Gene flow, barriers, speciation and hybridization in Parolinia species (Brassicaceae) endemic to Gran Canaria

Oceanic islands are natural laboratories where evolutionary processes can be studied more readily. In the present work we use nuclear microsatellites to quantitatively assess the roles of hybridization, colonization, gene flow and geographical barriers in four Parolinia spp. endemic to Gran Canaria in connection with known geological events throughout the dynamic geological ontogeny of the island. Our genetic analyses show that these Parolinia spp. share 69% of all alleles detected and display low genetic divergence among populations, suggesting a close genetic relationship and recent differentiation. This close relationship is more evident between Parolinia platypetala and Parolinia ornata, which were included in the same genetic pool in the STRUCTURE analysis, and probably represent the early stages of an incipient speciation process, as suggested by the absence of gene flow barriers between them. NEWHYBRIDS, STRUCTURE and MIGRATE analyses unequivocally suggest frequent past migration and hybridization from P. ornata to P. filifolia, but contemporary migration is low overall. Despite the overall genetic closeness among the Parolinia spp. assessed, microsatellites dispelled doubts regarding the appropriate name/s for two taxonomically conflicting populations. In line with the predictions of the surfing syngameon hypothesis, ancestral hybridization, vicariance and dispersal events linked to the complex ontogeny of the island may have been key factors to shape the current genetic diversity and structure of Parolinia in Gran Canaria.