(+) 
Origin —> 
Fig. 2.—Lactate dehydrogenase isozymes of six species of 
rena and four of Etheostoma. Electrophoresis was in pH 
} tris-citrate buffer. 
g. 4 also shows more detailed patterns of species poorly 
solved in Fig. 1 (E. flabellare and E. proeliare). 
Percina characteristics—such as less elaborate spawn- 
g behavior than in Etheostoma, the presence of a gas 
adder in most species, generally larger size, and a com- 
ste lateral line—leave no doubt that this genus includes 
> primitive darters, and the distinctive B, isozyme mo- 
ity is probably an expression of genetic conservatism 
sent in species of the more advanced genera (except E. 
lereum) . 
The genetic continuity demonstrated by the identical 
bility of the B, isozyme band in all 19 species of 
rcina examined is strong evidence of relationships 
long the species currently assigned to the genus. The 
species analyzed included representatives of all 8 
ognized subgenera (Bailey & Gosline 1955, Collette 
DD) . 
) 
FTONN DOO y 
Fig. 3.—Effects of antisera on the lactate dehydrogenase 
ymes of Percina sciera. (A) untreated LDH isozymes, (B) 
Serum alone, (C,D,E) effect of anti-LDH A serum on the 
ciera isozymes, (F,G,H) effect of anti-LDH B serum on the 
ctéra isozymes. The anodal LDH band is the Bs isozyme. 
A genus may be defined as a “monophyletic group of 
species, which is separated from other taxa of the same 
rank [other genera] by a decided gap” (Mayr 1969). The 
enzymatic (LDH B, mobility) and morphological (modi- 
fied scales) evidence for a monophyletic origin for all 
species in Percina is persuasive. Although the subgenus 
Percina is quite distinct in several ways from other sub- 
genera, to grant the subgenus Percina separate generic 
Status (as suggested by Curd 1967, Hubbs & Lagler 1958; 
Hubbs 1967, Minckley 1963, Stevenson 1971, and Winn 
1958) because of its distinctiveness from other Percina 
negates the criterion of monophyly (Hennig 1966) for the 
genus containing the remaining species. 
If the subgenus Percina were to be recognized as a 
separate genus, it would be a monophyletic group of four 
species, and the remaining species presumably would be 
put in Hadropterus as outlined by Bailey (1951). Of 
this composition, Hadropterus would not include all spe- 
cies descended from a common ancestor (Fig. 5), and 
therefore would not be a valid, monophyletic genus. The 
subgenus Percina shares with most other Percina sub- 
genera (Hadropterus, Swainia, Alvordius, Ericosma, Cot- 
togaster) the presence of a row of modified scales on the 
midbelly. ‘The row is lacking in the subgenus Hypohomus 
(Fig. 5). Since it is extremely doubtful that a mid- 
belly row of modified scales independently evolved twice, 
the separation of the subgenus Percina from the other 
subgenera with the row of modified scales almost cer- 
tainly occurred after the separation of the subgenus with- 
out the row (Hypohomus). Therefore if Percina is to be 
a genus of four species, and genera are to be monophy- 
letic, there also must at least be a genus Hypohomus and 
a genus Hadropterus (containing the subgenera Hadrop- 
terus, Swainia, Ericosma, Alvordius, Cottogaster, and 
? Imostoma). The morphological gaps among the species 
within the latter two genera are in some instances larger 
than that between genera, although the genera would 
probably be monophyletic. 
(+) & 
Fig. 4.—Lactate dehydrogenase isozymes of nine species of 
darters. Electrophoresis was in pH 8.7 EBT buffer. 
