in an incredible diversity of colors, shapes, smells, and sizes. This diversity has puzzled scientists for well over a century. Because many animals rely on fruits as important food sources, and many plants rely on animals as seed dispersers, it has been suggested that fruiting plants, and the animals that disperse their seeds, have coevolved. The dispersal syndrome hypothesis states that co-occurring sets of fruit traits, like color, size, and odor, have evolved to be more attractive to the animals that they rely on for seed dispersal, and that animals have evolved to better detect and select ripe fruits. In the last 15 years, exciting advances in the ability to quantify fruit traits, and to understand how they might look and smell to non-human animals, have led to growing interest in this hypothesis. At the same time, research has shown that many factors in addition to seed dispersers might be quite important in the evolution of fruits, like local environmental conditions, and the evolutionary history of plants. In this article, we review these advances to show that animal behavior has driven the evolution of various fruit traits. Among others, differences in size preference by, for example, large and small birds have driven the evolution of fruit size; differences in the ability to detect colour have driven the evolution of fruit colourful displays; and differences in the tendency to rely on the sense of smell have contributed to the evolution of fruit aroma. At the same time, we find that fruit traits are also likely to be shaped by other factors, like for example animals that feed on fruits but do not disperse seeds. We finish with suggestions for future directions to further explore how animal behavior has brought about the tremendous diversity of fruit traits.