Résumé
Adaptive radiations are bursts in biodiversity that generate new evolutionary lineages and phenotypes. However, because they typically occur over millions of years, it is unclear how their macroevolutionary dynamics vary through time and among groups of organisms. Phyllostomid bats radiated extensively for diverse diets—from insects to vertebrates, fruit, nectar, and blood—and we use their molars as a model system to examine the dynamics of adaptive radiations. Three-dimensional shape analyses of lower molars of Noctilionoidea (Phyllostomidae and close relatives) indicate that different diet groups exhibit distinct morphotypes. Comparative analyses further reveal that phyllostomids are a striking example of a hierarchical radiation; phyllostomids’ initial, higher-level diversification involved an “early burst” in molar morphological disparity as lineages invaded new diet-affiliated adaptive zones, followed by subsequent lower-level diversifications within adaptive zones involving less dramatic morphological changes. We posit that strong selective pressures related to initial shifts to derived diets may have freed molars from morpho-functional constraints associated with the ancestral molar morphotype. Then, lineages with derived diets (frugivores and nectarivores) diversified within broad adaptive zones, likely reflecting finer-scale niche partitioning. Importantly, the observed early burst pattern is only evident when examining molar traits that are strongly linked to diet, highlighting the value of ecomorphological traits in comparative studies. Our results support the hypothesis that adaptive radiations are commonly hierarchical and involve different tempos and modes at different phylogenetic levels, with early bursts being more common at higher levels.
[Display omitted]
•Phyllostomids radiated via an “early burst” only apparent in traits linked to diet•Within-diet-group diversifications do not demonstrate early burst patterns•The hierarchical radiation pattern seen here may be common among radiations•Results highlight the value of using ecomorphological traits in comparative studies
To assess macroevolutionary patterns of the phyllostomid bat radiation, Grossnickle et al. use molar traits that are strongly linked to diet. The radiation is hierarchical: the initial, higher-level diversification involves a diet-driven “early burst” in morphology, and subsequent, lower-level diversifications lack an early burst pattern.