A marine dwelling eusocial organism: synalpheus regalis  (Page 7/8)

Aphids are another fortress defender eusocial species, sharing several similarities with sponge-dwelling shrimp and termites. The gall-forming Pemphigus spyrothecae , along with all other aphid species, contain a caste of soldiers common to Synalpheus regalis and termite species (Benton et al. 1992). These soldiers cluster around the entrance to the gall, actively attacking predators with their sylets and hind legs. This act is very altruistic since it is common to die while defending their relatives. During summertime of peak reproduction, three hundred aphids could be found in a gall of which 50% are soldiers (Foster 1990). However, the soldiers also perform another function of housekeeping by removing any honeydew, exuviae (shed skins), and any other waste including dead aphids from the gall. This cleaning of the nest allows for growth of the juvenile aphids —yet is still a dangerous act due to the chance of falling from the gall entrance (Benton et al. 1992). Further research is necessary to determine alternative functions of the soldiers of Synalpheus regalis . The acts of soldiers, whether defense as in S. regalis or non-defensive as in gall-forming aphids, are seen as forms of altruism. By sacrificing their safety to house-keep or attack intruders, these fortress-defenders protect the important commodities of the nest, the reproductive individual, and of course the related juveniles that will ensure copies of their genes will pass to future generations.

Conclusion

The species of Synalpheus has been discovered to be eusocial species due to its adherence to the three contingencies of eusociality: cooperative care of young, reproductive division of labor, and overlapping of generations. As fortress defenders, a caste is present in all five Synalpheus species that constantly defend the precious commodity of the sponge. The sponge is important since it provides nourishment for the growing juveniles, while providing shelter for the colony. Ecological constraints limit individuals from dispersing due to the scarcity of unoccupied sponges ( [link] ). Also, conspecific species are still regarded as intruders, resulting in an attack from the sponge’s defenders—making the joining of a new sponge colony very difficult. Further research is necessary to determine what developmental pathways produce reproductive females and the soldiers. Perhaps even the soldiers of Synalpheus posses another function, similar to the eusocial aphids.