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A Comparison of the Ovaries of Two Species of Bufo 

 with Different Ecological Requirements 



CAROL BERGTHOLD CLARK AND ARTHUR N. BRAGG 



STUDIES on the breeding behavior of Salientia suggest at least three 

 major factors, the interrelated influences of which initiate breeding. 

 There are (1) environmental stimuli such as sufficient rainfall at the 

 proper temperature, (2) hormonal regulations, and (3) physiological cycles 

 in the gonads during the seasons in which sex products are produced. In 

 Oklahoma, rainfall (in both amount and rate of fall) is of greater signifi- 

 cance as a stimulus for some species than for others ( Bragg, 1946). Salientian 

 species in this state show three distinctly different breeding patterns (the 

 xeric, mesic, and intermediate) which occur respectively (1) in species gen- 

 erally limited to prairie habitat, (2) in others in woodland and savannahs 

 or limited to these, and (3) in those which range through several ecological 

 communities. With few easily explainable exceptions these relations hold 

 widely among the twenty-seven salientians known here. Rugh (1935) dem- 

 onstrated ovarian stimulation by the hormones of the anterior pituitary gland 

 as well as the initiation of typical breeding reactions, as the clasping reflex 

 of the male. Many laboratories now make use of his techniques to secure eggs 

 of various forms for experimental purposes out of the normal breeding sea- 

 son for the species in c]uestion. The seasonal events in the gonads, however, 

 are not well known and almost no study has compared these events in species 

 with different breeding patterns or different ecological requirements. Most 

 laboratory workers have studied species having the mesic pattern of breeding; 

 so far as we are aware, species with the xeric breeding pattern have been over- 

 looked regarding these matters. Fisher and Richards (this volume) traced 

 the seasonal changes in the ovaries of Acris crepitans Baird, a species having 

 the intermediate breeding pattern. This is the only paper known to us which 

 deals with the problem of the seasonal change in the gonads of any North 

 American salientian. 



This paper compares two species of Bufo which occur in large numbers 

 in Oklahoma but have different ecological requirements and correspond- 

 ingly different breeding patterns. Specifically we set ourselves to answer the 

 following questions: (1) Is there any significant difference in the volumes 

 of the ovaries of the two, each taken as percentage of total volumes of adults? 

 (2) Within each species, what fluctuations in ovarian volume can be deter- 

 mined during different months of the breeding period of each? (3) What 



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