Rethinking angiosperm diversification through the functional integration of mutualisms

Akira Yamawo 

Flowering plants have generated and maintained exceptional diversity for over 100 million years. Explaining this macroevolutionary success requires understanding not only how new lineages arise, but also how they persist after divergence. Although multiple interactions influence angiosperm diversification, their relative contributions to lineage generation and persistence remain poorly resolved, and their joint effects have rarely been evaluated. Here, I develop the Functionally Integrated Symbiotic System (FISS) as a testable hypothesis: mutualistic interactions are functionally integrated when they make distinct but complementary contributions across demographic and evolutionary bottlenecks. Pollination is expected to contribute disproportionately to lineage generation through reproductive isolation, whereas seed dispersal and mycorrhizal symbioses are expected to contribute more strongly to establishment and persistence by facilitating range expansion, recruitment, and environmental buffering. Climatic change may alter these contributions by changing whether dispersal, establishment, or reproduction limits lineage persistence. FISS proposes that mutualistic traits should show asymmetric associations with lineage generation and persistence, and that considering these interactions together should explain or predict long-term diversification better than considering individual interactions alone.