The evolution of seed dispersal is associated with environmental heterogeneity in Pinus

Abstract

Seed dispersal is a major life history stage for plants. Because of its influence on reproductive success, dispersal is expected to be under strong selection. Different ecological circumstances might favour dispersal towards few suitable sites or alternatively, the random distribution of propagules among suitable and unsuitable sites. However, the evolutionary dynamics favouring specific dispersal syndromes remain a matter of speculation in many cases. Here, we explore the linkage between dispersal and environmental conditions at an evolutionary scale. We use a comparative phylogenetic approach to investigate the evolution of dispersal morphology in the genus Pinus and its connection with climatic variability, aridity and fire. Our results show that dispersal appears to have evolved towards two alternative strategies: seeds with vs. without wings, closely matching the distribution of wind- and vertebrate- mediated dispersal within the genus. Moreover, we find a close evolutionary association between dispersal morphology and environmental conditions such that each morphology predominates under particular abiotic conditions. Seeds with bigger wings are selected for primarily in environments with high temperature variability and/or prone to fire, whereas wingless or remnant-winged seeds are evolutionarily linked primarily to environments that are arid or exhibit a high variability in rainfall. These findings suggest a role of seed dispersal in the adaptation to certain environmental conditions, along with the influence of such conditions on the evolution of plant functional traits.