Lunar and Tidal Periodicity of Molting and Reproduction in Stomatopod Crustacea: A Selfish Herd Hypothesis

During laboratory maintenance, G. zacae from the Gulf of California molts during neap tides or the transition from spring to neap tides; oviposition probably occurs during neap tides or the transition from spring to neap tides. G. falcatus from Hawaii tends to molt during spring tides or the transition from neap to spring tides; oviposition occurs during neap tides or the transition from spring to neap tides. Strong evidence suggests that H. glyptocercus from Eniwetok molts during neap tides or their approach. P. ciliata from three populations molt during the last lunar phase, providing the only substantive evidence for lunar rather than tidal control of molting in stomatopods. While P. ciliata from Hawaii and Florida lays eggs during neap or waxing neap tidal phases, those maintained in Thailand deposit eggs during waning neap tidal cycles. G. falcatus and G. graphurus from Australia molt in opposite tidal cycles; G. graphurus molts during neap tides but reproduces during spring tides. The five species of Gonodactylidae from Australia oviposit during spring tides.2. Field data demonstrate significantly more molting during spring than neap tidal cycles in a gonodactylid community comprised of seven species in Phuket, Thailand. Laboratory maintenance increases variation in the pattern of molting across tidal cycles, although molting still occurs significantly more frequently in spring than neap tidal cycles. G. chiragra molts significantly more frequently than expected during spring than neap tides in the field. Both field and laboratory data demonstrate significant correlation of oviposition with spring tides among the species in 1973 but not 1974.3. These data support a temporal selfish herd hypothesis that synchrony of molting in the population reduces mortality due to conspecific and congeneric aggression in stomatopods. Observed data do not support predictions from alternative hypotheses that physical factors, feeding, or predation impose molting and reproductive rhythms. Molting synchrony is more consistent with the idea that stomatopod populations are limited by the availability of burrows than by food. The initiation of molting synchrony in the population can be explained by selection for response to environmental cues, by chance, and/or by small, local populations with synchronous hatching of young. Oviposition rhythms therefore may subserve the primary molting rhythm.