Editing Directional selection (section)

=== Soapberry Bugs ===
[[File:Red Shouldered Bug, Ant, Mum.jpg|thumb|''Jadera Haematoloma'']]
[[Soapberry bug|Soapberry Bugs]] (''[[Jadera haematoloma]]'') primarily feed on seeds produced by plants of the [[Sapindaceae]] family. These soapberry bugs use their beaks to feed on the seeds within the fruits of these plants, so it is crucial that their beak size is long enough to reach the seeds from the exterior of the fruits. However, the distance from the exterior of the fruit to the seed can vary. Scott Carroll and Christin Boyd (1992) conducted an experiment where they would observe how three newly introduced plant species introduced to North America that were colonized by these soapberry bugs would affect the natural selection of the insect’s beak length. Each new plant species hosted fruits of different sizes compared to the native hosts. They found that there was indeed a close correlation between the radius of the fruit and the length of the beak. There was a positive directional selection for larger beaks when the radius of the fruit was larger, and there was a positive directional selection for smaller beaks when the radius of the fruit was smaller. To confirm that these differences were caused by genetic differences and not through phenotypic plasticity, Carroll raised young soapberry bugs from the populations based on the introduced plant species and found that their beak length was retained when they were developed on the alternative host. <ref>{{Cite journal |last=Carroll |first=Scott P. |last2=Boyd |first2=Christin |date=1 August 1992 |title=HOST RACE RADIATION IN THE SOAPBERRY BUG: NATURAL HISTORY WITH THE HISTORY |url=https://academic.oup.com/evolut/article/46/4/1052/6870325 |journal=Evolution |language=en |volume=46 |issue=4 |pages=1052–1069 |doi=10.1111/j.1558-5646.1992.tb00619.x |issn=0014-3820}}</ref>