Necturus Chromosome Evolution 



41 



N. alabamensis 



N. punctatus 



Fig. 1. Map showing approximate distribution of species of the genus Nectu- 

 rus used in this study (adapted from Conant 1975). 



Specimens of N. beyeri from Texas have identical karyotypes to 

 that of N. maculosus, with 12 (6 pairs) telocentric chromosomes (Fig. 

 5). As in the other species, two of these pairs of asymmetrical chromo- 

 somes are medium-size, and the remaining telocentrics are small. The 

 Y-chromosome of N. beyeri is also virtually identical to that of N. 

 maculosus. 



A karyotype and idiogram of N. maculosus were presented earlier 

 (Sessions 1980), but a new C-band idiogram of this species was con- 

 structed for this study (Fig. 3). It shows the position of the sex chromo- 

 somes and the 6 pairs of telocentric chromosomes in the karyotype. The 

 subtelocentric Y-chromosome of this species is more heterochromatic 

 than that in any of the other species of Necturus (Fig. 4). 



DISCUSSION 



Our karyological data support previously reported electrophoretic 

 evidence (Ashton et al. 1980) that N. lewisi, N. punctatus, and N. macu- 

 losus are distinct, probably long-isolated species. These data further 

 suggest that N. alabamensis, which has not been studied electrophoreti- 

 cally, may represent another distinct species, and that N. beyeri is only a 

 little-differentiated southern form of N. maculosus. Karyological evi- 



