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 manytaxa, and a number of hypotheses have been developed to explainthis phenomenon. Several authors have suggested the importanceof male mate-guarding behavior in the evolution of social monogamy,although empirical support for this hypothesis is lacking. Inthe caridean shrimp genus Alpheus, social monogamy may resultfrom selection on males for long-term guarding of females becausemating is temporally restricted to a short time after the female'smolt. I used Alpheus angulatus to test two predictions of theextended mate-guarding hypothesis: Males should (1) be physiologicallycapable of predicting the timing of female sexual receptivity,and (2) prefer to associate with (guard) females that are closerto sexual receptivity. Data from a Y-maze experiment testingfor distance chemical communication showed that males of A.angulatus were attracted to water treated by exposure to premoltfemales, repulsed by water treated by exposure to intermoltmales and females, and did not appear to respond in either directionto water treated by exposure to premolt males. In mate choiceexperiments, significantly more males paired with premolt femalesthan with postmolt females. These data suggest that males ofA. angulatus engage in precopulatory mate-guarding behavior.Other factors (population density, sex ratio) may have playeda role in the temporal extension of mate guarding to socialmonogamy.