Crabs, Flies, Yeast, Drip: A Maggot's Take on Evolution and Adaptation



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In 1974, geneticist Bruce Wallace heard an address delivered by Hampton Carson describing three species of Drosophila that had independently adapted to live as obligate commensals of land crabs, spending at least the larval stages in the crab’s nephritic patch. Wallace wondered if he could encourage flies to adapt in the laboratory by simulating the conditions of the nephritic patch (Wallace, pers. comm.). An artificial land crab was created: synthetic turf was inoculated with a soil-yeast solution and subjected to slowly dripping human urine (Wallace, 1978, and pers. comm.). A few Drosophila virilis managed to survive in the artificial crab, and after a year, there was a steady population of approximately 40 individuals. In an effort to clean the artificial crab, adults flies were removed and placed on standard media. The flies laid eggs that hatched, but the resulting larvae remained small and eventually died, apparently unable to feed on the food their ancestors had lived on for years in the university laboratory (Wallace, 1978). In the current study, I reproduced Wallace’s artificial land crab with the goal of examining previously unasked questions about the early stages of adaptation, especially changes in the growth, morphology, and behavior of the larvae.



evolution, Drosophila, adaptation, urea tolerance