A population of soapberry bugs (Jadera haematoloma) originally fed on the native balloon vine, which has thick fruit walls requiring long beaks to reach the seeds. Following the introduction of the flat-podded goldenrain tree, which has thin fruit walls, some bugs colonized this new host. Within 50 years, the average beak length in the population feeding on the goldenrain tree decreased significantly.
An evolutionary biologist wanted to determine whether this change in beak length was due to natural selection resulting in genetic adaptation, or phenotypic plasticity (an environmental effect). Which of the following experimental designs and predicted outcomes would provide definitive evidence that evolution by natural selection has occurred?
Raise offspring from both populations in a shared laboratory environment on the same diet of goldenrain tree fruit. If the offspring of both populations develop identical, intermediate beak lengths, it demonstrates that directional selection has fixed different alleles in each population.
Raise offspring from both populations in a shared laboratory environment on the same diet of goldenrain tree fruit. If the offspring of the goldenrain tree population continue to develop significantly shorter beaks than those of the balloon vine population, it demonstrates a genetic basis for the phenotypic difference.
Translocate adult bugs from the goldenrain tree population onto the balloon vine in the wild. If these translocated adult bugs undergo rapid beak elongation within their lifetime to successfully feed on the larger fruit, it proves that natural selection has occurred.
Compare the total genomic DNA sequence of both populations. If there is a very high level of overall genetic similarity (over 99%99\%99%) between the two populations, it proves that the change in beak length must be due to directional selection rather than genetic drift.