Sexual Modes in the Colonial Kamptozoan Genus Barentsia

Sexual mode in colonial animals is expressed at the zooid, colony, and genet level; all three must be characterized to understand sexuality in these animals. I carried out such an examination of the sexual mode of a colonial kamptozoan (entoproct), Barentsia hildegardae, at Friday Harbor, Washington. Calyces never contained both ovaries and testes, and colonies never contained both male and female calyces. Calyces and colonies (including replicate colonies from the same genet) monitored over two years did not change sex. These results suggest that B. hildegardae is comprehensively gonochoric. For comparison, I examined the sexual mode of five other species in the genus Barentsia. Barentsia benedeni, B. conferta, and B. ramosa also appear to be comprehensively gonochoric. Barentsia discreta is hermaphroditic at the colony level, with gonochoric calyces whose sex is environmentally determined, as noted by previous workers. Barentsia aggregata has simultaneously hermaphroditic calyces; this was reported by the authors who described it, but has escaped notice in subsequent reviews of kamptozoan biology. There are thus three contrasting modes of sex within the genus Barentsia. All three modes also occur in colonial cnidarians, and two of them are known in bryozoans, colonial hemichordates, and colonial urochordates. These disparate sexual modes may have evolved as adaptations to differing environmental conditions or population densities.