Elizabeth Stacy and Donald Price (both Life Sciences), along with two former graduate students from the Stacy lab, have a paper in press, "Varieties of the Highly Dispersible and Hypervariable Tree, Metrosideros polymorpha, Differ in Response to Mechanical Stress and Light Across a Sharp Ecotone" in the American Journal of Botany. This study examines the drivers of isolation between sympatric populations of long-lived and highly-dispersible conspecific trees, which are poorly understood.  The authors looked for the causes of differential local adaptation of the Hawaii Island-endemic riparian tree, Metrosideros polymorpha var. newellii, and its progenitor, M. polymorpha var. glaberrima. Results demonstrate that the riparian zone is harsh and that selection involving the mechanical stress of rushing water, and secondarily light, lead to significant reciprocal immigrant inviability in adjacent forest and riparian environments. These findings suggest that disruptive selection across a sharp ecotone contributes to the maintenance of an incipient riparian ecotype from within a continuous population of a long-lived and highly dispersible tree species.