ON THE STERILIZATION OF DROSOPIIILA BY HIGH 



TEMPERATURE. 



WILLIAM C. YOUNG AND HAROLD H. PLOUGH, 

 FROM THE BIOLOGICAL LABORATORY OF AMHERST COLLEGE, AMHERST. 



Breeding experiments with Drosophila melanogaster at high 

 temperatures have demonstrated that at a point 5 C. to 9 C. 

 above the normal optimum of 24 C. no offspring are produced 

 after one generation. This fact was first noted by Northrop (i) 

 for a single stock. Plough and Strauss (2) showed that the 

 exact temperature at which complete sterilization occurred varied 

 with different stocks, but was approximately constant for any 

 particular one. In all cases a temperature was found which 

 produced complete sterilization after an exposure of four days 

 or more, even though adult flies continued to live for some time 

 at this temperature, and newly laid eggs developed, pupated and 

 went through metamorphosis normally enough. The additional 

 fact was noted by all these workers that flies thus sterilized 

 would usually recover normal fertility if they were replaced for 

 a day or two at a temperature of 24 degrees. Northrop stated 

 however: "If after they have emerged from the pupae they are 

 left longer than ten days at the higher temperature the injury 

 becomes permanent and they are no longer able to produce eggs 

 capable of development at any temperature." 



Attempts to explain this sterility in terms of effects on the germ 

 cells have not been entirely successful. Northrop stated, though 

 without crucial evidence, that "Imagos raised and kept perma- 

 nently at a temperature of 30 degrees, are unable to produce eggs 

 capable of development at this temperature." Plough and 

 Strauss demonstrated that this could not be the correct explana- 

 tion by crossing both males and females hatched at 31 degrees 

 to females and males respectively bred at 25 degrees, carrying 

 the crosses at 31 degrees. Most of the 31 degree females mated 

 to normal males gave offspring at 31 degrees, and about half of 

 the 31 degree males likewise. The actual figures summarized 



from Plough and Strauss, Table II., are: 



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