Résumé
Karst ecosystems in southern China are species-rich and have high levels
of endemism, yet little is known regarding the evolutionary processes
responsible for the origin and diversification of karst biodiversity. The
genus Primulina (Gesneriaceae) comprises ca. 170 species endemic to
southern China with high levels of ecological (edaphic) specialization,
providing an exceptional model to study the plant diversification in
karsts. We used molecular data from nine chloroplast and 11 nuclear
regions and macroevolutionary analyses to assess the origin and cause of
species diversification due to paleoenvironmental changes and edaphic
specialization in Primulina. We found that speciation was positively
associated with changes in past temperatures and East Asian monsoons
through the evolutionary history of Primulina. Climatic change around the
mid-Miocene triggered an early burst followed by a slowdown of
diversification rate towards the present with the climate cooling. We
detected different speciation rates among edaphic types, and transitions
among soil types were infrequently and did not impact the overall
speciation rate. Our findings suggest that both global temperature changes
and East Asian monsoons have played crucial roles in floristic
diversification within the karst ecosystems in southern China, such that
speciation was higher when climate was warmer and wetter. This is the
first study to directly demonstrate that past monsoon activity is
positively correlated with speciation rate in East Asia. This case study
could motivate further investigations to assess the impacts of past
environmental changes on the origin and diversification of biodiversity in
global karst ecosystems, most of which are under threat.