Darwin’s entangled bank through deep time: Structural stability of mutualistic networks over evolutionary timescales
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Mutualistic interactions form species-rich, complex networks that play essential roles for ecosystem function. Over macroevolutionary time scales, these networks change as species emerge and go extinct, yet the stability of their structural organization remains poorly understood. Here, we show that ancestral interaction networks can be reconstructed from present-day phylogenetic and interaction data. Focusing on large biogeographic scales, we infer the ancestral networks of plant mutualisms involving arbuscular mycorrhizal fungi, bat pollinators, and bird seed dispersers. We find that these mutualistic networks exhibit a modular structure that has persisted for millions of years, maintained by the evolutionary conservatism of species interactions. As species diversify, they show limited shifts in mutualistic partners. This minimal evolutionary rewiring results in a remarkable long-term stability of mutualistic network structure.
Significance statement
Plants have engaged in diverse mutualistic interactions since their colonization of land and the emergence of flowers and fleshy fruits. However, the macroevolution of such complex interaction networks remains poorly understood because fossil evidence of plant mutualisms is scarce. By reconstructing ancient interaction networks from present-day phylogenies and ecological data, we show that plant mutualisms with mycorrhizal fungi, pollinating bats, and seed-dispersing birds have maintained a consistent modular organization for millions of years. This persistence arises because species tend to retain their partners over deep evolutionary timescales. Our findings reveal that the architecture of mutualistic networks is remarkably stable, underscoring the enduring role of evolutionary conservatism in shaping present-day biodiversity.
