Chinese golden rain tree, fruit or seed pods. Image credits: Wikimedia Commons
As stated in Living on Earth, the length of the beak for the bugs eating from the golden rain tree had become significantly reduced, becoming nearly 30 percent shorter than the beak of bugs eating the native balloon vine within the course of only 50 years. A 1992 study first documented the beak-length divergence between host populations In what can be termed an immediate attraction to the non-native plant, the soapberry bug, which is an insect that uses its long, sharp beak to penetrate plants in search of food, started using the newly introduced tree for food.
It was in the 1950s that Florida landscape gardeners planted the golden rain tree (Koelreuteria elegans), a non-native ornamental from Taiwan with yellow flowers and light, papery seed pods, as the UF/IFAS Assessment of Non-Native Plants and other sources on the species confirm.
The basis for the experiment was established in the paper ‘Host Race Radiation in the Soapberry Bug: Natural History with the History,’ which appeared in Evolution in 1992, written by Scott P. Another observation made in the 1992 study is that variations were observed in development time and survival rate based on the host plant from which a particular population of bugs fed, indicating that variation in beak size was just one of several adaptations Carroll and Boyd documented. A 2016 follow-up study found the native-adapted ecotype had largely disappeared However, in 2016, a second study titled ‘Adaptation to an invasive host is driving the loss of a native ecotype’ was published by Meredith Cenzer in the journal Evolution , which sought to test how well the local adaptation pattern persisted in these same Florida populations.
Carroll and Christin Boyd. In the study, the authors took a closer look at these Florida populations, using both museum material and current sampling. The insects adapting to the golden rain tree showed more changes than just the reduced length of their mouthparts. The later study conducted by Carroll et al. took these discoveries further and showed some genetically-based differences in performance when comparing insects from their native host with those from another host. With the golden rain tree producing abundant amounts of seeds on all trees grown across suburban and urban Florida, the adaptation of the bugs to this abundant and accessible host provided a good example for studying the evolution process. Cenzer combined field surveys with morphology and host-use data and found that bugs were still present on the native balloon vine, but their phenotypes had converged with those of the invasive-host population: the distinct, long-beaked native-adapted ecotype was essentially gone, replaced by populations that were now better adapted to the golden rain tree across the board, likely through gene flow from the invasive-host populations. The mechanism behind this may be gene flow. Bugs adapted to the golden rain tree may have hybridized with balloon vine populations enough to reduce the prevalence of genes associated with the long-beaked form, regardless of whether balloon vine disappeared from the environment. However, more recent research on this system indicates that maladaptive plasticity also contributed to the development of this scenario, suggesting that gene flow alone is not the only explanation. Together, the two studies show how quickly evolutionary patterns can shift and then reverse Together, the two studies serve as an example of how quickly natural selection can drive a significant physical change, and of how quickly that change can be undone by gene flow rather than by a genuine reversal. As far as evolutionary biology is concerned, the soapberry bug example can serve as a good one for consideration since it demonstrates both aspects of evolution in a rather easy-to-follow system.
the later study found that the short-beaked, invasive-adapted form had instead spread through the whole regional population, swamping and erasing the longer-beaked native-adapted ecotype rather than the population reverting to it While the earlier study traced the evolution of differences in beak length within just a few decades of the golden rain tree’s introduction.
