Ecological and Spatial Drivers of Diversification and Hybridization in Phalacrocarpum (Anthemideae, Asteraceae)

ABSTRACT Aims Range shifts and niche differentiation can promote hybridization and homoploid hybrid speciation by bringing different lineages into contact and afterwards facilitating their reproductive isolation. The Iberian endemic angiosperm genus Phalacrocarpum is a suitable model to explore these processes. While previous genomic research has documented recurrent hybridization throughout its evolutionary history, the roles of ecological divergence and geographic isolation as drivers of hybridization and diversification remain unclear. This study aims to assess the role of environmental niche dynamics in the hybridization processes and diversification of the genus. Location Iberian Peninsula. Time Period From the Late Pleistocene to the present. Taxon Phalacrocarpum (Anthemideae–Asteraceae). Methods We calibrated bioclimatic correlative species distribution models (SDMs) to depict the climatic tolerances of the taxonomic groups in Phalacrocarpum and predict their potential distributions under current and past climatic conditions during the Last Interglacial, Last Glacial Maximum and Mid‐Holocene. We also investigated climatic niche divergence between these groups by performing climatic niche equivalency and similarity tests. Results Models yielded good predictive accuracy. Partial overlap in the predicted climatically suitable areas in current and past periods is congruent with recurrent hybridization events inferred, especially between P. oppositifolium subsp. anomalum and subsp. hoffmannseggii, but also between the latter and subsp. oppositifolium . Significant niche divergence observed in incipient hybrid species identified in our previous work (subsp. oppositifolium and the Galician‐Portuguese border group) highlights a role for ecological isolation in their differentiation from other groups. Additionally, the reduction of suitable habitats and the loss of connectivity during warm interglacial periods suggest that geographic isolation also shaped the current diversity of this genus. Main Conclusions Our study reveals how ecological and geographical factors have shaped diversification and hybridization through Pleistocene climatic fluctuations, emphasising the interplay between ecological divergence, geographic isolation and hybridization.