THE AMPHIBIA OF OKLAHOMA 



mental rate, Microhyla c. olivacea is next, the bufos a close third, Ps. darhjl 

 almost as fast as the bufos (faster than some of them), with Pseiidacris 

 strec\eri, Hyla v. versicolor following somewhat later and R. berlandieri 

 taking the longest time of any observed sufficiently-' for conclusions to be 

 drawn. 



Rana berlandieri is especially interesting as well as somewhat puzzling. 

 Elsewhere (Bragg, 1940b) I reported that in a fast evaporating pool, half- 

 grown tadpoles may go into metamorphosis and behave as though seeking 

 the bank rather than the deeper water still available. Since those observations 

 were made, I have noticed many times that in deeper pools these tadpoles 

 grow larger and remain longer in a pool before metamorphosis than in more 

 shallow pools. This could be due to temperature differences (in general, the 

 deeper the water the lower the temperature) or it might be an effect of salt- 

 concentration due to evaporation in the more shallow pools. The observations 

 reported above give evidence against temperature as the major factor, for 

 in the deep pool under investigation the animals became large and failed to 

 metamorphose under temperatures sufficiently high to kill some of them. 



The behavior of some kinds of tadpoles as they feed in a pool shows 

 nothing of peculiar interest, but there are some in which it does so, especially 

 in Scaphiopus. Recent observations on this genus (Bragg, 1944a, 1945a, 1946) 

 have shown that social aggregation, with or without an accompanying active 

 cannibalism commonly observed in certain species, may have a direct bear- 

 ing upon survival in a dry climate. As the pool evaporates, developmental 

 rate increases just at the time that food resources tend to run low. In the in- 

 tense struggle for survival as the water becomes dangerously low, aggrega- 

 tion with its tendency to cut down evaporation rate may save the lives of 

 many tadpoles. If aggregation is accompanied by cannibalism, food is in- 

 sured for at least a few individuals which in this way have a chance to survive 

 and to metamorphose before all the water disappears. (For detailed evidence 

 of this, see the papers cited.) I have thus far searched in vain among other 

 genera for these phenomena. 



(6) Metamorphosis and Dispersal. 



Once out of water, the behavior of the young differs interspecitically in 

 two significant ways, (a) in methods of protection from desiccation and (b) 

 in time of dispersal. The second of these has already been covered in other 

 connections but the first needs further presentation. 



The semiaquatic forms (Rana, Acris), some of the fossorial forms (Bujo 

 cognatus, B. compactilis, B. insidior, B. w. woodhousii) , and some of the 

 nocturnal species which seek protection beneath objects [Vs. clarkji) remain 

 about their natal pool for some weeks. Others of the fossorial species {B. t. 

 americanus , B. w. fowleri, all s{)ecies of Scaphiopus, Pseiidacris strecl{eri, and 

 Microhyla c. oiivacea) do not. Should the pool disappear immediately alter 



" It should be especially noted that I am not comparing R. berlandieri with the green 

 frog ( R. ciamitans) nor with the bullfrog (R. catesheiana) whose larvae typically do not 

 transform during their Hrst season. 



86 



