Environment-driven trait and genetic divergence in a neotropical mangrove tree. Avicennia schaueriana

Integrating genomic and ecological data are instrumental for understanding the mechanisms of adaptive processes in natural ecosystems. We integrated molecular and ecophysiological approaches to assess non-neutral variation in the mangrove species Avicennia schaueriana, a new-world tree found from tropical to temperate coastal forests in the Atlantic coast of the Americas. We found substantial divergence between populations occurring north and south of the northeastern extremity of South America, underpinning roles of contrasting environmental forces in shaping the genetic structure of the species. Individuals from equatorial and subtropical forests grown in a common garden experiment diverged in key traits involved in water balance and carbon acquisition. RNA-sequencing highlighted molecular effects of different light, temperature and air humidity regimes under field conditions at contrasting latitudes. Genetic polymorphisms with signatures of selection were detected in putative protein-coding sequences associated with the biogenesis of the photosynthetic apparatus, with anthocyanin biosynthesis and with osmotic and hypoxia stress responses. Our findings elucidate key functional divergences between the populations, with a north-south structure of diversity, which is also observed in other distantly related sea-dispersed plants. Our work demonstrates the power of a multidisciplinary approach in local adaptation studies of dominant non-model species in endangered ecosystems.