Adaptive Significance of Reproductive Cycles in the Fiddler Crab Uca pugilator: A Hypothesis.

Semimonthly peaks in courtship behavior of male crabs coincide with peaks in the temporal distribution of receptive females. Females mate once each month, 4 to 5 days before one of the semimonthly spring tides. The relation of the time of reproduction to tide cycles may be an adaptation to increase to a maximum the probability that the final stage of the planktonic larvae will be transported by tidal currents to substrates suitable for adults.