The megaherbivore gap after the non-avian dinosaur extinctions modified trait evolution and diversification of tropical palms

Africa as an evolutionary arena for large fruits

Strong paleoclimatic change and few Late Quaternary megafauna extinctions make mainland Africa unique among continents. Here, we hypothesize that, compared with elsewhere, these conditions created the ecological opportunity for the macroevolution and geographic distribution of large fruits. We assembled global phylogenetic, distribution and fruit size data for palms (Arecaceae), a pantropical, vertebrate-dispersed family with > 2600 species, and integrated these with data on extinction-driven body size reduction in mammalian frugivore assemblages since the Late Quaternary. We applied evolutionary trait, linear and null models to identify the selective pressures that have shaped fruit sizes. We show that African palm lineages have evolved towards larger fruit sizes and exhibited faster trait evolutionary rates than lineages elsewhere. Furthermore, the global distribution of the largest palm fruits across species assemblages was explained by occurrence in Africa, especially under low canopies, and extant megafauna, but not by mammalian downsizing. These patterns strongly deviated from expectations under a null model of stochastic (Brownian motion) evolution. Our results suggest that Africa provided a distinct evolutionary arena for palm fruit size evolution. We argue that megafaunal abundance and the expansion of savanna habitat since the Miocene provided selective advantages for the persistence of African plants with large fruits.

From genome size to trait evolution during angiosperm radiation

Angiosperm diversity arises from trait flexibility and repeated evolutionary radiations, but the role of genomic characters in these radiations remains unclear. In this opinion article, we discuss how genome size can influence angiosperm diversification via its intricate link with cell size, tissue packing, and physiological processes which, in turn, influence the macroevolution of functional traits. We propose that integrating genome size, functional traits, and phylogenetic data across a wide range of lineages allows us to test whether genome size decrease consistently leads to increased trait flexibility, while genome size increase constrains trait evolution. Combining theories from molecular biology, functional ecology and macroevolution, we provide a framework to better understand the role of genome size in trait evolution, evolutionary radiations, and the global distribution of angiosperms.

When lizards try out a more plant-based lifestyle: The macroevolution of mutualistic lizard-plant-interactions (Squamata: Sauria/Lacertilia)

Pollination and seed dispersal of plants by animals are key mutualistic processes for the conservation of plant diversity and ecosystem functioning. Although different animals frequently act as pollinators or seed dispersers, some species can provide both functions, so-called 'double mutualists', suggesting that the evolution of pollination and seed dispersal may be linked. Here, we assess the macroevolution of mutualistic behaviours in lizards (Lacertilia) by applying comparative methods to a phylogeny comprising 2,838 species. We found that both flower visitation (potential pollination) (recorded in 64 species [2.3% of total] across 9 families) and seed dispersal (recorded in 382 species [13,5% of total] across 26 families) have evolved repeatedly in Lacertilia. Furthermore, we found that seed dispersal activity pre-dated flower visitation and that the evolution of seed dispersal activity and flower visitation was correlated, illustrating a potential evolutionary mechanism behind the emergence of double mutualisms. Finally, we provide evidence that lineages with flower visitation or seed dispersal activity have higher diversification rates than lineages lacking these behaviours. Our study illustrates the repeated innovation of (double) mutualisms across Lacertilia and we argue that island settings may provide the ecological conditions under which (double) mutualisms persist over macroevolutionary timescales.

The megaherbivore gap after the non-avian dinosaur extinctions modified trait evolution and diversification of tropical palms

The Cretaceous-Palaeogene (K-Pg) extinction of the non-avian dinosaurs (66 Ma) led to a 25 million year gap of megaherbivores (>1000 kg) before the evolution of megaherbivorous mammals in the Late Eocene (40 Ma). The botanical consequences of this 'Palaeocene megaherbivore gap' (PMHG) remain poorly explored. We hypothesize that the absence of megaherbivores should result in changes in the diversification and trait evolution of associated plant lineages. We used phylogenetic time- and trait-dependent diversification models with palms (Arecaceae) and show that the PMHG was characterized by speciation slowdowns, decreased evolution of armature and increased evolution of megafaunal (≥4 cm) fruits. This suggests that the absence of browsing by megaherbivores during the PMHG may have led to a loss of defence traits, but the absence of megaherbivorous seed dispersers did not lead to a loss of megafaunal fruits. Instead, increases in PMHG fruit sizes may be explained by simultaneously rising temperatures, rainforest expansion, and the subsequent radiation of seed-dispersing birds and mammals. We show that the profound impact of the PMHG on plant diversification can be detected even with the overwriting of adaptations by the subsequent Late Eocene opening up of megaherbivore-associated ecological opportunities. Our study provides a quantitative, comparative framework to assess diversification and adaptation during one of the most enigmatic periods in angiosperm history.