FOOD AND PARTHENOGENETIC REPRODUCTION 



AS RELATED TO THE CONSTITUTIONAL 



VIGOR OF HYDATINA SENT A. 1 



W. V. LAMBERT. W. S. RICE, AND H. C. A. WALKER. 



There has been a general belief for many years that cross- 

 fertilization is beneficial to a race. Darwin studied the effects 

 of inbreeding and crossbreeding in many plants and came to the 

 general conclusion that while inbreeding has a deleterious effect, 

 crossbreeding has a beneficial effect upon the races involved. 



In experiments with infusoria Calkins has found that if 

 conjugation is prevented the race gradually weakened and finally 

 died. He observed, however, that by the artificial stimuli of 

 various chemicals in the culture water he was able to prolong the 

 life of one race of Paramecium caudautam to the 742d generation. 



Investigations in regard to the effects of parthenogenetic 

 reproduction have been carried on by Shull and Whitney with 

 the rotifer, Hydatina senta. Both of these investigators have 

 found that continued parthenogenesis in pedigree races of rotifers 

 has resulted in a gradual weakening and loss of vigor, and in 

 some experiments death. In Whitney's experiments one race of 

 rotifers died out from general exhaustion in the 384th generation 

 and another in the 546th generation. A third race, discontinued 

 in the 443d parthenogenetic generation had also shown a marked 

 decrease in constitutional vigor. 



Investigations of other workers, however, do not seem to 

 confirm these general results. Woodruff, in his observations on 

 the Paramecium aurelia, found that a race of these animals kept 

 in cultures made from natural pond waters did not undergo 

 marked depression or physiological changes. This race at the 

 end of eight years, after having passed through 5250 generations 

 without conjugation, was in a normal condition. Another race, 

 however, subjected to the relatively constant hay infusion 

 cultures generally employed, died after passing through several 

 hundred generations. 



1 Studies from the Zoological Laboratory, The University of Nebraska, No. 134. 



192 



