Tests of the mate-guarding hypothesis for social monogamy: male snapping shrimp prefer to associate with high-value females

Social monogamy without biparental care has evolved in many taxa, and a number of hypotheses have been developed to explain this phenomenon. Several authors have suggested the importance of male mate-guarding behavior in the evolution of social monogamy, although empirical support for this hypothesis is lacking. In the caridean shrimp genus Alpheus, social monogamy may result from selection on males for long-term guarding of females because mating is temporally restricted to a short time after the female's molt. I used Alpheus angulatus to test two predictions of the extended mate-guarding hypothesis: Males should (1) be physiologically capable of predicting the timing of female sexual receptivity, and (2) prefer to associate with (guard) females that are closer to sexual receptivity. Data from a Y-maze experiment testing for distance chemical communication showed that males of A. angulatus were attracted to water treated by exposure to premolt females, repulsed by water treated by exposure to intermolt males and females, and did not appear to respond in either direction to water treated by exposure to premolt males. In mate choice experiments, significantly more males paired with premolt females than with postmolt females. These data suggest that males of A. angulatus engage in precopulatory mate-guarding behavior. Other factors (population density, sex ratio) may have played a role in the temporal extension of mate guarding to social monogamy. Copyright 2003.