From the flowers to the cells: a trait-based and cytogenomic study of Macaronesian Aeonium genus (Crassulaceae)

Macaronesian region comprises five archipelagos (i.e., Azores, Madeira, Selvagens, Canary Islands and Cabo Verde) in the Northeastern Atlantic Ocean. Volcanic in nature, all archipelagos reach high altitudes even in relatively small areas and harbor an extremely rich endemic flora, including notable examples of plant radiation, such as the genus Aeonium (ca. 41 taxa), Sonchus (ca. 31 taxa) and Echium (ca. 27 taxa). Considered a biodiversity hotspot, Macaronesia is recognized as a model for studying the evolutionary processes involved in flora diversification. Aeonium genus (Crassulaceae) includes about 41 taxa and is considered the most speciose radiation of Macaronesia, occupying many contrasting habitat types in the Canary Islands, Madeira and Cabo Verde. The great species richness and the wide range of characters observed in Aeonium species make it a model of study par excellence. This dissertation aimed to study the reproductive traits and cytogenomic variation patterns of Aeonium genus in order to understand the characters that influence the distribution of the most speciose radiation of Macaronesian Region. For these purposes, a holistic approach was used that integrates different methods in the areas of reproductive biology (Chapter 2), cytogenomics (Chapter 3) and conservation biology (Chapter 4), based on extensive fieldwork on the islands of the Canary Islands. The reproductive trait-based results (Chapter 2) showed that inflorescence height was positively correlated to flower number and geographic range size. This suggested that species that invest in taller inflorescences and more reproductive units have wider distributions and a more generalist behavior. According to the cytogenomic results (Chapter 3), Aeonium species tend to have small genomes, being subshrubs the large-genomed ones. Comparative analysis across the genus revealed a positive correlation between 2C-values and conservation status, owning endangered species, on average, large genomes. Finally, in a conservation approach (Chapter 4), most of Aeonium taxa occur in Tenerife in Teno Rural Park and Anaga Rural Parks, being there their hotspot of biodiversity. The representation of Aeonium endemics in the network of the Protected Areas is relatively high once a large area (40%) of Canary Islands is classified as protected. Thus, by integrating the knowledge of the various approaches applied in the three chapters (2 – 4) of this dissertation, it was possible to contribute with new data to explain the distribution of Aeonium and detect hotspots areas of species diversity, based on inflorescence height, genome size and abiotic factors. Some species have their limited range of occurrence, among other external factors (e.g., anthropogenic action and invasive species), by the reduced inflorescence height. On the other hand, species with a larger genome do not respond to this trend and have also limited dispersal ranges. However, further morphological, cytogenomic analyzes and more fieldwork in all Macaronesian Islands to inventory all Aeonium species will reinforce the results and identify the main factors leading to the large diversification of largest plant radiation of Macaronesia, contributing to the preservation of the unique biodiversity existing in these island ecosystems.