Sex-specific responses to climate change in unisexual bryophytes

Global climate change represents a threat to biodiversity. While we have gained knowledge about impacts on ranges shifts across ecosystems and species, we lack understanding at the infraspecific or population level. Unisexual poikilohydric species may be especially susceptible to global warming as they often exhibit spatial segregation of sexes, driven by physiological and morphological adaptations to specific habitats. Here, we use Ensemble of Small Models (ESMs) to investigate how climate change may differentially affect the distribution range of each sex in four unisexual bryophyte species. We focused on two threatened Macaronesian endemics (Exsertotheca intermedia, Frullania polysticta) and two, primarily restricted to Macaronesia and western Europe (Frullania teneriffae, Porella canariensis). All species are predicted to lose over 95% of their climatically suitable areas in the Macaronesia by 2100. However, the Atlantic coastal fringe of Europe and northwestern Africa are predicted to serve as refugia for both male and female Macaronesian endemics. A northward shift in suitable areas is particularly evident for Frullania teneriffae, with both sexes expected to expand into areas such as Ireland and the United Kingdom. In contrast, Porella canariensis exhibited sex-specific responses on the continent, where female plants showed a clear northward shift into new habitats, while male plants are predicted to face near-extinction in Iberian Peninsula due to reduced environmental tolerance. This study underscores the susceptibility of Macaronesian bryophytes to climate change, emphasizes the necessity of sex-specific strategies in conservation planning, and identifies refugia may facilitate long-term survival, provided Macaronesian bryophytes track climate change in North Atlantic.