Inter-island colonization, and evolutionary processes in the Canarian endemic genus Parolinia Webb (Brassicaceae): implications for its conservation

The Canary Islands are oceanic islands that encompass a wide diversity of geological ages, sizes, ecological regions, and orographic contexts that determine different isolation frameworks and provide a suitable geographical setting to address questions regarding genetic variation patterns and colonization processes. In the present study, we used nuclear microsatellites to quantitatively determine gene flow, colonization patterns, and geographical barriers in the Canarian endemic genus Parolinia, taking into account the dynamic geological ontogeny of the islands. Our genetic analyses showed a high number of shared alleles (68%) and low interspecific genetic differentiation, suggesting both a close relationship among the species of Parolinia and a likely recent origin of this Canarian endemic genus. MIGRATE analysis suggested a westward stepping stone colonization pattern from Gran Canaria to Tenerife, and then to La Palma and La Gomera. Supporting this hypothesis, P. schizogynoides (La Gomera Island) and P. aridanae (La Palma Island) clustered together in the STRUCTURE and PCoA analyses, and showed a high number of shared alleles and low genetic differentiation, which also suggests a recent migration from an ancestor from Tenerife Island. In addition, these analyses also point to P. ornata (Gran Canaria Island) as the genetically closest taxon to the putative ancestor of the genus. In view of the existence of genetic relationships within Parolinia, any population reinforcement programs should be carried out using genetic material with strict geographic and, when possible, genetic traceability to prevent anthropogenic hybridization. Translocations of individuals between different distribution areas should be avoided, and the most endangered species should be adequately represented in seed banks.