Among-population variation in seed mass for 190 Tibetan plant species: Phylogenetic pattern and ecological correlates

It is widely assumed that seed mass, as a proxy of both dispersability and competitiveness, can affect community composition and diversity. Numerous studies have validated the influence of seed mass at the interspecific level. However, little is known about patterns of among-population variation in seed mass (APVSM), which may influence a species’ persistence under climate change. We characterized the naturally occurring variation in seed mass among populations across 190 Tibetan plant species (2503 populations). We tested for relationships between APVSM and plant life-history traits (mean seed mass, seed dormancy type, seed dispersal mode, life form, and pollination system) and an environmental factor, elevation. We also tested patterns of phylogenetic signal in APVSM and identified the lineages (clades) with an exceptionally high or low APVSM. We found that APVSM varied > 5-fold among species, ranging from 0.085 in Bromus sinensis to 0.447 in Anaphalis flavescens. Furthermore, wind-dispersed species tended to have greater APVSM. Finally, we found that APVSM exhibited a significant phylogenetic signal (i.e., closely related species were more or less variable in their seed size than would be expected by chance) that was driven by a few major lineages. Clades with significantly less APVSM included Brassicaceae, Campanulaceae, Ranunculaceae (including Thalictrum, Trollius, Aconitum and Anemone), Roegneria, Rumex. Clades with significantly greater APVSM included Bignoniaceae, Lamiaceae, Orobanchaceae, Anaphalis, Cotoneaster and Sorbus. In summary, our study suggested that APVSM is partly due to trade-offs in evolutionary history and its associations with other life-history traits.