' 



SPAWNING BEHAVIOR AND SEXUAL DIMORPHISM 



IN FUNDULUS HETEROCLITUS AND 



ALLIED FISH. 



(CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORIES OF THE UNIVERSITY OF 



MICHIGAN. No. 108. ) 



H. II. NEWMAN. 

 INTRODUCTION. 



Of recent years much stress has been laid upon the structural 

 basis of behavior, especially among the lower organisms. Among 

 the higher animals, on the other hand it has long been under- 

 stood that function and structure are simply dynamic and static 

 phases of the same thing. There would be little excuse for the 

 present paper, then, unless it should serve to show that these 

 ideas of structure and function --sexual dimorphism and spawn- 

 ing behavior have a far wider application than has commonly 

 been supposed. It will be shown that even minute, temporary 

 structures, that have previously escaped the eye of the investi- 

 gator, are as truly adaptations for spawning as are the more 

 obvious secondary sexual characters, such as differences in the 

 sizes of fins, in color pattern, in body form, etc. 



My attention was first called to this subject by chance. One 

 day early in the summer of 1906, while engaged in cross-breed- 

 ing species of Fundulus at the Marine Biological Laboratory of 

 Woods Hole, I was fortunate enough to observe the spawning act 

 in the species Fundiilus lictcroclitus. These fish were spawning in 

 a small aquarium and in a good light so that the entire process 

 could be observed in minute detail without difficulty. After- 

 wards I was fortunate in being able to observe the spawning of 

 Cyprinodon under equally favorable conditions. These observa- 

 tions led to a closer study of the behavior of these species and 

 to a consideration of their sexual dimorphism as the structural 

 basis of this behavior. The other two available species of 

 Fundiilus, F. viajalis and F. diapliamis were then brought in for 

 purposes of comparison. 



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