Necturus Chromosome Evolution 39 



1980); neither N. beyeri nor N. alabamensis have been so examined. 

 Relative to other salamanders, N. maculosus has a karyotype that is 

 distinctive in chromosome number and morphology, and particularly in 

 the degree of differentiation of the sex chromosomes (Sessions 1980). 

 Our study was carried out to ascertain the degree to which karyological 

 changes have accompanied diversification and divergence within the 

 genus Necturus, and to elucidate the relationship between the geogra- 

 phic distribution and the evolutionary history of this group of sala- 

 manders. 



MATERIALS AND METHODS 



The following specimens were used in this study and unless other- 

 wise indicated all have been deposited in the Museum of Vertebrate 

 Zoology, University of California, Berkeley. Abbreviations used below: 

 ASU = Department of Biology, Appalachian State University, Boone, 

 NC; CR = county road; SR = state road. 



Necturus alabamensis.— 2$$, 19, Black Creek at SR 20, 1.6 km 

 W of Bruce, Walton Co., FL; 20 May 1980; 1$, Juniper Creek, 

 approx. 1.6 km S of Juniper, 137 m elevation, Marion Co., GA; 30 

 November 1980. 



Necturus beyeri. — 19, 1$ (deposited at ASU), approx. 24 km S 

 of Nacogdoches on Bernaldo Creek, Stephen F. Austin State Univer- 

 sity Experimental Forest, Nacogdoches Co., TX; 29 March 1981. 



Necturus lewisi. — \$, 19, Tar River along State Hwy 44, 2.9 km 

 NNW of Tarboro, Edgecombe Co., NC; January 1980; 1#, Tar River, 

 14.1 km S of Nashville, Nash Co., NC; January 1980. 



Necturus maculosus. — 19, Wisconsin (exact locality not availa- 

 ble); from Carolina Biological Supply Co. 



Necturus punctatus. — 3##, Little River, crossing of CR 2224, 

 Wake Co., NC; August and January, 1981. 



Mitotic chromosomes were prepared from colchicine-treated intes- 

 tinal epithelium and spleen, following the technique described in Kezer 

 and Sessions (1979). Air and flame dried slides were also made from 

 peripheral blood after in vivo treatment with phytohemagglutinin (PHA, 

 Sigma) and Colcemid (Sigma). C-banding was carried out on squash 

 preparations of intestinal epithelium and spleen cells, using the tech- 

 nique of Schmid et al. (1979). At least three mitotic cells were examined 

 from each individual. Idiograms were constructed from measurements 

 of a single representative mitotic spread for N. alabamensis, N. lewisi, 

 N. maculosus, and N. punctatus. 



RESULTS 



All species of Necturus studied have 19 pairs of chromosomes (2n = 

 38), including a pair of well-differentiated heteromorphic sex chromo- 



