Format: ORAL

Filip Vandelook1,2, Angelino Carta3

1 Meise Botanic Garden, Meise, Belgium 2 Katholieke Universiteit Leuven, Leuven, Belgium 3 University of Pisa, Pisa, Italy

Seeds are the main dispersal and propagation units of angiosperms and they are very diverse in their external and internal features. When dispersed, seeds consist of an embryo, the next generation of a plant, surrounded by the seed and/or fruit coat and by an alternative storage tissue (endosperm or perisperm), in case the nutritive reserves are not stored in the cotyledons. Examining the relative allocation of seed reserves by quantifying the relative embryo size at dispersal (i.e. size of the embryo relative to the seed, ES) across angiosperms, sets the basis to track the evolutionary history of this key reproductive trait related to germination timing and offspring survival. We used macroevolutionary approaches to estimate adaptive shifts of ES in the entire angiosperm radiation. We also evaluated how tempo (i.e. evolutionary rates) and mode (i.e. evolutionary process) of ES evolution changed through time and the role of paleo-temperatures on ES evolutionary rates. Early angiosperms typically had a low ES, which is still reflected in contemporary magnoliids and ANA-grade species. The analysis of major shifts in ES throughout angiosperm evolution revealed that these shifts occurred after 145 mya and were predominantly associated with the formation of the main angiosperm lineages. Comparison of a series of paleo-inspired models showed that tempo and mode of ES evolution altered from a very dynamic ES evolution early in angiosperm history towards a more static evolution driven by stronger stabilizing selection. Finally, a consistent trend for a slowdown in rates of ES evolution during periods of climate warming was found. Fast evolutionary rates under cold climates are consistent with the macroecological observation that rates of phenotypic evolution are higher at high latitudes. This study provides crucial new insights in seed trait evolution, which contribute to understanding the diversification of reproductive strategies in angiosperms.