Is there sperm storage in the clam shrimp Eulimnadia texana?

Androdioecy is a rare form of mating system in which species comprise males and hermaphrodites. One recently described case of androdioecy is the fres hwater crustacean Eulimnadia texana. A mathematical model of the mating sys tem of this shrimp suggests that males and hermaphrodites should only coexi st under limited circumstances. One possible factor not considered in this model would extend the conditions for coexistence: the possibility of sperm storage in the hermaphrodites. Here we use genetically marked matings betw een males and hermaphrodites to determine if hermaphrodites can store male sperms. Eggs were collected from hermaphrodites both in the presence of a m ale and after the male was removed. A total of 30 of these matings had succ essful hatches, but only 14 of these 30 could be used to test for sperm sto rage. In these 14 cases, an average of 35% of the eggs were outcrossed when males were present, but only 0.4% were outcrossed after males were removed . Thus, sperm storage by hermaphrodites was an insignificant factor in the production of offspring. These data suggest that sperm storage cannot help explain the coexistence of males and hermaphrodites in natural populations of this crustacean.