A marine dwelling eusocial organism: synalpheus regalis  (Page 3/8)

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The success of group living in synalpheus regalis

S. regalis occupies the small internal canals of tropical sponges, with colonies as large as several hundred individuals. The sponge-dwelling shrimp, Synalpheus regalis , has increased reproductive success though group living. Experiments show that larger groups out-reproduce smaller groups in this species. In [link] , it is documented that the larger the colony size, the more eggs produced by the colony, thus greater reproductive success (Duffy 1996b). Through the sampling of unmanipulated colonies, data shows the colonies’ reproductive yield increasing by a factor of 177 times in colony sizes ranging from 2-356 individuals (Duffy et al 2002). The colonies of S. regalis consist of large kin groups with adults of at least two generations, allowing for the non-reproducing individuals to still pass on their genes through rearing relatives—whether it be through foraging, defending, or any other job that increases juvenile survival—rather than having their own offspring.

Within the colony there are large males that defend the colony from intruders. Their sole duty is to protect the remaining two castes, the sole reproductive female and the juveniles ( [link] ). Experimental data by J. Emmett Duffy show the emergence of castes in the eusocial shrimp—with large males more likely to snap and attack heterospecific intruders than juveniles or female queens ( [link] ). Thus the first requirement of eusociality, reproductive division of labor, is satisfied in S. regalis (Duffy 1998). This is fulfilled by adults remaining in their natal nests due to the difficulty of colonizing another unoccupied nest. Attempting to join another colony is also difficult since conspecific organisms are also seen as intruders to the defenders, causing them to be attacked. Along with the reproductive division of labor, the overlapping of generations and the cooperative care of young are all traits commonly found in eusocial species (Duffy et al. 2002).

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