Latent Genetic Effects of Past Selection on Blood Feeding: History Matters

SIMPLE SUMMARY: Conventional wisdom argues that strong directional selection over time decreases genetic variation, thus reducing adaptive ability in an ever-changing world. We find the opposite. Directional selection on blood feeding in low-biting, southern pitcher-plant mosquitoes results in an avid biting population. When selection is withdrawn and no longer imposed, biting rapidly reverts to the original, ancestral state. When selection is re-imposed on the previously selected population, side-by-side with the unselected control population, biting quickly resumes in the selected line, but, importantly, not in the control line, contrary to expectations. Hence, past selection leaves an enduring legacy on a population. History matters. ABSTRACT: Conventional wisdom is that selection decreases genetic variation in populations, variation that should enable and be essential for population persistence in an ever-changing world. Basically, we find the opposite. Response to selection on biting in the pitcher-plant mosquito, Wyeomyia smithii, increases from 20 to 80% in 19 generations, but reverts back to the original 20% after seven generations of relaxed (not reversed) selection. At the same time, biting in the control line remains at the original 20% through 30 generations without blood feeding. Imposition of selection on biting in both lines elicits a rapid response in the previously selected line, but, importantly, not in the control line. Genetic variation for biting has increased, not decreased, as a consequence of long-term directional selection, contrary to expectations. Convergent phenotypes belie the underlying difference in future adaptive potential. Selection events over time in the background of individuals or populations will determine outcomes of applied research, be it in the fields of medicine, agriculture, or conservation. In short, history matters.