Pollination niche shifts in sympatric globular cacti Eriosyce: Consequences on reproductive isolation and species formation

Pollination niches, which encompass the factors influencing pollen exchange among angiosperms, are fundamental to understanding reproductive success and the intricate eco-evolutionary dynamics of plants. In this study, we investigated pollination niche shift among four sympatric <i>Eriosyce</i> cacti with restricted distributions in the South American Mediterranean region. Utilizing a comprehensive approach-including pollination niche analysis, pollinator color perception studies, reproductive output assessments, molecular phylogenetics, gene flow analyses, and species distribution modeling-we revealed a significant pollination niche displacement in <i>E. chilensis</i> and its variety, <i>E. chilensis</i> var<i>. albidiflora</i>. These taxa transitioned from a hummingbird-pollinated system prevalent in the <i>Eriosyce</i> sect. <i>Neoporteria</i>, characteristic of their sister species <i>E. litoralis</i>, to a bee-pollination strategy akin to that of the co-occurring species <i>E. mutabilis</i>. This shift highlights a simultaneous convergence of <i>E. chilensis</i> toward <i>E. mutabilis</i> and divergence from <i>E. litoralis</i> in pollination strategies, providing adaptive advantages by reducing pollen limitation and enhancing seed production. The morphological and flowering phenological similarities between <i>E. chilensis</i> and <i>E. mutabilis</i> suggest the evolution of a shared advertising display, potentially indicative of floral mimicry, wherein both species benefit from attracting shared bee pollinators. Genomic analyses reveal distinct pollinator-driven selection pressures, with <i>E. chilensis/E. albidiflora</i> exhibiting traits that promote reproductive isolation from <i>E. litoralis</i>, supporting a scenario of rapid speciation occurring within the past half of million years in the absence of geographic barriers. These findings underscore the pivotal role of pollinator interactions in shaping angiosperm speciation and biodiversity, highlighting their dynamic influence on ecological and evolutionary processes.