Local adaptation insights from genomics and ecophysiology of a neotropical mangrove

Integrating genomic and ecological data is instrumental for understanding the mechanisms of adaptive processes in natural ecosystems. In non-model species, such studies can be particularly challenging but often yield results with implications for conservation. Here, we integrate molecular and ecophysiological approaches to assess the role of selection in the north-south organisation of genetic variation in the mangrove species Avicennia schaueriana, a new-world tree found in tropical to temperate coastal forests along the Atlantic coast of the Americas. We found substantial divergences between populations occurring north and south of the north-eastern extremity of South America, possibly reflecting the roles of contrasting environmental forces in shaping the genetic structure of the species. In a common garden experiment, individuals from equatorial and subtropical forests were found to be divergent in traits involved in water balance and carbon acquisition, suggesting a genetic basis of the observed differences. RNA-sequencing highlighted the molecular effects of different light, temperature and air humidity regimes on individuals under field conditions at contrasting latitudes. Additionally, genome-wide polymorphisms in trees sampled along most of the species range showed signatures of selection in sequences associated with the biogenesis of the photosynthetic apparatus, anthocyanin biosynthesis and osmotic and hypoxia stress responses. The observed functional divergence might differentially affect sensitivities of populations to our changing climate. We emphasize the necessity of independent conservation management for the long-term persistence of the species diversity. Moreover, we demonstrate the power of using a multidisciplinary approach in adaptation studies of non-model species.