A certаin seа slug, Elysiа chlоrоtica, &quоt;steals" chloroplasts from algae it normally feeds upon, and then uses the chloroplasts to conduct photosynthesis during times of low food availability. Scientists found that the slug carries a chloroplast-maintenance gene in its genome, a gene identical to one found in the algae. The process by which the slug first acquired the gene is called what?