16 Richard Highton 



The isolating mechanisms that keep P. aureolus from interbreeding with P. 

 teyahalee apparently are present in the aureolus-jordani hybrids in suffi- 

 cient degree to prevent the usual interbreeding of P. jordani and P. 

 teyahalee at all 3 Sassafras Ridge sites (localities 46-48). 



Since without genetic data it is extremely difficult to correctly identify 

 many individuals of this complex of southern Appalachian large Pleth- 

 odon, particularly some P. aureolus and P. glutinosus, there is a problem 

 in assigning individuals to species before examining the genetic data. After 

 a long search for a site where the two widely sympatric species, P. teyahalee 

 and P. aureolus, contact the parapatric species, P. glutinosus, a localilty 

 was discovered along Ellis Branch, near Springtown, Polk County, Ten- 

 nessee (locality 4), where the three forms are sympatric. Nei genetic identi- 

 ties between all 24 individuals from this localilty are clustered in a 

 UPGM A phenogram (Fig. 4). The results clearly show that the 24 animals 

 are separable into three groups consisting of 1 3 P. teyahalee, 5 P. aureolus 

 and 6 P. glutinosus. Four additional very small animals from locality 4 

 were also examined at some of the diagnostic loci and were identified as 

 P. teyahalee, but are not included in the genetic analysis because of 

 incomplete genetic data for several loci. Each of these samples clusters 

 with others of its own species (Fig. 3), and only the P. glutinosus sample 

 has a higher than average H value (Table 3). The alleUc data in Table 4 

 indicate that there is only one locus (Ldh-muscle) in which there are 

 fixed differences between all three species. At the other differential loci, 

 sometimes two of the species have identical electromorphs and some- 

 times there are rare electromorphs of the same kind found in one or 

 both of the other species. This latter pattern of variation is also present 

 in sympatric populations of P. glutinosus and P. kentucki (Highton and 

 MacGregor 1983) and could result from inheritance of the same elec- 

 tromorphs from their common ancestor, or occasional hybridization 

 between the species after complete differentiation had occurred. The 

 relationships in Figures 3 and 4 and the data in Tables 2, 3 and 4 are 

 considered strong evidence for the recognition of all three forms as dis- 

 tinct species. The Ldh-muscle data clearly show that there is not a single 

 F| hybrid between any of the three species at the Ellis Branch locality, 

 as does the pattern of variation at the other differential loci. 



I have no explanation as to why in three cases an electromorph from 

 another species appears as a rare homozygote instead of in the expected 

 heterozygous condition [P. teyahalee #9, Alb; P. aureolus #21, Idh-2; and 

 P. glutinosus #16, Ldh (heart)] (see Table 4). 



The Pep electromorphs of P. aureolus are faster than those of the 

 other two species at locality 4 and are indicated as different in Table 4. This 

 difference could not be consistently detected on comparison gels of sam- 

 ples of the three species at other localities and is therefore not regarded as a 



