Divergent Drought Adaptation

Adaptive divergence across environmental gradients is a key driver of speciation. Precipitation seasonality gradients are common in the tropics, yet drought adaptation is nearly unexplored in neotropical understory herbs. Costus villosissimus is adapted to seasonal drought while C. allenii is reliant on perennial water.  To uncover the basis of drought adaptation, we combined ecophysiological trait measurements in the field and greenhouse with experimental and observational assessments of real-time drought response to determine how Costus villosissimus differs from C. allenii to achieve drought adaptation. We found that drought-adapted C. villosissimus employs flexible dehydration avoidance via a fast economic strategy. During drought, C. villosissimus displays facultative drought-deciduousness, losing lower leaves during the dry season and rapidly growing new leaves in the wet season (see graphical abstract below). This drought adaptation strategy has not previously been documented in tropical herbs. Divergent drought adaptation evolved recently between these species and is an important component of their reproductive isolation, indicating that adaptive shifts to survive seasonal drought may be an under-appreciated axis of neotropical understory plant diversification. Check out the full article here!