A XY chromosome system in Laurus azorica, an endemic dioecious laurel from the Azores.

Abstract

Baker's law posits that self-fertilization facilitates colonization, a key concept for understanding population dynamics and the evolution of sexual systems in plants. However, the prevalence of dioecious species (those with separate sexes) on oceanic islands presents a notable exception to this law, raising questions that have persisted since the initial debate between Baker and Carlquist nearly 60 years ago. Despite a number of important studies, we still lack comprehensive explanations for this intriguing pattern. Progress in this area may come from integrating various approaches, including botany, ecology, population genetics, and genomics. In this study, we aim to establish the Laurus genus as a model for investigating dioecy in oceanic islands. As a first step towards this goal, we have characterized the sex-determination type of Laurus azorica - a dioecious laurel endemic to the Azores - using a unique methodology to analyze sex chromosomes. Our findings indicate that L. azorica possesses an XY system that emerged approximately 5-10 million years ago, before the split with Laurus nobilis, its mainland counterpart. For the next steps, we plan to extend our analysis to L. nobilis and Laurus novocanariensis (endemic to Madeira and the Canary Islands) and conduct additional genomic studies to comprehensively characterize the sex-determination systems of these species, as well as their evolutionary dynamics and implications for the colonization of the Macaronesian islands.