Neighbor-joining tree of LDHA protein sequences from 85 isolates in the Daphnia pulex species complex. The number of sequences shared by multiple isolates of a particular species is given in brackets. "Slow" and "Fast" refer to electrophoretic mobility in allozyme analyses. C = North American D. pulicaria, X = North American D. pulex and CX = hybrid isolates. Other taxon codes are defined in Figure 3.