no. 362! CRAYFISH FROM ALABAMA CAVES HOBBS 15 



A consideration as to the range and time of the existence of the 

 ancestral stock from which these crayfishes have been derived has 

 resulted in the hypothesis that the ancestral precursors occupied an 

 area of the southeastern United States that extended northward 

 from Alabama and encompassed the Cumberland Plateau. Because 

 of the presence of 0. pellucidus australis in the subterranean refugia 

 of the Cumberland Plateau and the contiguous limestone areas south 

 to Alabama, of the primitive Cambarus pristinus and C. obeyensis 

 Hobbs and Shoup (1947, p. 138), both occupying limited ranges on 

 the Plateau, and of P. pecki in northern Alabama, it seems probable 

 that the centers of origin for Orconectes, Cambarus, and the Mexicanus 

 Section of the genus Procambarus existed in the area of northern 

 Alabama northward through the limestone belt of Tennessee onto the 

 Cumberland Plateau. 



This differs slightly from the postulate proposed by Ortmann 

 (1905a, plate 3) that the center of origin for the genus Orconectes 

 (=his subgenus Faxonius) was situated somewhat more to the west 

 and did not embrace the Cumberland Plateau. 



In the area of the Cumberland Plateau, much of the primary 

 divergence in the genera Orconectes and Cambarus occurred with 

 stocks radiating from this center: in Orconectes principally to the 

 north and west, and in Cambarus, for the most part, to the east and 

 south, although two or three stocks of the latter moved westward 

 and reached the Ozark-Ouichita region relatively early. Procambarus 

 pecki probably remains in the area of its ancestral home but its 

 closest relatives moved southwestward into Mexico and to Cuba. 



Villalobos (1955) has discussed the origin of the Mexicanus Group, 

 and Hobbs and Villalobos (1964) have considered the origin of the Cu- 

 bensis Group. Their conclusions are that, inasmuch as the Mexicanus 

 Group occupies an area south of the Cordillera Volcanica Transversal, 

 which arose no later than the late Tertiary and probably during the 

 upper Miocene, the arrival of the ancestral stock of this group in the 

 area to the south of these mountains must have occurred sometime 

 prior to the end of that era. They also joined other earlier students 

 of Antillean zoogeography in postulating a tertiary land bridge be- 

 tween Cuba and the Central American-Mexican region across which 

 members of this stock reached Cuba. In light of recent studies (in- 

 cluding Kendall and Schwartz (1964) on the ability of cambarine 

 crayfishes to tolerate higher salinities than has been supposed, a land 

 bridge seems less a necessity than before. Regardless, however, of the 

 means by which the crayfishes reached Cuba, the time of their arrival 

 on the island must have been prior to the Pleistocene and probably as 

 early as the Miocene. 



