Vol. XXXIII. October, 1917. No. 4 



BIOLOGICAL BULLETIN 



INHERITABLE MODIFICATION OF THE WATER 



RELATION IN HIBERNATION OF LEP- 



TINOTARSA DECEM-LINEATA. 



WILLIAM LAWRENCE TOWER. 



A series of experiments in which Leptinotarsa decem-lineata 

 was introduced into the environmental complexes of the deserts 

 at Tucson, Ariz., in nine years of experimentation, have given 

 the results described in this paper; and show how the introduc- 

 tion of an organism from one habitat into another in these 

 experiments from a mesophytic into desert environment produce 

 alteration of the water relation in ways that are adaptive in 

 direction and inheritable in character. 



The specific result of the experiments concerns the develop- 

 ment in the organism, during the period of the experiments, of 

 the capacity to hold water within the tissues so that the intense 

 desiccation of the dry seasons which are passed in hibernation- 

 does not result in death, and the elimination of the introduced 

 population. The change is adaptive; directly in line with the 

 environmental pressure that is incident upon the population, and 

 in tests is shown to be gametic; in crossing with the normal 

 behaving as a Mendelian dominant; and is not easily reversible. 



The materials in the entire series have been pure strains from 

 my laboratory at Chicago; their history, reactions, and genetic 

 composition known for generations before introduction into the 

 Arizona deserts. The materials have at no period in their 

 history been subjected to any experimental operations at Chicago, 

 but are the natural animals, reared under normal conditions, 

 under continuous observation and record. Two strains have 

 been used, No. 99 and No. 100, both derived from nature on the 



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