Practice question

After aggregation Dictyostelium forms motile multicellular slug capable of phototactic and thermotactic migration before culmination. Slug displays positive phototaxis moving toward light source guided by lens effect of slug tip focusing light onto prestalk region and via opsin-like proteins modulating ammonia and cAMP chemotaxis. Migration toward bright, warm, elevated surfaces enhances spore dispersal by wind and reduces competition. Movement to dark or nutrient-rich areas would be counterproductive for dispersal. Therefore slug phototaxis to bright regions represents adaptive strategy seeking optimal site with stalk formation triggered at illuminated apex.