Social organization and caste formation in three additional parasitic flatworm species

Abstract

There are many examples of reproductive division of labor in terrestrial animal societies, but only a few have been reported in aquatic systems. A recent study discovered social organization of a trematode parasite in a marine system which included reproductive and soldier castes. Here I expand that work, reporting on caste formation in 3 species of trematodes infecting the Asian mud snail Batillaria attramentaria, to demonstrate the generality of this phenomenon. I found that the trematodes Philophthalmid sp. I, Philophthalmid sp. II and Acanthoparyphium sp. I have 2 types of morphologically and functionally distinct larval trematode morphs in their colonies. Large morphs were reproductive and filled with embryos, while small morphs had no embryos. Small soldier morphs were disproportionately common in regions within the host where new infections occur, and had relatively large mouthparts. Finally, only small soldier morphs attacked heterospecifics. Division of labor in trematodes is geographically widespread and has now been documented in North America, East Asia and Oceania; this may provide a useful model for comparing ecology and evolution of social organization in animal societies. © 2012 Inter-Research.