GENETIC-VARIATION IN SUBTROPICAL POPULATIONS OF SIMOCEPHALUS (CRUSTACEA, CLADOCERA)

Subtropical populations of the cladoceran Simocephalus serrulatus were assayed for allozymic and quantitative genetic variation. The observe d levels of variation were generally lower than those observed for cla doceran populations (primarily Daphnia) in the temperate zone. This wo uld seem to be attributable either to the subtropical location, to pro longed clonal selection, or to some inherent characteristic of the gen us. A survey of cladoceran literature for data on allozyme variation v s. latitude revealed no pattern. The lack of departure from Hardy-Wein berg equilibrium in the S. serrulatus populations suggests that long-t erm clonal selection is not likely. Therefore, subtropical location an d long-term clonal selection do not seem to be likely causes of the lo w amount of genetic variation. This suggests that some inherent charac teristic of Simocephalus, such as the fact that they deposit only one resting egg at a time, may be the cause of this level of genetic varia tion.