Carbon dioxide sensitivity in Drosophila affinis and Drosophila athabasca.

ENSITIVITY to carbon dioxide in Drosophila melanogaster, discovered in 1937 by L’HfiRITIER and TEISSIER, has been the object of considerable research by L’HBRITIER and his co-workers in France (L’H~~RITIER 1948, 1951, 1958). Since ‘no study had previously been made in species other than D. melanogaster, it was decided to investigate the occurrence of CO, sensitivity in several of the American Drosophila species. All testing with GO, has been conducted at the D. melanogaster standard conditions, viz., 15 minutes at 13°C with pure CO, (PLUS 1954) . Following the treatment, any fly which cannot right itself and walk after 15 minutes in an atmosphere of free air is classified as sensitive. During the last few years CO, sensitivity has been encountered in laboratory stocks and/or wild-caught flies of several native American species: Drosophila affinis from Georgia, Minnesota, Missouri, Nebraska, and Tennessee; D. algonquin from Minnesota and Nebraska; D. athabasca from Alaska and Minnesota; D. psedoobscura from Nebraska; D. robusta from Nebraska; D. tolteca from Nicaragua and Mexico. In these species, CO, sensitivity has been found only rarely in D. algonquin, D. pseudoobscura, D. robusta, and D. tolteca. However, in D. athabasca from three to 20 percent of the wild-caught flies have been found to be CO, sensitive (Table 1) , while in D. affinis the frequency of CO, sensitivity has been found to be somewhat greater-from 16 to 39 percent (Table 2 ) . Entirely sensitive strains have been established in D. afinis and D. athabasca, and the nature of the inheritance of CO, sensitivity in these two species has been studied. In addition, D. melanogaster collected in Nebraska has been found to be 1.6 percent CO, sensitive out of 6,300 flies tested. Also, MR. DOUGLAS LUND of the University of Nebraska (personal communication) has found CO, sensitivity in laboratory stocks of D. azteca from Mexico; D. macrospina from Arizona, Georgia, Mexico, Nebraska, New Mexico, South Carolina, and Texas; D. pallidipennis from Colombia; D. prosaltans from Mexico. Studies of the genetic basis: L’HBRITIER (1948) describes the mode of inheritance of CO, sensitivity in D. melanogaster as being maternal, though not strictly so, since males also transmit sensitivity, but with less efficiency. For many years CO, sensitivity was held as a clear case of cytoplasmic heredity and the word genoid was used in reference to the CO, sensitivity agent. Following the discovery