Effect of food addition on the reproductive intensity and timing of both sexes of an intertidal crab

Abstract

Males and females of most animals time reproduction and synchronize their reproductive activity to maximize lifetime fitness. When food is abundant, however, the 2 sexes may time investments in reproduction differently due to sexual differences in how energy limits reproductive success. Many intertidal animals have reproductive cycles with semilunar or lunar periods timed to coincide with a certain phase of the tidal amplitude cycle when offspring survive best. Given an optimal time to breed, well-fed females may increase their investment in offspring but not change when they breed, while males may invest more both before and after the mating peak. We explored this possibility by feeding a mixed-sex population of the fiddler crab Uca terpsichores in field enclosures over 2 sequential trials of 1 mo each. Food addition increased male courtship intensity, particularly in the latter part of the semilunar reproductive cycles, but did not change the peak days of reproductive activity. Food addition had no consistent effects on female mate-searching intensity or reproductive timing during either month-long trial. These results suggest that female reproductive cycles and their timing do not result from semilunar variation in food. However, since females breed at most once a month, the trials may not have been of sufficient duration to reveal an effect of food on female reproductive investment. Previous studies suggest that semilunar variation in predation on larvae is the most important factor regulating reproductive timing by both sexes. Our results indicate that additional food also influences the schedule of male reproductive investment.