ADAPTATIONS AND DISTRIBUTION 



Ps. styccl{a-i is like H. cognatus, Ps. ciiirl{i!, and A/, c. olivacca in de- 

 veloping huge congresses alter rains, but is unlike them in not being de- 

 pendent upon the stimulus of rain for initiation of breeding behavior of 

 males. Males call in winter and spring, in greatest numbers after rains of 

 considerable volume (1-2 inches). Females, however, seldom join males ex- 

 cept during or just after rainfall (Bragg, 1^M2), and even the males fail to 

 call in exceptionally dry years. Members ol />. /. americanus and H. v. versi- 

 color, while greatly stimulated by rain during spring, nevertheless breed only 

 within a definite breeding period. Except that this both starts and ends later 

 in the season, they resemble Ps. strcc\cn in this. B. w. jowlcri has a breeding 

 season beginning only after nights have become quite warm and ending to- 

 ward midsummer. Its close relative, B. w. woodhousii, breeds intermittently, 

 some individuals as early as in March, others as late certainly as in August 

 and perhaps in September (Bragg, 1940a). 



In summary, in Oklahoma there is much variation between species in 

 the initiation of breeding behavior and in the migration to breeding sites. 

 There is no simple universal pattern such as is often implied for many species 

 of Europe and for most forms living in the eastern United States. Some 

 species manifest a breeding season, others do not; some breed only after rain 

 of one-half inch or more; others, irrespective of rains; still others, mostly after 

 moderate to heavy rain, although some individuals breed each year whether 

 rains come or not. Some closely related species, even in the same subgenus 

 (Scaphiopus), differ in sensitivity to so great an extent that they react dif- 

 ferently to the amount of rain and to its rate of fall. This is true, for example, 

 of S. hurterii and S. couchii , the former being stimulated more by the volume 

 of rain, the latter by its rate of fall. ( Bragg, 1944a, 1945a.) 



(3) Sex Recognition and Mating. 



The problem of sex recognition may be expressed in the form of ques- 

 tions: How does a male, usually calling in the dark, recognize the object 

 clasped as a female.'' What sensory cues are used.'' A partial answer to the 

 first question is that he does not always do so. Various objects, other than 

 females, may be clasped and retained for long periods; I have even seen a 

 male of B. cognatus hang tenaciously to a chunk of mud. But no male salien- 

 tian ever retains his sexual clasp on another normal adult male in a breeding 

 pool. It would seem, therefore, that some behavior, secretion, differential 

 in the sense of touch, or the sound made by a clasped male always stimulates 

 the release mechanism of the clasping male. Also as pointed out hy Noble and 

 Ferris (1929), the sensory cues used by the males of one species need not 

 necessarily be utilized by another, particularly when variation rather than 

 constancy appears to be the rule in so many other phenomena in breeding 

 behavior. Even so, one might expect greater uniformity in this matter than 

 in other phases of the breeding pattern, because environmental factors op- 

 erating during sex recognition are, and apparently always have been, more 

 uniform than those operative outside the water of the breeding site. If con- 

 stant interspecific variations in behavior are adaptive, as they may well be, 



