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 investigate whether the beak-length difference has a genetic basis or is solely due to phenotypic plasticity (an environmental effect). Which of the following experimental designs and predicted outcomes would provide the strongest evidence for a genetic contribution to the difference?
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, this supports a genetic contribution to 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.
122 exam-style questions on OCR GCSE Biology 5.2 Natural selection and evolution, covering 5.2.1 Genetic variation within a population, 5.2.2 Developments in classification systems, 5.2.3 How evolution occurs through natural selection, 5.2.4 Evolution as change over time, 5.2.5 Evidence for evolution, and 5.2.6 Darwin and Wallace. Each one has a worked solution and a mark scheme showing where the marks go.