Collapse of local adaptation in Florida soapberry bugs (Jadera haematoloma)

The soapberry bugs (Rhopalidae: Serenithinae) have been studied for their rapid, repeated adaptation to novel host plants throughout the world.  In the early 1990s, Scott Carroll and colleagues demonstrated that populations of Jadera haematoloma had locally adapted to an invasive host plant (golden rain tree, Koelreuteria elegans) in Florida after its introduction and spread in the mid-1900s, and that a trade-off existed between ability to use the invasive and the native host (balloon vine, Cardiospermum corindum), leading to two distinct sets of host-associated populations with fitness peaks on their local host.  Key morphological adaptations (beak length) also showed clear differentiation.

            However, this no longer seems to be the case.  Returning to these populations 25 years after the original work, both morphological measurements and cross-rearing experiments demonstrate that populations on both hosts are now more well adapted to the invasive host plant.  Populations using the invasive host have changed relatively little in the past 25 years.  However, populations on the native host are now very similar to those on the invasive host morphologically and have increased survival on the invasive compared to the native host. 

It is likely that the much larger populations supported by the invasive host, and range expansion since its introduction, have contributed to increased gene flow swamping out adaptation to the native host.  Given the variable nature of host abundance and stability in many systems in the field, this is likely to be a common phenomenon that requires long-term monitoring to detect.