“Maladaptive plasticity masks the effects of natural selection in the red-shouldered soapberry bug”

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Meredith L. Cenzer

Maladaptive plasticity generated by gene flow masks the effects of natural selection in soapberry bugs

Soapberry bugs (Jadera haematoloma) feeding in the field. Left, mating female feeding through a closed green pod of balloon vine (Cardiospermum corindum). Upper right, females feeding on open, dry pod of balloon vine. Lower right, mating pair feeding on open, dry pod of golden rain tree (Koelreuteria elegans).
(Credit: Scott P. Carroll)

When species are introduced to new areas, they can have profound effects on the evolution of native species. When the golden rain tree was introduced to Florida from Taiwan in the 1950s, some native soapberry bugs started eating its seeds instead of seeds of their native host plant, balloon vine. After several decades, two distinct types of soapberry bugs had evolved, each suited to one plant.

Like many invasive species, golden rain trees continued to spread in Florida over the last 30 years, increasing the number of soapberry bugs using this host instead of balloon vine. When soapberry bugs travel from golden rain tree back to balloon vine, they mate with local bugs and produce offspring with a mix of genes adapted to each host. This mixing of genes (‘gene flow’) that haven’t evolved together can produce unexpected detrimental effects, similar to what happens when two separate species mate.

Meredith Cenzer shows that this gene flow is causing soapberry bugs to respond incorrectly to their environment. She first confirms that long beaks are favored on balloon vine due to the large seedpods protecting its seeds, and that bugs living on balloon vine in nature are still genetically ‘longer beaked’ than those on golden rain tree. However, when bugs grow up on balloon vine, they develop short beaks that can’t reach the seeds of this host. As a result, populations of soapberry bugs living on the two plants in nature no longer look adapted to their local host, because the effects of growing up on each plant hide genetic differences. This unexpected evolutionary consequence of an invasive plant is making it increasingly difficult for soapberry bugs to maintain the ability to use their original native host in Florida. Read the Article