Associated evolution of fruit size, fruit color and spines in Neotropical palms

Understanding how ecological interactions have shaped the evolutionary dynamics of species traits remains a challenge in evolutionary ecology. Combining trait evolution models and phylogenies, we analyzed the evolution of characters associated with seed dispersal (fruit size and color) and herbivory (spines) in Neotropical palms to infer the role of these opposing animal-plant interactions in driving evolutionary patterns. We found that the evolution of fruit color and fruit size were associated in Neotropical palms, supporting the adaptive interpretation of seed-dispersal syndromes and highlighting the role of frugivores in shaping plant evolution. Furthermore, we revealed a positive association between fruit size and the presence of spines on palm leaves, bracteas and stems. We hypothesize that interactions between palms and large-bodied frugivores/herbivores may explain the evolutionary relationship between fruit size and spines. Large-bodied frugivores, such as extinct megafauna, besides consuming the fruits and dispersing large seeds, may also have consumed the leaves or damaged the plants, thus simultaneously favoring the evolution of large fruits and defensive structures. Our findings show how current trait patterns can be understood as the result of the interplay between antagonistic and mutualistic interactions that have happened throughout the evolutionary history of a clade.
Methods
We built a dataset on palm traits using information from the literature. Most of the data on traits was obtained from Henderson et al. (1995). In cases where no information from Henderson et al. (1995) was found, we completed the dataset with information from Lorenzi et al. (2004). We classified palm species into two categories according to the predominant color of the mature fruit: "colorful fruits" (red, black and purple) and "dull-colored fruits" (green, yellow, brown and orange), reflecting colors that have been related to bird and mammal frugivory, respectively (Gautier-Hion et al. 1985, Nevo et al. 2018a). We considered only the color of ripe fruits and discarded those species for which the information about color was ambiguous. We also classified all species according to the presence ("with spines") and absence ("spineless") of spines. We consider spines to be any stiff sharply pointed structure (Grubb 1992) that is present either at the stem, peduncular bract, rachis or petioles, which is often associated with defense specifically related to mammalian herbivory (Charles-Dominique et al. 2016).