THE AMPHIBIA OF OKLAHOMA 



it follows that habit patterns change most during evolution in a varied, as 

 opposed to a uniform, environment. 



Noble and Aronson (1942) have reviewed much of the literature on sex 

 recognition. It seems that, of the possible factors considered, most workers 

 are agreed that sight and special secretions have been ruled out for all forms 

 studied so far. Voice of the male and girth or firmness of the female are the 

 factors most constantly favored by the evidence of most workers; but differ- 

 ential behavior of the sexes seems to be of some importance in some species. 

 See Bragg (1940) for observations on Bufo cognatus. 



Voice plays an important part in many of the Oklahoma species, par- 

 ticularly in Bufo and Scaphiopus. All species of Bufo, except B. punctatus, 

 and all of Scaphiopus within the state have been studied from this viewpoint. 

 In B. cognatus and B. compactdis, sexually stimulated males congregate in 

 large numbers in a limited area and behave as though trying to attack each 

 other; each actively tries to clasp those near him. Sometimes there are so many 

 thus engaged that a pool may be a seething mass of struggling males. I have 

 seen as many as five males piled on top of one another, each struggling to 

 retain its sexual clasp upon the one next below. Such piles of clasping males 

 always separate into their component individuals within a period of two to 

 three minutes. However, if a single male clasps another in a pool, their sepa- 

 ration typically comes about in less than one-half minute. Why should there 

 be this marked difference in time between the two types of cases? 



Six seasons of close observation of thousands of individual toads breed- 

 ing in nature have convinced me that it is largely a matter of voice. When 

 clasped, each male utters a protesting note characteristic of its species and, 

 upon this note's being recognized by the clasping male, is immediately re- 

 leased. But if three or more males are involved, each, except the bottommost 

 and the topmost, are acting under two stimuli at once. They are actively 

 attempting to hold another toad while protesting vigorously to being held 

 themselves. Since each is making so much fuss, it does not immediately recog- 

 nize the protesting note of the individual directly below it and hence toads 

 in a pile do not separate as quickly as two individuals will do. The protesting 

 notes of these toads are also accompanied by a rapid movement of the sides 

 of the body, caused by rapid alternating contraction and relaxation of the 

 muscles of the body wall. Possibly the sense of touch is involved here instead 

 of (or in conjunction with) hearing. But it seems likely that hearing is by 

 far the more important of the two possible factors, since, in Bufo cognatus 

 in nature, males which have not yet developed this protesting note are held 

 by adult males as tenaciously as are mature females, although they may move 

 their sides vigorously as though trying to protest. Some mature and most 

 sexually undeveloped females also do the same thing when picked up by an 

 observer and they may do so when clasped by a male. 



I do not believe rigidity of the female's body, which appears to be sig- 

 nificant in some frogs (Noble and Ferris, 1929; Noble and Aronson, 1942) 

 to be important in B. cognatus nor B. compactilis, and I c]uestion it for other 

 species of toads (Bufo). It is often emphasizetl that the female's body be- 



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