PHOTOPERIODISM IN REPTILES 



GEORGE A. BARTHOLOMEW 



Department of Zoology, University of California, Los Angeles 



Relatively little information is available on the reproductive physiology 

 of reptiles, and much of the experimental work on reptilian endocrin- 

 ology has been a repetition of classical work done originally on 

 mammals. As a result, the data tend to be fragmentary and out of 

 context biologically, and usually contribute little to the understanding 

 of the factors controlling the timing of reproduction in this group. The 

 literature on reptilian reproduction, though limited in comparison 

 with that on birds and mammals, is still extensive enough to be con- 

 fusing. At the present time, it is difficult to generalize beyond saying 

 that the reproductive activities of a wide variety of reptiles are seasonal 

 and that the major patterns of pituitary-gonad relations in reptiles are 

 qualitatively similar to those that have been worked out for other 

 terrestrial vertebrates. 



A guide to the literature on the reproduction and natural occur- 

 ring reproductive cycles of reptiles can be found in papers by Evans 

 and Clapp (1940), Cieslak (1945), Miller (1948), Fox (1952), 

 and Kehl and Combescot (1955). The present paper will review the 

 scant literature on photoperiodism in reptiles, but its main purpose is 

 the presentation of a point of view that may help to supply an appro- 

 priate ecological orientation to the problem of relating day length to 

 breeding season in this group. 



Although it is a familiar fact that many reptiles have markedly 

 seasonal patterns of breeding, the role of environmental factors in the 

 determination of this periodicity has been studied in only a few species 

 and in no case has it been possible to make an adequate synthesis of 

 physiological and ecological data. The paucity of information on 

 photoperiodism in reptiles and its fragmentary nature is indicated 

 by the brevity of the literature summary which follows. Mellish (1936) 

 reported that exposure to continuous light and a temperature of 35°C 



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