Mating behavior and fertilization success of three ontogenetic stages of male rock shrimp Rhynchocinetes typus (Decapoda : Caridea)

The mating behavior and fertilization capacity of three different ontogenet ic stages of male rock shrimp Rhynchocinetes typus were examined. The first ontogenetic stage is the typus morphotype, which is similar in morphology to the female. The last ontogenetic stage, the robustus morphotype, is char acterized by extremely long third maxillipeds and powerful chelae, During o ntogenetic development between these two morphs, males undergo several inte rmediate molts, which are termed "intermedius." In mating experiments with pairs of single males and females, all ontogenetic male stages (typus, inte rmedius, robustus) behaved in a similar manner. First, they followed the fe male, then embraced it with the second pereiopods and held it beneath their bodies, encaged by the pereiopods, the 3(rd) maxillipeds, and the abdomen. Various stimulating and checking behaviors preceded the placement of the f irst spermatophore, which usually coincided with the start of the spawning process. Most spermatophores were placed during the first 30 minutes of spa wning. Following spermatophore placement, males guarded the females during almost the entire spawning process, which could last longer than 120 minute s. The number of spermatophore transfer events during the mating process va ried significantly between the two extreme ontogenetic male stages, being t ypus greater than robustus. No significant differences were found in the pe rcentage of eggs lost by females that were fertilized by the three ontogene tic male stages. These results suggest that all male stages have the same p otential to mate successfully with females in a competition-free environmen t. However, we propose that male mating success may change drastically when different ontogenetic male stages compete directly for access to reproduct ive females.